Crystal structure and doping in synthetic enstatite: an analysis of Li/Fe³⁺-doped single-crystal samples

A series of Li⁺/Fe³⁺-doped enstatite crystals of com­position Mg_(2–2x)Li_xFe_xSi₂O₆ were synthesized and structurally characterized. Under the selected experimental conditions, we grew three crystals of Pbca orthopy­rox­ene (OPX: x = 0.270–0.313) and two crystals of Pbcn protopy­rox­ene (PPX: x = 0.156–0.164) using the flux-growth technique. The observed variation in the polyhedral volume and distortion of the M2 octa­hedron as a function of Li/Fe³⁺ doping suggests the presence of an upper limit, at least for the OPX samples. The same linear relation was observed between the polyhedral volume and 〈M1—O〉 bond length across all analysed samples, including the endmembers protoenstatite (PEN), orthoenstatite (OEN) and LiFe³⁺Si₂O₆. It seems that the M2 octa­hedron plays a crucial role in stabilizing the py­rox­ene topology in either the PEN or the OEN form, because the PPX and OPX samples show two distinct linear relations between the M2O₆ polyhedral volume and 〈M2—O〉, with the PPX trend converging toward the parameters of the LiFe³⁺Si₂O₆ endmember, whereas the OPX trend, including OEN, diverges largely from these parameters.

1. Introduction

Magnesium silicate Mg₂Si₂O₆ can occur in six polymorphic modifications. Two of them are ortho­rhom­bic, namely, Pbcn protoenstatite (PEN: Kanzaki & Xue, 2017) and Pbca orthoenstatite (OEN: Ganguly & Ghose, 1979; Sasaki et al., 1982), whereas four monoclinic modifications have been described so far, namely, P2₁/c low-pressure/low-tem­per­a­ture clinoenstatite (LPCEN/LTCEN: Ohashi & Finger, 1976; Ohashi, 1984; Pannhorst, 1984), C2/c (metastable) high-tem­per­a­ture clinoenstatite (HTCEN: Yoshiasa et al., 2013), C2/c high-pressure clinoenstatite (HPCEN: Angel et al., 1992) and P2₁/c high-pressure clinoenstatite (HPCEN2: Lazarz et al., 2019). PEN has not been found in nature and is stable in a relatively small low-pressure range (<1 GPa) at tem­per­a­tures (T) exceeding 1000 °C, potentially up to its incongruent melting point at 1550 °C (Boyd et al., 1964). OEN has a large stability field at low pressure extending from ∼600 °C (forsterite Mg₂SiO₄ + liquid) up to melting (except for the small field occupied by PEN) and is the polymorphic form ubiquitously found in both igneous and metamorphic rocks. LPCEN/LTCEN is uncommon in nature, and it has been synthesized at T < 566 °C, clearly indicating that it is the low-tem­per­a­ture form of Mg₂Si₂O₆. A simplified P–T diagram of Mg₂Si₂O₆ is shown in Fig. 1. Lithium-bearing olivines (Ballirano et al., 2024) were initially chosen as a test case for modelling Li⁺ + Fe³⁺ ↔ 2 Mg²⁺ coupled substitution in silicates. Next, we selected Mg₂Si₂O₆ for further investigation on this issue, owing to its capability to crystallize in different space groups. We focused, in particular, on the ortho­rhom­bic polymorphs of Mg₂Si₂O₆ as two synthetic Pbcn protopy­rox­ene crystals of Mg_(2–2x)Li_xSc_xSi₂O₆ com­position (x = 0.23 and 0.30) have been prepared and described so far (Smyth & Ito, 1977; Yang et al., 1999), possibly suggesting that the partial coupled substitution (Li + ^VIMe³⁺) for 2Mg plays the role of stabilizer of such a py­rox­ene topology. Despite the small differences in the corresponding ionic radii (Li⁺ = 0.760 Å and Sc³⁺ = 0.745 Å; Shannon, 1976), Li was fully ordered at the M2 site, whereas Sc³⁺ occupies the M1 site (Smyth & Ito, 1977; Yang et al., 1999). However, upon recent revision of the ^VILi ion radius to 0.812 Å (Hawthorne & Gagné, 2024), this site preference is perfectly explainable. The latter forms a polyhedron that is smaller and much less distorted com­pared to M2O₆. Owing to the significantly smaller ionic radius of Fe³⁺ com­pared to Sc³⁺ (0.649 versus 0.732 Å, respectively: Hawthorne & Gagné, 2024), we can hypothesize the onset of a similar ordering scheme for the Li ⁺ + Fe³⁺ ↔ 2 Mg²⁺ substitution. It is worth noting that the LiFe³⁺Si₂O₆ endmember com­position crystallizes as C2/c clinopy­rox­ene (Redhammer & Roth, 2004), with Li allotted at M2 and Fe³⁺ at M1. In the following, coordination polyhedra are denoted by the central cation site: thus, M2 octa­hedron.

Figure 1 Simplified P–T diagram of Mg2Si2O6. Abbreviations: protoenstatite (PEN), orthoenstatite (OEN), forsterite (Fo) and clinoenstatite (CEN).

According to the well-known MgO–SiO₂ phase diagram at room pressure, the synthesis of ortho­rhom­bic enstatite requires rather high tem­per­a­tures. To decrease these tem­per­a­tures, many studies have been carried out testing different synthesis procedures, such as the sol–gel technique (Mitchell et al., 1998; Ban et al., 1999; Douy, 2002) or the flux method (Ito, 1975; Grandin de L'éprevier & Ito, 1983; Ushio et al., 1991) to obtain enstatite and forsterite. Although the sol–gel technique opens the way to the synthesis of impurity-free films, to obtain these in a crystalline form it is still necessary to use thermal treatment. Otherwise, the flux method is preferable for obtaining larger crystals and enhance doping (Smyth & Ito, 1977). During cooling, nutrient depletion in the melt and decreased solubility can alter the original molar ratios and lead to the formation of unintended mineral phases (Bloise et al., 2009; Bloise et al., 2011). As reported previously, Mg₂Si₂O₆ may crystallize as three polymorphs, leading to further com­plications: PEN, stable at high tem­per­a­tures (1000–1575 °C), and OEN and LTCEN stable at lower tem­per­a­tures, the extent of crystallization of which has been reported as depending on the cooling rate (Smyth, 1974; Ito, 1975; Catalano et al., 2014). Consequently, slight variations in the synthesis conditions or the molar ratios can lead to the formation of additional phases, making it challenging to achieve stoichiometric control of the single phase due to the particular thermodynamic and kinetic conditions required.

For this work, crystals were grown using the flux-growth technique with lithium–vanadomolybdate as the melting agent (Ozima, 1982; Ozima & Akimoto, 1983; Grandin de L'éprevier & Ito, 1983). The acidity of the flux is crucial for enhancing the solubility of SiO₂ by converting it into orthosilicic acid Si(OH)₄. This can be done using MoO₃ and V₂O₅ together. Fluxes lacking either vanadate or molybdate are ineffective in solubilizing SiO₂ (Smyth & Ito, 1977; Ushio et al., 1991). Indeed, MgO and SiO₂ exhibit minimal mutual reactivity, while the presence of silicic acid promotes the formation of Si—O—Mg bonds, hence favouring the formation of phases such as enstatite and forsterite (Douy, 2002; Gu et al., 2018; Bloise et al., 2009). The formation of LiFeSi₂O₆, which begins at 500 °C when CO₂ is released from the dissolution of Li₂CO₃ (Tanaka & Takei, 1997), plays a crucial role in lowering the formation tem­per­a­ture of py­rox­enes and is responsible for their doping. This effect, as reported previously (e.g. Ito, 1975; Grandin de L'éprevier & Ito, 1983; Smyth & Ito, 1977), stabilizes PEN (the high-tem­per­a­ture polymorph of enstatite), thereby extending its stability range to lower tem­per­a­tures.

The present work investigates the crystal chemistry of the Li⁺ + Fe³⁺ ↔ 2 Mg²⁺ coupled substitution along the Mg₂Si₂O₆–LiFe³⁺Si₂O₆ com­positional joint by single-crystal X-ray diffraction (SCXRD). The incorporation of Li and Fe³⁺ can significantly influence the properties and behaviour of enstatite crystals, with possible implications as cathode materials for lithium-ion batteries (LiBs), given the inter­est generated by the first report on the electrochemical and structural properties of the py­rox­ene-type LiFeSi₂O₆ by Zhou et al. (2014).

2. Experimental

2.1. Synthesis

The route commonly used to synthesize Fe-doped enstatite crystals, ideally Fe_0.2Mg_1.8Si₂O₆, was followed. Granular quartz (SiO₂; code No. 364011), magnesium oxide (MgO; code No. 459586), metallic iron (Fe; code No. 451377) and hematite (Fe₂O₃; code No. 451824) from Carlo Erba (reagent grade with purity ≥ 98%) were used as the starting materials without further purification.

Pre-heating was necessary to enhance the reactivity between the starting materials: granular quartz was converted into cristobalite by heating the powdered SiO₂ to 1400 °C for 12 h, while MgO, Fe and Fe₂O₃ powders were heated for a week at 110 °C, to ensure com­plete dehydration. Iron(II) oxide was prepared through partial reduction of hematite by metallic iron, following the reaction: 1/3Fe + 1/3Fe₂O₃ = FeO. Molybdenum(VI) oxide (MoO₃; code No. 267856), vanadium(V) oxide (V₂O₅; code No. 223794) and lithium carbonate (Li₂CO₃; code No. 62470) from Sigma–Aldrich (reagent grade with purity ≥98%) were used as flux. The flux com­position was as follows: MoO₃ = 55.9 wt%, V₂O₅ = 9.8 wt% and Li₂CO₃ = 34.3 wt% (Bloise et al., 2011). Approximately 1.25 g of finely powdered starting materials (grain size < 0.177 mm), prepared according to the ideal Fe_0.2Mg_1.8Si₂O₆ stoichiometry of Fe-doped enstatite, along with flux, were loaded into a 100 ml platinum crucible and placed in a vertical furnace. The lithium–vanadomolybdate flux was added to the starting materials/flux, maintaining a consistent starting materials (g)/ flux (g) ratio of 0.5.

Iron-doped enstatite crystals were grown in a furnace equipped with a Super Kanthal heating element (0–1700 °C), with tem­per­a­ture control provided by PtRh–PtRh thermocouples, with a precision of ±4 °C.

The thermal run proceeded as follows: a steep increment up to 1050 °C was followed by 100 h where the tem­per­a­ture was kept constant to bring about com­plete dissolution and homogenization of the mixture. The resulting melt was then cooled slowly to 650 °C at a rate of 1.25 °C h⁻¹, followed by rapid quenching to room tem­per­a­ture by immersion of the crucible in water.

The growth conditions for enstatite followed well-established protocols from the literature (Bloise et al., 2011; Catalano et al., 2014; Catalano et al., 2015). As a result, orthopy­rox­ene crystals with the com­position Mg_(2–2x)Li_xFe³⁺_xSi₂O₆ (0.15 < x < 0.31) were obtained. Euhedral colourless crystals, averaging 800 µm in length, were separated from the solidified flux by sonication in hot water. The crystals were recovered using a binocular microscope, selected and subsequently characterized by SCXRD.

2.2. Single-crystal X-ray diffraction

Five crystal fragments (labelled as 1, 2, 3, 4a and 4d) were selected for X-ray diffraction measurements on a Bruker Kappa APEXII single-crystal diffractometer (Sapienza University of Rome, Earth Sciences Department), equipped with a CCD area detector (6.2 × 6.2 cm active detection area, 512 × 512 pixels) and a graphite-crystal monochromator, using Mo Kα radiation from a fine-focus sealed X-ray tube. The sample-to-detector distance was 4 cm. Preliminary scrutiny of the reciprocal lattice of the samples clearly indicated their ortho­rhom­bic symmetry. Samples 1, 2 and 3 have Pbca symmetry (a ∼ 18.17 Å, b ∼ 8.77 Å and c ∼ 5.19 Å, i.e. that of orthopy­rox­enes OPX) and samples 4a and 4d have Pbcn symmetry (i.e. that of protopy­rox­enes PPX), showing a halved a parameter. Diffraction data for 1, 2, 4a and 4d were collected up to sin θ_max/λ = 1.000 Å⁻¹ and those for 3 up to sin θ_max/λ = 1.184 Å⁻¹.

A total of 1708 (and 1365 for sample 3) exposures (step = 0.4°, time/step = 15 s) covering a full reciprocal sphere with a com­pleteness > 96% and redundancy of approximately 5 were collected. Final unit-cell parameters were refined using the SAINT program (Bruker, 2016) with numbers of reflections ranging between 3347 and 9984, with I > 10σ(I) in the range 6 < 2θ < 91°. The associated intensities of all collected reflections were processed and corrected for Lorentz and background effects plus polarization, using APEX2 software (Bruker, 2016). The data were corrected for absorption using a multi-scan method (SADABS; Bruker, 2016). The absorption correction led to a significant improvement in wR2_int (from about 0.04 to about 0.02).

2.3. Structure refinement

Structure refinements were carried out using SHELXL2013 (Sheldrick, 2015) and ShelXle (Hübschle et al., 2011). The starting coordinates were taken from Ganguly & Ghose (1979) for OPX (samples 1, 2 and 3) and from Smyth & Ito (1977) for PPX (samples 4a and 4d).

The key difference between the two ortho­rhom­bic py­rox­ene structures lies in their crystallographically distinct T and O sites. In Pbcn PPX, there is only one T site and three distinct O sites (O1, O2 and O3). In contrast, Pbca OPX has two distinct T sites (T1 and T2) and six distinct O sites (O1a, O1b, O2a, O2b, O3a and O3b). Both structures contain octa­hedrally coordinated cations at two distinct M1 and M2 sites.

The following parameters were refined: scale factor, extinction coefficient, atom coordinates, site-scattering values and anisotropic atomic displacement factors. In the starting stages of the refinements, Mg was used as the scatterer at the M1 and M2 sites. The observed excess of electron density at M1 and the deficiency in M2 indicated unequivocally the partition of Fe³⁺ at M1 and Li at M2. This scheme is analogous to that observed in Li/Sc PPX (Sc at M1 and Li at M2; Smyth & Ito, 1977). Subsequently, the M1 and M2 sites were modelled using Mg versus Fe and Mg versus Li scattering factors, respectively. A first set of refinements was done using neutral scattering curves for all atoms. Finally, following Hawthorne et al. (1995) and the results of Ballirano et al. (2021) for amphiboles and Ballirano et al. (2024) for Li/Fe³⁺-doped olivines, further refinements were done modelling the T1 and T2 sites using the Si⁰ versus Si⁴⁺ scattering factors, whereas the anion sites were modelled with the O⁰ versus O²⁻ scattering factors. The coefficients for analytical approximation to the scattering factors were from Table 6.1.1.4 of the Inter­national Tables for Crystallography (Volume C; Brown et al., 2006), the only exception being those of O²⁻ which were taken from Hovestreydt (1983). A significant improvement of the statistical indicators was observed passing from neutral to partly ionized scattering curves.

In the final stages of the refinement, it was observed that the site occupancy factor (sof) of Fe at M1 and of Li at M2 were almost coincident (the sof of Li at M2 slightly exceeding that of Fe at M1: Δ = 0.003–0.013) and therefore they were constrained to be equal. The small discrepancy has been attributed to the presence of minor V³⁺ (ionic radius = 0.641 Å; Hawthorne & Gagné, 2024) replacing Fe³⁺, owing to its smaller scattering power (23 versus 26 e⁻). This result is an indirect proof that all iron occurs as Fe³⁺. The application of this constraint did not affect the various statistical indicators.

Table S1 reports space groups, unit-cell parameters, 2θ_max and sin θ_max/λ of the various data collections, and relevant statistical indicators of the refinements. Table S2 lists the M1 and M2 site populations, the ion charges for O and Si, and the equivalent displacement parameters. Relevant bond distances and several parameters describing the extent of polyhedral distortion are reported in Table S3, and the results of a bond valence analysis in Table S4.

3. Results and discussion

Refinements substanti­ally confirmed the findings of Ballirano et al. (2021, 2024) regarding the use of partially ionized scattering curves of O and Si for tremolite and olivine to em­pirically com­pensate for perturbation of the electron density caused by the inter­action with other atoms (Table S2 in the supporting information). The refined ion charges for O and Si were in the range −1.492 to −1.381 and 0.377 to 0.720, respectively.

OPX samples were characterized by a coupled Li/Fe³⁺ substitution level in the 0.270 (1)–0.313 (1) sof range, whereas PPX samples were in the 0.156 (1)–0.164 (1) sof range. This finding suggests that, under the present experimental conditions, the PPX topology is favoured at smaller doping levels than in the case of Li/Sc³⁺, where crystals were obtained in the 0.23–0.30 sof range (Smyth & Ito, 1977; Yang et al., 1999).

3.1. Unit-cell parameters

Unit-cell parameters as a function of com­position are illustrated in Figs. 2–4 (see also Fig. S1 in the supporting information), where LiFe³⁺Si₂O₆ was considered the common endmember for both the OPX and the PPX series. To obtain a com­parable data set, the a parameter of LiFe³⁺Si₂O₆ was recalculated based on an ortho­rhom­bic cell, according to the well-known relationship a_orth = 2a_monsinβ, whereas for the PPX samples, the a parameter was multiplied by two, in both cases resulting in a doubled unit-cell volume. The OPX and PPX samples show a different behaviour for each unit-cell parameter, coherent with the significantly different volumes of the OEN and PEN endmembers. For OPX samples, the unit-cell volume dependence on com­position follows a bell-shaped curve (i.e. inter­mediate com­positions have a volume smaller than both endmembers), whereas there is a marked decrease from PEN to LiFe³⁺Si₂O₆ (Fig. S1). For both series, the a unit-cell parameters contract from Mg₂Si₂O₆ to LiFe³⁺Si₂O₆. However, the contraction is remarkably higher and linear for the PPX samples, whereas the trend is nonlinear and decreases at a significantly smaller rate for the OPX samples (Fig. 2). The trend in reversed in the case of the b unit-cell parameter (Fig. 3). Conversely, the c unit-cell parameter shows a strong expansion from OEN to LiFe³⁺Si₂O₆, whereas the PPX series is characterized by a small contraction (Fig. 4). Both trends are nonlinear.

Figure 2 Dependence of the a parameter from the Li site occupancy factor (sof). The blue dashed curve is a guide to the eye showing the variation of Li in the OPX. The linear fit of the variation of Li in the PPX is reported as a red solid line. Cpx = clinopyroxene.

Figure 3 Dependence of the b parameter from the Li sof. The red dashed curve is a guide to the eye showing the variation of Li in the PPX. The linear fit of the variation of Li in the OPX is reported as a blue solid line.

Figure 4 Dependence of the c parameter from the Li sof. The red and blue dashed curves are guides to the eye showing the variation of Li in the PPX and OPX, respectively.

3.2. Structural features

Before discussing how the structural features of the two series of orthopy­rox­enes depend on their com­position, it is worth noting that reference structural data for PEN were obtained through Rietveld refinement of laboratory powder X-ray diffraction data collected in reflection mode (Kanzaki & Xue, 2017). However, no details of the refinement procedure were reported in the related article, particularly regarding the use of soft constraints on bond distances and how preferred orientation was accounted for. As a consequence, the accuracy of the structural parameters for PEN might be somewhat lower than that of the results. Therefore, any correlations drawn for PPX samples should be approached with some caution.

That said, unit-cell parameters and 〈M1—O〉 and 〈M2—O〉 show similar correlations with the Li/Fe³⁺ sof (Figs. 5 and 6). For the OPX samples, there is a noticeable increase of 〈M2—O〉 from OEM (2.151 Å) to LiFe³⁺Si₂O₆ (2.249 Å). In contrast, in the case of the PPX samples, PEN has a slightly larger 〈M2—O〉 (2.157 Å) than OEN and the doped samples do not show appreciable variations from that value (2.155 Å), but they are still significantly lower than the LiFe³⁺Si₂O₆ value. The 〈M1—O〉 decreases smoothly in both series of samples from 2.078 (OEN) or 2.089 (PEN) to 2.025 Å for LiFe³⁺Si₂O₆. The trend for OPX is linear and almost linear for PPX if the value for PEN is accepted as accurate.

Figure 5 Variation of 〈M2—O〉 as a function of the Li sof. The red dashed curve is a guide to the eye showing the variation of Li in the PPX. The linear fit of the variation of Li in the OPX is reported as a blue solid line.

Figure 6 Variation of 〈M1—O〉 as a function of the Fe^3+ sof. The red dashed curve is a guide to the eye showing the variation of Fe^3+ in the PPX. The linear fit of the variation of Fe^3+ in the OPX is reported as a blue solid line.

Analysis of the volume and deviation from ideal shape of the M2 and M1 octa­hedra (Figs. 7–11) took into consideration several parameters (Table S3): polyhedral volume (Swanson & Peterson, 1980), polyhedral volume distortion (Makovicky & Balić-Žunić, 1998), distortion index (Baur, 1974), mean quadratic elongation and bond angle variance (Robinson et al., 1971), and effective coordination number (Hoppe, 1979). The volume of the M2 octa­hedron is larger than that of the M1 octa­hedron for the OPX series of samples (∼12.7–12.8 ų versus ∼11.5 ų; Figs. 7 and 9). Moreover, the M2 octa­hedron is significantly more distorted than the M1 octa­hedron, as indicated by the mean quadratic elongation of ∼1.06 versus 1.01. This same behaviour holds true for the LiFe³⁺Si₂O₆ monoclinic endmember, in which the M2 octa­hedron has a very large quadratic elongation (1.229) typical of the Li-bearing clinopy­rox­enes (Cameron & Papike, 1981). In contrast, for the PPX samples, the polyhedral volume of the M2 octa­hedron is smaller than that of the M1 octa­hedron (∼11.1 ų versus ∼11.7 ų) and has a larger distortion, even larger than that of the OPX samples (mean quadratic elongation ∼1.13 versus 1.01). The smaller dimension of the M2 octa­hedron in the PEN and PPX samples with respect to the OPX samples is caused by the sharing of two edges of the octa­hedron with tetra­hedra for the former, whereas in the case of the OEN and OPX samples, no polyhedral edges are shared (Cameron & Papike, 1981). Comparison of Figs. 7 and 8 suggests that for OEN and OPX samples, the increase of the volume of the M2 octa­hedron as a function of a growing level of doping is coupled to an increase in the mean quadratic elongation. In contrast, PEN and PPX samples do not show a well-defined dependence. OPX samples show an increase of the volume of the M2 octa­hedron with an increased level of doping and much larger than that of the LiFe³⁺Si₂O₆ monoclinic endmember, whose volume is com­parable to that of PPX but with a larger mean quadratic elongation value, much larger than for the OPX and PPX samples. This difference between OPX and LiFe³⁺Si₂O₆ could potentially impose an upper limit on the level of coupled Li/Fe³⁺ substitution. Inter­estingly, recalculation of the original structural data of Smyth & Ito (1977) and Yang et al. (1999) for Li/Sc³⁺-doped PPX samples (Table S3) results in mean quadratic elongations of the M2 octa­hedron (where a similar Li versus Mg substitution occurs) that aligns almost perfectly with the curve in Fig. 8 for the present Li/Fe³⁺-doped PPX samples. In contrast, the polyhedral volume is slightly greater than that of PEN, possibly suggesting that the value reported by Kanzaki & Xue (2017) is too large. Fig. 11 shows the variation in polyhedral volume of the M2 and M1 octa­hedra in Li/Fe³⁺-doped orthopy­rox­enes as a function of 〈M—O〉. As can be seen, the volume of the M1 octa­hedron is linearly correlated with 〈M—O〉 for both OPX and PPX samples. Conversely, two separate dependences, one for OPX and one for PPX samples, are observed for the M2 octa­hedron. The displaced position of PEN from this trend suggests that the polyhedral volume of PEN is wrong (too large) and may possibly be related to a lower accuracy of the bond distances as arising from powder X-ray diffraction data with respect to the rest of the data set which is derived from single-crystal SREF.

Figure 7 Variation of the volume of the M2 octa­hedron as a function of the Li sof.

Figure 8 Variation of the quadratic elongation (QE) of the M2 octa­hedron as a function of the Li sof. The red and blue dashed curves are guides to the eye showing the variation of Li in the PPX and OPX, respectively.

Figure 9 Variation of the volume of the M1 octa­hedron as a function of the Fe^3+ sof. The red dashed curve is a guide to the eye showing the variation of Fe^3+ in the PPX. The linear fit of the variation of Fe^3+ in the OPX is reported as a blue solid line.

Figure 10 Variation of the quadratic elongation (QE) of the M1 octa­hedron as a function of the Li sof. The red dashed curve is a guide to the eye showing the variation of Fe^3+ in the PPX. The linear fit of the variation of Fe^3+ in the OPX is reported as a blue solid line.

Figure 11 Variation of the polyhedral volume of the M2 and M1 octa­hedra as a function of 〈M—O〉. The dashed lines are guides to the eye. Key: red diamonds represent the M2O6 polyhedral volume for OPX; blue diamonds the M2O6 polyhedral volume for PPX, PEN and LiFe^3+Si2O6Cpx; red squares the M1O6 polyhedral volume for OPX; blue squares the M1O6 polyhedral volume for PPX, PEN and LiFe^3+Si2O6. Cpx = clinopyroxene.

Fig. S2 and Table S4 report the dependence of the bond valence sum at the various O sites. The parameters used for the calculations were taken from Gagné & Hawthorne (2015). Trends are clearly seen for the analysed samples and there are positive and negative deviations from the valence-sum rule.

4. Conclusions

In this study, we have investigated the crystal structure and doping of enstatite crystals with Li and Fe³⁺. The incorporation of these dopants can significantly influence the properties and behaviour of enstatite crystals, making them inter­esting. Under the experimental conditions, we recovered five samples of Mg_(2–2x)Li_xFe³⁺_xSi₂O₆ py­rox­enes, namely, three ortho­pyrox­ene (OPX) with 0.270 < x < 0.313 and two clinopy­rox­ene (PPX) with 0.156 < x < 0.164. This shows that varying levels of doping preferentially affect the py­rox­ene topologies.

Analysis of the ship between the volume and distortion of the M2 octa­hedron versus the level of doping indicates a possible upper limit for the coupled substitution of (Li + Fe³⁺) for Mg, at least for OPX. The significant role of this polyhedron in stabilizing a specific py­rox­ene topology is further supported by the observation that for all analysed samples (including the endmembers PEN, OEN and LiFe³⁺Si₂O₆), the relationship between the polyhedral volume and 〈M1—O〉 is linear. Conversely, there are two distinct linear relations for PPX and OPX samples between the M2O₆ polyhedral volume and 〈M2—O〉, with only the PPX trend converging toward the LiFe³⁺Si₂O₆ endmember. Notably, the smaller M2 octa­hedron in PPX shares two edges with Si tetra­hedra, whereas the larger M2 octa­hedron in OPX does not share two edges with Si tetra­hedra.

This research enhances the understanding of crystal structure and doping in enstatite crystals, suggesting a potential use of Li/Fe³⁺-doped enstatite in energy storage devices where a very stable structural framework is required for long-term Li⁺ ion extraction/insertion.

5. Related literature

The following references are cited in the supporting information: Ilinca (2022); Momma & Izumi (2011).

Supporting information

Computing details

(OPX_1)

Crystal data

Si·3(O)·0.135(Fe)·0.73(Mg)·0.135(Li)	Dx = 3.282 Mg m^−3
Mr = 102.31	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbca	Cell parameters from 9984 reflections
a = 18.1735 (4) Å	θ = 3.0–45.3°
b = 8.77666 (18) Å	µ = 2.04 mm^−1
c = 5.19316 (10) Å	T = 293 K
V = 828.32 (3) Å^3	Anhedral
Z = 16	0.65 × 0.50 × 0.45 mm
F(000) = 867

Data collection

Bruker Smart Breeze diffractometer	5429 independent reflections
Radiation source: fine-focus sealed tube	4934 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.019
Detector resolution: 512 pixels mm^-1	θmax = 57.3°, θmin = 2.2°
φ and ω scans	h = −42→30
Absorption correction: multi-scan SADABS (Sheldrick, 2015)	k = −16→20
Tmin = 0.307, Tmax = 0.400	l = −11→11
27573 measured reflections

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0059P)^2 + 0.3411P] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.028	(Δ/σ)max = 0.001
wR(F^2) = 0.050	Δρmax = 0.69 e Å^−3
S = 1.27	Δρmin = −0.50 e Å^−3
5429 reflections	Extinction correction: SHELXL-2018/3 (Sheldrick 2018), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
95 parameters	Extinction coefficient: 0.0041 (4)

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Mg1	0.37538 (2)	0.65012 (2)	0.87318 (3)	0.00574 (3)	0.7302 (9)
Fe1	0.37538 (2)	0.65012 (2)	0.87318 (3)	0.00574 (3)	0.2698 (9)
Mg2	0.37657 (2)	0.48686 (3)	0.36389 (5)	0.00774 (5)	0.7302 (9)
Li2	0.37657 (2)	0.48686 (3)	0.36389 (5)	0.00774 (5)	0.2698 (9)
Si1A	0.27236 (2)	0.34093 (2)	0.05339 (3)	0.00374 (2)	0.820 (14)
Si1B	0.27236 (2)	0.34093 (2)	0.05339 (3)	0.00374 (2)	0.180 (14)
Si2A	0.47393 (2)	0.33747 (2)	0.79450 (3)	0.00384 (2)	0.820 (14)
Si2B	0.47393 (2)	0.33747 (2)	0.79450 (3)	0.00384 (2)	0.180 (14)
O1A	0.18350 (2)	0.33779 (5)	0.04225 (7)	0.00568 (4)	0.297 (17)
O2A	0.31019 (2)	0.50405 (5)	0.04725 (7)	0.00675 (5)	0.297 (17)
O3A	0.30371 (2)	0.22559 (5)	0.83081 (7)	0.00673 (5)	0.297 (17)
O1B	0.56325 (2)	0.33845 (5)	0.79707 (7)	0.00577 (4)	0.297 (17)
O2B	0.43396 (2)	0.48742 (5)	0.69556 (8)	0.00742 (5)	0.297 (17)
O3B	0.44750 (2)	0.19999 (5)	0.59420 (7)	0.00706 (5)	0.297 (17)
O1AA	0.18350 (2)	0.33779 (5)	0.04225 (7)	0.00568 (4)	0.703 (17)
O2AA	0.31019 (2)	0.50405 (5)	0.04725 (7)	0.00675 (5)	0.703 (17)
O3AA	0.30371 (2)	0.22559 (5)	0.83081 (7)	0.00673 (5)	0.703 (17)
O1BA	0.56325 (2)	0.33845 (5)	0.79707 (7)	0.00577 (4)	0.703 (17)
O2BA	0.43396 (2)	0.48742 (5)	0.69556 (8)	0.00742 (5)	0.703 (17)
O3BA	0.44750 (2)	0.19999 (5)	0.59420 (7)	0.00706 (5)	0.703 (17)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mg1	0.00502 (4)	0.00681 (5)	0.00540 (4)	0.00025 (3)	−0.00079 (3)	−0.00070 (3)
Fe1	0.00502 (4)	0.00681 (5)	0.00540 (4)	0.00025 (3)	−0.00079 (3)	−0.00070 (3)
Mg2	0.00851 (8)	0.00813 (10)	0.00658 (9)	−0.00118 (7)	−0.00222 (6)	0.00083 (7)
Li2	0.00851 (8)	0.00813 (10)	0.00658 (9)	−0.00118 (7)	−0.00222 (6)	0.00083 (7)
Si1A	0.00339 (4)	0.00442 (5)	0.00342 (4)	−0.00052 (3)	0.00023 (3)	−0.00012 (3)
Si1B	0.00339 (4)	0.00442 (5)	0.00342 (4)	−0.00052 (3)	0.00023 (3)	−0.00012 (3)
Si2A	0.00338 (4)	0.00445 (5)	0.00368 (4)	0.00041 (3)	−0.00041 (3)	0.00017 (3)
Si2B	0.00338 (4)	0.00445 (5)	0.00368 (4)	0.00041 (3)	−0.00041 (3)	0.00017 (3)
O1A	0.00337 (8)	0.00755 (12)	0.00610 (10)	−0.00005 (8)	0.00009 (7)	−0.00061 (8)
O2A	0.00747 (10)	0.00551 (12)	0.00728 (11)	−0.00251 (9)	−0.00043 (8)	0.00087 (8)
O3A	0.00570 (9)	0.00968 (14)	0.00480 (10)	0.00049 (9)	−0.00024 (7)	−0.00300 (8)
O1B	0.00368 (8)	0.00783 (13)	0.00580 (10)	−0.00024 (8)	−0.00049 (7)	0.00018 (8)
O2B	0.00801 (10)	0.00722 (13)	0.00704 (12)	0.00304 (9)	−0.00018 (8)	0.00192 (9)
O3B	0.00594 (9)	0.00902 (14)	0.00622 (11)	−0.00083 (9)	0.00030 (8)	−0.00350 (9)
O1AA	0.00337 (8)	0.00755 (12)	0.00610 (10)	−0.00005 (8)	0.00009 (7)	−0.00061 (8)
O2AA	0.00747 (10)	0.00551 (12)	0.00728 (11)	−0.00251 (9)	−0.00043 (8)	0.00087 (8)
O3AA	0.00570 (9)	0.00968 (14)	0.00480 (10)	0.00049 (9)	−0.00024 (7)	−0.00300 (8)
O1BA	0.00368 (8)	0.00783 (13)	0.00580 (10)	−0.00024 (8)	−0.00049 (7)	0.00018 (8)
O2BA	0.00801 (10)	0.00722 (13)	0.00704 (12)	0.00304 (9)	−0.00018 (8)	0.00192 (9)
O3BA	0.00594 (9)	0.00902 (14)	0.00622 (11)	−0.00083 (9)	0.00030 (8)	−0.00350 (9)

Geometric parameters (Å, º)

Mg1—O2A^i	1.9658 (4)	Mg2—O1A^ii	2.1020 (5)
Mg1—O2B	2.0059 (4)	Mg2—O3A^ix	2.2934 (5)
Mg1—O1A^ii	2.0273 (4)	Mg2—O3B^ix	2.5125 (5)
Mg1—O1B^iii	2.0461 (4)	Mg2—Si1A	2.7977 (3)
Mg1—O1A^iv	2.1514 (4)	Si1A—O2A	1.5885 (4)
Mg1—O1B^v	2.1812 (4)	Si1A—O1A	1.6161 (3)
Mg1—Mg2^i	2.9236 (3)	Si1A—O3A^x	1.6387 (4)
Mg1—Mg2	3.0081 (3)	Si1A—O3A^ix	1.6556 (4)
Mg1—Mg1^vi	3.1330 (2)	Si2A—O2B	1.5886 (4)
Mg1—Mg1^vii	3.1330 (2)	Si2A—O1B	1.6233 (3)
Mg2—O2B	2.0136 (5)	Si2A—O3B^xi	1.6616 (4)
Mg2—O2A	2.0450 (5)	Si2A—O3B	1.6639 (4)
Mg2—O1B^viii	2.0605 (5)
O2A^i—Mg1—O2B	93.846 (18)	O3A^ix—Mg2—Mg1^x	109.204 (14)
O2A^i—Mg1—O1A^ii	96.076 (16)	O3B^ix—Mg2—Mg1^x	80.666 (12)
O2B—Mg1—O1A^ii	85.847 (16)	Si1A—Mg2—Mg1^x	73.561 (8)
O2A^i—Mg1—O1B^iii	88.605 (16)	O2A—Si1A—O1A	116.56 (2)
O2B—Mg1—O1B^iii	97.495 (16)	O2A—Si1A—O3A^x	113.09 (2)
O1A^ii—Mg1—O1B^iii	174.072 (18)	O1A—Si1A—O3A^x	108.16 (2)
O2A^i—Mg1—O1A^iv	90.679 (16)	O2A—Si1A—O3A^ix	100.74 (2)
O2B—Mg1—O1A^iv	175.318 (17)	O1A—Si1A—O3A^ix	111.65 (2)
O1A^ii—Mg1—O1A^iv	92.484 (14)	O3A^x—Si1A—O3A^ix	106.041 (14)
O1B^iii—Mg1—O1A^iv	83.803 (15)	O2A—Si1A—Mg2	46.052 (15)
O2A^i—Mg1—O1B^v	171.404 (17)	O1A—Si1A—Mg2	134.816 (16)
O2B—Mg1—O1B^v	94.683 (16)	O3A^x—Si1A—Mg2	116.999 (15)
O1A^ii—Mg1—O1B^v	83.489 (15)	O3A^ix—Si1A—Mg2	55.037 (15)
O1B^iii—Mg1—O1B^v	91.338 (14)	O2A—Si1A—Mg1^xii	110.859 (16)
O1A^iv—Mg1—O1B^v	80.772 (14)	O1A—Si1A—Mg1^xii	33.873 (13)
O2A^i—Mg1—Mg2^i	44.276 (12)	O3A^x—Si1A—Mg1^xii	132.993 (15)
O2B—Mg1—Mg2^i	92.751 (13)	O3A^ix—Si1A—Mg1^xii	81.011 (13)
O1A^ii—Mg1—Mg2^i	140.218 (13)	Mg2—Si1A—Mg1^xii	105.132 (8)
O1B^iii—Mg1—Mg2^i	44.806 (12)	O2A—Si1A—Mg2^xii	86.287 (16)
O1A^iv—Mg1—Mg2^i	91.328 (12)	O1A—Si1A—Mg2^xii	33.444 (15)
O1B^v—Mg1—Mg2^i	136.130 (12)	O3A^x—Si1A—Mg2^xii	111.282 (15)
O2A^i—Mg1—Mg2	95.624 (14)	O3A^ix—Si1A—Mg2^xii	135.524 (15)
O2B—Mg1—Mg2	41.647 (12)	Mg2—Si1A—Mg2^xii	121.665 (7)
O1A^ii—Mg1—Mg2	44.224 (12)	Mg1^xii—Si1A—Mg2^xii	55.947 (6)
O1B^iii—Mg1—Mg2	139.050 (13)	O2B—Si2A—O1B	117.10 (2)
O1A^iv—Mg1—Mg2	136.640 (12)	O2B—Si2A—O3B^xi	109.55 (2)
O1B^v—Mg1—Mg2	90.050 (12)	O1B—Si2A—O3B^xi	106.403 (19)
Mg2^i—Mg1—Mg2	122.198 (11)	O2B—Si2A—O3B	105.46 (2)
O2A^i—Mg1—Mg1^vi	89.073 (12)	O1B—Si2A—O3B	107.31 (2)
O2B—Mg1—Mg1^vi	141.214 (12)	O3B^xi—Si2A—O3B	111.017 (15)
O1A^ii—Mg1—Mg1^vi	132.321 (13)	O2B—Si2A—Mg2	33.456 (16)
O1B^iii—Mg1—Mg1^vi	43.858 (11)	O1B—Si2A—Mg2	124.568 (16)
O1A^iv—Mg1—Mg1^vi	39.950 (10)	O3B^xi—Si2A—Mg2	125.949 (15)
O1B^v—Mg1—Mg1^vi	84.947 (12)	O3B—Si2A—Mg2	72.229 (16)
Mg2^i—Mg1—Mg1^vi	63.376 (6)	O2B—Si2A—Mg2^viii	84.652 (16)
Mg2—Mg1—Mg1^vi	174.406 (9)	O1B—Si2A—Mg2^viii	32.708 (15)
O2A^i—Mg1—Mg1^vii	138.250 (12)	O3B^xi—Si2A—Mg2^viii	125.173 (16)
O2B—Mg1—Mg1^vii	90.987 (12)	O3B—Si2A—Mg2^viii	115.448 (15)
O1A^ii—Mg1—Mg1^vii	42.956 (11)	Mg2—Si2A—Mg2^viii	95.355 (8)
O1B^iii—Mg1—Mg1^vii	131.773 (12)	O2B—Si2A—Mg1^iii	122.080 (17)
O1A^iv—Mg1—Mg1^vii	84.827 (12)	O1B—Si2A—Mg1^iii	31.781 (13)
O1B^v—Mg1—Mg1^vii	40.537 (10)	O3B^xi—Si2A—Mg1^iii	75.640 (14)
Mg2^i—Mg1—Mg1^vii	175.303 (9)	O3B—Si2A—Mg1^iii	126.981 (15)
Mg2—Mg1—Mg1^vii	62.475 (6)	Mg2—Si2A—Mg1^iii	147.383 (8)
Mg1^vi—Mg1—Mg1^vii	111.947 (9)	Mg2^viii—Si2A—Mg1^iii	53.736 (6)
O2B—Mg2—O2A	173.31 (2)	Si1A—O1A—Mg1^xii	119.75 (2)
O2B—Mg2—O1B^viii	94.028 (19)	Si1A—O1A—Mg2^xii	121.49 (2)
O2A—Mg2—O1B^viii	86.103 (18)	Mg1^xii—O1A—Mg2^xii	93.501 (16)
O2B—Mg2—O1A^ii	83.702 (18)	Si1A—O1A—Mg1^xiii	121.65 (2)
O2A—Mg2—O1A^ii	89.652 (18)	Mg1^xii—O1A—Mg1^xiii	97.092 (15)
O1B^viii—Mg2—O1A^ii	84.816 (18)	Mg2^xii—O1A—Mg1^xiii	97.027 (16)
O2B—Mg2—O3A^ix	111.415 (19)	Si1A—O2A—Mg1^x	149.07 (3)
O2A—Mg2—O3A^ix	70.072 (16)	Si1A—O2A—Mg2	99.94 (2)
O1B^viii—Mg2—O3A^ix	151.77 (2)	Mg1^x—O2A—Mg2	93.573 (17)
O1A^ii—Mg2—O3A^ix	109.175 (18)	Si1A^i—O3A—Si1A^xi	135.40 (2)
O2B—Mg2—O3B^ix	102.278 (18)	Si1A^i—O3A—Mg2^xi	130.55 (2)
O2A—Mg2—O3B^ix	84.411 (17)	Si1A^xi—O3A—Mg2^xi	88.691 (18)
O1B^viii—Mg2—O3B^ix	89.266 (17)	Si2A—O1B—Mg1^iii	123.52 (2)
O1A^ii—Mg2—O3B^ix	171.892 (19)	Si2A—O1B—Mg2^viii	122.10 (2)
O3A^ix—Mg2—O3B^ix	73.966 (16)	Mg1^iii—O1B—Mg2^viii	90.786 (16)
O2B—Mg2—Si1A	147.646 (18)	Si2A—O1B—Mg1^xiv	120.26 (2)
O2A—Mg2—Si1A	34.005 (12)	Mg1^iii—O1B—Mg1^xiv	95.606 (15)
O1B^viii—Mg2—Si1A	117.785 (15)	Mg2^viii—O1B—Mg1^xiv	97.354 (16)
O1A^ii—Mg2—Si1A	103.745 (14)	Si2A—O2B—Mg1	133.13 (2)
O3A^ix—Mg2—Si1A	36.272 (10)	Si2A—O2B—Mg2	120.76 (3)
O3B^ix—Mg2—Si1A	74.170 (12)	Mg1—O2B—Mg2	96.903 (18)
O2B—Mg2—Mg1^x	138.435 (17)	Si2A^ix—O3B—Si2A	130.21 (3)
O2A—Mg2—Mg1^x	42.151 (12)	Si2A^ix—O3B—Mg2^xi	122.77 (2)
O1B^viii—Mg2—Mg1^x	44.409 (11)	Si2A—O3B—Mg2^xi	105.839 (19)
O1A^ii—Mg2—Mg1^x	91.226 (14)

Symmetry codes: (i) x, y, z+1; (ii) −x+1/2, −y+1, z+1/2; (iii) −x+1, −y+1, −z+2; (iv) −x+1/2, y+1/2, z+1; (v) −x+1, y+1/2, −z+3/2; (vi) x, −y+3/2, z+1/2; (vii) x, −y+3/2, z−1/2; (viii) −x+1, −y+1, −z+1; (ix) x, −y+1/2, z−1/2; (x) x, y, z−1; (xi) x, −y+1/2, z+1/2; (xii) −x+1/2, −y+1, z−1/2; (xiii) −x+1/2, y−1/2, z−1; (xiv) −x+1, y−1/2, −z+3/2.

(OPX_2)

Crystal data

Si·3(O)·0.145(Fe)·0.71(Mg)·0.145(Li)	Dx = 3.287 Mg m^−3
Mr = 102.45	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbca	Cell parameters from 5746 reflections
a = 18.1654 (4) Å	θ = 3.2–45.3°
b = 8.7730 (2) Å	µ = 2.07 mm^−1
c = 5.1958 (1) Å	T = 293 K
V = 828.03 (3) Å^3	Anhedral
Z = 16	0.24 × 0.18 × 0.06 mm
F(000) = 870

Data collection

Bruker Smart Breeze diffractometer	3483 independent reflections
Radiation source: fine-focus sealed tube	2907 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.028
Detector resolution: 512 pixels mm^-1	θmax = 45.3°, θmin = 2.2°
φ and ω scans	h = −27→36
Absorption correction: multi-scan SADABS (Sheldrick, 2015)	k = −14→17
Tmin = 0.646, Tmax = 0.883	l = −10→8
20177 measured reflections

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0139P)^2 + 0.243P] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.021	(Δ/σ)max = 0.001
wR(F^2) = 0.042	Δρmax = 0.44 e Å^−3
S = 1.01	Δρmin = −0.44 e Å^−3
3483 reflections	Extinction correction: SHELXL-2019/3 (Sheldrick 2019), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
95 parameters	Extinction coefficient: 0.0029 (3)

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Mg1	0.37536 (2)	0.64997 (2)	0.87375 (3)	0.00580 (3)	0.7101 (9)
Fe1	0.37536 (2)	0.64997 (2)	0.87375 (3)	0.00580 (3)	0.2899 (9)
Mg2	0.37654 (2)	0.48689 (3)	0.36462 (6)	0.00829 (6)	0.7101 (9)
Li2	0.37654 (2)	0.48689 (3)	0.36462 (6)	0.00829 (6)	0.2899 (9)
Si1A	0.27243 (2)	0.34082 (2)	0.05376 (3)	0.00398 (3)	0.871 (15)
Si1B	0.27243 (2)	0.34082 (2)	0.05376 (3)	0.00398 (3)	0.129 (15)
Si2A	0.47398 (2)	0.33747 (2)	0.79407 (3)	0.00408 (3)	0.871 (15)
Si2B	0.47398 (2)	0.33747 (2)	0.79407 (3)	0.00408 (3)	0.129 (15)
O1A	0.18351 (2)	0.33752 (5)	0.04320 (8)	0.00596 (6)	0.309 (16)
O2A	0.31012 (2)	0.50425 (5)	0.04755 (9)	0.00691 (6)	0.309 (16)
O3A	0.30376 (2)	0.22584 (5)	0.83070 (8)	0.00689 (6)	0.309 (16)
O1B	0.56337 (2)	0.33829 (5)	0.79667 (8)	0.00581 (6)	0.309 (16)
O2B	0.43409 (2)	0.48797 (5)	0.69631 (9)	0.00763 (6)	0.309 (16)
O3B	0.44747 (2)	0.20054 (5)	0.59326 (9)	0.00733 (6)	0.309 (16)
O1AA	0.18351 (2)	0.33752 (5)	0.04320 (8)	0.00596 (6)	0.691 (16)
O2AA	0.31012 (2)	0.50425 (5)	0.04755 (9)	0.00691 (6)	0.691 (16)
O3AA	0.30376 (2)	0.22584 (5)	0.83070 (8)	0.00689 (6)	0.691 (16)
O1BA	0.56337 (2)	0.33829 (5)	0.79667 (8)	0.00581 (6)	0.691 (16)
O2BA	0.43409 (2)	0.48797 (5)	0.69631 (9)	0.00763 (6)	0.691 (16)
O3BA	0.44747 (2)	0.20054 (5)	0.59326 (9)	0.00733 (6)	0.691 (16)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mg1	0.00517 (5)	0.00680 (6)	0.00544 (6)	0.00022 (4)	−0.00078 (4)	−0.00066 (4)
Fe1	0.00517 (5)	0.00680 (6)	0.00544 (6)	0.00022 (4)	−0.00078 (4)	−0.00066 (4)
Mg2	0.00903 (10)	0.00857 (11)	0.00726 (11)	−0.00115 (8)	−0.00227 (9)	0.00095 (9)
Li2	0.00903 (10)	0.00857 (11)	0.00726 (11)	−0.00115 (8)	−0.00227 (9)	0.00095 (9)
Si1A	0.00369 (5)	0.00458 (6)	0.00365 (5)	−0.00047 (4)	0.00021 (4)	−0.00007 (4)
Si1B	0.00369 (5)	0.00458 (6)	0.00365 (5)	−0.00047 (4)	0.00021 (4)	−0.00007 (4)
Si2A	0.00369 (5)	0.00466 (6)	0.00389 (5)	0.00037 (4)	−0.00041 (4)	0.00023 (4)
Si2B	0.00369 (5)	0.00466 (6)	0.00389 (5)	0.00037 (4)	−0.00041 (4)	0.00023 (4)
O1A	0.00365 (11)	0.00784 (14)	0.00640 (14)	0.00000 (10)	0.00014 (10)	−0.00050 (12)
O2A	0.00764 (12)	0.00590 (14)	0.00718 (15)	−0.00256 (11)	−0.00019 (12)	0.00077 (12)
O3A	0.00582 (12)	0.00992 (15)	0.00494 (13)	0.00038 (11)	−0.00014 (11)	−0.00322 (12)
O1B	0.00357 (11)	0.00803 (14)	0.00584 (14)	−0.00030 (10)	−0.00051 (11)	0.00010 (12)
O2B	0.00822 (13)	0.00721 (14)	0.00747 (15)	0.00305 (11)	0.00008 (12)	0.00208 (12)
O3B	0.00613 (12)	0.00938 (15)	0.00647 (14)	−0.00098 (11)	0.00039 (11)	−0.00378 (12)
O1AA	0.00365 (11)	0.00784 (14)	0.00640 (14)	0.00000 (10)	0.00014 (10)	−0.00050 (12)
O2AA	0.00764 (12)	0.00590 (14)	0.00718 (15)	−0.00256 (11)	−0.00019 (12)	0.00077 (12)
O3AA	0.00582 (12)	0.00992 (15)	0.00494 (13)	0.00038 (11)	−0.00014 (11)	−0.00322 (12)
O1BA	0.00357 (11)	0.00803 (14)	0.00584 (14)	−0.00030 (10)	−0.00051 (11)	0.00010 (12)
O2BA	0.00822 (13)	0.00721 (14)	0.00747 (15)	0.00305 (11)	0.00008 (12)	0.00208 (12)
O3BA	0.00613 (12)	0.00938 (15)	0.00647 (14)	−0.00098 (11)	0.00039 (11)	−0.00378 (12)

Geometric parameters (Å, º)

Mg1—O2A^i	1.9633 (4)	Mg2—O1A^ii	2.1033 (5)
Mg1—O2B	2.0020 (4)	Mg2—O3A^ix	2.2938 (5)
Mg1—O1A^ii	2.0262 (4)	Mg2—O3B^ix	2.5203 (5)
Mg1—O1B^iii	2.0450 (4)	Mg2—Si1A	2.7977 (3)
Mg1—O1A^iv	2.1508 (4)	Si1A—O2A	1.5891 (4)
Mg1—O1B^v	2.1800 (4)	Si1A—O1A	1.6166 (4)
Mg1—Mg2^i	2.9245 (3)	Si1A—O3A^x	1.6385 (4)
Mg1—Mg2	3.0075 (4)	Si1A—O3A^ix	1.6542 (5)
Mg1—Mg1^vi	3.1352 (2)	Si2A—O2B	1.5894 (4)
Mg1—Mg1^vii	3.1352 (2)	Si2A—O1B	1.6238 (4)
Mg2—O2B	2.0157 (5)	Si2A—O3B^xi	1.6612 (5)
Mg2—O2A	2.0477 (5)	Si2A—O3B	1.6624 (5)
Mg2—O1B^viii	2.0607 (5)
O2A^i—Mg1—O2B	94.085 (19)	O3A^ix—Mg2—Mg1^x	109.076 (16)
O2A^i—Mg1—O1A^ii	96.116 (18)	O3B^ix—Mg2—Mg1^x	80.504 (13)
O2B—Mg1—O1A^ii	85.951 (18)	Si1A—Mg2—Mg1^x	73.481 (8)
O2A^i—Mg1—O1B^iii	88.636 (18)	O2A—Si1A—O1A	116.48 (2)
O2B—Mg1—O1B^iii	97.545 (18)	O2A—Si1A—O3A^x	113.05 (2)
O1A^ii—Mg1—O1B^iii	173.906 (18)	O1A—Si1A—O3A^x	108.18 (2)
O2A^i—Mg1—O1A^iv	90.553 (18)	O2A—Si1A—O3A^ix	100.86 (2)
O2B—Mg1—O1A^iv	175.234 (18)	O1A—Si1A—O3A^ix	111.53 (2)
O1A^ii—Mg1—O1A^iv	92.471 (15)	O3A^x—Si1A—O3A^ix	106.147 (16)
O1B^iii—Mg1—O1A^iv	83.646 (17)	O2A—Si1A—Mg2	46.156 (18)
O2A^i—Mg1—O1B^v	171.313 (18)	O1A—Si1A—Mg2	134.691 (18)
O2B—Mg1—O1B^v	94.524 (17)	O3A^x—Si1A—Mg2	117.101 (17)
O1A^ii—Mg1—O1B^v	83.347 (17)	O3A^ix—Si1A—Mg2	55.054 (17)
O1B^iii—Mg1—O1B^v	91.378 (15)	O2A—Si1A—Mg1^xii	110.716 (17)
O1A^iv—Mg1—O1B^v	80.818 (16)	O1A—Si1A—Mg1^xii	33.803 (16)
O2A^i—Mg1—Mg2^i	44.332 (14)	O3A^x—Si1A—Mg1^xii	133.095 (16)
O2B—Mg1—Mg2^i	92.889 (15)	O3A^ix—Si1A—Mg1^xii	81.004 (15)
O1A^ii—Mg1—Mg2^i	140.319 (14)	Mg2—Si1A—Mg1^xii	105.008 (8)
O1B^iii—Mg1—Mg2^i	44.794 (13)	O2A—Si1A—Mg2^xii	86.158 (17)
O1A^iv—Mg1—Mg2^i	91.196 (14)	O1A—Si1A—Mg2^xii	33.536 (16)
O1B^v—Mg1—Mg2^i	136.158 (14)	O3A^x—Si1A—Mg2^xii	111.190 (17)
O2A^i—Mg1—Mg2	95.688 (15)	O3A^ix—Si1A—Mg2^xii	135.524 (17)
O2B—Mg1—Mg2	41.708 (14)	Mg2—Si1A—Mg2^xii	121.610 (8)
O1A^ii—Mg1—Mg2	44.272 (13)	Mg1^xii—Si1A—Mg2^xii	55.934 (7)
O1B^iii—Mg1—Mg2	139.167 (14)	O2B—Si2A—O1B	117.06 (2)
O1A^iv—Mg1—Mg2	136.678 (14)	O2B—Si2A—O3B^xi	109.49 (2)
O1B^v—Mg1—Mg2	89.978 (13)	O1B—Si2A—O3B^xi	106.43 (2)
Mg2^i—Mg1—Mg2	122.297 (11)	O2B—Si2A—O3B	105.53 (2)
O2A^i—Mg1—Mg1^vi	138.218 (13)	O1B—Si2A—O3B	107.34 (2)
O2B—Mg1—Mg1^vi	90.907 (13)	O3B^xi—Si2A—O3B	110.995 (17)
O1A^ii—Mg1—Mg1^vi	42.888 (12)	O2B—Si2A—Mg2	33.684 (18)
O1B^iii—Mg1—Mg1^vi	131.734 (13)	O1B—Si2A—Mg2	124.653 (18)
O1A^iv—Mg1—Mg1^vi	84.892 (13)	O3B^xi—Si2A—Mg2	125.893 (17)
O1B^v—Mg1—Mg1^vi	40.463 (12)	O3B—Si2A—Mg2	72.058 (18)
Mg2^i—Mg1—Mg1^vi	175.229 (9)	O2B—Si2A—Mg2^viii	84.570 (17)
Mg2—Mg1—Mg1^vi	62.450 (6)	O1B—Si2A—Mg2^viii	32.772 (16)
O2A^i—Mg1—Mg1^vii	89.047 (14)	O3B^xi—Si2A—Mg2^viii	125.343 (17)
O2B—Mg1—Mg1^vii	141.167 (13)	O3B—Si2A—Mg2^viii	115.348 (17)
O1A^ii—Mg1—Mg1^vii	132.226 (13)	Mg2—Si2A—Mg2^viii	95.365 (8)
O1B^iii—Mg1—Mg1^vii	43.774 (12)	O2B—Si2A—Mg1^iii	121.837 (18)
O1A^iv—Mg1—Mg1^vii	39.877 (12)	O1B—Si2A—Mg1^iii	31.799 (16)
O1B^v—Mg1—Mg1^vii	84.970 (13)	O3B^xi—Si2A—Mg1^iii	75.698 (16)
Mg2^i—Mg1—Mg1^vii	63.333 (7)	O3B—Si2A—Mg1^iii	127.159 (17)
Mg2—Mg1—Mg1^vii	174.350 (9)	Mg2—Si2A—Mg1^iii	147.398 (8)
Mg1^vi—Mg1—Mg1^vii	111.916 (9)	Mg2^viii—Si2A—Mg1^iii	53.775 (7)
O2B—Mg2—O2A	173.27 (2)	Si1A—O1A—Mg1^xii	119.85 (2)
O2B—Mg2—O1B^viii	93.98 (2)	Si1A—O1A—Mg2^xii	121.34 (2)
O2A—Mg2—O1B^viii	85.96 (2)	Mg1^xii—O1A—Mg2^xii	93.468 (18)
O2B—Mg2—O1A^ii	83.59 (2)	Si1A—O1A—Mg1^xiii	121.64 (2)
O2A—Mg2—O1A^ii	89.70 (2)	Mg1^xii—O1A—Mg1^xiii	97.236 (17)
O1B^viii—Mg2—O1A^ii	84.782 (19)	Mg2^xii—O1A—Mg1^xiii	96.997 (18)
O2B—Mg2—O3A^ix	111.62 (2)	Si1A—O2A—Mg1^x	148.97 (3)
O2A—Mg2—O3A^ix	70.070 (18)	Si1A—O2A—Mg2	99.81 (2)
O1B^viii—Mg2—O3A^ix	151.60 (2)	Mg1^x—O2A—Mg2	93.598 (19)
O1A^ii—Mg2—O3A^ix	109.32 (2)	Si1A^i—O3A—Si1A^xi	135.51 (3)
O2B—Mg2—O3B^ix	102.486 (19)	Si1A^i—O3A—Mg2^xi	130.30 (3)
O2A—Mg2—O3B^ix	84.244 (19)	Si1A^xi—O3A—Mg2^xi	88.71 (2)
O1B^viii—Mg2—O3B^ix	89.268 (19)	Si2A—O1B—Mg1^iii	123.47 (2)
O1A^ii—Mg2—O3B^ix	171.80 (2)	Si2A—O1B—Mg2^viii	121.98 (2)
O3A^ix—Mg2—O3B^ix	73.791 (17)	Mg1^iii—O1B—Mg2^viii	90.846 (18)
O2B—Mg2—Si1A	147.814 (19)	Si2A—O1B—Mg1^xiv	120.25 (2)
O2A—Mg2—Si1A	34.036 (13)	Mg1^iii—O1B—Mg1^xiv	95.765 (17)
O1B^viii—Mg2—Si1A	117.659 (17)	Mg2^viii—O1B—Mg1^xiv	97.377 (19)
O1A^ii—Mg2—Si1A	103.862 (16)	Si2A—O2B—Mg1	133.27 (3)
O3A^ix—Mg2—Si1A	36.237 (12)	Si2A—O2B—Mg2	120.38 (3)
O3B^ix—Mg2—Si1A	73.966 (13)	Mg1—O2B—Mg2	96.930 (19)
O2B—Mg2—Mg1^x	138.343 (18)	Si2A^ix—O3B—Si2A	130.43 (3)
O2A—Mg2—Mg1^x	42.069 (13)	Si2A^ix—O3B—Mg2^xi	122.73 (2)
O1B^viii—Mg2—Mg1^x	44.361 (13)	Si2A—O3B—Mg2^xi	105.57 (2)
O1A^ii—Mg2—Mg1^x	91.297 (16)

Symmetry codes: (i) x, y, z+1; (ii) −x+1/2, −y+1, z+1/2; (iii) −x+1, −y+1, −z+2; (iv) −x+1/2, y+1/2, z+1; (v) −x+1, y+1/2, −z+3/2; (vi) x, −y+3/2, z−1/2; (vii) x, −y+3/2, z+1/2; (viii) −x+1, −y+1, −z+1; (ix) x, −y+1/2, z−1/2; (x) x, y, z−1; (xi) x, −y+1/2, z+1/2; (xii) −x+1/2, −y+1, z−1/2; (xiii) −x+1/2, y−1/2, z−1; (xiv) −x+1, y−1/2, −z+3/2.

(OPX_3)

Crystal data

Si·3(O)·0.157(Fe)·0.687(Mg)·0.157(Li)	Dx = 3.290 Mg m^−3
Mr = 102.62	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbca	Cell parameters from 9569 reflections
a = 18.1718 (4) Å	θ = 3.4–45.2°
b = 8.7706 (2) Å	µ = 2.13 mm^−1
c = 5.1992 (1) Å	T = 293 K
V = 828.64 (3) Å^3	Anhedral
Z = 16	0.24 × 0.18 × 0.06 mm
F(000) = 877

Data collection

Bruker Smart Breeze diffractometer	3458 independent reflections
Radiation source: fine-focus sealed tube	3231 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.020
Detector resolution: 512 pixels mm^-1	θmax = 45.3°, θmin = 3.2°
φ and ω scans	h = −36→29
Absorption correction: multi-scan SADABS (Sheldrick, 2015)	k = −13→17
Tmin = 0.638, Tmax = 0.880	l = −10→10
20229 measured reflections

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0129P)^2 + 0.1879P] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.019	(Δ/σ)max = 0.002
wR(F^2) = 0.041	Δρmax = 0.48 e Å^−3
S = 1.17	Δρmin = −0.44 e Å^−3
3458 reflections	Extinction correction: SHELXL-2019/3 (Sheldrick 2019), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
95 parameters	Extinction coefficient: 0.0110 (6)

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Mg1	0.37534 (2)	0.64975 (2)	0.87437 (2)	0.00581 (3)	0.6865 (9)
Fe1	0.37534 (2)	0.64975 (2)	0.87437 (2)	0.00581 (3)	0.3135 (9)
Mg2	0.37650 (2)	0.48689 (3)	0.36523 (5)	0.00829 (5)	0.6865 (9)
Li2	0.37650 (2)	0.48689 (3)	0.36523 (5)	0.00829 (5)	0.3135 (9)
Si1A	0.27250 (2)	0.34081 (2)	0.05404 (2)	0.00393 (3)	0.886 (16)
Si1B	0.27250 (2)	0.34081 (2)	0.05404 (2)	0.00393 (3)	0.114 (16)
Si2A	0.47402 (2)	0.33749 (2)	0.79363 (3)	0.00404 (3)	0.886 (16)
Si2B	0.47402 (2)	0.33749 (2)	0.79363 (3)	0.00404 (3)	0.114 (16)
O1A	0.18354 (2)	0.33734 (4)	0.04383 (7)	0.00587 (5)	0.254 (16)
O2A	0.31006 (2)	0.50439 (4)	0.04793 (7)	0.00688 (5)	0.254 (16)
O3A	0.30382 (2)	0.22610 (4)	0.83055 (7)	0.00696 (5)	0.254 (16)
O1B	0.56344 (2)	0.33808 (4)	0.79630 (7)	0.00592 (5)	0.254 (16)
O2B	0.43426 (2)	0.48839 (4)	0.69697 (7)	0.00767 (5)	0.254 (16)
O3B	0.44749 (2)	0.20110 (4)	0.59206 (7)	0.00744 (5)	0.254 (16)
O1AA	0.18354 (2)	0.33734 (4)	0.04383 (7)	0.00587 (5)	0.746 (16)
O2AA	0.31006 (2)	0.50439 (4)	0.04793 (7)	0.00688 (5)	0.746 (16)
O3AA	0.30382 (2)	0.22610 (4)	0.83055 (7)	0.00696 (5)	0.746 (16)
O1BA	0.56344 (2)	0.33808 (4)	0.79630 (7)	0.00592 (5)	0.746 (16)
O2BA	0.43426 (2)	0.48839 (4)	0.69697 (7)	0.00767 (5)	0.746 (16)
O3BA	0.44749 (2)	0.20110 (4)	0.59206 (7)	0.00744 (5)	0.746 (16)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mg1	0.00508 (5)	0.00683 (5)	0.00554 (5)	0.00024 (3)	−0.00081 (3)	−0.00071 (3)
Fe1	0.00508 (5)	0.00683 (5)	0.00554 (5)	0.00024 (3)	−0.00081 (3)	−0.00071 (3)
Mg2	0.00897 (10)	0.00851 (9)	0.00739 (9)	−0.00123 (7)	−0.00244 (7)	0.00084 (7)
Li2	0.00897 (10)	0.00851 (9)	0.00739 (9)	−0.00123 (7)	−0.00244 (7)	0.00084 (7)
Si1A	0.00356 (4)	0.00445 (4)	0.00377 (5)	−0.00053 (3)	0.00023 (3)	−0.00011 (3)
Si1B	0.00356 (4)	0.00445 (4)	0.00377 (5)	−0.00053 (3)	0.00023 (3)	−0.00011 (3)
Si2A	0.00357 (4)	0.00447 (4)	0.00408 (5)	0.00042 (3)	−0.00041 (3)	0.00017 (3)
Si2B	0.00357 (4)	0.00447 (4)	0.00408 (5)	0.00042 (3)	−0.00041 (3)	0.00017 (3)
O1A	0.00347 (10)	0.00784 (11)	0.00630 (11)	−0.00005 (8)	0.00017 (8)	−0.00056 (9)
O2A	0.00769 (11)	0.00537 (11)	0.00759 (12)	−0.00258 (9)	−0.00034 (9)	0.00082 (9)
O3A	0.00573 (11)	0.01000 (12)	0.00517 (11)	0.00042 (9)	−0.00015 (8)	−0.00318 (9)
O1B	0.00369 (10)	0.00791 (11)	0.00616 (11)	−0.00020 (8)	−0.00043 (8)	0.00024 (9)
O2B	0.00808 (12)	0.00735 (11)	0.00758 (12)	0.00322 (9)	−0.00009 (9)	0.00213 (10)
O3B	0.00592 (11)	0.00974 (12)	0.00666 (11)	−0.00095 (9)	0.00025 (8)	−0.00395 (10)
O1AA	0.00347 (10)	0.00784 (11)	0.00630 (11)	−0.00005 (8)	0.00017 (8)	−0.00056 (9)
O2AA	0.00769 (11)	0.00537 (11)	0.00759 (12)	−0.00258 (9)	−0.00034 (9)	0.00082 (9)
O3AA	0.00573 (11)	0.01000 (12)	0.00517 (11)	0.00042 (9)	−0.00015 (8)	−0.00318 (9)
O1BA	0.00369 (10)	0.00791 (11)	0.00616 (11)	−0.00020 (8)	−0.00043 (8)	0.00024 (9)
O2BA	0.00808 (12)	0.00735 (11)	0.00758 (12)	0.00322 (9)	−0.00009 (9)	0.00213 (10)
O3BA	0.00592 (11)	0.00974 (12)	0.00666 (11)	−0.00095 (9)	0.00025 (8)	−0.00395 (10)

Geometric parameters (Å, º)

Mg1—O2A^i	1.9613 (4)	Mg2—O1A^ii	2.1046 (4)
Mg1—O2B	2.0000 (4)	Mg2—O3A^ix	2.2949 (4)
Mg1—O1A^ii	2.0276 (4)	Mg2—O3B^ix	2.5298 (5)
Mg1—O1B^iii	2.0447 (4)	Mg2—Si1A	2.7983 (3)
Mg1—O1A^iv	2.1512 (4)	Si1A—O2A	1.5891 (4)
Mg1—O1B^v	2.1803 (4)	Si1A—O1A	1.6177 (4)
Mg1—Mg2^i	2.9246 (3)	Si1A—O3A^x	1.6390 (4)
Mg1—Mg2	3.0080 (3)	Si1A—O3A^ix	1.6538 (4)
Mg1—Mg1^vi	3.1385 (1)	Si2A—O2B	1.5894 (4)
Mg1—Mg1^vii	3.1385 (1)	Si2A—O1B	1.6251 (3)
Mg2—O2B	2.0191 (4)	Si2A—O3B^xi	1.6596 (4)
Mg2—O2A	2.0500 (4)	Si2A—O3B	1.6618 (4)
Mg2—O1B^viii	2.0623 (4)
O2A^i—Mg1—O2B	94.361 (16)	O3A^ix—Mg2—Mg1^x	108.957 (13)
O2A^i—Mg1—O1A^ii	96.149 (15)	O3B^ix—Mg2—Mg1^x	80.334 (11)
O2B—Mg1—O1A^ii	86.052 (15)	Si1A—Mg2—Mg1^x	73.395 (7)
O2A^i—Mg1—O1B^iii	88.726 (15)	O2A—Si1A—O1A	116.459 (19)
O2B—Mg1—O1B^iii	97.578 (15)	O2A—Si1A—O3A^x	113.01 (2)
O1A^ii—Mg1—O1B^iii	173.705 (15)	O1A—Si1A—O3A^x	108.190 (18)
O2A^i—Mg1—O1A^iv	90.450 (15)	O2A—Si1A—O3A^ix	100.950 (19)
O2B—Mg1—O1A^iv	175.077 (15)	O1A—Si1A—O3A^ix	111.452 (19)
O1A^ii—Mg1—O1A^iv	92.404 (13)	O3A^x—Si1A—O3A^ix	106.199 (13)
O1B^iii—Mg1—O1A^iv	83.553 (14)	O2A—Si1A—Mg2	46.221 (14)
O2A^i—Mg1—O1B^v	171.237 (15)	O1A—Si1A—Mg2	134.624 (15)
O2B—Mg1—O1B^v	94.314 (15)	O3A^x—Si1A—Mg2	117.158 (14)
O1A^ii—Mg1—O1B^v	83.222 (14)	O3A^ix—Si1A—Mg2	55.074 (14)
O1B^iii—Mg1—O1B^v	91.353 (13)	O2A—Si1A—Mg1^xii	110.599 (14)
O1A^iv—Mg1—O1B^v	80.854 (14)	O1A—Si1A—Mg1^xii	33.774 (13)
O2A^i—Mg1—Mg2^i	44.393 (12)	O3A^x—Si1A—Mg1^xii	133.200 (14)
O2B—Mg1—Mg2^i	93.039 (12)	O3A^ix—Si1A—Mg1^xii	81.013 (13)
O1A^ii—Mg1—Mg2^i	140.417 (12)	Mg2—Si1A—Mg1^xii	104.907 (7)
O1B^iii—Mg1—Mg2^i	44.836 (11)	O2A—Si1A—Mg2^xii	86.103 (15)
O1A^iv—Mg1—Mg2^i	91.129 (11)	O1A—Si1A—Mg2^xii	33.589 (14)
O1B^v—Mg1—Mg2^i	136.176 (11)	O3A^x—Si1A—Mg2^xii	111.118 (14)
O2A^i—Mg1—Mg2	95.767 (13)	O3A^ix—Si1A—Mg2^xii	135.540 (14)
O2B—Mg1—Mg2	41.788 (12)	Mg2—Si1A—Mg2^xii	121.599 (7)
O1A^ii—Mg1—Mg2	44.300 (11)	Mg1^xii—Si1A—Mg2^xii	55.912 (5)
O1B^iii—Mg1—Mg2	139.282 (12)	O2B—Si2A—O1B	117.04 (2)
O1A^iv—Mg1—Mg2	136.640 (11)	O2B—Si2A—O3B^xi	109.48 (2)
O1B^v—Mg1—Mg2	89.886 (11)	O1B—Si2A—O3B^xi	106.444 (19)
Mg2^i—Mg1—Mg2	122.410 (10)	O2B—Si2A—O3B	105.55 (2)
O2A^i—Mg1—Mg1^vi	138.182 (11)	O1B—Si2A—O3B	107.320 (19)
O2B—Mg1—Mg1^vi	90.830 (11)	O3B^xi—Si2A—O3B	111.012 (14)
O1A^ii—Mg1—Mg1^vi	42.830 (10)	O2B—Si2A—Mg2	33.894 (15)
O1B^iii—Mg1—Mg1^vi	131.633 (11)	O1B—Si2A—Mg2	124.768 (15)
O1A^iv—Mg1—Mg1^vi	84.877 (11)	O3B^xi—Si2A—Mg2	125.846 (14)
O1B^v—Mg1—Mg1^vi	40.395 (10)	O3B—Si2A—Mg2	71.863 (15)
Mg2^i—Mg1—Mg1^vi	175.140 (8)	O2B—Si2A—Mg2^viii	84.513 (15)
Mg2—Mg1—Mg1^vi	62.428 (6)	O1B—Si2A—Mg2^viii	32.830 (13)
O2A^i—Mg1—Mg1^vii	89.032 (11)	O3B^xi—Si2A—Mg2^viii	125.488 (15)
O2B—Mg1—Mg1^vii	141.122 (11)	O3B—Si2A—Mg2^viii	115.209 (14)
O1A^ii—Mg1—Mg1^vii	132.123 (11)	Mg2—Si2A—Mg2^viii	95.420 (7)
O1B^iii—Mg1—Mg1^vii	43.710 (10)	O2B—Si2A—Mg1^iii	121.606 (15)
O1A^iv—Mg1—Mg1^vii	39.848 (10)	O1B—Si2A—Mg1^iii	31.788 (13)
O1B^v—Mg1—Mg1^vii	84.987 (11)	O3B^xi—Si2A—Mg1^iii	75.771 (13)
Mg2^i—Mg1—Mg1^vii	63.312 (6)	O3B—Si2A—Mg1^iii	127.317 (14)
Mg2—Mg1—Mg1^vii	174.259 (8)	Mg2—Si2A—Mg1^iii	147.412 (7)
Mg1^vi—Mg1—Mg1^vii	111.846 (7)	Mg2^viii—Si2A—Mg1^iii	53.763 (5)
O2B—Mg2—O2A	173.26 (2)	Si1A—O1A—Mg1^xii	119.90 (2)
O2B—Mg2—O1B^viii	93.892 (17)	Si1A—O1A—Mg2^xii	121.24 (2)
O2A—Mg2—O1B^viii	85.887 (16)	Mg1^xii—O1A—Mg2^xii	93.413 (15)
O2B—Mg2—O1A^ii	83.558 (17)	Si1A—O1A—Mg1^xiii	121.657 (19)
O2A—Mg2—O1A^ii	89.711 (17)	Mg1^xii—O1A—Mg1^xiii	97.321 (15)
O1B^viii—Mg2—O1A^ii	84.766 (17)	Mg2^xii—O1A—Mg1^xiii	96.990 (16)
O2B—Mg2—O3A^ix	111.812 (18)	Si1A—O2A—Mg1^x	148.85 (2)
O2A—Mg2—O3A^ix	70.051 (15)	Si1A—O2A—Mg2	99.74 (2)
O1B^viii—Mg2—O3A^ix	151.464 (19)	Mg1^x—O2A—Mg2	93.597 (16)
O1A^ii—Mg2—O3A^ix	109.429 (17)	Si1A^i—O3A—Si1A^xi	135.61 (2)
O2B—Mg2—O3B^ix	102.632 (16)	Si1A^i—O3A—Mg2^xi	130.08 (2)
O2A—Mg2—O3B^ix	84.109 (16)	Si1A^xi—O3A—Mg2^xi	88.708 (17)
O1B^viii—Mg2—O3B^ix	89.232 (16)	Si2A—O1B—Mg1^iii	123.46 (2)
O1A^ii—Mg2—O3B^ix	171.683 (18)	Si2A—O1B—Mg2^viii	121.88 (2)
O3A^ix—Mg2—O3B^ix	73.672 (15)	Mg1^iii—O1B—Mg2^viii	90.813 (15)
O2B—Mg2—Si1A	147.989 (16)	Si2A—O1B—Mg1^xiv	120.289 (19)
O2A—Mg2—Si1A	34.035 (11)	Mg1^iii—O1B—Mg1^xiv	95.896 (14)
O1B^viii—Mg2—Si1A	117.569 (14)	Mg2^viii—O1B—Mg1^xiv	97.362 (16)
O1A^ii—Mg2—Si1A	103.911 (13)	Si2A—O2B—Mg1	133.37 (2)
O3A^ix—Mg2—Si1A	36.217 (10)	Si2A—O2B—Mg2	120.07 (2)
O3B^ix—Mg2—Si1A	73.825 (11)	Mg1—O2B—Mg2	96.908 (17)
O2B—Mg2—Mg1^x	138.243 (16)	Si2A^ix—O3B—Si2A	130.70 (2)
O2A—Mg2—Mg1^x	42.011 (11)	Si2A^ix—O3B—Mg2^xi	122.69 (2)
O1B^viii—Mg2—Mg1^x	44.353 (11)	Si2A—O3B—Mg2^xi	105.250 (18)
O1A^ii—Mg2—Mg1^x	91.349 (13)

Symmetry codes: (i) x, y, z+1; (ii) −x+1/2, −y+1, z+1/2; (iii) −x+1, −y+1, −z+2; (iv) −x+1/2, y+1/2, z+1; (v) −x+1, y+1/2, −z+3/2; (vi) x, −y+3/2, z−1/2; (vii) x, −y+3/2, z+1/2; (viii) −x+1, −y+1, −z+1; (ix) x, −y+1/2, z−1/2; (x) x, y, z−1; (xi) x, −y+1/2, z+1/2; (xii) −x+1/2, −y+1, z−1/2; (xiii) −x+1/2, y−1/2, z−1; (xiv) −x+1, y−1/2, −z+3/2.

(PPX_4a)

Crystal data

Si·3(O)·0.082(Fe)·0.836(Mg)·0.082(Li)	Dx = 3.166 Mg m^−3
Mr = 101.60	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbcn	Cell parameters from 6514 reflections
a = 9.2232 (2) Å	θ = 3.2–45.3°
b = 8.7040 (2) Å	µ = 1.62 mm^−1
c = 5.3107 (1) Å	T = 293 K
V = 426.34 (2) Å^3	Anhedral
Z = 8	0.40 × 0.32 × 0.25 mm
F(000) = 435

Data collection

Bruker Smart Breeze diffractometer	1753 independent reflections
Radiation source: fine-focus sealed tube	1661 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.015
Detector resolution: 512 pixels mm^-1	θmax = 45.3°, θmin = 3.2°
φ and ω scans	h = −17→17
Absorption correction: multi-scan SADABS (Sheldrick, 2015)	k = −14→17
Tmin = 0.542, Tmax = 0.667	l = −10→9
10336 measured reflections

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0154P)^2 + 0.0476P] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.014	(Δ/σ)max = 0.001
wR(F^2) = 0.035	Δρmax = 0.34 e Å^−3
S = 1.14	Δρmin = −0.34 e Å^−3
1753 reflections	Extinction correction: SHELXL-2018/3 (Sheldrick 2018), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
52 parameters	Extinction coefficient: 0.094 (2)

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Mg1	0.000000	0.09896 (2)	0.750000	0.00580 (4)	0.8361 (9)
Fe1	0.000000	0.09896 (2)	0.750000	0.00580 (4)	0.1639 (9)
Mg2	0.000000	0.26368 (2)	0.250000	0.00691 (5)	0.8361 (9)
Li2	0.000000	0.26368 (2)	0.250000	0.00691 (5)	0.1639 (9)
SiB	0.29263 (2)	0.09090 (2)	0.07181 (2)	0.00417 (3)	0.902 (10)
SiBB	0.29263 (2)	0.09090 (2)	0.07181 (2)	0.00417 (3)	0.098 (10)
O1B	0.11769 (3)	0.09247 (3)	0.07878 (5)	0.00573 (4)	0.287 (16)
O1BB	0.11769 (3)	0.09247 (3)	0.07878 (5)	0.00573 (4)	0.713 (16)
O2B	0.37515 (3)	0.25119 (3)	0.07138 (5)	0.00805 (4)	0.287 (16)
O2BB	0.37515 (3)	0.25119 (3)	0.07138 (5)	0.00805 (4)	0.713 (16)
O3B	0.35046 (3)	0.97953 (3)	0.30011 (5)	0.00821 (4)	0.287 (16)
O3BB	0.35046 (3)	0.97953 (3)	0.30011 (5)	0.00821 (4)	0.713 (16)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mg1	0.00553 (7)	0.00653 (6)	0.00532 (6)	0.000	−0.00055 (4)	0.000
Fe1	0.00553 (7)	0.00653 (6)	0.00532 (6)	0.000	−0.00055 (4)	0.000
Mg2	0.00762 (9)	0.00727 (7)	0.00585 (7)	0.000	−0.00086 (6)	0.000
Li2	0.00762 (9)	0.00727 (7)	0.00585 (7)	0.000	−0.00086 (6)	0.000
SiB	0.00368 (4)	0.00471 (4)	0.00413 (4)	−0.00063 (2)	0.00017 (2)	0.00007 (2)
SiBB	0.00368 (4)	0.00471 (4)	0.00413 (4)	−0.00063 (2)	0.00017 (2)	0.00007 (2)
O1B	0.00373 (9)	0.00756 (8)	0.00592 (8)	0.00024 (6)	0.00013 (6)	−0.00025 (6)
O1BB	0.00373 (9)	0.00756 (8)	0.00592 (8)	0.00024 (6)	0.00013 (6)	−0.00025 (6)
O2B	0.00936 (11)	0.00673 (8)	0.00806 (8)	−0.00391 (7)	0.00030 (7)	−0.00057 (6)
O2BB	0.00936 (11)	0.00673 (8)	0.00806 (8)	−0.00391 (7)	0.00030 (7)	−0.00057 (6)
O3B	0.00591 (10)	0.01204 (9)	0.00669 (8)	0.00053 (7)	0.00066 (7)	0.00460 (7)
O3BB	0.00591 (10)	0.01204 (9)	0.00669 (8)	0.00053 (7)	0.00066 (7)	0.00460 (7)

Geometric parameters (Å, º)

Mg1—O2B^i	1.9816 (3)	Mg2—O1B	2.0557 (3)
Mg1—O2B^ii	1.9816 (3)	Mg2—O2B^viii	2.0629 (3)
Mg1—O1B^iii	2.0567 (3)	Mg2—O2B^i	2.0629 (3)
Mg1—O1B^iv	2.0567 (3)	Mg2—O3B^ix	2.3458 (3)
Mg1—O1B^v	2.1867 (3)	Mg2—O3B^x	2.3458 (3)
Mg1—O1B^vi	2.1867 (3)	Mg2—SiB^i	2.8602 (1)
Mg1—Mg2^iv	3.0177 (1)	Mg2—SiB^viii	2.8602 (1)
Mg1—Mg2	3.0177 (1)	SiB—O2B	1.5893 (3)
Mg1—Mg2^v	3.1564 (3)	SiB—O1B	1.6140 (3)
Mg1—Mg1^v	3.1652 (2)	SiB—O3B^xi	1.6414 (3)
Mg1—Mg1^vii	3.1652 (2)	SiB—O3B^xii	1.6560 (3)
Mg2—O1B^iii	2.0557 (3)
O2B^i—Mg1—O2B^ii	97.677 (18)	O2B^viii—Mg2—O3B^x	68.174 (10)
O2B^i—Mg1—O1B^iii	85.317 (11)	O2B^i—Mg2—O3B^x	118.183 (12)
O2B^ii—Mg1—O1B^iii	96.764 (11)	O3B^ix—Mg2—O3B^x	73.567 (15)
O2B^i—Mg1—O1B^iv	96.764 (11)	O1B^iii—Mg2—SiB^i	114.179 (8)
O2B^ii—Mg1—O1B^iv	85.317 (11)	O1B—Mg2—SiB^i	103.414 (8)
O1B^iii—Mg1—O1B^iv	176.854 (15)	O2B^viii—Mg2—SiB^i	153.556 (11)
O2B^i—Mg1—O1B^v	171.513 (12)	O2B^i—Mg2—SiB^i	32.877 (7)
O2B^ii—Mg1—O1B^v	90.804 (11)	O3B^ix—Mg2—SiB^i	35.377 (7)
O1B^iii—Mg1—O1B^v	94.020 (10)	O3B^x—Mg2—SiB^i	96.116 (9)
O1B^iv—Mg1—O1B^v	83.573 (11)	O1B^iii—Mg2—SiB^viii	103.413 (8)
O2B^i—Mg1—O1B^vi	90.804 (11)	O1B—Mg2—SiB^viii	114.178 (8)
O2B^ii—Mg1—O1B^vi	171.513 (12)	O2B^viii—Mg2—SiB^viii	32.877 (7)
O1B^iii—Mg1—O1B^vi	83.573 (11)	O2B^i—Mg2—SiB^viii	153.556 (11)
O1B^iv—Mg1—O1B^vi	94.020 (10)	O3B^ix—Mg2—SiB^viii	96.116 (9)
O1B^v—Mg1—O1B^vi	80.716 (14)	O3B^x—Mg2—SiB^viii	35.377 (6)
O2B^i—Mg1—Mg2^iv	96.230 (9)	SiB^i—Mg2—SiB^viii	127.472 (9)
O2B^ii—Mg1—Mg2^iv	42.784 (8)	O1B^iii—Mg2—Mg1	42.808 (8)
O1B^iii—Mg1—Mg2^iv	139.469 (8)	O1B—Mg2—Mg1	92.569 (10)
O1B^iv—Mg1—Mg2^iv	42.780 (8)	O2B^viii—Mg2—Mg1	134.282 (10)
O1B^v—Mg1—Mg2^iv	89.778 (7)	O2B^i—Mg2—Mg1	40.728 (8)
O1B^vi—Mg1—Mg2^iv	136.714 (7)	O3B^ix—Mg2—Mg1	106.301 (7)
O2B^i—Mg1—Mg2	42.784 (8)	O3B^x—Mg2—Mg1	118.707 (7)
O2B^ii—Mg1—Mg2	96.229 (9)	SiB^i—Mg2—Mg1	71.607 (3)
O1B^iii—Mg1—Mg2	42.780 (8)	SiB^viii—Mg2—Mg1	137.392 (2)
O1B^iv—Mg1—Mg2	139.469 (8)	O1B^iii—Mg2—Mg1^xiii	92.568 (9)
O1B^v—Mg1—Mg2	136.714 (7)	O1B—Mg2—Mg1^xiii	42.807 (7)
O1B^vi—Mg1—Mg2	89.778 (7)	O2B^viii—Mg2—Mg1^xiii	40.728 (8)
Mg2^iv—Mg1—Mg2	123.268 (9)	O2B^i—Mg2—Mg1^xiii	134.282 (10)
O2B^i—Mg1—Mg2^v	131.161 (9)	O3B^ix—Mg2—Mg1^xiii	118.708 (7)
O2B^ii—Mg1—Mg2^v	131.161 (9)	O3B^x—Mg2—Mg1^xiii	106.301 (7)
O1B^iii—Mg1—Mg2^v	88.427 (8)	SiB^i—Mg2—Mg1^xiii	137.392 (2)
O1B^iv—Mg1—Mg2^v	88.427 (8)	SiB^viii—Mg2—Mg1^xiii	71.607 (3)
O1B^v—Mg1—Mg2^v	40.358 (7)	Mg1—Mg2—Mg1^xiii	123.268 (9)
O1B^vi—Mg1—Mg2^v	40.358 (7)	O2B—SiB—O1B	118.125 (15)
Mg2^iv—Mg1—Mg2^v	118.366 (4)	O2B—SiB—O3B^xi	111.337 (15)
Mg2—Mg1—Mg2^v	118.366 (4)	O1B—SiB—O3B^xi	108.238 (14)
O2B^i—Mg1—Mg1^v	87.515 (8)	O2B—SiB—O3B^xii	99.755 (14)
O2B^ii—Mg1—Mg1^v	139.447 (8)	O1B—SiB—O3B^xii	110.191 (14)
O1B^iii—Mg1—Mg1^v	43.354 (7)	O3B^xi—SiB—O3B^xii	108.680 (11)
O1B^iv—Mg1—Mg1^v	134.207 (9)	O2B—SiB—Mg2^xiv	44.798 (11)
O1B^v—Mg1—Mg1^v	86.222 (9)	O1B—SiB—Mg2^xiv	132.722 (10)
O1B^vi—Mg1—Mg1^v	40.219 (7)	O3B^xi—SiB—Mg2^xiv	119.036 (11)
Mg2^iv—Mg1—Mg1^v	175.391 (7)	O3B^xii—SiB—Mg2^xiv	55.095 (10)
Mg2—Mg1—Mg1^v	61.341 (4)	O2B—SiB—Mg1^xiii	112.613 (12)
Mg2^v—Mg1—Mg1^v	57.025 (4)	O1B—SiB—Mg1^xiii	33.661 (9)
O2B^i—Mg1—Mg1^vii	139.447 (8)	O3B^xi—SiB—Mg1^xiii	133.043 (11)
O2B^ii—Mg1—Mg1^vii	87.515 (8)	O3B^xii—SiB—Mg1^xiii	79.291 (11)
O1B^iii—Mg1—Mg1^vii	134.207 (9)	Mg2^xiv—SiB—Mg1^xiii	103.622 (3)
O1B^iv—Mg1—Mg1^vii	43.354 (7)	O2B—SiB—Mg2	89.536 (12)
O1B^v—Mg1—Mg1^vii	40.219 (7)	O1B—SiB—Mg2	32.258 (9)
O1B^vi—Mg1—Mg1^vii	86.222 (9)	O3B^xi—SiB—Mg2	109.268 (11)
Mg2^iv—Mg1—Mg1^vii	61.340 (4)	O3B^xii—SiB—Mg2	134.148 (11)
Mg2—Mg1—Mg1^vii	175.392 (7)	Mg2^xiv—SiB—Mg2	121.841 (3)
Mg2^v—Mg1—Mg1^vii	57.025 (4)	Mg1^xiii—SiB—Mg2	56.008 (3)
Mg1^v—Mg1—Mg1^vii	114.051 (9)	SiB—O1B—Mg2	122.968 (15)
O1B^iii—Mg2—O1B	87.076 (17)	SiB—O1B—Mg1^xiii	120.556 (14)
O1B^iii—Mg2—O2B^viii	91.475 (12)	Mg2—O1B—Mg1^xiii	94.413 (11)
O1B—Mg2—O2B^viii	83.297 (11)	SiB—O1B—Mg1^v	119.955 (14)
O1B^iii—Mg2—O2B^i	83.298 (11)	Mg2—O1B—Mg1^v	96.104 (12)
O1B—Mg2—O2B^i	91.475 (12)	Mg1^xiii—O1B—Mg1^v	96.429 (11)
O2B^viii—Mg2—O2B^i	172.805 (18)	SiB—O2B—Mg1^xiv	148.803 (17)
O1B^iii—Mg2—O3B^ix	147.232 (9)	SiB—O2B—Mg2^xiv	102.325 (14)
O1B—Mg2—O3B^ix	108.682 (11)	Mg1^xiv—O2B—Mg2^xiv	96.488 (12)
O2B^viii—Mg2—O3B^ix	118.183 (12)	SiB^xv—O3B—SiB^xvi	139.248 (19)
O2B^i—Mg2—O3B^ix	68.174 (10)	SiB^xv—O3B—Mg2^xvii	125.470 (15)
O1B^iii—Mg2—O3B^x	108.681 (11)	SiB^xvi—O3B—Mg2^xvii	89.528 (11)
O1B—Mg2—O3B^x	147.232 (9)

Symmetry codes: (i) −x+1/2, −y+1/2, z+1/2; (ii) x−1/2, −y+1/2, −z+1; (iii) −x, y, −z+1/2; (iv) x, y, z+1; (v) −x, −y, −z+1; (vi) x, −y, z+1/2; (vii) −x, −y, −z+2; (viii) x−1/2, −y+1/2, −z; (ix) −x+1/2, y−1/2, z; (x) x−1/2, y−1/2, −z+1/2; (xi) x, y−1, z; (xii) x, −y+1, z−1/2; (xiii) x, y, z−1; (xiv) −x+1/2, −y+1/2, z−1/2; (xv) x, y+1, z; (xvi) x, −y+1, z+1/2; (xvii) x+1/2, y+1/2, −z+1/2.

(PPX_4d)

Crystal data

Si·3(O)·0.078(Fe)·0.844(Mg)·0.078(Li)	Dx = 3.165 Mg m^−3
Mr = 101.60	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, Pbcn	Cell parameters from 3347 reflections
a = 9.2255 (2) Å	θ = 3.2–45.3°
b = 8.7052 (2) Å	µ = 1.62 mm^−1
c = 5.3106 (1) Å	T = 293 K
V = 426.49 (2) Å^3	Anhedral
Z = 8	0.40 × 0.32 × 0.25 mm
F(000) = 435

Data collection

Bruker Smart Breeze diffractometer	1760 independent reflections
Radiation source: fine-focus sealed tube	1539 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.024
Detector resolution: 512 pixels mm^-1	θmax = 45.3°, θmin = 3.2°
φ and ω scans	h = −15→18
Absorption correction: multi-scan SADABS (Sheldrick, 2015)	k = −15→17
Tmin = 0.543, Tmax = 0.667	l = −10→10
10429 measured reflections

Refinement

Refinement on F^2	0 restraints
Least-squares matrix: full	w = 1/[σ^2(Fo^2) + (0.0168P)^2 + 0.0318P] where P = (Fo^2 + 2Fc^2)/3
R[F^2 > 2σ(F^2)] = 0.018	(Δ/σ)max < 0.001
wR(F^2) = 0.040	Δρmax = 0.37 e Å^−3
S = 1.08	Δρmin = −0.45 e Å^−3
1760 reflections	Extinction correction: SHELXL-2018/3 (Sheldrick 2018), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
51 parameters	Extinction coefficient: 0.0359 (17)

Special details

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq	Occ. (<1)
Mg1	0.000000	0.09881 (2)	0.750000	0.00594 (5)	0.8439 (11)
Fe1	0.000000	0.09881 (2)	0.750000	0.00594 (5)	0.1561 (11)
Mg2	0.000000	0.26371 (4)	0.250000	0.00705 (6)	0.8439 (11)
Li2	0.000000	0.26371 (4)	0.250000	0.00705 (6)	0.1561 (11)
SiB	0.29262 (2)	0.09092 (2)	0.07166 (2)	0.00435 (3)	0.906 (13)
SiBB	0.29262 (2)	0.09092 (2)	0.07166 (2)	0.00435 (3)	0.094 (13)
O1B	0.11764 (3)	0.09254 (4)	0.07875 (6)	0.00585 (5)	0.299 (17)
O1BB	0.11764 (3)	0.09254 (4)	0.07875 (6)	0.00585 (5)	0.701 (17)
O2B	0.37521 (4)	0.25107 (5)	0.07118 (7)	0.00816 (6)	0.299 (17)
O2BB	0.37521 (4)	0.25107 (5)	0.07118 (7)	0.00816 (6)	0.701 (17)
O3B	0.35041 (3)	0.97958 (5)	0.30001 (7)	0.00827 (6)	0.299 (17)
O3BB	0.35041 (3)	0.97958 (5)	0.30001 (7)	0.00827 (6)	0.701 (17)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Mg1	0.00571 (7)	0.00679 (10)	0.00532 (7)	0.000	−0.00050 (5)	0.000
Fe1	0.00571 (7)	0.00679 (10)	0.00532 (7)	0.000	−0.00050 (5)	0.000
Mg2	0.00784 (10)	0.00750 (13)	0.00581 (10)	0.000	−0.00083 (7)	0.000
Li2	0.00784 (10)	0.00750 (13)	0.00581 (10)	0.000	−0.00083 (7)	0.000
SiB	0.00386 (4)	0.00505 (6)	0.00414 (5)	−0.00061 (3)	0.00016 (3)	0.00011 (3)
SiBB	0.00386 (4)	0.00505 (6)	0.00414 (5)	−0.00061 (3)	0.00016 (3)	0.00011 (3)
O1B	0.00383 (9)	0.00758 (14)	0.00612 (11)	0.00013 (8)	0.00012 (7)	−0.00028 (9)
O1BB	0.00383 (9)	0.00758 (14)	0.00612 (11)	0.00013 (8)	0.00012 (7)	−0.00028 (9)
O2B	0.00948 (11)	0.00695 (14)	0.00805 (12)	−0.00389 (10)	0.00030 (9)	−0.00063 (10)
O2BB	0.00948 (11)	0.00695 (14)	0.00805 (12)	−0.00389 (10)	0.00030 (9)	−0.00063 (10)
O3B	0.00603 (10)	0.01215 (16)	0.00664 (11)	0.00036 (10)	0.00054 (8)	0.00455 (10)
O3BB	0.00603 (10)	0.01215 (16)	0.00664 (11)	0.00036 (10)	0.00054 (8)	0.00455 (10)

Geometric parameters (Å, º)

Mg1—O2B^i	1.9837 (4)	Mg2—O1B	2.0555 (4)
Mg1—O2B^ii	1.9837 (4)	Mg2—O2B^viii	2.0619 (4)
Mg1—O1B^iii	2.0564 (3)	Mg2—O2B^i	2.0619 (4)
Mg1—O1B^iv	2.0564 (3)	Mg2—O3B^ix	2.3465 (5)
Mg1—O1B^v	2.1863 (4)	Mg2—O3B^x	2.3465 (5)
Mg1—O1B^vi	2.1863 (4)	Mg2—SiB^i	2.8600 (2)
Mg1—Mg2^iv	3.0185 (2)	Mg2—SiB^viii	2.8600 (2)
Mg1—Mg2	3.0185 (2)	SiB—O2B	1.5887 (4)
Mg1—Mg2^v	3.1558 (4)	SiB—O1B	1.6148 (3)
Mg1—Mg1^v	3.1639 (2)	SiB—O3B^xi	1.6414 (4)
Mg1—Mg1^vii	3.1639 (2)	SiB—O3B^xii	1.6559 (4)
Mg2—O1B^iii	2.0555 (4)
O2B^i—Mg1—O2B^ii	97.59 (2)	O2B^viii—Mg2—O3B^x	68.159 (14)
O2B^i—Mg1—O1B^iii	85.259 (14)	O2B^i—Mg2—O3B^x	118.162 (17)
O2B^ii—Mg1—O1B^iii	96.754 (14)	O3B^ix—Mg2—O3B^x	73.583 (19)
O2B^i—Mg1—O1B^iv	96.754 (14)	O1B^iii—Mg2—SiB^i	114.184 (10)
O2B^ii—Mg1—O1B^iv	85.259 (14)	O1B—Mg2—SiB^i	103.404 (9)
O1B^iii—Mg1—O1B^iv	176.96 (2)	O2B^viii—Mg2—SiB^i	153.537 (17)
O2B^i—Mg1—O1B^v	171.567 (16)	O2B^i—Mg2—SiB^i	32.860 (11)
O2B^ii—Mg1—O1B^v	90.843 (15)	O3B^ix—Mg2—SiB^i	35.379 (9)
O1B^iii—Mg1—O1B^v	94.070 (13)	O3B^x—Mg2—SiB^i	96.124 (13)
O1B^iv—Mg1—O1B^v	83.604 (14)	O1B^iii—Mg2—SiB^viii	103.404 (9)
O2B^i—Mg1—O1B^vi	90.843 (15)	O1B—Mg2—SiB^viii	114.184 (10)
O2B^ii—Mg1—O1B^vi	171.567 (16)	O2B^viii—Mg2—SiB^viii	32.860 (11)
O1B^iii—Mg1—O1B^vi	83.604 (14)	O2B^i—Mg2—SiB^viii	153.537 (17)
O1B^iv—Mg1—O1B^vi	94.070 (13)	O3B^ix—Mg2—SiB^viii	96.124 (13)
O1B^v—Mg1—O1B^vi	80.731 (19)	O3B^x—Mg2—SiB^viii	35.379 (9)
O2B^i—Mg1—Mg2^iv	96.190 (13)	SiB^i—Mg2—SiB^viii	127.478 (13)
O2B^ii—Mg1—Mg2^iv	42.742 (11)	O1B^iii—Mg2—Mg1	42.781 (9)
O1B^iii—Mg1—Mg2^iv	139.416 (12)	O1B—Mg2—Mg1	92.549 (13)
O1B^iv—Mg1—Mg2^iv	42.759 (10)	O2B^viii—Mg2—Mg1	134.270 (14)
O1B^v—Mg1—Mg2^iv	89.794 (10)	O2B^i—Mg2—Mg1	40.766 (10)
O1B^vi—Mg1—Mg2^iv	136.743 (10)	O3B^ix—Mg2—Mg1	106.337 (9)
O2B^i—Mg1—Mg2	42.742 (11)	O3B^x—Mg2—Mg1	118.711 (9)
O2B^ii—Mg1—Mg2	96.190 (13)	SiB^i—Mg2—Mg1	71.640 (4)
O1B^iii—Mg1—Mg2	42.759 (10)	SiB^viii—Mg2—Mg1	137.378 (3)
O1B^iv—Mg1—Mg2	139.416 (12)	O1B^iii—Mg2—Mg1^xiii	92.549 (13)
O1B^v—Mg1—Mg2	136.743 (10)	O1B—Mg2—Mg1^xiii	42.781 (9)
O1B^vi—Mg1—Mg2	89.794 (10)	O2B^viii—Mg2—Mg1^xiii	40.766 (10)
Mg2^iv—Mg1—Mg2	123.208 (13)	O2B^i—Mg2—Mg1^xiii	134.269 (14)
O2B^i—Mg1—Mg2^v	131.207 (12)	O3B^ix—Mg2—Mg1^xiii	118.711 (10)
O2B^ii—Mg1—Mg2^v	131.207 (12)	O3B^x—Mg2—Mg1^xiii	106.338 (9)
O1B^iii—Mg1—Mg2^v	88.480 (12)	SiB^i—Mg2—Mg1^xiii	137.378 (3)
O1B^iv—Mg1—Mg2^v	88.480 (12)	SiB^viii—Mg2—Mg1^xiii	71.640 (4)
O1B^v—Mg1—Mg2^v	40.365 (10)	Mg1—Mg2—Mg1^xiii	123.207 (13)
O1B^vi—Mg1—Mg2^v	40.365 (10)	O2B—SiB—O1B	118.15 (2)
Mg2^iv—Mg1—Mg2^v	118.396 (6)	O2B—SiB—O3B^xi	111.32 (2)
Mg2—Mg1—Mg2^v	118.396 (6)	O1B—SiB—O3B^xi	108.220 (18)
O2B^i—Mg1—Mg1^v	87.504 (11)	O2B—SiB—O3B^xii	99.75 (2)
O2B^ii—Mg1—Mg1^v	139.462 (10)	O1B—SiB—O3B^xii	110.207 (18)
O1B^iii—Mg1—Mg1^v	43.370 (10)	O3B^xi—SiB—O3B^xii	108.675 (13)
O1B^iv—Mg1—Mg1^v	134.274 (13)	O2B—SiB—Mg2^xiv	44.763 (14)
O1B^v—Mg1—Mg1^v	86.263 (12)	O1B—SiB—Mg2^xiv	132.749 (14)
O1B^vi—Mg1—Mg1^v	40.234 (9)	O3B^xi—SiB—Mg2^xiv	119.029 (13)
Mg2^iv—Mg1—Mg1^v	175.457 (11)	O3B^xii—SiB—Mg2^xiv	55.128 (14)
Mg2—Mg1—Mg1^v	61.335 (6)	O2B—SiB—Mg1^xiii	112.672 (15)
Mg2^v—Mg1—Mg1^v	57.062 (7)	O1B—SiB—Mg1^xiii	33.664 (12)
O2B^i—Mg1—Mg1^vii	139.462 (10)	O3B^xi—SiB—Mg1^xiii	133.004 (14)
O2B^ii—Mg1—Mg1^vii	87.504 (11)	O3B^xii—SiB—Mg1^xiii	79.294 (12)
O1B^iii—Mg1—Mg1^vii	134.274 (13)	Mg2^xiv—SiB—Mg1^xiii	103.671 (4)
O1B^iv—Mg1—Mg1^vii	43.370 (10)	O2B—SiB—Mg2	89.579 (15)
O1B^v—Mg1—Mg1^vii	40.234 (9)	O1B—SiB—Mg2	32.237 (13)
O1B^vi—Mg1—Mg1^vii	86.263 (12)	O3B^xi—SiB—Mg2	109.246 (13)
Mg2^iv—Mg1—Mg1^vii	61.334 (6)	O3B^xii—SiB—Mg2	134.159 (13)
Mg2—Mg1—Mg1^vii	175.458 (11)	Mg2^xiv—SiB—Mg2	121.857 (5)
Mg2^v—Mg1—Mg1^vii	57.062 (7)	Mg1^xiii—SiB—Mg2	56.016 (3)
Mg1^v—Mg1—Mg1^vii	114.123 (13)	SiB—O1B—Mg2	122.99 (2)
O1B^iii—Mg2—O1B	87.08 (2)	SiB—O1B—Mg1^xiii	120.534 (18)
O1B^iii—Mg2—O2B^viii	91.489 (16)	Mg2—O1B—Mg1^xiii	94.459 (14)
O1B—Mg2—O2B^viii	83.314 (15)	SiB—O1B—Mg1^v	119.953 (19)
O1B^iii—Mg2—O2B^i	83.313 (15)	Mg2—O1B—Mg1^v	96.094 (15)
O1B—Mg2—O2B^i	91.488 (16)	Mg1^xiii—O1B—Mg1^v	96.395 (14)
O2B^viii—Mg2—O2B^i	172.84 (3)	SiB—O2B—Mg1^xiv	148.83 (2)
O1B^iii—Mg2—O3B^ix	147.241 (13)	SiB—O2B—Mg2^xiv	102.38 (2)
O1B—Mg2—O3B^ix	108.667 (13)	Mg1^xiv—O2B—Mg2^xiv	96.491 (15)
O2B^viii—Mg2—O3B^ix	118.162 (17)	SiB^xv—O3B—SiB^xvi	139.28 (2)
O2B^i—Mg2—O3B^ix	68.159 (14)	SiB^xv—O3B—Mg2^xvii	125.47 (2)
O1B^iii—Mg2—O3B^x	108.667 (13)	SiB^xvi—O3B—Mg2^xvii	89.494 (16)
O1B—Mg2—O3B^x	147.241 (13)

Symmetry codes: (i) −x+1/2, −y+1/2, z+1/2; (ii) x−1/2, −y+1/2, −z+1; (iii) −x, y, −z+1/2; (iv) x, y, z+1; (v) −x, −y, −z+1; (vi) x, −y, z+1/2; (vii) −x, −y, −z+2; (viii) x−1/2, −y+1/2, −z; (ix) −x+1/2, y−1/2, z; (x) x−1/2, y−1/2, −z+1/2; (xi) x, y−1, z; (xii) x, −y+1, z−1/2; (xiii) x, y, z−1; (xiv) −x+1/2, −y+1/2, z−1/2; (xv) x, y+1, z; (xvi) x, −y+1, z+1/2; (xvii) x+1/2, y+1/2, −z+1/2.