research communications
RbZnFe(PO4)2: synthesis and crystal structure
aUnité de recherche, Matériaux Inorganiques, Faculté des Sciences, Université de Monastir, 5019 Monastir, Tunisia
*Correspondence e-mail: badri_abdessalem@yahoo.fr
A new iron phosphate, rubidium zinc iron(III) phosphate, RbZnFe(PO4)2, has been synthesized as single crystals by the method. This compound is isostructural to the previously reported KCoAl(PO4)2 [Chen et al. (1997). Acta Cryst. C53,1754–1756]. Its structure consists of a three-dimensional framework built up from corner-sharing PO4 and (Zn,Fe)O4 tetrahedra. This mode of linkage forms channels parallel to the [100], [010] and [001] directions in which the Rb+ ions are located.
Keywords: crystal structure; iron phosphate; rubidium; open-framework structure.
CCDC reference: 1488120
1. Chemical context
Phosphates with open-framework structures, similar to other porous materials such as zeolites, are interesting because of their wide industrial and environmental applications ranging from catalysis to ion-exchange and separation (Gier & Stucky, 1991; Maspoch et al., 2007). Among them, iron phosphates (Redrup & Weller, 2009; Lajmi et al., 2009) are particularly attractive because of their rich crystal chemistry (Moore, 1970; Gleitzer, 1991) and they present interesting and variable physical properties (Elbouaanani et al., 2002; Riou-Cavellec et al., 1999). Among the variety of iron orthophosphates synthesized and characterized over the past three decades, only two rubidium-containing compounds have been reported, namely Rb9Fe7(PO4)10 (Hidouri et al., 2010) and RbCuFe(PO4)2 (Badri et al., 2013). In this paper, we report the structure of a new rubidium iron orthophosphate, RbZnFe(PO4)2, synthesized during our investigation of the Rb3PO4–Zn3(PO4)2–FePO4 quasi-system. This compound is isostructural to KCoAl(PO4)2 (Chen et al., 1997) and KZnFe(PO4)2 (Badri et al., 2014).
2. Structural commentary
The structure is made up of a three-dimensional assemblage of MO4 (M = 0.5Zn + 0.5Fe) and PO4 tetrahedra through corner-sharing. This framework delimits crossing channels along the [100] and [001] directions, in which the Rb+ ions are located (Figs. 1 and 2). A projection of the structure along [001] direction reveals that each MO4 tetrahedron is linked to four PO4 tetrahedra by sharing corners. In addition, it shows the presence of two kinds of rings through corner-sharing of MO4 and PO4 tetrahedra (Fig. 2). The first presents an elliptical form and comprises four MO4 and four PO4 tetrahedra, the second consists of two MO4 and two PO4 tetrahedra and has a quasi-rectangular form. From an examination of the inter-atomic distances (cation–oxygen), the M(1) and M(2) sites exhibit similar regular tetrahedral environments, as seen in the cation–oxygen distances which vary from 1.877 (5) to 1.900 (5) Å for M(1) and from 1.860 (6) to 1.919 (5) Å for M(2). The average distances of 1.885 (2) and 1.888 (2) Å are between the values of 1.926 (2) Å observed for tetrahedrally coordinated Zn2+ ions in the zinc phosphate RbZnPO4 (Elammari & Elouadi, 1991) and 1.865 Å reported for the Fe3+ ions with the same coordination in the iron phosphate in FePO4 (Long et al., 1983). The P—O distances within the PO4 tetrahedra are between 1.514 (5) and 1.535 (5) Å and with mean distances of 1.523 (9) Å for P(1) and 1.520 (3) Å for P(2), consistent with the value of 1.537 Å calculated by Baur (1974) for orthophosphate groups.
The Rb+ ions occupy a single site at the intersection of the crossing tunnels. Their environment was determined assuming all cation–oxygen distances to be shorter than the shortest distance between Rb+ and its nearest cation. This environment (Fig. 3) then consists of ten O atoms with Rb—O distances ranging from 2.925 (6) to 3.298 (7) Å.
3. Synthesis and crystallization
Single crystals of RbZnFe(PO4)2 were grown in a of rubidium dimolybdate Rb2Mo2O7, in an atomic ratio P:Mo = 4:1. Appropriate amounts of Rb2CO3, Zn(NO3)2·6H2O, Fe(NO3)3·9H2O, (NH4)2HPO4 and MoO3 were used. All of the chemicals were analytically pure from commercial sources and used without further purification. The reagents were weighted in the atomic ratio P:Mo = 2:1 and dissolved in nitric acid and then dried for 24 h at 353 K. The dry residue was gradually heated to 873 K in a platinum crucible to remove the decomposition products. In a second step, the mixture was ground, melted for 1 h at 1173 K and subsequently cooled at a rate of 10 K h−1 to 773 K, after which the furnace was turned off. The crystals obtained by washing the final product with warm water in order to dissolve the are essentially comprised of beige hexagonally shaped crystals of RbZnFe(PO4)2.
4. Refinement
Crystal data, data collection and structure . The application of revealed the Rb atoms and located two sites, labelled M(1) and M(2), statistically occupied by the Fe3+ and Zn2+ ions. This distribution was supported by the M(1)—O and M(2)—O distances which are between the classical pure Zn—O and Fe—O values. Succeeding difference Fourier syntheses led to the positions of all the remaining atoms.
details are summarized in Table 1Despite several synthesis attempts, all the obtained crystals of RbZnFe(PO4)2 were of poor quality, resulting in the large discrepancies found in a number of reflections; hence in this study the was performed using a filter of the reflections by [sin (θ)/λ]. The four reflections (85, 34, 85 and 75) were omitted as the difference between the observed and calculated structure factors was larger than 10σ.
Supporting information
CCDC reference: 1488120
https://doi.org/10.1107/S205698901601046X/br2261sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S205698901601046X/br2261Isup2.hkl
Cell
CAD-4 EXPRESS (Enraf–Nonius, 1994); data reduction: XCAD4 (Harms & Wocadlo, 1995); program(s) used to solve structure: SIR92 (Altomare et al., 1993); program(s) used to refine structure: SHELXL2014 (Sheldrick, 2015); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: WinGX (Farrugia, 2012).RbZnFe(PO4)2 | F(000) = 1496 |
Mr = 396.63 | Dx = 3.301 Mg m−3 |
Monoclinic, C2/c | Mo Kα radiation, λ = 0.71073 Å |
a = 13.601 (4) Å | Cell parameters from 25 reflections |
b = 13.304 (5) Å | θ = 8.1–11.1° |
c = 8.978 (9) Å | µ = 11.29 mm−1 |
β = 100.76 (5)° | T = 293 K |
V = 1596.0 (18) Å3 | Prism, brown |
Z = 8 | 0.43 × 0.25 × 0.18 mm |
Enraf–Nonius TurboCAD-4 diffractometer | Rint = 0.089 |
Radiation source: fine-focus sealed tube | θmax = 25.0°, θmin = 2.2° |
non–profiled ω/2τ scans | h = −16→15 |
Absorption correction: part of the refinement model (ΔF) (Walker & Stuart 1983) | k = 0→15 |
Tmin = 0.054, Tmax = 0.070 | l = 0→10 |
1409 measured reflections | 2 standard reflections every 120 min |
1409 independent reflections | intensity decay: 1% |
1227 reflections with I > 2σ(I) |
Refinement on F2 | 118 parameters |
Least-squares matrix: full | 0 restraints |
R[F2 > 2σ(F2)] = 0.036 | w = 1/[σ2(Fo2) + (0.0565P)2 + 31.2735P] where P = (Fo2 + 2Fc2)/3 |
wR(F2) = 0.110 | (Δ/σ)max < 0.001 |
S = 1.05 | Δρmax = 0.85 e Å−3 |
1409 reflections | Δρmin = −0.76 e Å−3 |
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. |
x | y | z | Uiso*/Ueq | Occ. (<1) | |
Rb | 0.18260 (6) | 0.24668 (6) | 0.22827 (9) | 0.0316 (3) | |
Zn1 | 0.87122 (6) | 0.55912 (6) | 0.11383 (9) | 0.0169 (3) | 0.5 |
Fe1 | 0.87122 (6) | 0.55912 (6) | 0.11383 (9) | 0.0169 (3) | 0.5 |
Zn2 | 0.92406 (6) | 0.12098 (6) | −0.05652 (9) | 0.0166 (3) | 0.5 |
Fe2 | 0.92406 (6) | 0.12098 (6) | −0.05652 (9) | 0.0166 (3) | 0.5 |
P1 | 0.14761 (12) | 0.06205 (13) | −0.08572 (19) | 0.0166 (4) | |
O11 | 0.1420 (4) | −0.0526 (4) | −0.0852 (6) | 0.0295 (12) | |
O12 | 0.2450 (3) | 0.1026 (4) | 0.0096 (6) | 0.0243 (11) | |
O13 | 0.3570 (5) | 0.3996 (5) | 0.2456 (6) | 0.0397 (15) | |
O14 | 0.0638 (4) | 0.1055 (5) | −0.0151 (7) | 0.0385 (14) | |
P2 | 0.92645 (12) | 0.36174 (12) | −0.03358 (18) | 0.0144 (4) | |
O21 | 0.8903 (5) | 0.2550 (4) | −0.0146 (7) | 0.0323 (13) | |
O22 | 0.0389 (4) | 0.3613 (4) | −0.0253 (6) | 0.0269 (11) | |
O23 | 0.3731 (4) | 0.0942 (5) | 0.3168 (6) | 0.0367 (14) | |
O24 | 0.8990 (4) | 0.4217 (4) | 0.0972 (6) | 0.0252 (11) |
U11 | U22 | U33 | U12 | U13 | U23 | |
Rb | 0.0383 (5) | 0.0321 (5) | 0.0259 (4) | 0.0006 (3) | 0.0097 (3) | −0.0044 (3) |
Zn1 | 0.0197 (4) | 0.0151 (5) | 0.0149 (4) | 0.0019 (3) | 0.0006 (3) | −0.0023 (3) |
Fe1 | 0.0197 (4) | 0.0151 (5) | 0.0149 (4) | 0.0019 (3) | 0.0006 (3) | −0.0023 (3) |
Zn2 | 0.0194 (5) | 0.0149 (5) | 0.0149 (4) | −0.0013 (3) | 0.0021 (3) | −0.0026 (3) |
Fe2 | 0.0194 (5) | 0.0149 (5) | 0.0149 (4) | −0.0013 (3) | 0.0021 (3) | −0.0026 (3) |
P1 | 0.0191 (8) | 0.0138 (8) | 0.0156 (8) | −0.0026 (7) | −0.0004 (6) | 0.0035 (6) |
O11 | 0.043 (3) | 0.014 (3) | 0.033 (3) | −0.003 (2) | 0.013 (2) | 0.003 (2) |
O12 | 0.019 (2) | 0.023 (3) | 0.028 (3) | −0.0014 (19) | −0.003 (2) | −0.003 (2) |
O13 | 0.059 (4) | 0.043 (3) | 0.015 (3) | −0.011 (3) | 0.002 (3) | 0.011 (2) |
O14 | 0.021 (3) | 0.042 (3) | 0.052 (4) | 0.000 (2) | 0.007 (3) | −0.017 (3) |
P2 | 0.0211 (9) | 0.0095 (8) | 0.0127 (8) | −0.0020 (6) | 0.0031 (6) | 0.0001 (6) |
O21 | 0.053 (4) | 0.016 (3) | 0.034 (3) | −0.010 (2) | 0.024 (3) | −0.010 (2) |
O22 | 0.023 (3) | 0.023 (3) | 0.037 (3) | 0.000 (2) | 0.010 (2) | 0.006 (2) |
O23 | 0.037 (3) | 0.056 (4) | 0.016 (3) | −0.006 (3) | 0.004 (2) | −0.011 (2) |
O24 | 0.040 (3) | 0.014 (2) | 0.023 (3) | 0.005 (2) | 0.009 (2) | −0.0051 (19) |
Rb—O21i | 2.925 (6) | Zn1—O22vi | 1.900 (5) |
Rb—O12 | 2.979 (5) | Zn2—O13vii | 1.860 (6) |
Rb—O14 | 3.098 (6) | Zn2—O14viii | 1.878 (5) |
Rb—O13 | 3.107 (6) | Zn2—O21 | 1.897 (5) |
Rb—O22 | 3.109 (5) | Zn2—O11ix | 1.919 (5) |
Rb—O24i | 3.123 (5) | P1—O13iii | 1.514 (5) |
Rb—O11ii | 3.181 (5) | P1—O14 | 1.519 (6) |
Rb—O12iii | 3.215 (6) | P1—O11 | 1.527 (5) |
Rb—O23 | 3.269 (6) | P1—O12 | 1.535 (5) |
Rb—O21iv | 3.298 (7) | P2—O22viii | 1.517 (5) |
Zn1—O23v | 1.877 (5) | P2—O23vii | 1.520 (5) |
Zn1—O24 | 1.879 (5) | P2—O24 | 1.523 (5) |
Zn1—O12v | 1.886 (5) | P2—O21 | 1.522 (5) |
O21i—Rb—O12 | 142.06 (14) | O12iii—Rb—O23 | 102.79 (14) |
O21i—Rb—O14 | 115.16 (17) | O21i—Rb—O21iv | 76.81 (19) |
O12—Rb—O14 | 47.17 (13) | O12—Rb—O21iv | 98.31 (14) |
O21i—Rb—O13 | 108.19 (16) | O14—Rb—O21iv | 139.07 (14) |
O12—Rb—O13 | 98.37 (15) | O13—Rb—O21iv | 54.77 (14) |
O14—Rb—O13 | 136.49 (16) | O22—Rb—O21iv | 148.78 (13) |
O21i—Rb—O22 | 110.80 (16) | O24i—Rb—O21iv | 89.55 (14) |
O12—Rb—O22 | 92.90 (15) | O11ii—Rb—O21iv | 80.58 (14) |
O14—Rb—O22 | 66.86 (16) | O12iii—Rb—O21iv | 98.09 (13) |
O13—Rb—O22 | 94.89 (14) | O23—Rb—O21iv | 44.69 (13) |
O21i—Rb—O24i | 47.19 (13) | O23v—Zn1—O24 | 110.7 (3) |
O12—Rb—O24i | 169.12 (13) | O23v—Zn1—O12v | 104.6 (2) |
O14—Rb—O24i | 128.20 (14) | O24—Zn1—O12v | 115.9 (2) |
O13—Rb—O24i | 79.99 (16) | O23v—Zn1—O22vi | 112.0 (3) |
O22—Rb—O24i | 76.59 (15) | O24—Zn1—O22vi | 110.8 (2) |
O21i—Rb—O11ii | 56.47 (13) | O12v—Zn1—O22vi | 102.6 (2) |
O12—Rb—O11ii | 85.60 (14) | O13vii—Zn2—O14viii | 118.1 (3) |
O14—Rb—O11ii | 76.11 (17) | O13vii—Zn2—O21 | 103.5 (3) |
O13—Rb—O11ii | 135.33 (15) | O14viii—Zn2—O21 | 109.7 (3) |
O22—Rb—O11ii | 129.51 (14) | O13vii—Zn2—O11ix | 110.9 (3) |
O24i—Rb—O11ii | 103.19 (13) | O14viii—Zn2—O11ix | 113.5 (3) |
O21i—Rb—O12iii | 139.13 (14) | O21—Zn2—O11ix | 98.8 (2) |
O12—Rb—O12iii | 78.67 (16) | O13iii—P1—O14 | 111.5 (4) |
O14—Rb—O12iii | 95.38 (16) | O13iii—P1—O11 | 110.3 (3) |
O13—Rb—O12iii | 45.51 (13) | O14—P1—O11 | 109.7 (3) |
O22—Rb—O12iii | 55.68 (13) | O13iii—P1—O12 | 106.8 (3) |
O24i—Rb—O12iii | 92.85 (14) | O14—P1—O12 | 105.7 (3) |
O11ii—Rb—O12iii | 163.87 (13) | O11—P1—O12 | 112.8 (3) |
O21i—Rb—O23 | 101.14 (15) | O22viii—P2—O23vii | 110.8 (3) |
O12—Rb—O23 | 56.67 (14) | O22viii—P2—O24 | 110.8 (3) |
O14—Rb—O23 | 94.63 (15) | O23vii—P2—O24 | 109.5 (3) |
O13—Rb—O23 | 80.27 (17) | O22viii—P2—O21 | 109.5 (3) |
O22—Rb—O23 | 147.51 (14) | O23vii—P2—O21 | 110.3 (3) |
O24i—Rb—O23 | 132.85 (14) | O24—P2—O21 | 105.7 (3) |
O11ii—Rb—O23 | 64.93 (15) |
Symmetry codes: (i) −x+1, y, −z+1/2; (ii) x, −y, z+1/2; (iii) −x+1/2, −y+1/2, −z; (iv) x−1/2, −y+1/2, z+1/2; (v) x+1/2, y+1/2, z; (vi) −x+1, −y+1, −z; (vii) x+1/2, −y+1/2, z−1/2; (viii) x+1, y, z; (ix) −x+1, −y, −z. |
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