Reaction of hexanuclear niobium and tantalum halide clusters with mercury(II) halides. II. Semiconducting compounds with [Ta6Cl12] unit

A series of paramagnetic clusters of the composition (Ta₆Cl₁₂)Cl(H₂O)₅]HgX₄] · 9H₂)O (X = Cl, Br, I) has been prepared by the reaction of Ta₆Cl₁₂]³⁺ methanol-water solutions with HgX₂ and NaX halides. The structure of (Ta₆Cl₁₂)Cl(H₂O)₅]HgBr₄] · 9H₂O has been solved by X-ray diffraction in the cubic space group Fd 3m. Crystal data: a = 20.036(2) Å, V = 8043.0(1) ų, Z = 8, R = 0.048 (R_w = 0.051). The structure is composed of an octahedral (Ta₆Cl₁₂)Cl(H₂O)₅]²⁺ cluster cation, tetrahedral HgBr₄]²⁻ anion and crystal water molecules. The 2mm symmetry of the octahedron is reduced by the statistical distribution of the five water molecules, O(1), and chlorine, Cl(2), at the terminal coordination sites. Thus, the distances Ta-O(1) and Ta-Cl(2) are averaged to the value of 2.32(2) Å. The Ta-Ta and Ta-Cl(1) bond distances are 2.911(1) Å and 2.440(3) Å, respectively, whereas the Hg-Br bond distance is 2.564(3) Å. The cluster (Ta₆Cl₁₂)Cl(H₂O)₅]HgBr₄] · 9H₂O is semiconducting with two levels governing conductivity with respective activation energies, E_al = 0.24 eV and E_a2 = 0.17 eV.