Extended chains in vanadium O-centered complex [V4OSe8I5]∞: synthesis and structure.

O-centered tetranuclear vanadium selenoiodide [V4OSe8I5]∞ (1) was synthesized by an ampoule method from the elements with addition of water. Its X-ray crystal structure (space group C2/c, a = 21.146(2) Å, b = 5.8953(5) Å, c = 18.735(1) Å, β = 126.421(2)°, V = 1879.4(3) Å3, T = 150 K, Z = 4) is a packing of chains built from O-centered tetranuclear [V4(μ4-O)(μ-Se2)4(μ4-I)2/2I4] fragments. In the O-centered fragment, vanadium atoms form a distorted tetrahedron around an oxygen atom, V atoms are bridged by four μ2-(Se2)2- and two I- ligands. The latter iodide ligands bridge the neighboring fragments, thus forming a chain [V4(μ4-O)(μ-Se2)4(μ4-I)2/2I4]∞. The synthesis of the chain [V4OSe8I5]∞ takes place at the temperature of 290 °C, while at lower temperatures (220-250 °C) molecular compounds [V4OSe8I6]·X form. The direct 'cluster to chain' transformation is also observed and discussed in this work. Electrical resistance of the [V4OSe8I5]∞ polycrystalline pressed sample shows that the compound 1 is a narrow gap semiconductor, which is in agreement with the DFT calculations.