A contribution to the stereochemistry of earth alkaline selenites: Synthesis and crystal structure of Ca-2(SeO3)(Se2O5), Ba(SeO3), and Ba(Se2O5)

摘要

The compounds Ca-2(SeO3)(Se2O5), Ba(SeO3), and Ba(Se2O5) were obtained at low-hydrothermal conditions from aqueous solutions of SeO2 by reaction with the respective earth alkaline carbonate. The crystal structures were determined by direct methods from single crystal Xray diffraction data. Ca-2(SeO3)(Se2O5): space group P (1) over bar, Z=2, a=5.517(1), b=8.210(2), c=8.716(2) Angstrom, alpha = 92.47(2), beta = 95.92(2), gamma = 97.15(2)degrees, V-389.0(2) Angstrom(3), R-1 = 0.017; Ba(SeO3): space group P2(1)/m, Z = 2, a = 4.677(2), b = 5.645(2), c = 6.851(3) Angstrom, beta = 107.16(2)degrees, V = 172.8(1) Angstrom(3), R-1 = 0.022, Ba(Se2O5): space group P2(1)/c, Z= 4, a = 4.553(1), b = 11.724(3), c = 9.758(2) Angstrom, beta = 92.66(2)degrees, V = 520.3(2)Angstrom(3), R-1 = 0.027. All three compounds have framework structures; in the case of Ca-2(SeO3)(Se2O5), subunits of edge-sharing CaOn polyhedra forming sheets parallel to (010) can be emphasized. Ba(SeO3) belongs to the structure type of KClO3. In Ba(Se2O5), chains of face-sharing BaO9 polyhedra along [100] are present. The calcium atoms are 7- and 8-coordinated with mean Ca-O bond lengths of 2.42 and 2.48 Angstrom, the barium atoms have nine oxygen ligands with mean Ba-O bond lengths of 2.87 Angstrom. [References: 23]