Redetermination of the low-temperature polymorph of Li2MnSiO4 from single-crystal X-ray data

Sato, M.; Ishigaki, T.; Uematsu, K.; Toda, K.; Okawa, H.

doi:10.1107/S1600536812035040

inorganic compounds

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ISSN: 2056-9890

Volume 68| Part 9| September 2012| Pages i68-i69

doi:10.1107/S1600536812035040

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Redetermination of the low-temperature polymorph of Li₂MnSiO₄ from single-crystal X-ray data

Mineo Sato,^a ^* Tadashi Ishigaki,^b Kazuyoshi Uematsu,^a Kenji Toda ^c and Hirokazu Okawa ^d

^aDepartment of Chemistry and Chemical Engineering, Faculty of Engineering, Niigata University, Ikarashi 2-no-cho, Niigata City 950-2181, Japan, ^bCenter for Transdiciplinary Research, Niigata University, 8050 Ikarashi 2-no-cho, Niigata 950-2181, Japan, ^cGraduate School of Science and Technology, Niigata University, 8050 Ikarashi 2-nocho, Niigata 950-2181, Japan, and ^dDepartment of Earth Science and Technology, Faculty of Engineering and Resource Science, Akita University, Tegata Gakuen-machi, Akita 010-8502, Japan
^*Correspondence e-mail: msato@eng.niigata-u.ac.jp

(Received 5 July 2012; accepted 8 August 2012; online 15 August 2012)

Crystals of dilithium manganese(II) silicate were grown under high-temperature hydrothermal conditions in the system LiOH—MnO₂—SiO₂. The title compound crystallizes in the β_II-Li₃PO₄ structure type. The coordination polyhedra of all cations are slightly distorted tetrahedra (m symmetry for MnO₄ and SiO₄), which are linked by corner-sharing to each other. The vertices of the tetrahedra point to the same direction perpendicular to the distorted hexagonal close-packed (hcp) array of O atoms within which half of the tetrahedral voids are occupied by cations. In comparison with the previous refinement from powder X-ray data [Dominko et al. (2006 ). Electrochem. Commun. 8, 217–222], the present reinvestigation from single-crystal X-ray data allows a more precise determination of the distribution of the Li⁺ and Mn²⁺ cations, giving a perfectly site-ordered structure model for both Li⁺ and Mn²⁺.

Related literature

For background to structural studies of Li₂MSiO₄ (M = Mn, Fe, Co) compounds, see: Islam et al. (2011 ); Santamaría-Pérez et al. (2012 ); Setoguchi (1988 ); Yamaguchi et al. (1979 ). Polymorphism of Li₂MnSiO₄ was reported by Arroyo-de Dompablo et al. (2006 , 2008 ); Belharouak et al. (2009 ); Dominko et al. (2006); Kokalj et al. (2007 ); Politaev et al. (2007 ); Wu et al. (2009 ); Zhong et al. (2010 ). For notation of Li₃PO₄ polymorphs, see: West & Glasser (1972 ). For theoretical studies of the redox potentials and Li migration paths of Li₂MnSiO₄, see: Kuganathan & Islam (2009 ); Mali et al. (2010 ); Duncan et al. (2011 ), and for NMR studies of this material, see: Sirisopanaporn et al. (2011 ). For the bond-valence method, see: Brown & Altermatt (1985 ). For crystallographic background, see: Cooper et al. (2002 ).

Experimental

Crystal data

Li₂MnSiO₄
M_r = 160.91
Orthorhombic, P m n 2₁
a = 6.3133 (16) Å
b = 5.3677 (14) Å
c = 4.9685 (12) Å
V = 168.37 (7) Å³
Z = 2
Mo Kα radiation
μ = 4.11 mm⁻¹
T = 295 K
0.26 × 0.19 × 0.18 mm

Data collection

Rigaku Mercury375R diffractometer
Absorption correction: multi-scan (REQAB; Rigaku, 1998 ) T_min = 0.377, T_max = 0.477
1636 measured reflections
423 independent reflections
419 reflections with I > 2σ(I)
R_int = 0.019

Refinement

R[F² > 2σ(F²)] = 0.015
wR(F²) = 0.037
S = 1.14
423 reflections
45 parameters
1 restraint
Δρ_max = 0.25 e Å⁻³
Δρ_min = −0.62 e Å⁻³
Absolute structure: Flack (1983 ), 189 Friedel pairs
Flack parameter: 0.171 (15)

Table 1
Selected geometric parameters (Å, °)

Li1—O1ⁱ	1.936 (10)
Li1—O3	1.956 (6)
Li1—O3ⁱⁱ	1.99 (2)
Li1—O2ⁱⁱⁱ	2.009 (6)
Mn1—O3^iv	2.0585 (16)
Mn1—O1	2.065 (2)
Mn1—O2	2.090 (2)
Si1—O1^v	1.631 (3)
Si1—O3	1.6331 (17)
Si1—O2^vi	1.639 (2)

O1ⁱ—Li1—O3	112.0 (7)
O1ⁱ—Li1—O3ⁱⁱ	107.5 (5)
O3—Li1—O3ⁱⁱ	107.7 (7)
O1ⁱ—Li1—O2ⁱⁱⁱ	108.6 (6)
O3—Li1—O2ⁱⁱⁱ	113.9 (5)
O3ⁱⁱ—Li1—O2ⁱⁱⁱ	106.8 (6)
O3^iv—Mn1—O3	124.58 (8)
O3^iv—Mn1—O1	105.74 (5)
O3^iv—Mn1—O2	107.31 (6)
O1—Mn1—O2	104.54 (8)
O1^v—Si1—O3	109.35 (10)
O3—Si1—O3^vii	109.58 (13)
O1^v—Si1—O2^vi	108.23 (13)
O3—Si1—O2^vi	110.16 (10)
Symmetry codes: (i) x, y-1, z; (ii) $[-x+{\script{3\over 2}}, -y, z-{\script{1\over 2}}]$ ; (iii) $[-x+{\script{3\over 2}}, -y, z+{\script{1\over 2}}]$ ; (iv) -x+1, y, z; (v) $[-x+{\script{3\over 2}}, -y+1, z-{\script{1\over 2}}]$ ; (vi) $[-x+{\script{3\over 2}}, -y+1, z+{\script{1\over 2}}]$ ; (vii) -x+2, y, z.

Table 2
Bond-valence parameters derived from the present model and the previous studies.

Atom	Site	Present work	Dominko et al.¹⁾	Arroyo-de Dompablo et al.²⁾
Li	4b	1.02 (6)	1.0 (1)	0.9
Mn	2a	1.89 (5)	2.1 (1)	1.77
Si	2a	3.89 (7)	3.6 (2)	3.65
O1	2a	2.02 (9)	1.9 (3)	1.75
O2	4b	1.97 (7)	1.9 (2)	1.86
O3	2a	1.87 (7)	2.0 (2)	1.90
1) The data, referred to Dominko et al. (2006), are based on the coordinates for primary MO₄ (M = Li, Mn, Si) tetrahedra. 2) The data, referred to Arroyo-de Dompablo et al. (2008), are based on the coordinates for primary MO₄ (M = Li, Mn, Si) tetrahedra optimized by density functional theory (DFT) methods.

Data collection: CrystalClear (Rigaku, 2010 ); cell refinement: CrystalClear; data reduction: CrystalClear; program(s) used to solve structure: SIR97 (Altomare et al., 1999 ); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ); molecular graphics: VESTA (Momma & Izumi, 2011 ); software used to prepare material for publication: WinGX (Farrugia, 1999 ).

Supporting information

Crystal structure: contains datablocks global, I. DOI: 10.1107/S1600536812035040/wm2658sup1.cif

Structure factors: contains datablock I. DOI: 10.1107/S1600536812035040/wm2658Isup2.hkl

checkCIF report

Comment top

Lithium transition metal orthosilicates Li₂MSiO₄ (M = Mn, Fe, Co) have recently become attracting and received much attention as alternatives for the currently used cathode materials of lithium ion batteries, such as LiCoO₂, Li(Ni,Mn,Co)O₂, LiMn₂O₄ and LiMPO₄ (M = Fe, Mn), because of the natural abundance of silica, iron, and manganese, but also due to a possible high theoretical capacity through two electron delivery. In order to understand the intercalation mechanism of Li⁺ ions in Li₂MSiO₄ cathode materials, their crystal structures have been investigated mainly by means of powder methods using X-ray or synchrotron radiation. Summarized by structural studies up-to-date (Islam et al., 2011; Santamaría-Pérez et al., 2012), it could be concluded that the Li₂MSiO₄ compounds (M = Fe, Mn, Co) belong to a large family of materials known as derivatives of Li₃PO₄, where oxygen atoms form arrays with a distorted hexagonal-close-packing (hcp) within which half of the tetrahedral voids are occupied by cations. Depending on which site (up or down) of the array the cations occupy, the material shows a rich polymorphism. Such compounds may be divided into two families, designated as β- and γ-forms after the notations used for Li₃PO₄ polymorphs (West & Glasser, 1972). The γ-polymorphs are built up of both corner- and edge-sharing tetrahedra with half of the tetrahedra pointing along one direction perpendicular to the hcp array and the other half pointing along the opposite direction, while the β-polymorphs are built up of only corner-sharing tetrahedra, with all the tetrahedra pointing to the same direction perpendicular to the hcp array. Detailed structural information, particularly for electrochemically active Li₂MnSiO₄, were available from the previous studies. Li₂MnSiO₄ exhibit three polymorphs, namely a low-temperature form denoted as β_II (Pmn2₁), an intermediate temperature form denoted as γ_II (Pmnb), and a high-temperature form denoted as γ_o (P2₁/n) (Arroyo-de Dompablo et al., 2006, 2008; Belharouak et al., 2009; Dominko et al., 2006; Kokalj et al., 2007; Politaev et al., 2007; Wu et al., 2009; Zhong et al., 2010). It should be noted that in almost all polymorphs a site disorder for cationic sites, particularly for Li⁺ sites substituted by transition metal ions, was observed. Surprisingly, the structure models proposed for Li₂MSiO₄ (M = Mn, Fe, Co) have all been determined and refined by powder diffraction methods except for that of Li₂CoSiO₄ (Yamaguchi et al., 1979). In terms of the fact that lithium has quite low scattering factors for X-rays, this may be true even for neutron diffraction, the crystallographic information obtained for Li sites by powder diffraction should inevitably include ambiguity to some extent. Efforts to obtain single crystals for structure determination have not been rewarded for Li₂MSiO₄ (M = Mn, Fe). Although Setoguchi (1988) succeeded to grow single crystals of Li₂FeSiO₄ from a flux method using LiCl at elevated temperatures, he could not determine the structure because of suffering from twinned crystals. Here we describe the single-crystal growth of Li₂MnSiO₄ by means of a high temperature hydrothermal method and its structure determination using single-crystal X-ray diffraction, confirming a perfectly site-ordered structure for Li₂MnSiO₄ in its low-temperature β_II (Pmn2₁) polymorph.

The first detailed report on the description of the structure model for Li₂MnSiO₄ accompanied with numerical crystallographic data is probably that determined by Dominko et al. (2006) who performed Rietveld refinements in the space group Pmn2₁ with a = 6.3109 (9) Å, b = 5.3800 (9) Å, c = 4.9662 (8) Å and Z = 2. The obtained structure model is presented in Fig. 1. It contains significant site disorders for all cationic sites, though the primary sites for the cations are located within the tetrahedral voids situated among a fairly distorted hexagonal-close-packing (hcp) of oxygen atoms. The MO₄ (M = Li, Mn, Si) tetrahedra all point towards the same direction perpendicular to the hcp array, and are linked by corner-sharing. The partially occupied tetrahedral sites are located on the opposite sides of corresponding primary MO₄ tetrahedra, the vertices of which point to the opposite direction. The central metal atom pairs are separated by distances of 1.0 (2) Å for Li—Li pairs, 0.52 (10) Å for Mn—Mn pairs and 1.09 (15) Å for Si—Si pairs, forming kinds of (pseudo) trigonal-bipyramidal MO₅ polyhedra, as shown in Fig. 1(b). The structure can also be described as a typical β_II-Li₃PO₄ structure if cation sites with low site-occupancies are removed, as shown in Fig. 1(c) and (d). This structure model, which has such excessive disorders, may have somewhat possible deficiencies. Furthermore, the environment around Li⁺ ions is crucially important for understanding the lithium intercalation behavior during the charge/discharge process. Theroretical studies concerned with expectation of redox potentials and lithium migration paths for Li₂MnSiO₄ cathodes have been accomplished by several groups (Kokalj et al. 2007; Kuganathan & Islam, 2009; Wu et al. 2009; Mali et al. 2010; Zhong et al. 2010; Duncan et al. 2011) based on the model by Dominko et al. (2006); most of these studies adopted the cation site disorder model or the idealized ordered one only with primary sites.

The structure refined in the present study is a perfectly site-ordered one for all cationic sites (Fig. 2) though the fundamental framework structure is the same as that previously reported. Notably, the displacement ellipsoids are relatively large not only for lithium atoms but also for manganese atoms (Fig. 3). This may reflect a high diffusibility both of Li⁺ and Mn²⁺ ions in this cathode material. The ordered structure model found in the present study is consistent with the results of an NMR study by Sirisopanaporn et al. (2011). Unexpectedly, information on atomic coordinates available for Li₂MnSiO₄ is scarce in the literature, where the data were refined from powder diffraction analyses (Dominko et al., 2006) and obtained from an optimization by atomistic simulation (Arroyo-de Dompablo et al., 2008). Table 2 shows the results of the bond-valence sum (BVS) analysis (Brown & Altermatt, 1985) for cation tetrahedra estimated from refined atomic coordinates in Li₂MnSiO₄, together with those for the structure models proposed previously for comparison. The deviations from the formal valences of each ion are fairly large for the previous studies, in particularly for Si, while in the present study the values of the BVS calculation for all ions are in very good agreement with the theoretical ones. Moreover, it should be mentioned that the MO₄ tetrahedra in the present model have much more regular environments than the previous models.

No structural data based on single-crystal X-ray diffraction data have been reported for Li₂MnSiO₄, although recent works on positive electrode materials for rechargeable lithium batteries reported the electrochemical characterization of this cathode material. Our present structural study of Li₂MnSiO₄ provides more accurate information of its crystal structure than has been available up to now.

Related literature top

For background to structural studies of Li₂MSiO₄ (M = Mn, Fe, Co) compounds, see: Islam et al. (2011); Santamaría-Pérez et al. (2012); Setoguchi (1988); Yamaguchi et al. (1979). Polymorphism of Li₂MnSiO₄ was reported by Arroyo-de Dompablo et al. (2006, 2008); Belharouak et al. (2009); Dominko et al. (2006); Kokalj et al. (2007); Politaev et al. (2007); Wu et al. (2009); Zhong et al. (2010). For notation of Li₃PO₄ polymorphs, see: West & Glasser (1972). For theoretical studies of the redox potentials and Li migration paths of Li₂MnSiO₄, see: Kuganathan & Islam (2009); Mali et al. (2010); Duncan et al. (2011), and for NMR studies of this material, see: Sirisopanaporn et al. (2011). For the bond-valence method, see: Brown & Altermatt (1985). For crystallographic background: see: Cooper et al. (2002).

Experimental top

In order to synthesize Li₂MnSiO₄ single crystals, a high-temperature, high-pressure hydrothermal synthetic method was performed in a silver ampoule contained in a home-made autoclave made of stainless steel (SUS304) with 6 cm in outer diameter, 0.8 cm in inner diameter, and 1.8 cm³ in volume. The pressure was provided by water. High-purity chemical reagents of MnO₂, SiO₂ and LiOH^.2H₂O were used as reaction agents. A reaction mixture of LiOH, MnO₂ and SiO₂ with a molar ratio of Li:Mn:Si = 2:12:2 in a 3 cm long silver ampoule (inside diameter = 0.6 cm) was heated at 823 K for 3 days. The pressure was estimated to be 12 MPa at the reaction temperature according to the pressure-temperature diagram of pure water. The autoclave was then cooled to 323 K at 5 K/h and quenched to room temperature by removing the autoclave from the furnace. The product was filtered off, washed with water, rinsed with ethanol, and dried at ambient temperature. The reaction produced light-green rod-shaped crystals of Li₂MnSiO₄ that were obtained as a major product along with some quartz crystals.

The surface of the single crystals was observed by using optical (Olympus BX-60) and scanning electron microscopy (SEM, Jeol JSM-5310LVB). The elemental composition of the crystals was characterized by energy dispersive X-ray spectroscopy (EDS) attached to SEM (SEM/EDS, Nippon Denshi JED-2140).

Computing details top

Data collection: CrystalClear (Rigaku, 2010); cell refinement: CrystalClear (Rigaku, 2010); data reduction: CrystalClear (Rigaku, 2010); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: VESTA (Momma & Izumi, 2011); software used to prepare material for publication: WinGX (Farrugia, 1999).

Figures top

	Fig. 1. Structure model of Li₂MnSiO₄ determined by Dominko et al. (2006). The original structure model is projected (a) along [001] and (b) along [100], while the structure model where cation sites with low occupancies are removed is projected (c) along [001] and (d) along [100]. Polyhedra are indicated by red color for LiO₄, blue color for MnO₄, and green color for SiO₄.
	Fig. 2. Structure model of Li₂MnSiO₄ determined by the present study with (a) projection view along [001] and (b) projection view along [100]. Polyhedra are indicated by red color for LiO₄, blue color for MnO₄, and green color for SiO₄.
	Fig. 3. A perspective view of a part of the Li₂MnSiO₄ structure with the unit cell outlined. Displacement ellipsoids are drawn at the 70% probability level. Polyhedra are indicated by red color for LiO₄, blue color for MnO₄, and green color for SiO₄.

dilithium manganese(II) silicate top

Crystal data top

Li₂MnSiO₄	F(000) = 154
M_r = 160.91	D_x = 3.174 Mg m⁻³
Orthorhombic, Pmn2₁	Mo Kα radiation, λ = 0.71069 Å
Hall symbol: P 2ac -2	Cell parameters from 1684 reflections
a = 6.3133 (16) Å	θ = 3.2–27.5°
b = 5.3677 (14) Å	µ = 4.11 mm⁻¹
c = 4.9685 (12) Å	T = 295 K
V = 168.37 (7) Å³	Prism, light green
Z = 2	0.26 × 0.19 × 0.18 mm

Data collection top

Rigaku Mercury375R diffractometer	423 independent reflections
Radiation source: Sealed Tube	419 reflections with I > 2σ(I)
Graphite monochromator	R_int = 0.019
Detector resolution: 13.6612 pixels mm^-1	θ_max = 27.4°, θ_min = 3.8°
profile data from ω–scans	h = −8→8
Absorption correction: multi-scan (REQAB; Rigaku, 1998)	k = −6→6
T_min = 0.377, T_max = 0.477	l = −6→6
1636 measured reflections

Refinement top

Refinement on F²	Secondary atom site location: difference Fourier map
Least-squares matrix: full	w = 1/[σ²(F_o²) + (0.0217P)²] where P = (F_o² + 2F_c²)/3
R[F² > 2σ(F²)] = 0.015	(Δ/σ)_max < 0.001
wR(F²) = 0.037	Δρ_max = 0.25 e Å⁻³
S = 1.14	Δρ_min = −0.62 e Å⁻³
423 reflections	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
45 parameters	Extinction coefficient: 0.392 (13)
1 restraint	Absolute structure: Flack (1983), 189 Friedel pairs
0 constraints	Absolute structure parameter: 0.171 (15)
Primary atom site location: structure-invariant direct methods

Crystal data top

Li₂MnSiO₄	V = 168.37 (7) Å³
M_r = 160.91	Z = 2
Orthorhombic, Pmn2₁	Mo Kα radiation
a = 6.3133 (16) Å	µ = 4.11 mm⁻¹
b = 5.3677 (14) Å	T = 295 K
c = 4.9685 (12) Å	0.26 × 0.19 × 0.18 mm

Data collection top

Rigaku Mercury375R diffractometer	423 independent reflections
Absorption correction: multi-scan (REQAB; Rigaku, 1998)	419 reflections with I > 2σ(I)
T_min = 0.377, T_max = 0.477	R_int = 0.019
1636 measured reflections

Refinement top

R[F² > 2σ(F²)] = 0.015	1 restraint
wR(F²) = 0.037	Δρ_max = 0.25 e Å⁻³
S = 1.14	Δρ_min = −0.62 e Å⁻³
423 reflections	Absolute structure: Flack (1983), 189 Friedel pairs
45 parameters	Absolute structure parameter: 0.171 (15)

Special details top

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

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > 2σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² are statistically about twice as large as those based on F, and R- factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
Li1	0.7503 (4)	−0.1688 (4)	0.995 (5)	0.0090 (7)
Mn1	0.5	0.33172 (5)	0.9968	0.00733 (15)
Si1	1	0.32090 (9)	0.9851 (3)	0.00350 (17)
O1	0.5	0.6868 (3)	1.1569 (5)	0.0071 (5)
O2	0.5	0.3867 (3)	0.5804 (4)	0.0081 (4)
O3	0.7887 (2)	0.1799 (2)	1.0979 (4)	0.0075 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Li1	0.0084 (17)	0.0061 (15)	0.0125 (15)	−0.0009 (7)	0.0000 (14)	−0.002 (2)
Mn1	0.0055 (2)	0.0072 (2)	0.0093 (2)	0	0	0.0000 (2)
Si1	0.0035 (3)	0.0028 (3)	0.0042 (4)	0	0	−0.0003 (3)
O1	0.0075 (9)	0.0083 (8)	0.0056 (11)	0	0	−0.0004 (6)
O2	0.0098 (8)	0.0048 (7)	0.0096 (10)	0	0	0.0001 (7)
O3	0.0068 (5)	0.0067 (6)	0.0089 (7)	−0.0009 (4)	0.0008 (7)	0.0000 (5)

Geometric parameters (Å, º) top

Li1—O1ⁱ	1.936 (10)	Mn1—O1	2.065 (2)
Li1—O3	1.956 (6)	Mn1—O2	2.090 (2)
Li1—O3ⁱⁱ	1.99 (2)	Si1—O1^v	1.631 (3)
Li1—O2ⁱⁱⁱ	2.009 (6)	Si1—O3	1.6331 (17)
Mn1—O3^iv	2.0585 (16)	Si1—O3^vi	1.6331 (17)
Mn1—O3	2.0585 (15)	Si1—O2^vii	1.639 (2)

O1ⁱ—Li1—O3	112.0 (7)	O3^iv—Mn1—O2	107.31 (6)
O1ⁱ—Li1—O3ⁱⁱ	107.5 (5)	O3—Mn1—O2	107.31 (6)
O3—Li1—O3ⁱⁱ	107.7 (7)	O1—Mn1—O2	104.54 (8)
O1ⁱ—Li1—O2ⁱⁱⁱ	108.6 (6)	O1^v—Si1—O3	109.35 (10)
O3—Li1—O2ⁱⁱⁱ	113.9 (5)	O1^v—Si1—O3^vi	109.35 (10)
O3ⁱⁱ—Li1—O2ⁱⁱⁱ	106.8 (6)	O3—Si1—O3^vi	109.58 (13)
O3^iv—Mn1—O3	124.58 (8)	O1^v—Si1—O2^vii	108.23 (13)
O3^iv—Mn1—O1	105.74 (5)	O3—Si1—O2^vii	110.16 (10)
O3—Mn1—O1	105.74 (5)	O3^vi—Si1—O2^vii	110.16 (10)

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

Experimental details

Crystal data
Chemical formula	Li₂MnSiO₄
M_r	160.91
Crystal system, space group	Orthorhombic, Pmn2₁
Temperature (K)	295
a, b, c (Å)	6.3133 (16), 5.3677 (14), 4.9685 (12)
V (Å³)	168.37 (7)
Z	2
Radiation type	Mo Kα
µ (mm⁻¹)	4.11
Crystal size (mm)	0.26 × 0.19 × 0.18

Data collection
Diffractometer	Rigaku Mercury375R diffractometer
Absorption correction	Multi-scan (REQAB; Rigaku, 1998)
T_min, T_max	0.377, 0.477
No. of measured, independent and observed [I > 2σ(I)] reflections	1636, 423, 419
R_int	0.019
(sin θ/λ)_max (Å⁻¹)	0.648

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.015, 0.037, 1.14
No. of reflections	423
No. of parameters	45
No. of restraints	1
Δρ_max, Δρ_min (e Å⁻³)	0.25, −0.62
Absolute structure	Flack (1983), 189 Friedel pairs
Absolute structure parameter	0.171 (15)

Computer programs: CrystalClear (Rigaku, 2010), SIR97 (Altomare et al., 1999), SHELXL97 (Sheldrick, 2008), VESTA (Momma & Izumi, 2011), WinGX (Farrugia, 1999).

Selected geometric parameters (Å, º) top

Li1—O1ⁱ	1.936 (10)	Mn1—O1	2.065 (2)
Li1—O3	1.956 (6)	Mn1—O2	2.090 (2)
Li1—O3ⁱⁱ	1.99 (2)	Si1—O1^v	1.631 (3)
Li1—O2ⁱⁱⁱ	2.009 (6)	Si1—O3	1.6331 (17)
Mn1—O3^iv	2.0585 (16)	Si1—O2^vi	1.639 (2)

O1ⁱ—Li1—O3	112.0 (7)	O3^iv—Mn1—O1	105.74 (5)
O1ⁱ—Li1—O3ⁱⁱ	107.5 (5)	O3^iv—Mn1—O2	107.31 (6)
O3—Li1—O3ⁱⁱ	107.7 (7)	O1—Mn1—O2	104.54 (8)
O1ⁱ—Li1—O2ⁱⁱⁱ	108.6 (6)	O1^v—Si1—O3	109.35 (10)
O3—Li1—O2ⁱⁱⁱ	113.9 (5)	O3—Si1—O3^vii	109.58 (13)
O3ⁱⁱ—Li1—O2ⁱⁱⁱ	106.8 (6)	O1^v—Si1—O2^vi	108.23 (13)
O3^iv—Mn1—O3	124.58 (8)	O3—Si1—O2^vi	110.16 (10)

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

Bond-valence parameters derived from the present model and the previous studies. top

Atom	Site	Present work	Dominko et al.¹⁾	Arroyo-de Dompablo et al.²⁾
Li	4b	1.02 (6)	1.0 (1)	0.9
Mn	2a	1.89 (5)	2.1 (1)	1.77
Si	2a	3.89 (7)	3.6 (2)	3.65
O1	2a	2.02 (9)	1.9 (3)	1.75
O2	4b	1.97 (7)	1.9 (2)	1.86
O3	2a	1.87 (7)	2.0 (2)	1.90

1) The data, referred to Dominko et al. (2006), are based on the coordinates for primary MO₄ (M = Li, Mn, Si) tetrahedra. 2) The data, referred to Arroyo-de Dompablo et al. (2008), are based on the coordinates for primary MO₄ (M = Li, Mn, Si) tetrahedra optimized by density functional theory (DFT) methods.

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