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Tetraammonium cadmium dihydrogenselenite(IV) diselenate(VI), (NH
4)
4Cd(HSe
IVO
3)
2(Se
VIO
4)
2, is the third example of a compound containing both hydrogen selenite and selenate anions, and has a new structure type. It contains kröhnkite-like heteropolyhedral chains in which CdO
6 octahedra are linked
via bridging HSeO
3 groups, having their remaining two
trans apices decorated by SeO
4 groups. The charge-balancing NH
4 groups are involved in weak hydrogen bonding, whereas the H atom of the HSeO
3 group provides a strong hydrogen bond [O
O = 2.614 (5) Å]. The average Cd-O bond length is 2.298 Å. All atoms are on general positions except Cd (on
). Relations to the kröhnkite-type compounds Na
2Mg(SO
3)·2H
2O, Ba
2CoCl
2(SeO
3)
2 and Ba
2Ca(HPO
4)
2(H
2PO
4)
2, and to the mineral curetonite are discussed. Unit-cell data are given for an isotypic Mn
II analogue.
Supporting information
The title compound was prepared by the controlled evaporation at room temperature of an acidic aqueous solution (with unknown pH) of cadmium carbonate, selenic acid and ammonia. The title compound crystallized as sheaves of colourless pseudo-orthorhombic invariably twinned prismatic crystals. On further evaporation, large colourless twinned prisms of (NH4)2SeO4 crystallized.
All N—H and O—H distances were restrained to a maximum of 0.90 (5) Å. The deepest hole (−1.22 e/Å3) is 0.86 Å from the Cd site and the highest peak (1.85 e/Å3) is 0.86 Å from the Se1 site.
Data collection: COLLECT (Nonius, 2002); cell refinement: HKL SCALEPACK (Otwinowski & Minor 1997); data reduction: HKL DENZO (Otwinowski & Minor, 1997) and SCALEPACK; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ATOMS (Dowty, 1999) and ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: SHELXL97.
tetraammonium cadmium dihydrogenselenite(IV) diselenate(VI)
top
Crystal data top
(NH4)4Cd(HSeO3)2(SeO4)2 | Z = 1 |
Mr = 726.42 | F(000) = 342 |
Triclinic, P1 | Dx = 2.955 Mg m−3 |
Hall symbol: -P 1 | Mo Kα radiation, λ = 0.71073 Å |
a = 5.791 (1) Å | Cell parameters from 2196 reflections |
b = 7.411 (1) Å | θ = 2.0–30.0° |
c = 10.736 (2) Å | µ = 10.33 mm−1 |
α = 90.05 (3)° | T = 293 K |
β = 105.02 (3)° | Prism, colourless |
γ = 112.61 (3)° | 0.18 × 0.04 × 0.03 mm |
V = 408.20 (17) Å3 | |
Data collection top
Nonius KappaCCD area-detector diffractometer | 2368 independent reflections |
Radiation source: fine-focus sealed tube | 2003 reflections with I > 2σ(I) |
Graphite monochromator | Rint = 0.027 |
ψ and ω scans | θmax = 30.0°, θmin = 3.0° |
Absorption correction: multi-scan HKL SCALEPACK (Otwinowski & Minor, 1997) | h = −8→8 |
Tmin = 0.258, Tmax = 0.747 | k = −10→10 |
4514 measured reflections | l = −14→15 |
Refinement top
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.038 | All H-atom parameters refined |
wR(F2) = 0.101 | w = 1/[σ2(Fo2) + (0.058P)2 + 0.1P] where P = (Fo2 + 2Fc2)/3 |
S = 1.07 | (Δ/σ)max = 0.001 |
2368 reflections | Δρmax = 1.85 e Å−3 |
143 parameters | Δρmin = −1.22 e Å−3 |
9 restraints | Extinction correction: SHELXL97 (Sheldrick, 1997), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4 |
Primary atom site location: structure-invariant direct methods | Extinction coefficient: 0.0173 (19) |
Crystal data top
(NH4)4Cd(HSeO3)2(SeO4)2 | γ = 112.61 (3)° |
Mr = 726.42 | V = 408.20 (17) Å3 |
Triclinic, P1 | Z = 1 |
a = 5.791 (1) Å | Mo Kα radiation |
b = 7.411 (1) Å | µ = 10.33 mm−1 |
c = 10.736 (2) Å | T = 293 K |
α = 90.05 (3)° | 0.18 × 0.04 × 0.03 mm |
β = 105.02 (3)° | |
Data collection top
Nonius KappaCCD area-detector diffractometer | 2368 independent reflections |
Absorption correction: multi-scan HKL SCALEPACK (Otwinowski & Minor, 1997) | 2003 reflections with I > 2σ(I) |
Tmin = 0.258, Tmax = 0.747 | Rint = 0.027 |
4514 measured reflections | |
Refinement top
R[F2 > 2σ(F2)] = 0.038 | 9 restraints |
wR(F2) = 0.101 | All H-atom parameters refined |
S = 1.07 | Δρmax = 1.85 e Å−3 |
2368 reflections | Δρmin = −1.22 e Å−3 |
143 parameters | |
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 | |
Cd | 0.0000 | 1.0000 | 1.0000 | 0.01992 (15) | |
Se1 | −0.30508 (8) | 0.66588 (6) | 0.70424 (4) | 0.01855 (15) | |
Se2 | −0.44491 (9) | 0.95670 (6) | 1.17649 (4) | 0.01930 (15) | |
N1 | 0.2256 (10) | 0.5281 (7) | 0.8977 (5) | 0.0313 (10) | |
N2 | −0.1594 (10) | 0.2294 (7) | 0.5369 (5) | 0.0328 (10) | |
O1 | −0.3238 (8) | 0.8566 (6) | 0.6377 (4) | 0.0402 (9) | |
O2 | −0.5896 (7) | 0.4829 (6) | 0.6614 (4) | 0.0352 (8) | |
O3 | −0.0842 (7) | 0.6066 (6) | 0.6666 (4) | 0.0362 (9) | |
O4 | −0.2218 (7) | 0.7089 (5) | 0.8639 (3) | 0.0306 (8) | |
O5 | −0.7602 (7) | 0.8285 (5) | 1.1036 (4) | 0.0329 (8) | |
O6 | −0.3077 (7) | 0.8426 (5) | 1.1027 (4) | 0.0347 (8) | |
O7 | −0.3990 (8) | 0.8726 (6) | 1.3280 (3) | 0.0352 (9) | |
H1 | 0.161 (16) | 0.558 (13) | 0.822 (6) | 0.08 (3)* | |
H2 | 0.294 (15) | 0.635 (9) | 0.950 (7) | 0.07 (2)* | |
H3 | 0.356 (10) | 0.519 (10) | 0.897 (7) | 0.04 (2)* | |
H4 | 0.121 (12) | 0.424 (8) | 0.914 (8) | 0.06 (2)* | |
H5 | −0.125 (17) | 0.146 (11) | 0.593 (7) | 0.08 (3)* | |
H6 | −0.100 (11) | 0.346 (7) | 0.578 (5) | 0.031 (16)* | |
H7 | −0.022 (10) | 0.259 (9) | 0.511 (6) | 0.033 (16)* | |
H8 | −0.311 (9) | 0.210 (9) | 0.478 (5) | 0.034 (16)* | |
H9 | −0.418 (17) | 0.750 (8) | 1.339 (8) | 0.07 (3)* | |
Atomic displacement parameters (Å2) top | U11 | U22 | U33 | U12 | U13 | U23 |
Cd | 0.0193 (2) | 0.0198 (2) | 0.0218 (3) | 0.00794 (18) | 0.00735 (18) | 0.00340 (18) |
Se1 | 0.0202 (2) | 0.0174 (2) | 0.0174 (2) | 0.00719 (17) | 0.00472 (17) | 0.00213 (17) |
Se2 | 0.0208 (2) | 0.0166 (2) | 0.0192 (2) | 0.00605 (17) | 0.00579 (17) | 0.00228 (17) |
N1 | 0.030 (3) | 0.031 (3) | 0.033 (2) | 0.012 (2) | 0.008 (2) | 0.005 (2) |
N2 | 0.034 (3) | 0.027 (2) | 0.030 (2) | 0.005 (2) | 0.008 (2) | 0.000 (2) |
O1 | 0.045 (2) | 0.030 (2) | 0.043 (2) | 0.0144 (18) | 0.0067 (18) | 0.0139 (18) |
O2 | 0.0241 (18) | 0.035 (2) | 0.041 (2) | 0.0084 (15) | 0.0049 (16) | 0.0041 (17) |
O3 | 0.031 (2) | 0.048 (2) | 0.041 (2) | 0.0230 (18) | 0.0171 (17) | 0.0053 (19) |
O4 | 0.041 (2) | 0.0282 (18) | 0.0184 (15) | 0.0094 (16) | 0.0090 (15) | −0.0003 (14) |
O5 | 0.0245 (18) | 0.0223 (17) | 0.044 (2) | 0.0076 (14) | −0.0003 (16) | 0.0034 (16) |
O6 | 0.043 (2) | 0.0269 (18) | 0.044 (2) | 0.0132 (17) | 0.0309 (18) | 0.0051 (17) |
O7 | 0.056 (3) | 0.034 (2) | 0.0196 (17) | 0.0248 (19) | 0.0059 (17) | 0.0083 (16) |
Geometric parameters (Å, º) top
Cd—O6 | 2.275 (3) | Se2—O6 | 1.678 (3) |
Cd—O6i | 2.275 (3) | Se2—O7 | 1.735 (3) |
Cd—O4 | 2.309 (4) | N1—H1 | 0.87 (5) |
Cd—O4i | 2.309 (4) | N1—H2 | 0.86 (5) |
Cd—O5ii | 2.311 (3) | N1—H3 | 0.78 (4) |
Cd—O5iii | 2.311 (3) | N1—H4 | 0.83 (5) |
Se1—O1 | 1.612 (4) | N2—H5 | 0.90 (5) |
Se1—O2 | 1.629 (4) | N2—H6 | 0.87 (4) |
Se1—O3 | 1.641 (3) | N2—H7 | 0.86 (4) |
Se1—O4 | 1.651 (3) | N2—H8 | 0.90 (4) |
Se2—O5 | 1.665 (4) | O7—H9 | 0.88 (5) |
| | | |
O6—Cd—O6i | 180 | O5—Se2—O7 | 103.65 (19) |
O6—Cd—O4i | 99.14 (13) | O6—Se2—O7 | 100.96 (19) |
O6—Cd—O4 | 80.86 (13) | H1—N1—H2 | 106 (8) |
O4i—Cd—O4 | 180 | H1—N1—H3 | 108 (8) |
O6—Cd—O5ii | 91.15 (14) | H2—N1—H3 | 97 (7) |
O4—Cd—O5ii | 98.13 (13) | H1—N1—H4 | 111 (8) |
O6—Cd—O5iii | 88.85 (14) | H2—N1—H4 | 122 (8) |
O4—Cd—O5iii | 81.87 (13) | H3—N1—H4 | 111 (8) |
O5ii—Cd—O5iii | 180 | H5—N2—H6 | 109 (7) |
O1—Se1—O2 | 109.8 (2) | H5—N2—H7 | 96 (7) |
O1—Se1—O3 | 111.2 (2) | H6—N2—H7 | 92 (5) |
O2—Se1—O3 | 111.0 (2) | H5—N2—H8 | 128 (7) |
O1—Se1—O4 | 110.7 (2) | H6—N2—H8 | 108 (6) |
O2—Se1—O4 | 106.62 (19) | H7—N2—H8 | 118 (6) |
O3—Se1—O4 | 107.38 (19) | Se2—O7—H9 | 123 (6) |
O5—Se2—O6 | 101.24 (19) | | |
Symmetry codes: (i) −x, −y+2, −z+2; (ii) −x−1, −y+2, −z+2; (iii) x+1, y, z. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O3 | 0.87 (5) | 2.03 (5) | 2.866 (6) | 163 (8) |
N1—H2···O5iii | 0.86 (5) | 2.34 (6) | 3.099 (6) | 147 (7) |
N1—H2···O6iii | 0.86 (5) | 2.38 (6) | 3.105 (7) | 142 (7) |
N1—H3···O4iii | 0.78 (4) | 2.43 (5) | 3.078 (6) | 141 (6) |
N1—H4···O5iv | 0.83 (5) | 2.17 (5) | 2.958 (6) | 160 (7) |
N2—H5···O1v | 0.90 (5) | 2.13 (7) | 2.868 (6) | 138 (8) |
N2—H6···O3 | 0.87 (4) | 2.11 (4) | 2.947 (7) | 161 (5) |
N2—H7···O3vi | 0.86 (4) | 2.26 (5) | 2.919 (6) | 133 (5) |
N2—H8···O1vii | 0.90 (4) | 2.02 (4) | 2.915 (7) | 172 (5) |
O7—H9···O2iv | 0.88 (5) | 1.75 (5) | 2.614 (5) | 167 (8) |
Symmetry codes: (iii) x+1, y, z; (iv) −x−1, −y+1, −z+2; (v) x, y−1, z; (vi) −x, −y+1, −z+1; (vii) −x−1, −y+1, −z+1. |
Experimental details
Crystal data |
Chemical formula | (NH4)4Cd(HSeO3)2(SeO4)2 |
Mr | 726.42 |
Crystal system, space group | Triclinic, P1 |
Temperature (K) | 293 |
a, b, c (Å) | 5.791 (1), 7.411 (1), 10.736 (2) |
α, β, γ (°) | 90.05 (3), 105.02 (3), 112.61 (3) |
V (Å3) | 408.20 (17) |
Z | 1 |
Radiation type | Mo Kα |
µ (mm−1) | 10.33 |
Crystal size (mm) | 0.18 × 0.04 × 0.03 |
|
Data collection |
Diffractometer | Nonius KappaCCD area-detector diffractometer |
Absorption correction | Multi-scan HKL SCALEPACK (Otwinowski & Minor, 1997) |
Tmin, Tmax | 0.258, 0.747 |
No. of measured, independent and observed [I > 2σ(I)] reflections | 4514, 2368, 2003 |
Rint | 0.027 |
(sin θ/λ)max (Å−1) | 0.703 |
|
Refinement |
R[F2 > 2σ(F2)], wR(F2), S | 0.038, 0.101, 1.07 |
No. of reflections | 2368 |
No. of parameters | 143 |
No. of restraints | 9 |
H-atom treatment | All H-atom parameters refined |
Δρmax, Δρmin (e Å−3) | 1.85, −1.22 |
Selected geometric parameters (Å, º) topCd—O6 | 2.275 (3) | Se1—O3 | 1.641 (3) |
Cd—O4 | 2.309 (4) | Se1—O4 | 1.651 (3) |
Cd—O5i | 2.311 (3) | Se2—O5 | 1.665 (4) |
Se1—O1 | 1.612 (4) | Se2—O6 | 1.678 (3) |
Se1—O2 | 1.629 (4) | Se2—O7 | 1.735 (3) |
| | | |
O1—Se1—O2 | 109.8 (2) | O3—Se1—O4 | 107.38 (19) |
O1—Se1—O3 | 111.2 (2) | O5—Se2—O6 | 101.24 (19) |
O2—Se1—O3 | 111.0 (2) | O5—Se2—O7 | 103.65 (19) |
O1—Se1—O4 | 110.7 (2) | O6—Se2—O7 | 100.96 (19) |
O2—Se1—O4 | 106.62 (19) | | |
Symmetry code: (i) x+1, y, z. |
Hydrogen-bond geometry (Å, º) top
D—H···A | D—H | H···A | D···A | D—H···A |
N1—H1···O3 | 0.87 (5) | 2.03 (5) | 2.866 (6) | 163 (8) |
N1—H2···O5i | 0.86 (5) | 2.34 (6) | 3.099 (6) | 147 (7) |
N1—H2···O6i | 0.86 (5) | 2.38 (6) | 3.105 (7) | 142 (7) |
N1—H3···O4i | 0.78 (4) | 2.43 (5) | 3.078 (6) | 141 (6) |
N1—H4···O5ii | 0.83 (5) | 2.17 (5) | 2.958 (6) | 160 (7) |
N2—H5···O1iii | 0.90 (5) | 2.13 (7) | 2.868 (6) | 138 (8) |
N2—H6···O3 | 0.87 (4) | 2.11 (4) | 2.947 (7) | 161 (5) |
N2—H7···O3iv | 0.86 (4) | 2.26 (5) | 2.919 (6) | 133 (5) |
N2—H8···O1v | 0.90 (4) | 2.02 (4) | 2.915 (7) | 172 (5) |
O7—H9···O2ii | 0.88 (5) | 1.75 (5) | 2.614 (5) | 167 (8) |
Symmetry codes: (i) x+1, y, z; (ii) −x−1, −y+1, −z+2; (iii) x, y−1, z; (iv) −x, −y+1, −z+1; (v) −x−1, −y+1, −z+1. |
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The title compound has a new triclinic structure type. However, a topological analysis shows that it contains heteropolyhedral chains similar to those in kröhnkite, Na2CuII(SVIO4)2·2H2O (Dahlman, 1952; Hawthorne & Ferguson, 1975). In our recent review and classification of natural and synthetic oxysalt compounds with kröhnkite-type and -like chains (Fleck Kolitsch & Hertweck, 2002), and in an update (Fleck & Kolitsch, 2003), we showed that all kröhnkite-type compounds contain infinite [M(XO4)2(H2O)2] chains, where M is divalent (Mg, Mn, Fe, Co, Ni, Cu, Zn or Cd) or trivalent (Al, Fe, In or Tl) and X is pentavalent (P or As) or hexavalent (S, Se, Cr, Mo or W). In these chains, MO6 octahedra are corner-linked to bridging XO4 tetrahedra. Large cations occupy the space between adjacent chains and provide charge balance. Several compounds were also recognized which contain kröhnkite-like chains, i.e. chains which differ in some aspects from the strictly kröhnkite-type topology (Fleck Kolitsch & Hertweck, 2002; Fleck & Kolitsch, 2003). Among these is one sulfite, Na2Mg(SO3)·2H2O (Lutz & Buchmeier, 1983), in which SO3 groups assume the role of the bridging SO4 groups in kröhnkite-type sulfates, and Ba2CoCl2(SeO3)2 (Johnston & Harrison, 2002), which, as subsequently pointed out by Fleck & Kolitsch (2003), is topologically very similar to Na2Mg(SO3)·2H2O in that it contains SeO3 groups bridging between CoO4Cl2 octahedra to form kröhnkite-like chains.
(NH4)4Cd(HSeIVO3)2(SeVIO4)2 contains one crystallographically unique Cd atom, two Se, two N, seven O and nine H atoms in its asymmetric unit. It represents the first example of a compound containing kröhnkite-like chains in which an HSeO3 group connects MO6 (M is CdII) octahedra (Fig. 1). The additional SeO4 groups decorate these chains by being attached via common ligands to the remaining two apices of the CdO6 octahedra in a trans arrangement (Figs. 1 and 2). The two non-equivalent charge-balancing NH4+ cations are located in voids between the decorated chains (Figs. 1–3). A single-crystal study of the morphological elongation of the prismatic crystals of the title compound demonstrated that their elongation is along the chain direction. The cell metric is pseudo-monoclinic, with a C-centred pseudo-cell and a = 13.68, b = 5.79 and c = 11.76 Å, and α = 90.8, β = 118.9 and γ = 89.6°. The closeness to the higher symmetry explains the pervasive twinning in the title compound. Twinning is very commonly observed in kröhnkite-type and -like compounds (e.g. Fleck & Kolitsch, 2003).
Bond-valence summations for the metal atoms, calculated using the parameters of Brese & O'Keeffe (1991), give 2.07 v.u. (valence units) for Cd, 6.08 v.u. for Se1 (SeVI) and 4.14 v.u. for Se2 (SeIV), i.e. values close to the theoretical valences. Bond-valence sums for the O atoms were calculated taking into account the contributions from the NH4+ cations and using bond-valence parameters recently proposed by García-Rodriguez et al. (2000). The values obtained are 1.94 (O1), 1.76 (O2), 1.96 (O3), 2.06 (O4), 2.04 (O5), 2.03 (O6), and 1.42 (O7) v.u. Atom O2 is underbonded, but accepts a strong hydrogen bond from the O7—H9 group (see below). The two NH4+ cations have nine (N1) and seven + one (N2) next-nearest O neighbours and are involved in weak hydrogen bonds, with O···O distances all > 2.86 Å (Table 2). These features of the NH4+ cations agree with the conclusions of Khan & Baur (1972) that NH4+ cations with large coordination numbers (seven to nine) have a pseudo-alkali character and do not show a pronounced tendency for hydrogen bonding. By contrast, the hydrogen bond involving the OH ligand of the HSeO3 group is fairly short, with an O···O distance of 2.614 (5) Å (Table 2). The acceptor of the strong hydrogen bond is the underbonded atom O2, and the bond strengthens the connection between two adjacent chains along the b axis (Fig. 2).
In the title compound, the HSeO3 and SeO4 groups show the characteristic pyramidal geometry for the SeIV-based anion and tetrahedral geometry for the SeVI-based anion. The average Se—O bond length in the SeO4 tetrahedron (1.633 Å) and the average Cd—O bond length in the CdO6 octahedron (2.298 Å) are close to the commonly observed values. The hydrogen selenite (HSeO3) group exhibits an elongated Se—O bond [1.735 (3) Å] to the protonated O atom (O7), a typical feature of this group for the optimization of the bond-valence sums incident at the involved atoms (e.g. Koskenlinna, 1996). The average Se—O bond length (1.693 Å) and the average O—Se—O angle (102°) show good agreement with the average values reported in reviews of hydrogen selenites [1.709 (10) Å and 100.1(1.3)° (Hawthorne et al., 1987); 1.70 (5) Å and 101 (3)° (Loub, 1995); 1.702 (20) Å and 100.1(2.6)° (Koskenlinna, 1996)].
As also briefly pointed out by Fleck Kolitsch & Hertweck (2002), there exist two kröhnkite-like compounds in which the heteropolyhedral chains are, similar to the situation in the title compound, also additionally decorated with either H2XO4 or XO4 groups. These two compounds are Ba2Ca(HPO4)2(H2PO4)2 (Toumi et al., 1997) and the mineral curetonite, Ba[(Al,TiIV)(PO4)(OH,O)F] (Cooper & Hawthorne, 1994), respectively. In Ba2Ca(HPO4)2(H2PO4)2, CaO6 octahedra and H2PO4 tetrahedra are corner-linked to form kröhnkite-like infinite chains. Unlike kröhnkite-type chains per se, the trans apices of the CaO6 octahedron are not formed by water molecules but are decorated with additional H2PO4 tetrahedra, thus giving an overall composition of [Ca(H2PO4)2(HPO4)2]4− for these chains. The charge-balancing Ba2+ cations are located in voids between the chains. The H atoms of the protonated PO4 groups have the role of providing hydrogen bonds to reinforce the structure. In curetonite, Ba[(Al,TiIV)(PO4)(OH,O)F] (Cooper & Hawthorne, 1994), which contains kröhnkite-type chains composed of (Al,Ti)O6 octahedra and PO4 tetrahedra, an additional corner-linkage between these chains is achieved via AlO4F2 octahedra. The resulting heteropolyhedral layers are separated by Ba atoms. It is also worthy to note that kröhnkite-based chains involving carbonate anions are found in the mineral sahamalite, (Mg,FeII)Ce2(CO3)4 (Pertlik & Preisinger, 1983). In that structure, the CO3 groups play a dual role: they link (Mg,FeII)O6 octahedra into a kröhnkite-like chain, but also decorate the two remaining trans apices of the octahedra.
The title compound is a rare example of an oxysalt containing both HSeO3 and SeO4 groups. In fact, only about eight compounds with mixed-valent selenium(IV/VI) anions are known (Weil & Kolitsch, 2002), and only two of them have the same types of anions as the title compound. The first of these two examples is La(HSeO3)(SeO4)·2H2O (Harrison & Zhang, 1997), which is built up from a densely packed network of irregular LaO9 groups, HSeO3 pyramids and SeO4 tetrahedra, sharing vertices and edges via La—O—La and La—O—Se bonds. The second example is Fe(HSeO3)(SeO4)·H2O (Giester, 1992), which is based on sheets formed by FeO5(H2O) octahedra sharing five of their corners with HSeO3 pyramids and SeO4 tetrahedra; these sheets are interconnected via hydrogen bonds only.
A determination of the unit-cell parameters of the title compound at 120 and 100 K indicated no change in symmetry upon cooling. An MnII analogue of (NH4)4Cd(HSeIVO3)2(SeVIO4)2 has been prepared by controlled evaporation at room temperature of an acidic aqueous solution (with unknown pH) of manganese(II) carbonate, selenic acid and ammonia. The MnII analogue formed sheaves of pale-rose-coloured elongated tabular pseudo-orthorhombic crystals which were also invariably twinned. A structure refinement was performed using a data set collected from a non-merohedrally twinned crystal at a large crystal-to-detector distance. Although the final RF value was only ca 0.09 and H atoms could not be located (insufficient quality of the data set due to the influence of twinning), the refinement confirmed that (NH4)4Mn(HSeIVO3)2(SeVIO4)2 is isotypic with (NH4)4Cd(HSeIVO3)2(SeVIO4)2. The refined unit-cell parameters of the MnII analogue are a = 5.700 (1), b = 7.397 (1) and c = 10.740 (2) Å, α = 90.63 (3), β = 104.45 (3) and γ = 112.73 (3)°, and V = 401.51 (12) Å3. As expected, the unit-cell volume is distinctly smaller than that of the Cd analogue.