New barium oxoantimonates(III):: Synthesis and crystal structures of Ba3[SbO3]2 and Ba2[Sb2O5]

The barium oxoantimonates(III) Ba-3[SbO3](2) (triclinic, P (1) over bar, a = 615.2(8), b = 981.4(3), c = 1215.4(5) pm, alpha = 74.683(9), beta = 89.710(6), gamma= 71.464(7)degrees, Z = 2, R1 = 0.0802) and Ba-2 [Sb2O5] (orthorhombic, Cmcm, a = 401.0(3), b = 1450.6(7), c = 636.6(6) pm, Z = 4, R1 = 0.0589) have been synthesized from melts of elemental barium and antimony oxide Sb2O3 at a temperature of 800 degreesC. Their oxoantimonate building units are strongly influenced by the stereochemically active lone pair electrons of the pentele element: In the Ba rich compound Ba-3[SbO3](2), isolated psi tetrahedra [SbO3](3-) are present, in Ba-2[Sb2O5], which crystallizes with the Sr2Bi2O5 structure type, two of these psi tetrahedra are condensed to form nucelar units [Sb2O5](4-). The two compounds are compared in terms of structure and bonding with the alkali antimonates on one hand and with the alkaline earth bismutates on the other.