Crystal structures and structural relationships of KFe₂(SeO₂OH)(SeO₃)₃ and SrCo₂(SeO₂OH)₂(SeO₃)₂.

The new phases KFe2(SeO2OH)(SeO3)3 and SrCo2(SeO2OH)2(SeO3)2 were synthesized under low-hydrothermal conditions and their structures were detd. by single-crystal x-ray methods. Both compds. are monoclinic; KFe2(SeO2OH)(SeO3)3belongs to space group P2, a 9.983(4), b 5.270(1), c 10.614(4) .ANG., beta 97.42(2)°, Z = 2; SrCo2(SeO2OH)2(SeO3)2 belongs to space group P2/n, a 14.984(2), b 5.286(1), c 13.790(2) .ANG., beta 94.72(1)°, Z = 4. The refinements converged to R-values of 2.9 and 3.6%, resp. At. coordinates are given. The at. arrangement in KFe2(SeO2OH)(SeO3)3 and SrCo2(SeO2OH)2(SeO3)2 is based on isolated MO6 octahedra (M = Fe3+, Co2+), which are corner-linked via trigonal pyramidal selenite groups to a framework structure. Interstitials are occupied by K or Sr atoms in ten- or eight-coordination, resp., and by the lone-pair electrons of the Se4+ atoms. The compds. are not isotypic but are closely related and may be interpreted as different distortions of an idealized structure type in space group P2/m, which was modeled for a theor. compd. SrFe2(SeO3)4 by distance least squares refinement (program DVLS).