Synthesis, Crystal Structure and Vibrational Spectrum of 2,3,5-Triphenyltetrazolium Hexachloridoniobate(V) and Oxidotetrachloridoniobate(V) Acetonitrile, [TPT][NbCl6] and [TPT][NbOCl4(CH3CN)]

Single crystals of 2,3,5-triphenyltetrazolium hexachloroniobate(V), [TPT] [NbCl6], (1) and of 2,3,5-triphenyltetrazolium oxotetrachloroniobate(V), [TPT] [NbOCl4(CH3CN)], (2) could be obtained and their crystal structures determined. The yellow compound 1 crystallizes in the monoclinic space group P21/c (C2h5, no. 14) with a = 1321.6(3), b = 1080.7(2), c = 1740.2(4) pm, β = 111.54(2)°, and Z = 4. Its structure is isotypic to that of the recently characterized [TPT] [SbCl6] and built up by [TPT]+ cations and octahedral [NbCl6]– anions. The light yellow compound 2 crystallizes in the orthorhombic space group Pbcm (D2h11, no. 57) with a = 1574.4(1), b = 1047.7(1), c = 1723.4(1) pm, and Z = 4. The ionic compound contains [TPT]+ cations and [NbOCl4(CH3CN)]– anions. The nitrogen atom of the acetonitrile solvate molecule is coordinated to the niobium ion in the trans-position to the oxo ligand. The Nb−O bond length of 169.6 pm corresponds to a double bond. The [TPT] [NbOCl4(CH3CN)] formation proceeds with the hydrate [TPT]Cl  H2O obvious via NbOCl3. The FT-Raman and FT-IR/FIR spectra of both compounds have been recorded and interpreted, especially with respect to the inorganic structure parts. The melting temperatures of 1 and 2 are given.