Supporting information
Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270106044519/bc3019sup1.cif | |
Structure factor file (CIF format) https://doi.org/10.1107/S0108270106044519/bc3019Isup2.hkl |
The title compound can be obtained easily using the self-flux technique in air. However, ZrO2 has low solubility in phosphate fluxes and ZrF4 was used as a starting Zr compound. CeF3 was used for the same reason.
In a first step, a mixture of 4.52 g of KPO3 and 3.4 g of K4P2O7 was melted in a platinum crucible at 1273 K for 1 h with stirring. It was then cooled quickly to 1173 K and a ground mixture of ZrF4 and CeF3 was added. The temperature of the crucible was kept constant for 30 min and then cooled at a rate of 25 K h−1 to 913 K and the molten glass was poured out. After cooling to room temperature and rinsing in hot deionized water, a mixture of yellow crystals of (I) (0.1–0.15 mm in size) and CePO4 powder was recovered. This mixture was separated by sedimentation in water. Crystals of (I) were dried at 400 K in air and sieved.
The purity of (I) was checked using powder X-ray diffraction (DRON-3 Ni-filtered Cu Kα radiation). CePO4 and other crystalline impurities were not detected. The ICP determination of K, Ce and Zr in (I) yielded an atomic ratio of the elements of 3.95:0.97:0.98. Further analysis for K, Ce, Zr and P was performed by energy dispersive spectroscopy; the analysis yielded atomic ratios equal to 3.9:1.05:1.03:4. The presence of fluorine was checked by the following procedure: the sample was melted with NaOH at 800 K in a gold crucible and washed with hot deionized water. Nitric acid was then added to the crucible. Fluoride ions were precipitated as PbClF and the chloride content was estimated by Volhard's method, from which the fluoride content was calculated (Vogel, 1962). No fluorine was detected in (I).
By the same technique, we also synthesized K4CeHf(PO4)4, but with smaller crystal dimensions (unpublished work).
The Ce and Zr atomic coordinates and displacement parameters were constrained and their occupancies were refined. After the final refinement cycles, the P and O atoms were found to have high values of Ueq and the convergence factors were also high. Three peaks were assigned as extra P and O positions according to the anion geometry. The occupancies of the P and O sites were calculated from the compound stoichiometry and fixed.
Data collection: CrysAlis CCD (Oxford Diffraction, 2005); cell refinement: CrysAlis CCD; data reduction: CrysAlis RED (Oxford Diffraction, 2005); program(s) used to solve structure: SIR2004 (Burla et al., 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: DIAMOND (Brandenburg, 1999); software used to prepare material for publication: WinGX (Farrugia, 1999).
K4CeZr(PO4)4 | Dx = 3.330 Mg m−3 |
Mr = 767.62 | Mo Kα radiation, λ = 0.71073 Å |
Tetragonal, I41/amd | Cell parameters from 320 reflections |
Hall symbol: -I 4bd 2 | θ = 15–25° |
a = 6.7039 (9) Å | µ = 5.24 mm−1 |
c = 17.065 (3) Å | T = 293 K |
V = 766.9 (2) Å3 | Tetragonal bipyramid, light yellow |
Z = 2 | 0.16 × 0.13 × 0.12 mm |
F(000) = 725 |
Oxford Diffraction XCalibur-3 diffractometer | 327 independent reflections |
Radiation source: fine-focus sealed tube | 292 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.034 |
ϕ and ω scans | θmax = 30.0°, θmin = 3.3° |
Absorption correction: multi-scan (Blessing, 1995) | h = −7→9 |
Tmin = 0.442, Tmax = 0.501 | k = −9→6 |
3037 measured reflections | l = −23→24 |
Refinement on F2 | 2 restraints |
Least-squares matrix: full | Primary atom site location: structure-invariant direct methods |
R[F2 > 2σ(F2)] = 0.029 | Secondary atom site location: difference Fourier map |
wR(F2) = 0.080 | w = 1/[σ2(Fo2) + (0.062P)2] where P = (Fo2 + 2Fc2)/3 |
S = 1.03 | (Δ/σ)max < 0.001 |
327 reflections | Δρmax = 0.59 e Å−3 |
41 parameters | Δρmin = −0.86 e Å−3 |
K4CeZr(PO4)4 | Z = 2 |
Mr = 767.62 | Mo Kα radiation |
Tetragonal, I41/amd | µ = 5.24 mm−1 |
a = 6.7039 (9) Å | T = 293 K |
c = 17.065 (3) Å | 0.16 × 0.13 × 0.12 mm |
V = 766.9 (2) Å3 |
Oxford Diffraction XCalibur-3 diffractometer | 327 independent reflections |
Absorption correction: multi-scan (Blessing, 1995) | 292 reflections with I > 2σ(I) |
Tmin = 0.442, Tmax = 0.501 | Rint = 0.034 |
3037 measured reflections |
R[F2 > 2σ(F2)] = 0.029 | 41 parameters |
wR(F2) = 0.080 | 2 restraints |
S = 1.03 | Δρmax = 0.59 e Å−3 |
327 reflections | Δρmin = −0.86 e Å−3 |
Experimental. The purity of (I) was checked using powder X-ray diffraction (DRON-3 Ni-filtered Cu Kα radiation λ=1.54178). CePO4 and other crystalline impurities were not detected. The ICP determination of K, Ce and Zr in (I) was performed on a `Spectroflame Modula ICP' (`Sectro', Germany) instrument. The atomic ratio of the elements in (I) was found to be 3.95:0.97:0.98. Further analysis for K, Ce, Zr and P was performed by energy dispersive spectroscopy using a Link Isis analyzer mounted on a Philips XL 30 FE 6 scanning electron microscope. The analysis yielded atomic ratios equal to 3.9:1.05:1.03:4. |
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) | |
Zr | 0 | 0.75 | 0.625 | 0.0232 (2) | 0.493 (3) |
Ce | 0 | 0.75 | 0.625 | 0.0232 (2) | 0.509 (4) |
K | 0.25 | 0.75 | 0.25 | 0.0566 (6) | |
PA | 0 | 0.75 | 0.4415 (5) | 0.0193 (12) | 0.5 |
PB | 0.0646 (16) | 0.75 | 0.4245 (6) | 0.0269 (17) | 0.25 |
O1 | 0 | 0.5685 (5) | 0.3842 (2) | 0.0376 (10) | |
O2A | 0.1788 (9) | 0.75 | 0.4971 (4) | 0.0283 (14) | 0.5 |
O2B | 0 | 0.75 | 0.5079 (6) | 0.044 (3) | 0.5 |
O3 | 0.302 (3) | 0.75 | 0.4205 (11) | 0.050 (4) | 0.25 |
U11 | U22 | U33 | U12 | U13 | U23 | |
Zr | 0.0160 (3) | 0.0160 (3) | 0.0375 (4) | 0 | 0 | 0 |
Ce | 0.0160 (3) | 0.0160 (3) | 0.0375 (4) | 0 | 0 | 0 |
K | 0.0371 (11) | 0.0611 (13) | 0.0715 (13) | 0 | 0.0037 (10) | 0 |
PA | 0.018 (4) | 0.020 (2) | 0.020 (4) | 0 | 0 | 0 |
PB | 0.043 (6) | 0.015 (2) | 0.022 (4) | 0 | −0.005 (3) | 0 |
O1 | 0.052 (3) | 0.0204 (17) | 0.0403 (19) | 0 | 0 | −0.0021 (14) |
O2A | 0.022 (3) | 0.040 (4) | 0.022 (3) | 0 | −0.002 (2) | 0 |
O2B | 0.064 (8) | 0.046 (7) | 0.022 (4) | 0 | 0 | 0 |
O3 | 0.056 (11) | 0.031 (8) | 0.063 (10) | 0 | −0.012 (9) | 0 |
Ce—O1i | 2.141 (4) | K—O3 | 2.930 (19) |
Ce—O1ii | 2.141 (4) | K—O1 | 3.087 (3) |
Ce—O1iii | 2.141 (4) | K—O1xviii | 3.087 (3) |
Ce—O1iv | 2.141 (4) | K—O1v | 3.087 (3) |
Ce—O2Av | 2.491 (6) | K—O1xvii | 3.087 (3) |
Ce—O2Avi | 2.491 (6) | K—Kv | 3.3520 (6) |
Ce—O2A | 2.491 (6) | PA—O2A | 1.529 (8) |
Ce—O2Avii | 2.491 (6) | PA—O2Av | 1.529 (8) |
Zr—O2Bvii | 1.998 (11) | PA—O1 | 1.561 (7) |
Zr—O2B | 1.998 (11) | PA—O1v | 1.561 (7) |
Zr—O1i | 2.141 (4) | PA—Kv | 3.672 (8) |
Zr—O1iv | 2.141 (4) | PB—PBv | 0.87 (2) |
Zr—O1ii | 2.141 (4) | PB—O1 | 1.464 (8) |
Zr—O1iii | 2.141 (4) | PB—O1v | 1.464 (8) |
Zr—Kviii | 4.3122 (5) | PB—O2B | 1.488 (14) |
Zr—Kix | 4.3122 (5) | PB—O3 | 1.59 (2) |
Zr—Kx | 4.3122 (5) | PB—Kxiii | 3.604 (11) |
Zr—Kxi | 4.3122 (5) | PB—Kxvi | 3.604 (11) |
Zr—Kxii | 4.3122 (5) | PB—Kv | 3.649 (13) |
Zr—Kxiii | 4.3122 (5) | O1—PBv | 1.464 (8) |
K—O3xiv | 2.532 (14) | O1—Ceiv | 2.141 (4) |
K—O3xiii | 2.532 (14) | O1—Zriv | 2.141 (4) |
K—O3xv | 2.532 (14) | O1—Kv | 3.087 (3) |
K—O3xvi | 2.532 (14) | O2A—Kxiii | 2.729 (5) |
K—O2Axiv | 2.729 (5) | O2A—Kxvi | 2.729 (5) |
K—O2Axiii | 2.729 (5) | O2B—PBv | 1.488 (14) |
K—O2Axv | 2.729 (5) | O3—Kxiii | 2.532 (14) |
K—O2Axvi | 2.729 (5) | O3—Kxvi | 2.532 (14) |
K—O3xvii | 2.930 (19) | ||
O2Bvii—Zr—O2B | 180.0000 (10) | O3xvi—K—O3 | 52.3 (6) |
O2Bvii—Zr—O1i | 85.81 (9) | O2Axiv—K—O3 | 95.3 (3) |
O2B—Zr—O1i | 94.19 (9) | O2Axiii—K—O3 | 84.7 (3) |
O2Bvii—Zr—O1iv | 94.19 (9) | O2Axv—K—O3 | 95.3 (3) |
O2B—Zr—O1iv | 85.81 (9) | O2Axvi—K—O3 | 84.7 (3) |
O1i—Zr—O1iv | 90.306 (14) | O3xvii—K—O3 | 180.000 (3) |
O2Bvii—Zr—O1ii | 85.81 (9) | O3xiv—K—O1xviii | 75.8 (3) |
O2B—Zr—O1ii | 94.19 (9) | O3xiii—K—O1xviii | 104.2 (3) |
O1i—Zr—O1ii | 171.62 (19) | O3xv—K—O1xviii | 99.7 (4) |
O1iv—Zr—O1ii | 90.306 (15) | O3xvi—K—O1xviii | 80.3 (4) |
O2Bvii—Zr—O1iii | 94.19 (9) | O2Axiv—K—O1xviii | 90.51 (12) |
O2B—Zr—O1iii | 85.81 (9) | O2Axiii—K—O1xviii | 89.49 (12) |
O1i—Zr—O1iii | 90.306 (15) | O2Axv—K—O1xviii | 129.11 (14) |
O1iv—Zr—O1iii | 171.62 (19) | O2Axvi—K—O1xviii | 50.89 (14) |
O1ii—Zr—O1iii | 90.306 (14) | O3xvii—K—O1xviii | 47.8 (3) |
O2Bvii—Zr—Kviii | 60.351 (6) | O3—K—O1xviii | 132.2 (3) |
O2B—Zr—Kviii | 119.649 (6) | O3xiv—K—O1v | 104.2 (3) |
O1i—Zr—Kviii | 64.93 (5) | O3xiii—K—O1v | 75.8 (3) |
O1iv—Zr—Kviii | 144.23 (7) | O3xv—K—O1v | 80.3 (4) |
O1ii—Zr—Kviii | 110.58 (5) | O3xvi—K—O1v | 99.7 (4) |
O1iii—Zr—Kviii | 42.35 (8) | O2Axiv—K—O1v | 89.49 (12) |
O2Bvii—Zr—Kix | 119.649 (6) | O2Axiii—K—O1v | 90.51 (12) |
O2B—Zr—Kix | 60.351 (6) | O2Axv—K—O1v | 50.89 (14) |
O1i—Zr—Kix | 144.23 (7) | O2Axvi—K—O1v | 129.11 (14) |
O1iv—Zr—Kix | 64.93 (5) | O3xvii—K—O1v | 132.2 (3) |
O1ii—Zr—Kix | 42.35 (8) | O3—K—O1v | 47.8 (3) |
O1iii—Zr—Kix | 110.58 (5) | O1xviii—K—O1v | 180 |
Kviii—Zr—Kix | 148.097 (2) | O2A—PA—O2Av | 103.3 (7) |
O2Bvii—Zr—Kx | 60.351 (6) | O2A—PA—O1 | 112.88 (14) |
O2B—Zr—Kx | 119.649 (6) | O2Av—PA—O1 | 112.88 (14) |
O1i—Zr—Kx | 110.58 (5) | O2A—PA—O1v | 112.88 (14) |
O1iv—Zr—Kx | 144.23 (7) | O2Av—PA—O1v | 112.88 (14) |
O1ii—Zr—Kx | 64.93 (5) | O1—PA—O1v | 102.4 (6) |
O1iii—Zr—Kx | 42.35 (8) | O2A—PA—Kv | 155.5 (4) |
Kviii—Zr—Kx | 45.743 (3) | O2Av—PA—Kv | 101.2 (3) |
Kix—Zr—Kx | 104.165 (5) | O1—PA—Kv | 56.1 (3) |
O2Bvii—Zr—Kxi | 119.649 (6) | O1v—PA—Kv | 56.1 (3) |
O2B—Zr—Kxi | 60.351 (6) | O2A—PA—K | 101.2 (3) |
O1i—Zr—Kxi | 144.23 (7) | O2Av—PA—K | 155.5 (4) |
O1iv—Zr—Kxi | 110.58 (5) | O1—PA—K | 56.1 (3) |
O1ii—Zr—Kxi | 42.35 (8) | O1v—PA—K | 56.1 (3) |
O1iii—Zr—Kxi | 64.93 (5) | Kv—PA—K | 54.31 (13) |
Kviii—Zr—Kxi | 104.165 (5) | PBv—PB—O1 | 72.8 (4) |
Kix—Zr—Kxi | 45.743 (3) | PBv—PB—O1v | 72.8 (4) |
Kx—Zr—Kxi | 68.929 (10) | O1—PB—O1v | 112.5 (8) |
O2Bvii—Zr—Kxii | 60.351 (6) | PBv—PB—O2B | 73.1 (5) |
O2B—Zr—Kxii | 119.649 (6) | O1—PB—O2B | 111.3 (4) |
O1i—Zr—Kxii | 110.58 (5) | O1v—PB—O2B | 111.3 (4) |
O1iv—Zr—Kxii | 42.35 (8) | PBv—PB—O3 | 177.5 (8) |
O1ii—Zr—Kxii | 64.93 (5) | O1—PB—O3 | 106.0 (5) |
O1iii—Zr—Kxii | 144.23 (7) | O1v—PB—O3 | 106.0 (5) |
Kviii—Zr—Kxii | 120.703 (12) | O2B—PB—O3 | 109.4 (11) |
Kix—Zr—Kxii | 68.929 (10) | PBv—PB—K | 112.7 (2) |
Kx—Zr—Kxii | 102.032 (8) | O1—PB—K | 71.3 (3) |
Kxi—Zr—Kxii | 104.165 (5) | O1v—PB—K | 71.3 (3) |
O2Bvii—Zr—Kxiii | 119.649 (6) | O2B—PB—K | 174.3 (7) |
O2B—Zr—Kxiii | 60.351 (6) | O3—PB—K | 64.9 (8) |
O1i—Zr—Kxiii | 42.35 (8) | PBv—PB—Kxiii | 144.08 (10) |
O1iv—Zr—Kxiii | 110.58 (5) | O1—PB—Kxiii | 142.6 (5) |
O1ii—Zr—Kxiii | 144.23 (7) | O1v—PB—Kxiii | 91.2 (3) |
O1iii—Zr—Kxiii | 64.93 (5) | O2B—PB—Kxiii | 83.9 (5) |
Kviii—Zr—Kxiii | 68.929 (10) | K—PB—Kxiii | 91.0 (2) |
Kix—Zr—Kxiii | 120.702 (12) | PBv—PB—Kxvi | 144.08 (10) |
Kx—Zr—Kxiii | 104.165 (5) | O1—PB—Kxvi | 91.2 (3) |
Kxi—Zr—Kxiii | 102.032 (8) | O1v—PB—Kxvi | 142.6 (5) |
Kxii—Zr—Kxiii | 148.097 (2) | O2B—PB—Kxvi | 83.9 (5) |
O3xiv—K—O3xiii | 180.0 (10) | K—PB—Kxvi | 91.0 (2) |
O3xiv—K—O3xv | 63.2 (8) | Kxiii—PB—Kxvi | 55.43 (18) |
O3xiii—K—O3xv | 116.8 (8) | PBv—PB—Kv | 54.69 (13) |
O3xiv—K—O3xvi | 116.8 (8) | O1—PB—Kv | 56.3 (4) |
O3xiii—K—O3xvi | 63.2 (8) | O1v—PB—Kv | 56.3 (4) |
O3xv—K—O3xvi | 180.0 (7) | O2B—PB—Kv | 127.8 (6) |
O3xiv—K—O2Axiv | 34.0 (5) | O3—PB—Kv | 122.8 (8) |
O3xiii—K—O2Axiv | 146.0 (5) | K—PB—Kv | 57.96 (18) |
O3xv—K—O2Axiv | 89.8 (4) | Kxiii—PB—Kv | 139.45 (18) |
O3xvi—K—O2Axiv | 90.2 (4) | Kxvi—PB—Kv | 139.45 (18) |
O3xiv—K—O2Axiii | 146.0 (5) | PB—O1—Ceiv | 149.7 (4) |
O3xiii—K—O2Axiii | 34.0 (5) | PBv—O1—Ceiv | 149.7 (5) |
O3xv—K—O2Axiii | 90.2 (4) | PA—O1—Ceiv | 145.4 (3) |
O3xvi—K—O2Axiii | 89.8 (4) | PB—O1—Zriv | 149.7 (4) |
O2Axiv—K—O2Axiii | 180.0 (3) | PBv—O1—Zriv | 149.7 (5) |
O3xiv—K—O2Axv | 89.8 (4) | PA—O1—Zriv | 145.4 (3) |
O3xiii—K—O2Axv | 90.2 (4) | PB—O1—Kv | 100.5 (4) |
O3xv—K—O2Axv | 34.0 (5) | PBv—O1—Kv | 82.0 (3) |
O3xvi—K—O2Axv | 146.0 (5) | PA—O1—Kv | 99.0 (3) |
O2Axiv—K—O2Axv | 104.18 (16) | Ceiv—O1—Kv | 109.81 (11) |
O2Axiii—K—O2Axv | 75.82 (16) | Zriv—O1—Kv | 109.81 (11) |
O3xiv—K—O2Axvi | 90.2 (4) | PB—O1—K | 82.0 (3) |
O3xiii—K—O2Axvi | 89.8 (4) | PBv—O1—K | 100.5 (4) |
O3xv—K—O2Axvi | 146.0 (5) | PA—O1—K | 99.0 (3) |
O3xvi—K—O2Axvi | 34.0 (5) | Ceiv—O1—K | 109.81 (11) |
O2Axiv—K—O2Axvi | 75.82 (16) | Zriv—O1—K | 109.81 (11) |
O2Axiii—K—O2Axvi | 104.18 (16) | Kv—O1—K | 65.76 (7) |
O2Axv—K—O2Axvi | 180.0000 (10) | PA—O2A—Kxiii | 129.0 (3) |
O3xiv—K—O3xvii | 52.3 (6) | PA—O2A—Kxvi | 129.0 (3) |
O3xiii—K—O3xvii | 127.7 (6) | Kxiii—O2A—Kxvi | 75.78 (16) |
O3xv—K—O3xvii | 52.3 (6) | PB—O2B—Zr | 163.1 (5) |
O3xvi—K—O3xvii | 127.7 (6) | PBv—O2B—Zr | 163.1 (5) |
O2Axiv—K—O3xvii | 84.7 (3) | PB—O3—Kxiii | 120.0 (8) |
O2Axiii—K—O3xvii | 95.3 (3) | PB—O3—Kxvi | 120.0 (8) |
O2Axv—K—O3xvii | 84.7 (3) | Kxiii—O3—Kxvi | 82.9 (6) |
O2Axvi—K—O3xvii | 95.3 (3) | PB—O3—K | 85.6 (9) |
O3xiv—K—O3 | 127.7 (6) | Kxiii—O3—K | 126.5 (5) |
O3xiii—K—O3 | 52.3 (6) | Kxvi—O3—K | 126.5 (5) |
O3xv—K—O3 | 127.7 (6) |
Symmetry codes: (i) y−1/4, x+3/4, z+1/4; (ii) −y+1/4, −x+3/4, z+1/4; (iii) x, y+1/2, −z+1; (iv) −x, −y+1, −z+1; (v) −x, −y+3/2, z; (vi) y−3/4, x+3/4, −z+5/4; (vii) −y+3/4, −x+3/4, −z+5/4; (viii) −x+1/2, −y+2, z+1/2; (ix) y−5/4, x+1/4, −z+3/4; (x) x−1/2, y+1/2, z+1/2; (xi) −y+1/4, −x+5/4, −z+3/4; (xii) x−1/2, y−1/2, z+1/2; (xiii) −y+5/4, −x+5/4, −z+3/4; (xiv) y−3/4, x+1/4, z−1/4; (xv) −y+3/4, −x+5/4, z−1/4; (xvi) y−1/4, x+1/4, −z+3/4; (xvii) −x+1/2, −y+3/2, −z+1/2; (xviii) x+1/2, y, −z+1/2. |
Experimental details
Crystal data | |
Chemical formula | K4CeZr(PO4)4 |
Mr | 767.62 |
Crystal system, space group | Tetragonal, I41/amd |
Temperature (K) | 293 |
a, c (Å) | 6.7039 (9), 17.065 (3) |
V (Å3) | 766.9 (2) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 5.24 |
Crystal size (mm) | 0.16 × 0.13 × 0.12 |
Data collection | |
Diffractometer | Oxford Diffraction XCalibur-3 diffractometer |
Absorption correction | Multi-scan (Blessing, 1995) |
Tmin, Tmax | 0.442, 0.501 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 3037, 327, 292 |
Rint | 0.034 |
(sin θ/λ)max (Å−1) | 0.703 |
Refinement | |
R[F2 > 2σ(F2)], wR(F2), S | 0.029, 0.080, 1.03 |
No. of reflections | 327 |
No. of parameters | 41 |
No. of restraints | 2 |
Δρmax, Δρmin (e Å−3) | 0.59, −0.86 |
Computer programs: CrysAlis CCD (Oxford Diffraction, 2005), CrysAlis CCD, CrysAlis RED (Oxford Diffraction, 2005), SIR2004 (Burla et al., 2005), SHELXL97 (Sheldrick, 1997), DIAMOND (Brandenburg, 1999), WinGX (Farrugia, 1999).
Ce—O1i | 2.141 (4) | K—O1 | 3.087 (3) |
Ce—O2A | 2.491 (6) | K—Kiii | 3.3520 (6) |
Zr—O2B | 1.998 (11) | PA—O2A | 1.529 (8) |
Zr—O1i | 2.141 (4) | PA—O1 | 1.561 (7) |
K—O3ii | 2.532 (14) | PB—O1 | 1.464 (8) |
K—O2Aii | 2.729 (5) | PB—O2B | 1.488 (14) |
K—O3 | 2.930 (19) | PB—O3 | 1.59 (2) |
O2A—PA—O2Aiii | 103.3 (7) | O1—PB—O2B | 111.3 (4) |
O2A—PA—O1 | 112.88 (14) | O1—PB—O3 | 106.0 (5) |
O1—PA—O1iii | 102.4 (6) | O2B—PB—O3 | 109.4 (11) |
O1—PB—O1iii | 112.5 (8) |
Symmetry codes: (i) −x, −y+1, −z+1; (ii) −y+5/4, −x+5/4, −z+3/4; (iii) −x, −y+3/2, z. |
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Cerium is only the lanthanide that forms compounds in the tetravalent as well as the trivalent oxidation state. Its chemical behavior as a tetravalent metal is similar to those of Zr, Hf, Th, U, Np and Pu. Such properties can be explained by the similar ionic radii and electron configurations of these elements (the presence of the f electrons). At the same time, there are only a few phosphates containing CeIV that have been synthesized at high temperature. At high temperatures, many Ce phosphates decompose to yield CePO4 (monazite) as a main product, owing to its chemical stability (Leonardos, 1974) and its elevated melting temperature in excess of 2223 K (Ueda & Korekawa, 1955). Another stable compound containing cerium is CeP2O7 (Völlenkle et al., 1963), which is easily prepared by the high-temperature recrystallization of the precipitate obtained by the mixing of CeIV sulfate and sodium pyrophosphate aqueous solutions. The CeIV phosphate CeIV(PO4)(HPO4)0.5(H2O)0.5 can also be synthesized from CeO2, H3PO4 and H2O (Nazaraly et al., 2005). Finally, Cd0.5CeIV2(PO4)3 can be prepared by solid-state reaction at 1373 K (Orlova et al., 2005). The latter compound is isostructural to monazite, with Cd and Ce atoms randomly occupying the same crystallographic site.
We present here the structure determination of a new mixed orthophosphate containing tetravalent cerium, K4CeZr(PO4)4, (I). The projection of the structure of (I) on to the bc plane shows the three-dimensional character of the [CeZr(PO4)4]∞ framework (Fig. 1). The structure can be described as a combination of [ZrO6] octahedra, [CeO8] dodecahedra and [PO4] tetrahedra linked together by sharing corners and edges. The rigid framework contains tunnels running along the a and b directions, in which the K+ cations are located.
A complex disorder involving the phosphate groups is observed in (I). The P positions are split equally over two sites, PA (8e site, 50% occupancy) and PB (16h site, 25% occupancy). The O1 (16h) position is fully occupied but the other O atoms are disordered over three sites, O2A (16h, 50% occupancy), O2B (8e, 50% occupancy) and O3 (16h, 25% occupancy) (Fig. 2). The disorder appears as a result of the mixed Ce/Zr occupancy and of their different sizes and bonding requirements. Three types of M—O distances are observed in (I): 1.998 (11), 2.141 (4) and 2.491 (6) Å. The latter distance is rather long for ZrIV atoms by comparison with K2Zr(PO4)2, with Zr—O distances of 2.060 (6) and 2.072 (3) Å (Doerffel & Liebertz, 1990). In Cd0.5CeIV2(PO4)3 (Orlova et al., 2005), the Ce—O distances are in the range 2.40 (1)–2.87 (1) Å for nine-coordinated CeIV atoms.
Four phosphate groups coordinate the M (= Ce or Zr) atom via O1 atoms forming an equatorial square-planar arrangement with M—O1 distances equal to 2.141 (4) Å. For M = Ce, the coordination is completed with four O2A atoms (Fig. 3a). A similar oxygen environment can be found for Zr in ZrSiO4 (Siegel or Siggel & Jansen, 1990). for M = Zr, the coordination is completed by two O2B atoms (Fig. 3b). Thus, Ce is eight-coordinated and Zr is six-coordinated. The O2B and O3 positions result from a rotation of 32.3 (6)° of the PO4 tetrahedron around the O1—O1I edge (Fig. 2). Bond valence sum (BVS) calculations confirm the six- and eightfold coordinations of the Zr and Ce atoms, respectively. The BVS around Zr is equal to 4.00 (4 Zr—O1 bonds with BV = 0.576 and 2 Zr—O2B bonds with BV = 0.848), while the BVS around Ce is equal to 4.09 (4 Ce—O1 bonds with BV = 0.737 and 4 Ce—O2A bonds with BV = 0.286) (Brese & O'Keeffe, 1991; Brown, 2002).
The potassium cations are located in tunnels running in two orthogonal directions parallel to the a and b axes with diameters of approximately 4 Å. Their oxygen environment depends on the orientation of the disordered PO4 group, which yields a wide range of K—O distances (2.532–3.087 Å). The BVS calculation gives a value of 1.1 taking into account the partial occupancies of the O sites. The K+ ions are at a distance of 3.3520 (6) Å from one another and ionic conductivity may be expected on the basis of the large tunnel dimensions.