Preparation of low-dimensional cluster materials:: Synthesis, structure, and properties of A2Ti2Nb6Cl14O5 (A = K, Rb, Cs), a series of one-dimensional titanium niobium oxychlorides

In the course of our systematic investigation of metal oxychloride systems aimed at the preparation of low-dimensional compounds, a new series of niobium oxychloride cluster compounds, A(2)Ti(2)Nb(6)Cl(14)O(5) (A = K, Rb, Cs), was obtained from stoichiometric amounts of ACl (A = K, Rb, Cs), Ti, Nb2O5, NbCl5, and Nb, heated at 750 degreesC. The crystal structures of the series were determined by single-crystal X-ray diffraction techniques. The compounds crystallize in the monoclinic system, space group C2/c, with unit cell parameters a = 21.503(3) Angstrom, b = 8.816(1) Angstrom, c = 15.710(2) Angstrom, beta = 116.21(1)degrees, V = 2672.1(6) Angstrom(3), and Z = 4 for A = Rb. The full-matrix least-squares refinement against F 2 converged to RI = 0.043 (F-o > 4sigma(F-o)) and wR2 = 0.089 (all data for A = Rb). The crystal structure of A(2)Ti(2)Nb(6)Cl(14)O(5) has one-dimensional character. It is based on chains formed by (Nb6Cl7i O-5(i))Cl-6(a) octahedral niobium 7 5 6 clusters connected to each other through apical chloride ligands and titanium counterions. The chains are held together by alkali metal cations. Intracluster bond distances analysis indicates that the cluster has 14 valence electrons. Magnetic susceptibility study shows paramagnetic behavior with a magnetic moment of 2.17 mu(B) per formula unit for two unpaired electrons contributed by two Ti3+.