New catenary octahedro-hexamolybdenum cluster bromides: Crystal structures of AMo₆Br₁₃ with A = Na, Ag

Reactions of MoBr₂ with NaBr and AgBr in sealed silica tubes at the temperature gradient 700/690 °C yield NaMo₆Br₁₃ (1) and AgMo₆Br₁₃ (2), respectively, at the low temperature zone. Both title compounds crystallize isostructurally in the triclinic space group P(no. 2) with the cell dimensions: (1) a = 9.299(1), b = 9.443(2), c = 14.480(3) Å, α = 96.55(1)°, β = 101.42(1)°, γ = 115.32(1)°, V = 1097.9(3) ų, Z = 2; (2) a = 9.183(1), b = 9.392(1), c = 14.328(2) Å, α = 95.85(1)°, β = 102.04(1)°, V = 114.298(7)°, V = 1076.8(3) A°³, Z = 2. The crystal structures are composed of monovalent cations and the _∞¹[(Mo₆Br_i⁸) B₄^aBr_2/2^a-a] anionic chains. The zigzag anionic chains result from two crystallographically independent [Mo₆Br₈ⁱ]Br₄^a Br₂^a-a cluster groups bridged by two opposite Br^a-a atoms. Both [Mo₆Br₈ⁱ]Br₄^ai Br₂^a-a cluster groups and monovalent cations can be approximately viewed as being hexagonally close-packed in respective planes.