The family of tetranuclear Nb4OI12−x clusters (x = 0, 1, 2): from the molecular Nb4OI12 cluster to extended chains and layers

Abstract

Unconventional reduction reactions in the Nb–O–I system have produced a number of niobium oxyiodides containing the oxygen-centered [Nb₄O] cluster. Crystalline Nb₄OI₁₂ and two modifications of Nb₄OI₁₁ were structurally characterized by means of single-crystal X-ray diffraction studies. The new compounds can be classified as members of the Nb₄OI_12−x family, together with the already known Nb₄OI₁₀. Nb₄OI₁₂ is represented by a molecular stucture, in which the two modifications of Nb₄OI₁₁ are forming structures with iodido-bridged strings, that can be assigned to represent one-dimensional structures. Measurements of b-Nb₄OI₁₁ single crystals reveal semiconducting behaviour, with an electrical conductivity in the order of 10⁻³ S m⁻¹ at 300 K and an electrical band gap estimated as 0.4 eV. The presence of varying numbers of cluster electrons in the given compounds is discussed in the light of second-order Jahn–Teller distortion.