Reaction of hexanuclear niobium and tantalum halide clusters with mercury(II) halides. II. Semiconducting compounds with [Ta6Cl12]3+ unit

Abstract A series of paramagnetic clusters of the composition [(Ta 6 Cl 12 )Cl(H 2 O) 5 ][HgX 4 ] · 9H 2 )O (X = Cl, Br, I) has been prepared by the reaction of [Ta 6 Cl 12 ] 3+ methanol-water solutions with HgX 2 and NaX halides. The structure of [(Ta 6 Cl 12 )Cl(H 2 O) 5 ][HgBr 4 ] · 9H 2 O has been solved by X-ray diffraction in the cubic space group Fd 3m . Crystal data: a = 20.036(2) A, V = 8043.0(1) A 3 , Z = 8, R = 0.048 ( R w = 0.051). The structure is composed of an octahedral [(Ta 6 Cl 12 )Cl(H 2 O) 5 ] 2+ cluster cation, tetrahedral [HgBr 4 ] 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) A. The Ta-Ta and Ta-Cl(1) bond distances are 2.911(1) A and 2.440(3) A, respectively, whereas the Hg-Br bond distance is 2.564(3) A. The cluster [(Ta 6 Cl 12 )Cl(H 2 O) 5 ][HgBr 4 ] · 9H 2 O is semiconducting with two levels governing conductivity with respective activation energies, E al = 0.24 eV and E a2 = 0.17 eV.