Combined single-crystal X-ray and neutron diffraction analysis of the structure of the [Zr6Cl18H5](3-)polyanion

The octahedral hexazirconium compound (Ph(4)P)(3)[Zr6Cl18H5] has been structurally characterized by a combined analysis of single-crystal X-ray and time-of-flight (TOF) neutron diffraction data. The space group is tetragonal, I4(1)/a, Z = 8, with lattice constants at 123 K of a = 32.957(8), c = 15.001(3) Angstrom, V = 16,294(6) Angstrom(3). Difference Fourier maps based on the neutron data exhibited negative troughs on the triangular faces of the hexazirconium octahedron which were introduced into the structure as hydrogen atoms. Refinement of the atomic positional and occupancy parameters for the hydrogen atoms resulted in about 0.7 H atoms on each triangular face for a total of 5.47(15) hydrogen atoms per hexazirconium cluster, in good accord with the H-1 NMR measurement (5.0) and the theoretical expectation of 5. The Zr - (mu(3)H) distances range from 1.8 to 2.1 Angstrom.