SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF 3 NEW COMPOUNDS CONTAINING [NB6CL12](2+) UNITS AS HYDRATED HYDROXIDES

Conditions have been established for the preparation of three different hydrated chloroniobium cluster hydroxide compounds from alkaline solutions: triclinic [Nb6Cl12(OH)(2)(H2O)(4)].4H(2)O 1 and two cubic compounds whose structures are uncertain with regard to the co-ordination of OH- ions. Nb6Cl12(OH)(2)(H2O)(14) 2 and Nb6Cl12(H2O)(14)(OMe)(2) 3. Based upon structural data 2 and 3 may contain either the cation [Nb6Cl12(H2O)(6)](2+)or the neutral cluster [Nb6Cl12(OH)(2)(H2O)(4)] containing hydroxo ligands. In 1 distinct distances of 2.147(5) for Nb-OH, and 2.250(5) and 2.289(5) Angstrom for Nb-OH2 were found. In 2 and 3 only distances of 2.19(1) and 2.193(7) Angstrom, respectively, were found for the Nb-O bonds of co-ordinated water (or hydroxide-water averaged). Compound 1 is triclinic, space group P (1) over bar, a = 8.930(3), b = 9.195(2), c = 9.118(1) Angstrom, alpha = 104.37(2), beta = 99.51(2) and gamma = 116.99(2)degrees, U = 611.9(3) Angstrom(3) Z = 1, R = 0.036. Compound 2 is cubic, space group Fm (3) over bar m, a = 14.59(2) Angstrom, U = 3105.7(1) Angstrom(3) Z = 4, R = 0.028. Compound 3 is also cubic, space group Fm (3) over bar m, a = 14.627(1) Angstrom, U = 3129.3(1) Angstrom(3), Z = 4. R = 0.031. IR spectra of 1 show strong O-H and Nb-O stretching bands that reflect the presence of co-ordinated OH- groups. In 2 and 3 the IR spectra are less definitive about possible co-ordination of hydroxide.