New catenary octahedro-hexamolybdenum cluster bromides:crystal structures of AMo_6Br_(13) with A = Na, Ag

摘要

Reactions of MoBr_2 with NaBr and AgBr in sealed silica tubes at the temperature gradient 700/690 ℃ yield NaMo_6Br_(13) (1) and AgMo_6Br_(13) (2), respectively, at the low temperature zone. Both title compounds crystallize isostructurally in the triclinic space group P(1-bar) (no. 2) with the cell dimensions: (1) a = 9.299(1), b = 9.433(2), c= 14.480(3) A, α= 96.55(1)°, β= 101.42(1)°, γ= 115.32(1)°, V = 1097.9(3) A~3, Z = 2; (2) a = 9.183(1), b = 9.392(1), c = 14.328(2) A, α= 95.85(1)°, β= 102.04(1)°, γ= 114.298(7)°, V = 1076.8(3) A~3, Z = 2; The crystal structures are composed of monovalent cations and the ∞~1[(Mo_6Br_8~i)Br_4~aBr_(2/2)~(a-a)] anionic chains. The zigzag anionic chains result from two crystallographically independent [Mo_6Br_8~i]Br_4~aBr_2~(a-a) cluster groups bridged by two opposite Br~(a-a) atoms. Both [Mo_6Br_8~i]Br_4~aBr_2~(a-a) cluster groups and monovalent cations can be approximately viewed as being hexagonally close-packed in respective planes.