Acta Cryst. (2007). E63, i199 [ doi:10.1107/S1600536807058588 ]
Crystals of dipotassium iron(III) tin(IV) tris(orthophosphate) were grown from a self-flux in the system K2O-P2O5-Fe2O3-SnO2. The title compound is isotypic with the mineral langbeinite, K2Mg2(SO4)3. Its three-dimensional [M2(PO4)3]![[infinity]](http://journals.iucr.org/logos/entities/infin_rmgif.gif)
framework is composed of [MO6] (M = Sn, Fe) octahedra and [PO4] tetrahedra interlinked via vertices. In comparison with the previous refinement from X-ray powder data [Aatiq, Haggouch, Bakri, Lakhdar & Saadoune. (2006). Powder Diffr. 21, 214-219], the present reinvestigation from single-crystal data allows a more precise determination of the distribution of the Fe and Sn atoms over two crystallographic positions and a revision of the P-O and M-O [M = K, (Fe, Sn)] bond lengths. For the two K+ cations, two different polyhedra with coordination numbers of 9 and 12 are observed. The (Fe, Sn) and K atoms are located on threefold axes.
Crystals of (I) were obtained in the pseudo-quaternary system K2O—P2O5—SnO2—Fe2O3 using the high-temperature flux crystallization technique. A well ground mixture of 0.9 g SnO2 (6.0 mmol), 1,44 g Fe2O3 (9.0 mmol), 6,63 g KPO3 (56.2 mmol) and 1,03 g K4P2O7 (3.1 mmol) was placed into a platinum crucible, and was heated up to 1373 K. The melt was exposed during 6 h at this temperature to dissolve the metal oxides, and then was cooled down 1013 K at a rate 25 K/h. At the final stage of crystallization the melt was sustained under isothermal conditions for 1 h to gain equilibrium, and was then poured out onto a copper sheet for quenching. Yellow-brownish crystals with mostly tetrahedral shape were recovered from the remaining flux by leaching out with deionized water.
As suggested from the previous powder refinement (Aatiq et al., 2006), the Fe and Sn atoms are statistically distributed. Their coordinates and displacement ellipsoids were constrained. Three additional restraints were applied, viz. two for full occupancies of the Fe/Sn sites and one for the total charge of iron and tin (charge sum = 7.00). The highest peak in the final Fourier map is located 0.87 Å from atom P1, and the deepest hole is 1.05 Å from atom Sn1.
Data collection: CrysAlis CCD (Oxford Diffraction, 2005); cell refinement: CrysAlis CCD; data reduction: CrysAlis RED (Oxford Diffraction, 2005); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 2006); software used to prepare material for publication: WinGX publication routines (Farrugia, 1999).
![[Figure 1]](./wm2157fig1thm.gif)
| Fig. 1. A part of the crystal structure of (I), displayed with ellipsoids at the 70% probability level. The blue line shows the [111] direction. |
![[Figure 2]](./wm2157fig2thm.gif)
| Fig. 2. Arrangement of [MO6] octahedra and [PO4] tetrahedra forming cavities around the K+ cations (70% probability displacement ellipsoids). [M1O6] octahedra are light brown, [M2O6] octahedra are dark red, and [PO4] tetrahedra are purple. |
| K2FeSn(PO4)3 | Z = 4 |
| Mr = 537.65 | F000 = 1020 |
| Cubic, P213 | Dx = 3.664 Mg m−3 |
| Hall symbol: P 2ac 2ab 3 | Mo Kα radiation λ = 0.71073 Å |
| a = 9.91473 (7) Å | Cell parameters from 5809 reflections |
| b = 9.91473 (7) Å | θ = 2.9–35.0º |
| c = 9.91473 (7) Å | µ = 5.47 mm−1 |
| α = 90º | T = 293 (2) K |
| β = 90º | Tetrahedron, yellow brown |
| γ = 90º | 0.08 × 0.06 × 0.05 mm |
| V = 974.636 (12) Å3 |
| XCalibur-3 diffractometer | 1338 reflections with I > 2σ(I) |
| Monochromator: graphite | Rint = 0.035 |
| T = 293(2) K | θmax = 35.0º |
| φ and ω scans | θmin = 2.9º |
| Absorption correction: multi-scan (Blessing; 1995) | h = −13→16 |
| Tmin = 0.669, Tmax = 0.772 | k = −15→15 |
| 5809 measured reflections | l = −15→16 |
| 1434 independent reflections |
| Refinement on F2 | w = 1/[σ2(Fo2) + (0.0194P)2 + 0.5777P] where P = (Fo2 + 2Fc2)/3 |
| Least-squares matrix: full | (Δ/σ)max < 0.001 |
| R[F2 > 2σ(F2)] = 0.021 | Δρmax = 0.50 e Å−3 |
| wR(F2) = 0.045 | Δρmin = −0.57 e Å−3 |
| S = 1.1 | Extinction correction: SHELXL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
| 1434 reflections | Extinction coefficient: 0.0058 (5) |
| 63 parameters | Absolute structure: Flack (1983), 621 Friedel Pairs |
| 3 restraints | Flack parameter: −0.03 (2) |
| K2FeSn(PO4)3 | γ = 90º |
| Mr = 537.65 | V = 974.636 (12) Å3 |
| Cubic, P213 | Z = 4 |
| a = 9.91473 (7) Å | Mo Kα |
| b = 9.91473 (7) Å | µ = 5.47 mm−1 |
| c = 9.91473 (7) Å | T = 293 (2) K |
| α = 90º | 0.08 × 0.06 × 0.05 mm |
| β = 90º |
| XCalibur-3 diffractometer | 1434 independent reflections |
| Absorption correction: multi-scan (Blessing; 1995) | 1338 reflections with I > 2σ(I) |
| Tmin = 0.669, Tmax = 0.772 | Rint = 0.035 |
| 5809 measured reflections |
| R[F2 > 2σ(F2)] = 0.021 | 3 restraints |
| wR(F2) = 0.045 | Δρmax = 0.50 e Å−3 |
| S = 1.1 | Δρmin = −0.57 e Å−3 |
| 1434 reflections | Absolute structure: Flack (1983), 621 Friedel Pairs |
| 63 parameters | Flack parameter: −0.03 (2) |
Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. |
| x | y | z | Uiso*/Ueq | Occ. (<1) | |
| K1 | 0.70742 (8) | 0.70742 (8) | 0.70742 (8) | 0.0278 (3) | |
| K2 | 0.93262 (6) | 0.93262 (6) | 0.93262 (6) | 0.0220 (2) | |
| Fe1 | 0.14686 (2) | 0.14686 (2) | 0.14686 (2) | 0.00732 (8) | 0.4464 (11) |
| Fe2 | 0.41421 (2) | 0.41421 (2) | 0.41421 (2) | 0.00737 (8) | 0.5538 (12) |
| Sn1 | 0.14686 (2) | 0.14686 (2) | 0.14686 (2) | 0.00732 (8) | 0.5536 (11) |
| Sn2 | 0.41421 (2) | 0.41421 (2) | 0.41421 (2) | 0.00737 (8) | 0.4462 (11) |
| P1 | 0.46113 (6) | 0.22920 (6) | 0.12592 (6) | 0.00634 (10) | |
| O1 | 0.31483 (18) | 0.2389 (2) | 0.0776 (2) | 0.0154 (4) | |
| O2 | 0.5516 (2) | 0.2973 (2) | 0.0223 (2) | 0.0180 (4) | |
| O3 | 0.5006 (2) | 0.08280 (19) | 0.1516 (2) | 0.0172 (3) | |
| O4 | 0.4825 (2) | 0.3057 (2) | 0.2572 (2) | 0.0203 (4) |
| U11 | U22 | U33 | U12 | U13 | U23 | |
| K1 | 0.0278 (3) | 0.0278 (3) | 0.0278 (3) | −0.0001 (3) | −0.0001 (3) | −0.0001 (3) |
| K2 | 0.0220 (2) | 0.0220 (2) | 0.0220 (2) | −0.0026 (2) | −0.0026 (2) | −0.0026 (2) |
| Fe1 | 0.00732 (8) | 0.00732 (8) | 0.00732 (8) | −0.00009 (7) | −0.00009 (7) | −0.00009 (7) |
| Fe2 | 0.00737 (8) | 0.00737 (8) | 0.00737 (8) | −0.00050 (7) | −0.00050 (7) | −0.00050 (7) |
| Sn1 | 0.00732 (8) | 0.00732 (8) | 0.00732 (8) | −0.00009 (7) | −0.00009 (7) | −0.00009 (7) |
| Sn2 | 0.00737 (8) | 0.00737 (8) | 0.00737 (8) | −0.00050 (7) | −0.00050 (7) | −0.00050 (7) |
| P1 | 0.0061 (2) | 0.0066 (2) | 0.0063 (2) | −0.00007 (18) | 0.00116 (17) | −0.00006 (17) |
| O1 | 0.0068 (7) | 0.0201 (9) | 0.0194 (9) | −0.0031 (6) | −0.0024 (7) | 0.0086 (8) |
| O2 | 0.0155 (9) | 0.0211 (10) | 0.0174 (9) | −0.0008 (7) | 0.0091 (7) | 0.0087 (8) |
| O3 | 0.0220 (9) | 0.0078 (7) | 0.0219 (9) | 0.0063 (7) | 0.0031 (8) | 0.0032 (8) |
| O4 | 0.0240 (11) | 0.0235 (11) | 0.0135 (9) | −0.0030 (8) | 0.0022 (8) | −0.0117 (8) |
| K1—O1i | 2.852 (2) | Fe1—O1xiv | 2.0195 (19) |
| K1—O1ii | 2.852 (2) | Fe1—K2xv | 3.6790 (12) |
| K1—O1iii | 2.852 (2) | Fe1—K1xvi | 3.8453 (6) |
| K1—O2iv | 3.013 (2) | Fe1—K1xvii | 3.8453 (6) |
| K1—O2v | 3.013 (2) | Fe1—K1xviii | 3.8453 (6) |
| K1—O2vi | 3.013 (2) | Fe2—O3i | 1.9830 (19) |
| K1—O4iv | 3.117 (2) | Fe2—O3ii | 1.9830 (19) |
| K1—O4v | 3.117 (2) | Fe2—O3iii | 1.9830 (19) |
| K1—O4vi | 3.117 (2) | Fe2—O4 | 2.010 (2) |
| K1—P1iv | 3.4419 (9) | Fe2—O4xiv | 2.010 (2) |
| K1—P1v | 3.4419 (9) | Fe2—O4xiii | 2.010 (2) |
| K1—P1vi | 3.4419 (9) | Fe2—K2xix | 3.7636 (4) |
| K2—O3iv | 2.868 (2) | Fe2—K2xx | 3.7636 (4) |
| K2—O3vi | 2.868 (2) | Fe2—K2xxi | 3.7636 (4) |
| K2—O3v | 2.868 (2) | P1—O4 | 1.521 (2) |
| K2—O2vii | 2.960 (2) | P1—O2 | 1.521 (2) |
| K2—O2viii | 2.960 (2) | P1—O3 | 1.525 (2) |
| K2—O2ix | 2.960 (2) | P1—O1 | 1.5306 (19) |
| K2—O4iv | 3.053 (3) | O1—K1xvi | 2.852 (2) |
| K2—O4v | 3.053 (3) | O2—Sn1xxii | 2.0032 (19) |
| K2—O4vi | 3.053 (3) | O2—Fe1xxii | 2.0032 (19) |
| K2—O4vii | 3.243 (2) | O2—K2xix | 2.960 (2) |
| K2—O4viii | 3.243 (2) | O2—K1xxi | 3.013 (2) |
| K2—O4ix | 3.243 (2) | O3—Sn2xvi | 1.9830 (19) |
| Fe1—O2x | 2.0032 (19) | O3—Fe2xvi | 1.9830 (19) |
| Fe1—O2xi | 2.0032 (19) | O3—K2xxi | 2.868 (2) |
| Fe1—O2xii | 2.0032 (19) | O4—K2xxi | 3.053 (3) |
| Fe1—O1xiii | 2.0195 (19) | O4—K1xxi | 3.117 (2) |
| Fe1—O1 | 2.0195 (19) | O4—K2xix | 3.243 (2) |
| O1i—K1—O1ii | 92.31 (7) | O3v—K2—O4viii | 86.13 (6) |
| O1i—K1—O1iii | 92.31 (7) | O2vii—K2—O4viii | 88.43 (6) |
| O1ii—K1—O1iii | 92.31 (7) | O2viii—K2—O4viii | 45.82 (5) |
| O1i—K1—O2iv | 57.28 (5) | O2ix—K2—O4viii | 100.56 (6) |
| O1ii—K1—O2iv | 81.42 (6) | O4iv—K2—O4viii | 137.22 (4) |
| O1iii—K1—O2iv | 148.35 (7) | O4v—K2—O4viii | 54.34 (8) |
| O1i—K1—O2v | 148.35 (7) | O4vi—K2—O4viii | 104.276 (11) |
| O1ii—K1—O2v | 57.28 (5) | O4vii—K2—O4viii | 115.51 (3) |
| O1iii—K1—O2v | 81.42 (6) | O3iv—K2—O4ix | 86.13 (6) |
| O2iv—K1—O2v | 119.065 (15) | O3vi—K2—O4ix | 156.82 (6) |
| O1i—K1—O2vi | 81.42 (6) | O3v—K2—O4ix | 56.20 (5) |
| O1ii—K1—O2vi | 148.35 (7) | O2vii—K2—O4ix | 100.56 (6) |
| O1iii—K1—O2vi | 57.28 (5) | O2viii—K2—O4ix | 88.43 (6) |
| O2iv—K1—O2vi | 119.065 (15) | O2ix—K2—O4ix | 45.82 (5) |
| O2v—K1—O2vi | 119.065 (15) | O4iv—K2—O4ix | 54.34 (8) |
| O1i—K1—O4iv | 103.75 (6) | O4v—K2—O4ix | 104.276 (11) |
| O1ii—K1—O4iv | 82.12 (6) | O4vi—K2—O4ix | 137.22 (4) |
| O1iii—K1—O4iv | 163.15 (6) | O4vii—K2—O4ix | 115.51 (3) |
| O2iv—K1—O4iv | 46.64 (6) | O4viii—K2—O4ix | 115.51 (3) |
| O2v—K1—O4iv | 82.20 (6) | O2x—Fe1—O2xi | 88.12 (9) |
| O2vi—K1—O4iv | 129.53 (7) | O2x—Fe1—O2xii | 88.12 (9) |
| O1i—K1—O4v | 163.15 (6) | O2xi—Fe1—O2xii | 88.12 (9) |
| O1ii—K1—O4v | 103.75 (6) | O2x—Fe1—O1xiii | 88.81 (8) |
| O1iii—K1—O4v | 82.12 (6) | O2xi—Fe1—O1xiii | 176.13 (9) |
| O2iv—K1—O4v | 129.53 (7) | O2xii—Fe1—O1xiii | 89.43 (9) |
| O2v—K1—O4v | 46.64 (6) | O2x—Fe1—O1 | 89.43 (9) |
| O2vi—K1—O4v | 82.20 (6) | O2xi—Fe1—O1 | 88.81 (8) |
| O4iv—K1—O4v | 83.78 (7) | O2xii—Fe1—O1 | 176.13 (9) |
| O1i—K1—O4vi | 82.12 (6) | O1xiii—Fe1—O1 | 93.51 (9) |
| O1ii—K1—O4vi | 163.15 (6) | O2x—Fe1—O1xiv | 176.13 (9) |
| O1iii—K1—O4vi | 103.75 (6) | O2xi—Fe1—O1xiv | 89.43 (9) |
| O2iv—K1—O4vi | 82.20 (6) | O2xii—Fe1—O1xiv | 88.81 (8) |
| O2v—K1—O4vi | 129.53 (7) | O1xiii—Fe1—O1xiv | 93.51 (9) |
| O2vi—K1—O4vi | 46.64 (6) | O1—Fe1—O1xiv | 93.51 (9) |
| O4iv—K1—O4vi | 83.78 (7) | O3i—Fe2—O3ii | 93.35 (9) |
| O4v—K1—O4vi | 83.78 (7) | O3i—Fe2—O3iii | 93.35 (9) |
| O3iv—K2—O3vi | 100.64 (6) | O3ii—Fe2—O3iii | 93.35 (9) |
| O3iv—K2—O3v | 100.64 (6) | O3i—Fe2—O4 | 172.59 (9) |
| O3vi—K2—O3v | 100.64 (6) | O3ii—Fe2—O4 | 93.04 (9) |
| O3iv—K2—O2vii | 95.91 (6) | O3iii—Fe2—O4 | 82.53 (9) |
| O3vi—K2—O2vii | 100.74 (6) | O3i—Fe2—O4xiv | 93.04 (9) |
| O3v—K2—O2vii | 149.93 (6) | O3ii—Fe2—O4xiv | 82.53 (9) |
| O3iv—K2—O2viii | 149.93 (6) | O3iii—Fe2—O4xiv | 172.59 (9) |
| O3vi—K2—O2viii | 95.91 (6) | O4—Fe2—O4xiv | 91.52 (9) |
| O3v—K2—O2viii | 100.74 (6) | O3i—Fe2—O4xiii | 82.53 (9) |
| O2vii—K2—O2viii | 56.14 (6) | O3ii—Fe2—O4xiii | 172.59 (9) |
| O3iv—K2—O2ix | 100.74 (6) | O3iii—Fe2—O4xiii | 93.04 (9) |
| O3vi—K2—O2ix | 149.93 (6) | O4—Fe2—O4xiii | 91.52 (9) |
| O3v—K2—O2ix | 95.91 (6) | O4xiv—Fe2—O4xiii | 91.52 (9) |
| O2vii—K2—O2ix | 56.14 (6) | O4—P1—O2 | 105.93 (13) |
| O2viii—K2—O2ix | 56.14 (6) | O4—P1—O3 | 107.23 (13) |
| O3iv—K2—O4iv | 48.81 (5) | O2—P1—O3 | 112.54 (12) |
| O3vi—K2—O4iv | 114.59 (7) | O4—P1—O1 | 111.60 (13) |
| O3v—K2—O4iv | 52.71 (6) | O2—P1—O1 | 108.63 (12) |
| O2vii—K2—O4iv | 132.57 (6) | O3—P1—O1 | 110.83 (12) |
| O2viii—K2—O4iv | 141.48 (6) | P1—O1—Fe1 | 130.29 (12) |
| O2ix—K2—O4iv | 95.42 (6) | P1—O1—K1xvi | 112.12 (11) |
| O3iv—K2—O4v | 114.59 (7) | Fe1—O1—K1xvi | 102.92 (7) |
| O3vi—K2—O4v | 52.71 (6) | P1—O2—Sn1xxii | 165.01 (15) |
| O3v—K2—O4v | 48.81 (5) | P1—O2—Fe1xxii | 165.01 (15) |
| O2vii—K2—O4v | 141.48 (6) | P1—O2—K2xix | 93.70 (9) |
| O2viii—K2—O4v | 95.42 (6) | Sn1xxii—O2—K2xix | 93.67 (8) |
| O2ix—K2—O4v | 132.57 (6) | Fe1xxii—O2—K2xix | 93.67 (8) |
| O4iv—K2—O4v | 85.96 (7) | P1—O2—K1xxi | 92.83 (10) |
| O3iv—K2—O4vi | 52.71 (6) | Sn1xxii—O2—K1xxi | 98.07 (8) |
| O3vi—K2—O4vi | 48.81 (5) | Fe1xxii—O2—K1xxi | 98.07 (8) |
| O3v—K2—O4vi | 114.59 (7) | K2xix—O2—K1xxi | 103.77 (7) |
| O2vii—K2—O4vi | 95.42 (6) | P1—O3—Sn2xvi | 148.98 (14) |
| O2viii—K2—O4vi | 132.57 (6) | P1—O3—Fe2xvi | 148.98 (14) |
| O2ix—K2—O4vi | 141.48 (6) | P1—O3—K2xxi | 105.79 (11) |
| O4iv—K2—O4vi | 85.96 (7) | Sn2xvi—O3—K2xxi | 100.16 (8) |
| O4v—K2—O4vi | 85.96 (7) | Fe2xvi—O3—K2xxi | 100.16 (8) |
| O3iv—K2—O4vii | 56.20 (5) | P1—O4—Fe2 | 151.99 (15) |
| O3vi—K2—O4vii | 86.13 (6) | P1—O4—K2xxi | 98.04 (10) |
| O3v—K2—O4vii | 156.82 (6) | Fe2—O4—K2xxi | 93.77 (8) |
| O2vii—K2—O4vii | 45.82 (5) | P1—O4—K1xxi | 88.91 (9) |
| O2viii—K2—O4vii | 100.56 (6) | Fe2—O4—K1xxi | 118.50 (9) |
| O2ix—K2—O4vii | 88.43 (6) | K2xxi—O4—K1xxi | 77.63 (6) |
| O4iv—K2—O4vii | 104.276 (11) | P1—O4—K2xix | 83.19 (10) |
| O4v—K2—O4vii | 137.22 (4) | Fe2—O4—K2xix | 88.28 (8) |
| O4vi—K2—O4vii | 54.34 (8) | K2xxi—O4—K2xix | 172.75 (8) |
| O3iv—K2—O4viii | 156.82 (6) | K1xxi—O4—K2xix | 95.28 (7) |
| O3vi—K2—O4viii | 56.20 (5) |
| Symmetry codes: (i) −z+1/2, −x+1, y+1/2; (ii) −x+1, y+1/2, −z+1/2; (iii) y+1/2, −z+1/2, −x+1; (iv) z+1/2, −x+3/2, −y+1; (v) −x+3/2, −y+1, z+1/2; (vi) −y+1, z+1/2, −x+3/2; (vii) −z+1, x+1/2, −y+3/2; (viii) −y+3/2, −z+1, x+1/2; (ix) x+1/2, −y+3/2, −z+1; (x) −y+1/2, −z, x−1/2; (xi) x−1/2, −y+1/2, −z; (xii) −z, x−1/2, −y+1/2; (xiii) y, z, x; (xiv) z, x, y; (xv) x−1, y−1, z−1; (xvi) −x+1, y−1/2, −z+1/2; (xvii) x−1/2, −y+1/2, −z+1; (xviii) −x+1/2, −y+1, z−1/2; (xix) x−1/2, −y+3/2, −z+1; (xx) −x+1, y−1/2, −z+3/2; (xxi) −x+3/2, −y+1, z−1/2; (xxii) x+1/2, −y+1/2, −z. |
| K1—O1i | 2.852 (2) | Fe1—O1v | 2.0195 (19) |
| K1—O2ii | 3.013 (2) | Fe2—O3i | 1.9830 (19) |
| K1—O4ii | 3.117 (2) | Fe2—O4 | 2.010 (2) |
| K2—O3ii | 2.868 (2) | P1—O4 | 1.521 (2) |
| K2—O2iii | 2.960 (2) | P1—O2 | 1.521 (2) |
| K2—O4ii | 3.053 (3) | P1—O3 | 1.525 (2) |
| K2—O4iii | 3.243 (2) | P1—O1 | 1.5306 (19) |
| Fe1—O2iv | 2.0032 (19) |
| Symmetry codes: (i) −z+1/2, −x+1, y+1/2; (ii) z+1/2, −x+3/2, −y+1; (iii) −z+1, x+1/2, −y+3/2; (iv) −y+1/2, −z, x−1/2; (v) y, z, x. |
Aatiq, A., Haggouch, B., Bakri, R., Lakhdar, Y. & Saadoune, I. (2006). Powder Diffr. 21, 214–219.
Blessing, R. H. (1995). Acta Cryst. A51, 33–38.
Brandenburg, K. (2006). DIAMOND. Version 3.1c. Crystal Impact GbR, Bonn, Germany.
Farrugia, L. J. (1999). J. Appl. Cryst. 32, 837–838.
Flack, H. D. (1983). Acta Cryst. A39, 876–881.
Norberg, S. T. (2002). Acta Cryst. B58, 743–749.
Ogorodnyk, I. V., Zatovsky, I. V., Baumer, V. N., Slobodyanik, N. S. & Shishkin, O. V. (2007). Cryst. Res. Technol. 42, 1076–1081.
Ogorodnyk, I. V., Zatovsky, I. V. & Slobodyanik, N. S. (2007). Russ. J. Inorg. Chem. 52, 121–125.
Ogorodnyk, I. V., Zatovsky, I. V., Slobodyanik, N. S., Baumer, V. N. & Shishkin, O. V. (2006). J. Solid State Chem. 179, 3461–3466.
Orlova, A. I., Trubach, I. G., Kurazhkovskaya, V. S., Pertierra, P., Salvado, M. A., Garcia-Granda, S., Khainakov, S. A. & Garcia, J. R. (2003). J. Solid State Chem. 173, 314–318.
Oxford Diffraction (2005). CrysAlis CCD and CrysAlis RED. Versions 1.171.28p4beta. Oxford Diffraction Ltd, Abingdon, Oxfordshire, England.
Sheldrick, G. M. (1997). SHELXS97 and SHELXL97. University of Göttingen, Germany.
Zemann, A. & Zemann, J. (1957). Acta Cryst. 10, 409–413.
Langbeinite-type frameworks [M2(PO4)3]∞ can be composed from various types of tetravalent and bi- or trivalent metal pairs. For example, the structures of K2M0.5Ti1.5(PO4)3 (M = Ni, Co, Mn) (Ogorodnyk et al., 2006; 2007a), K2MTi(PO4)3 (M = Y, Yb, Er) (Norberg, 2002), K2FeZr(PO4)3 (Orlova et al., 2003) and K2LuZr(PO4)3 (Ogorodnyk et al., 2007b) have been investigated in the past years. Among other langbeinite-related compounds, the structures of only two tin(IV)-containing phosphates, viz. K2MSn(PO4)3 (M = Fe, Yb) refined from X-ray powder data, were previously reported (Aatiq et al., 2006). Herein we report the single-crystal growth and re-investigation of K2FeSn(PO4)3 (I), a structure that is isotypic with the mineral langbeinite, K2Mg2(SO4)3 (Zemann, & Zemann, 1957).
Sn and Fe atoms are statistically distributed over two octahedrally coordinated positions with an insignificant priority of the M1 site occupation by Sn and of the M2 site by Fe. The {Sn(Fe)1-Sn(Fe)2-K1—K2} sequence runs along [111] (Fig. 1). K1 atoms are coordinated by 9 O atoms, while K2 atoms are surrounded by 12 O atoms (Fig. 2), with K—O bond lengths ranging from 2.852 (2) to 3.243 (2) Å.
Comparing the results from the single-crystal study with the results of the previous powder study, the following points are noteable. The distribution of two type of metals (Fe and Sn) over two octahedrally coordinated positions are close to those reported earlier, but the accuracy of single-crystal refinement is more precise. The values of corresponding Fe/Sn—O bond lengths insignificantly differs from one another in each type of octahedron in the present structure model, while the values found by Rietveld refinement differs a lot. Actually, the new results of the single-crystal refinement suggest a lower degree of distortion of the [(Fe,Sn)O6] polyhedra. Moreover, in contrast to the results of the powder refinement with each of the K+ cations in 9-fold coordination, we assume that K1 is 9-coordinate, while K2 is 12-coordinate, which agrees with the most of earlier discussed structures of langbeinite-related phosphates.