Preparation, structure, and properties of a series of anisotropic oxychloride cluster compounds AxNb6Cl12O2 (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 AxNb6Cl12O2 (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)Cl4aO2a 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 Cla–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.