New alkali-metal-molybdenum(VI)-selenium(IV) oxides: syntheses, structures, and characterization of A(2)SeMoO(6) (A=Na+, K+, or Rb+)

摘要

Three new quaternary selenites, A(2)SeMoO(6) (A=Na+, K+, or Rb+), were synthesized through the solid-state reaction of A(2)MoO(4) with SeO2 at 400degreesC. Although the reported materials are 'stoichiometrically equivalent', the compounds exhibit strikingly different crystal structures. Whereas Na2SeMoO6 has a three-dimensional crystal structure, K2SeMoO6 and Rb2ScMoO6 are molecular and uni-dimensional, respectively. However, all of the new materials have structures containing Mo6+ octahedra linked to Se4+ trigonal pyramids. Although the Mo6+ and Se4+ cations are in local asymmetric environments in all three materials, only Na2SeMoO6 is non-centrosymmetric. Single crystal X-ray data: Na2SeMoO6, cubic, space group, P2(1)3 (no. 198), a = 8.375(5)A, Z= 4, R(F) 0.0143; K2SeMoO6, monoclinic, space group, P2(1)/c (no. 14), a = 6.118(8)Angstrom, b = 15.395(2)Angstrom, c = 7.580(9) Angstrom, beta = 112.39(4)degrees, Z = 4, R(F) 0.0281; Rb2SeMoO6, orthorhombic, space group, Pnma (no. 62), a = 7.805(9) Angstrom b = 6.188(7) Angstrom, c = 14.405(4) Angstrom, Z = 4, R(F) = 0.0443. (C) 2003 Elsevier Inc. All rights reserved. [References: 46]