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

Abstract

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) ų, 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.