Preparation, structure, and properties of a series of anisotropic oxychloride cluster compounds A_xNb₆Cl₁₂O₂ (A=K, Rb, Cs, or In)

In the course of our investigation aimed at the preparation of anisotropic cluster materials using a combination of oxide and chloride ligands to induce directional bonding preferences in the cluster unit, a series of niobium oxychloride cluster compounds A_xNb₆Cl₁₂O₂ (A = K, x=0.72(2); A=Rb, x=0.736(7); A=Cs, x=0.938(4); A=In, x=0.634(8)) was obtained by solid state synthesis. The cluster framework is based on (Nb₆Cl₁₀ⁱO₂ⁱ)Cl₄ ^aO₂^a clusters connected via oxide ligands in the a^→ direction with two Nb-O linkages between adjacent clusters, which resembles intercluster bonding in Chevrel-Sergent phases, while in the other two directions, the linkages occur through single Cl^a-a bridges. The framework generates channels where the cations A⁺ are located. The electronic band structure of the series features a narrow partially occupied band originating from a Nb-Nb bonding state. Magnetic and ESR measurements show the presence of localized unpaired electrons, and resistivity measurements indicate a semiconducting behavior.