Synthesis and characterization of three new fluorovanadate complexes:: N(C2H5)4+[VOF4]-, N(CH3)4+[VOF3Cl]-, N(C4H9)4+[VOF3Br]- and theoretical calculations of VOF4-, VOF3Cl- and VOF3Br- ions

The reaction of VOF3 with (C2H5)(4)NF, (CH3)(4)NCl and (C4H9)(4)NBr salts in anhydrous CH3CN produced new complexes with the anion general formula [VOF3X](-) in that (X = F-, Cl-, Br-). These were characterized by elemental analysis, IR, UV/Visible and F-19 NMR spectroscopy. The optimized geometries and frequencies of the stationary point are calculated at the B3LYP/6-311G level of theory. Theoretical results showed that the V-X (X = F, Cl, Br) bond length values for the [VOF3X](-) in compounds 1-3 are 1.8247, 2.4031 and 2.5595 angstrom, respectively. Also, the V-F-5 bond length values in [VOF3X]- are 1.824, 1.812 and 1.802 angstrom, respectively. These results reveal that the bond order for V-X bonds decrease from compounds 1 to 3, while for V-F-5 bonds, the bond orders increase. It can be concluded that the decrease of V-X bonds lengths and the increase of V-F-5 bond lengths in compounds 1-3 result from the increase of the hyperconjugation from compounds 1 to 3. Harmonic vibrational frequencies and infrared intensities for VOF4-, VOF3Cl- and VCF3Br- are studied by means of theoretical and experimental methods. The calculated frequencies are in reasonable agreement with the experiment values. These data can be used in models of phosphoryl transfer enzymes because vanadate can often bind to phosphoryl transfer enzymes to form a trigonal-bipyramidal structure at the active site. (c) 2008 Elsevier B.V. All rights reserved.