The mixed-valent SeIV/VI compound tricadmium(II) bis-[selenite(IV)] selenate(VI), Cd3(SeO3)2SeO4, contains three crystallographically inequivalent CdII cations, one SeVIO4 tetrahedron and two independent SeIVO3 pyramids corresponding to the formula Cd3(SeO3)2(SeO4). The structure is composed of a three-dimensional network with channels extending parallel to the b axis. Distances and angles within the three [CdOx] polyhedra (x = 6, 8), as well as within the anionic framework, deviate only slightly from those of the isotypic mercury analogue, Hg3Se3O10.
Supporting information
Key indicators
- Single-crystal X-ray study
- T = 293 K
- Mean (Se-O) = 0.004 Å
- R factor = 0.018
- wR factor = 0.044
- Data-to-parameter ratio = 17.1
checkCIF results
No syntax errors found
ADDSYM reports no extra symmetry
Alert Level A:
DIFF_019 Alert A _diffrn_standards_number is missing
Number of standards used in measurement.
| Author response: An area detector system (CCD camera) was used for data collection.
No standard reflections were measured.
|
DIFF_020 Alert A _diffrn_standards_interval_count and
_diffrn_standards_interval_time are missing. Number of measurements
between standards or time (min) between standards.
| Author response: An area detector system (CCD camera) was used for data collection.
No standard reflections were measured.
|
DIFF_022 Alert A _diffrn_standards_decay_% is missing
Percentage decrease in standards intensity.
| Author response: An area detector system (CCD camera) was used for data collection.
No standard reflections were measured.
|
General Notes
ABSTM_02 When printed, the submitted absorption T values will be replaced
by the scaled T values. Since the ratio of scaled T's is
identical to the ratio of reported T values, the scaling does
not imply a change to the absorption corrections used in the
study.
Ratio of Tmax expected/reported 0.905
Tmax scaled 0.468 Tmin scaled 0.105
REFLT_03
From the CIF: _diffrn_reflns_theta_max 30.47
From the CIF: _reflns_number_total 2497
Count of symmetry unique reflns 1522
Completeness (_total/calc) 164.06%
TEST3: Check Friedels for noncentro structure
Estimate of Friedel pairs measured 975
Fraction of Friedel pairs measured 0.641
Are heavy atom types Z>Si present yes
Please check that the estimate of the number of Friedel pairs is
correct. If it is not, please give the correct count in the
_publ_section_exptl_refinement section of the submitted CIF.
3 Alert Level A = Potentially serious problem
0 Alert Level B = Potential problem
0 Alert Level C = Please check
Experiments intended to prepare single crystals of compounds with the general formula (CdSeO4)x(HgO)y(H2O)z, with x = 1, y = 1, 1.5 or 2 and z = 0 or 1 (Denk & Leschhorn, 1966), yielded colourless crystals with mostly rod-like habit of the title compound and colourless plates of composition (CdSeO4)(HgO)(H2O) [space group P2/n, a = 7.9895 (18) Å, b = 6.3307 (6) Å, c = 10.5738 (11) Å and β = 102.795 (2)°; Weil, 2002] by reacting HgO and CdSeO4(H2O)2 in the molar ratio 1:2 in demineralized water under hydrothermal conditions (teflon-lined steel autoclave, 523 K, 6 d).
Systematic absences k = 2n+1 for the (0k0) reflections and similar lattice parameters revealed isotypism with the mercury analogue, Hg3Se3O10. The crystal structure was therefore refined with the atomic coordinates of the mercury compound as starting parameters. Refinement of the occupation factors did not indicate any incorporation of HgII into the structure.
Data collection: SMART (Siemens, 1996); cell refinement: SAINT (Siemens, 1996); data reduction: SAINT; program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS for Windows (Dowty, 2000); software used to prepare material for publication: SHELXL97.
Tricadmium(II) bis(selenite(IV)) selenate(VI)
top
Crystal data top
Cd3(SeO3)2SeO4 | F(000) = 652 |
Mr = 734.08 | Dx = 5.352 Mg m−3 |
Monoclinic, P21 | Mo Kα radiation, λ = 0.71073 Å |
Hall symbol: P 2yb | Cell parameters from 4083 reflections |
a = 8.3031 (8) Å | θ = 2.7–30.5° |
b = 5.3377 (5) Å | µ = 18.97 mm−1 |
c = 10.8485 (11) Å | T = 293 K |
β = 108.659 (2)° | Rod, colourless |
V = 455.53 (8) Å3 | 0.20 × 0.04 × 0.04 mm |
Z = 2 | |
Data collection top
Siemens SMART diffractometer | 2497 independent reflections |
Radiation source: fine-focus sealed tube | 2402 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.023 |
ω scans | θmax = 30.5°, θmin = 2.0° |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | h = −11→11 |
Tmin = 0.116, Tmax = 0.518 | k = −7→7 |
4516 measured reflections | l = −14→14 |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | w = 1/[σ2(Fo2)] |
R[F2 > 2σ(F2)] = 0.018 | (Δ/σ)max = 0.001 |
wR(F2) = 0.044 | Δρmax = 0.97 e Å−3 |
S = 1.00 | Δρmin = −0.79 e Å−3 |
2497 reflections | Extinction correction: SHELXL97, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
146 parameters | Extinction coefficient: 0.0065 (3) |
1 restraint | Absolute structure: Flack (1983), 0000 Friedel pairs |
Primary atom site location: structure-invariant direct methods | Absolute structure parameter: 0.080 (9) |
Crystal data top
Cd3(SeO3)2SeO4 | V = 455.53 (8) Å3 |
Mr = 734.08 | Z = 2 |
Monoclinic, P21 | Mo Kα radiation |
a = 8.3031 (8) Å | µ = 18.97 mm−1 |
b = 5.3377 (5) Å | T = 293 K |
c = 10.8485 (11) Å | 0.20 × 0.04 × 0.04 mm |
β = 108.659 (2)° | |
Data collection top
Siemens SMART diffractometer | 2497 independent reflections |
Absorption correction: multi-scan (SADABS; Sheldrick, 1996) | 2402 reflections with I > 2σ(I) |
Tmin = 0.116, Tmax = 0.518 | Rint = 0.023 |
4516 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.018 | 1 restraint |
wR(F2) = 0.044 | Δρmax = 0.97 e Å−3 |
S = 1.00 | Δρmin = −0.79 e Å−3 |
2497 reflections | Absolute structure: Flack (1983), 0000 Friedel pairs |
146 parameters | Absolute structure parameter: 0.080 (9) |
Special details top
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. |
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 > σ(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 | Uiso*/Ueq | |
Cd1 | −0.00382 (4) | 0.25150 (8) | 0.12793 (2) | 0.01258 (7) | |
Cd2 | −0.01861 (4) | 0.25949 (8) | 0.61730 (2) | 0.01527 (8) | |
Cd3 | 0.36338 (4) | 0.73845 (9) | 0.20432 (3) | 0.02092 (9) | |
Se1 | 0.25424 (5) | 0.22642 (10) | 0.95611 (4) | 0.01246 (10) | |
Se2 | 0.26984 (5) | 0.28363 (10) | 0.42598 (4) | 0.01253 (10) | |
Se3 | 0.65260 (5) | 0.24831 (11) | 0.28455 (3) | 0.01370 (9) | |
O1 | 0.0935 (4) | 0.1330 (6) | 0.8235 (3) | 0.0204 (7) | |
O2 | 0.1159 (4) | 0.3891 (6) | 0.4852 (3) | 0.0192 (7) | |
O3 | 0.1592 (4) | 0.0678 (6) | 0.3134 (3) | 0.0167 (7) | |
O4 | 0.1569 (4) | 0.4555 (6) | 0.0177 (3) | 0.0161 (7) | |
O5 | 0.2256 (5) | −0.0108 (6) | 0.0509 (3) | 0.0232 (8) | |
O6 | 0.2527 (5) | 0.5314 (7) | 0.3248 (3) | 0.0245 (8) | |
O7 | 0.5285 (4) | 0.0451 (7) | 0.3226 (3) | 0.0246 (8) | |
O8 | 0.5350 (5) | 0.4382 (7) | 0.1709 (3) | 0.0247 (8) | |
O9 | 0.7526 (5) | 0.4118 (7) | 0.4124 (3) | 0.0243 (8) | |
O10 | 0.7827 (5) | 0.0992 (6) | 0.2245 (3) | 0.0235 (8) | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Cd1 | 0.01555 (14) | 0.01217 (17) | 0.00942 (12) | 0.00015 (19) | 0.00315 (9) | 0.00052 (15) |
Cd2 | 0.02123 (16) | 0.01518 (17) | 0.01064 (12) | −0.0002 (2) | 0.00685 (10) | 0.00057 (16) |
Cd3 | 0.01811 (16) | 0.02101 (19) | 0.02167 (14) | −0.0012 (2) | 0.00359 (11) | 0.01152 (18) |
Se1 | 0.01315 (18) | 0.0126 (2) | 0.01091 (16) | −0.0003 (2) | 0.00281 (13) | 0.00033 (18) |
Se2 | 0.01206 (18) | 0.0140 (2) | 0.01093 (16) | −0.00041 (18) | 0.00278 (13) | 0.00109 (18) |
Se3 | 0.01202 (18) | 0.0174 (2) | 0.01099 (15) | 0.0002 (3) | 0.00273 (13) | −0.0022 (2) |
O1 | 0.0250 (19) | 0.0213 (17) | 0.0106 (14) | −0.0049 (14) | −0.0001 (13) | 0.0005 (12) |
O2 | 0.0201 (18) | 0.0193 (16) | 0.0229 (16) | 0.0075 (13) | 0.0134 (14) | 0.0079 (13) |
O3 | 0.0212 (18) | 0.0155 (16) | 0.0103 (14) | −0.0041 (13) | 0.0009 (13) | −0.0011 (12) |
O4 | 0.0196 (19) | 0.0172 (17) | 0.0129 (15) | 0.0050 (13) | 0.0071 (14) | −0.0001 (12) |
O5 | 0.028 (2) | 0.0199 (18) | 0.0148 (16) | −0.0018 (15) | −0.0022 (15) | 0.0088 (14) |
O6 | 0.026 (2) | 0.0203 (18) | 0.033 (2) | 0.0038 (14) | 0.0174 (17) | 0.0133 (15) |
O7 | 0.0193 (19) | 0.032 (2) | 0.0236 (17) | −0.0094 (15) | 0.0088 (15) | 0.0047 (15) |
O8 | 0.022 (2) | 0.030 (2) | 0.0207 (17) | 0.0053 (15) | 0.0041 (14) | 0.0102 (14) |
O9 | 0.029 (2) | 0.0227 (18) | 0.0164 (16) | 0.0000 (15) | −0.0003 (15) | −0.0103 (13) |
O10 | 0.0218 (19) | 0.0232 (19) | 0.0316 (19) | −0.0018 (14) | 0.0169 (16) | −0.0069 (15) |
Geometric parameters (Å, º) top
Cd1—O3 | 2.258 (3) | Se1—O5ix | 1.696 (3) |
Cd1—O1i | 2.287 (3) | Se1—O4ix | 1.715 (3) |
Cd1—O4ii | 2.307 (3) | Se1—Cd1v | 3.2199 (7) |
Cd1—O4 | 2.327 (3) | Se1—Cd1ix | 3.2617 (6) |
Cd1—O10iii | 2.468 (4) | Se1—Cd1i | 3.4346 (7) |
Cd1—O5iv | 2.545 (4) | Se1—Cd3x | 3.6462 (7) |
Cd1—O5 | 2.703 (4) | Se1—Cd3ix | 3.7390 (7) |
Cd1—O6 | 2.902 (4) | Se1—Cd3vii | 4.0803 (6) |
Cd2—O2 | 2.191 (3) | Se2—O6 | 1.695 (3) |
Cd2—O1 | 2.235 (3) | Se2—O2 | 1.700 (3) |
Cd2—O3i | 2.280 (3) | Se2—O3 | 1.716 (3) |
Cd2—O2v | 2.286 (3) | Se2—Cd2i | 3.2244 (7) |
Cd2—O6v | 2.537 (4) | Se2—Cd2v | 3.4310 (8) |
Cd2—O9iii | 2.551 (3) | Se2—Cd3xi | 4.0061 (7) |
Cd2—O10vi | 2.814 (4) | Se2—Cd3vii | 4.1956 (6) |
Cd2—O9vii | 2.980 (4) | Se3—O9 | 1.624 (3) |
Cd3—O6 | 2.132 (3) | Se3—O10 | 1.636 (3) |
Cd3—O5viii | 2.157 (3) | Se3—O7 | 1.637 (3) |
Cd3—O8 | 2.250 (4) | Se3—O8 | 1.653 (3) |
Cd3—O7viii | 2.254 (4) | Se3—Cd3xi | 3.5488 (6) |
Cd3—O4 | 2.664 (3) | Se3—Cd1xii | 3.7586 (5) |
Cd3—O3viii | 2.940 (3) | Se3—Cd2xii | 3.7658 (5) |
Cd3—Se3 | 3.4687 (6) | Se3—Cd2vii | 3.8867 (7) |
Cd3—Se3viii | 3.5488 (6) | Se3—Cd2vi | 3.9679 (8) |
Se1—O1 | 1.694 (3) | | |
| | | |
O3—Cd1—O1i | 109.14 (11) | O6v—Cd2—O9iii | 87.29 (13) |
O3—Cd1—O4ii | 110.77 (11) | O2—Cd2—O10vi | 78.15 (12) |
O1i—Cd1—O4ii | 128.24 (12) | O1—Cd2—O10vi | 66.32 (10) |
O3—Cd1—O4 | 112.45 (11) | O3i—Cd2—O10vi | 70.35 (11) |
O1i—Cd1—O4 | 89.10 (12) | O2v—Cd2—O10vi | 157.33 (11) |
O4ii—Cd1—O4 | 104.43 (8) | O6v—Cd2—O10vi | 126.67 (10) |
O3—Cd1—O10iii | 77.66 (12) | O9iii—Cd2—O10vi | 120.34 (11) |
O1i—Cd1—O10iii | 82.20 (12) | O2—Cd2—O9vii | 64.89 (10) |
O4ii—Cd1—O10iii | 75.64 (11) | O1—Cd2—O9vii | 80.44 (11) |
O4—Cd1—O10iii | 168.54 (12) | O3i—Cd2—O9vii | 163.84 (10) |
O3—Cd1—O5iv | 167.67 (13) | O2v—Cd2—O9vii | 64.36 (11) |
O1i—Cd1—O5iv | 61.47 (10) | O6v—Cd2—O9vii | 112.38 (12) |
O4ii—Cd1—O5iv | 73.36 (11) | O9iii—Cd2—O9vii | 118.37 (8) |
O4—Cd1—O5iv | 76.64 (13) | O10vi—Cd2—O9vii | 94.12 (10) |
O10iii—Cd1—O5iv | 92.58 (13) | O6—Cd3—O5viii | 124.66 (15) |
O3—Cd1—O5 | 76.67 (11) | O6—Cd3—O8 | 98.57 (13) |
O1i—Cd1—O5 | 147.81 (12) | O5viii—Cd3—O8 | 121.65 (13) |
O4ii—Cd1—O5 | 73.84 (12) | O6—Cd3—O7viii | 109.30 (14) |
O4—Cd1—O5 | 60.47 (10) | O5viii—Cd3—O7viii | 93.69 (14) |
O10iii—Cd1—O5 | 129.31 (11) | O8—Cd3—O7viii | 107.93 (13) |
O5iv—Cd1—O5 | 115.60 (8) | O6—Cd3—O4 | 82.71 (13) |
O3—Cd1—O6 | 58.54 (10) | O5viii—Cd3—O4 | 73.26 (11) |
O1i—Cd1—O6 | 65.70 (11) | O8—Cd3—O4 | 76.14 (12) |
O4ii—Cd1—O6 | 166.04 (11) | O7viii—Cd3—O4 | 166.09 (11) |
O4—Cd1—O6 | 74.39 (10) | O6—Cd3—O3viii | 69.28 (12) |
O10iii—Cd1—O6 | 108.36 (10) | O5viii—Cd3—O3viii | 73.00 (12) |
O5iv—Cd1—O6 | 119.09 (11) | O8—Cd3—O3viii | 165.28 (10) |
O5—Cd1—O6 | 94.03 (10) | O7viii—Cd3—O3viii | 70.17 (11) |
O2—Cd2—O1 | 127.85 (13) | O4—Cd3—O3viii | 109.32 (9) |
O2—Cd2—O3i | 114.19 (12) | O1—Se1—O5ix | 94.02 (16) |
O1—Cd2—O3i | 88.92 (11) | O1—Se1—O4ix | 101.51 (16) |
O2—Cd2—O2v | 97.44 (9) | O5ix—Se1—O4ix | 96.94 (16) |
O1—Cd2—O2v | 101.23 (12) | O6—Se2—O2 | 93.95 (16) |
O3i—Cd2—O2v | 130.27 (12) | O6—Se2—O3 | 98.51 (17) |
O2—Cd2—O6v | 154.73 (12) | O2—Se2—O3 | 101.27 (17) |
O1—Cd2—O6v | 73.39 (12) | O9—Se3—O10 | 112.29 (18) |
O3i—Cd2—O6v | 75.58 (13) | O9—Se3—O7 | 109.40 (18) |
O2v—Cd2—O6v | 61.69 (11) | O10—Se3—O7 | 109.09 (19) |
O2—Cd2—O9iii | 73.90 (12) | O9—Se3—O8 | 109.05 (19) |
O1—Cd2—O9iii | 157.54 (13) | O10—Se3—O8 | 107.99 (18) |
O3i—Cd2—O9iii | 74.96 (11) | O7—Se3—O8 | 108.96 (17) |
O2v—Cd2—O9iii | 78.64 (12) | | |
Symmetry codes: (i) −x, y+1/2, −z+1; (ii) −x, y−1/2, −z; (iii) x−1, y, z; (iv) −x, y+1/2, −z; (v) −x, y−1/2, −z+1; (vi) −x+1, y+1/2, −z+1; (vii) −x+1, y−1/2, −z+1; (viii) x, y+1, z; (ix) x, y, z+1; (x) x, y−1, z+1; (xi) x, y−1, z; (xii) x+1, y, z. |
Experimental details
Crystal data |
Chemical formula | Cd3(SeO3)2SeO4 |
Mr | 734.08 |
Crystal system, space group | Monoclinic, P21 |
Temperature (K) | 293 |
a, b, c (Å) | 8.3031 (8), 5.3377 (5), 10.8485 (11) |
β (°) | 108.659 (2) |
V (Å3) | 455.53 (8) |
Z | 2 |
Radiation type | Mo Kα |
µ (mm−1) | 18.97 |
Crystal size (mm) | 0.20 × 0.04 × 0.04 |
|
Data collection |
Diffractometer | Siemens SMART diffractometer |
Absorption correction | Multi-scan (SADABS; Sheldrick, 1996) |
Tmin, Tmax | 0.116, 0.518 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 4516, 2497, 2402 |
Rint | 0.023 |
(sin θ/λ)max (Å−1) | 0.713 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.018, 0.044, 1.00 |
No. of reflections | 2497 |
No. of parameters | 146 |
No. of restraints | 1 |
Δρmax, Δρmin (e Å−3) | 0.97, −0.79 |
Absolute structure | Flack (1983), 0000 Friedel pairs |
Absolute structure parameter | 0.080 (9) |
Selected geometric parameters (Å, º) topCd1—O3 | 2.258 (3) | Cd3—O6 | 2.132 (3) |
Cd1—O1i | 2.287 (3) | Cd3—O5viii | 2.157 (3) |
Cd1—O4ii | 2.307 (3) | Cd3—O8 | 2.250 (4) |
Cd1—O4 | 2.327 (3) | Cd3—O7viii | 2.254 (4) |
Cd1—O10iii | 2.468 (4) | Cd3—O4 | 2.664 (3) |
Cd1—O5iv | 2.545 (4) | Cd3—O3viii | 2.940 (3) |
Cd1—O5 | 2.703 (4) | Se1—O1 | 1.694 (3) |
Cd1—O6 | 2.902 (4) | Se1—O5ix | 1.696 (3) |
Cd2—O2 | 2.191 (3) | Se1—O4ix | 1.715 (3) |
Cd2—O1 | 2.235 (3) | Se2—O6 | 1.695 (3) |
Cd2—O3i | 2.280 (3) | Se2—O2 | 1.700 (3) |
Cd2—O2v | 2.286 (3) | Se2—O3 | 1.716 (3) |
Cd2—O6v | 2.537 (4) | Se3—O9 | 1.624 (3) |
Cd2—O9iii | 2.551 (3) | Se3—O10 | 1.636 (3) |
Cd2—O10vi | 2.814 (4) | Se3—O7 | 1.637 (3) |
Cd2—O9vii | 2.980 (4) | Se3—O8 | 1.653 (3) |
| | | |
O1—Se1—O5ix | 94.02 (16) | O9—Se3—O10 | 112.29 (18) |
O1—Se1—O4ix | 101.51 (16) | O9—Se3—O7 | 109.40 (18) |
O5ix—Se1—O4ix | 96.94 (16) | O10—Se3—O7 | 109.09 (19) |
O6—Se2—O2 | 93.95 (16) | O9—Se3—O8 | 109.05 (19) |
O6—Se2—O3 | 98.51 (17) | O10—Se3—O8 | 107.99 (18) |
O2—Se2—O3 | 101.27 (17) | O7—Se3—O8 | 108.96 (17) |
Symmetry codes: (i) −x, y+1/2, −z+1; (ii) −x, y−1/2, −z; (iii) x−1, y, z; (iv) −x, y+1/2, −z; (v) −x, y−1/2, −z+1; (vi) −x+1, y+1/2, −z+1; (vii) −x+1, y−1/2, −z+1; (viii) x, y+1, z; (ix) x, y, z+1. |
Numerous phases within the system Cd–Se–O–(H) are listed in standard handbooks about cadmium and its compounds (Gmelins Handbuch der Anorganischen Chemie, 1959), and most of these compounds have been crystallographically well characterized in the meantime. For the anhydrous selenites(IV) α-CdSeO3, β-CdSeO3 (Valkonen, 1994a) and CdSe2O5 (Valkonen, 1994b), for the hydrous selenites(IV) CdSeO3(H2O) (Bäumer et al., 1998), Cd3(HSeO3)2(SeO3)2 (Valkonen, 1994b) and (CdSeO3)4(H2O)3 (Valkonen, 1994a), as well as for the selenates(VI) CdSeO4(H2O) (Stålhandske, 1981), CdSeO4, Cd(HSeO4)2(H2O) (Morozov et al., 1999) and CdSeO4(H2O)2 (Weil, 2002), full structure analyses based on single-crystal data have been reported. Powder data are given for the tetraselenite(IV) Cd3Se4O11 (Markovskii & Sapozhnikov, 1961).
Cd3Se3O10 is reported for the first time and reveals isotypism with its mercury analogue, Hg3Se3O10, whose preparation and crystal structure was recently described in detail (Weil & Kolitsch, 2002). The crystal structure is composed of three independent CdII cations, two SeIVO3 groups and a SeVIO4 group as the main building units. Cd3Se3O10 is the first Cd compound to contain both selenium(IV) and selenium(VI) oxo groups within the structure.
The building units are linked via common oxygen atoms to form a three-dimensional network. Edge-sharing [CdO8] polyhedra build layers 2∞[CdO8/2] parallel to the bc plane which are bridged by the SeIVO3 groups. Two adjacent layers are connected via SeVIO4 tetrahedra and [Cd3O6] polyhedra along the a axis to form channels extending parallel to the b axis, as depicted in Fig. 1. The selenite(IV) groups are situated above and below the cavities of the 2∞[CdO8/2] layers with the non-bonding orbitals, directed towards each other into the cavities of the structure.
If bonding interactions are being considered for distances d(Cd—O) < 3.0 Å, Cd1 and Cd2 are eight-coordinate with four short, two medium and two longer distances, resulting in a [4 + 2+2]-coordination with similar mean distances of ¯d(Cd1—O) = 2.475 Å and ¯d(Cd2—O) = 2.484 Å. Cd3 shows a [4 + 2]-coordination, with a slightly shorter mean of ¯d(Cd3—O) = 2.400 Å.
Both selenite(IV) (Se1 and Se2) and selenate(VI) (Se3) groups display the well known geometry of a trigonal pyramid [Se1: ¯d(Se1—O) = 1.702 Å, mean angle: 97.5°; Se2: ¯d(Se2—O) = 1.704 Å, mean angle 97.9°] and a tetrahedron [¯d(Se3—O) = 1.638 Å, mean angle 109.5°], respectively.
The bond-valence sums, as calculated with the parameters given by Brese and O'Keeffe (1991), are in agreement with the expected values: Cd1 (CN = 8, 1.972), Cd2 (8, 2.082), Cd3 (6, 2.016), Se1 (3, 4.032), Se2 (3, 4.010), Se3 (4, 6.013), O1 (3, 2.133), O2 (3, 2.167), O3 (4, 2.099), O4 (4, 2.079), O5 (4, 2.163), O6 (4, 2.155), O7 (2, 1.892), O8 (2, 1.835), O9 (3, 1.787), O10 (3, 1.813). The O atoms which belong to selenite(IV) groups are O1–O6, and the O atoms of the selenate(VI) group are O7–O10.