Abstract
The tetrabutylammonium salt of mononiobotungstate [(n-C4H9)(4)N](3)NbW5O19 (1) and the tetrabutylammonium salt of monovanadotungstate [(n-C4H9)(4)N](3)VW5O19 (2) are isotypes; both crystallize in the monoclinic system, space group C2/c (N degrees 15) with Z = 8. The cell parameters for 1 are a = 30.4038(8) angstrom, b = 18.5948(8) angstrom, c = 27.3330(3) angstrom, beta = 112.4555(6)degrees, V = 14281.1(7) angstrom(3) and the final reliability factors are R = 0.043 and R-w = 0.047 for 5801 reflections. The cell parameters for 2 are a = 30.096(8) angstrom, b = 18.373(3) angstrom, c = 27.201(6) angstrom, beta = 112.402(14)degrees, V = 13906(5) angstrom(3) and the final reliability factors are R = 0.048 and R-w = 0.054 for 6122 reflections. Both anions, [NbW5O19]3- and [VW5O19]3- exhibit the Lindqvist structure of the parent hexatungstate anion. The six metal positions are disordered and for each metal site the occupation factor is close to 1/6 M (M = Nb, V) and 5/6 W. Furthermore the two compounds were characterized by IR in the solid state, and W-183 solution NMR. The W-183 spectrum of [NbW5O19]3- presents two resonances with relative intensities 4:1 in agreement with the C-4v symmetry of the anion.