Synthesis, crystal structure, and properties of polymeric Rb12Nb6Se35, a novel ternary niobium selenide consisting of infinite anionic chains built up by Nb2Se11 units containing an uncommon Se34--fragment

Rb12Nb6Se35 is the first ternary niobium polyselenide composed of infinite anionic chains. These are well separated by rubidium cations. It crystallizes in the orthorhombic space group Pbcn with unit cell dimensions a = 8.5811(1) Angstrom, b = 13.7152(1) Angstrom, c = 56.5225(4) Angstrom, and Z = 4. The least-squares refinement against F-2 With anisotropic displacement parameters for all atoms yields RI = 5.78 and wR2 = 12.81. The anionic polymeric chains are arranged in layers parallel to the (010) plane, and successive planes are rotated by 35 degrees against each other. Nb2Se11 units composed of two face-sharing NbSe7 pentagonal bipyramids are the building blocks of the structure. They are interconnected by Se-2(2-) and Se-3(2-) polyanions, giving rise to infinite (1)(infinity)[Nb6Se35](12-) chains. Within the Nb2Se11 units an unusual nearly linear Se, fragment is found which must be formulated as Se-3(4-). (C) 1998 Academic Press.