화학공학소재연구정보센터
Inorganic Chemistry, Vol.46, No.23, 9827-9840, 2007
4-amino- and 4-nitrodipicolinatovanadium(V) hydroxylamido derivatives: Synthesis, aqueous, and solid-state properties
A number of 4-substituted, dipicolinatodioxovanadium(V) complexes and their hydroxylamido derivatives were synthesized to characterize the solid state and solution properties of five- and seven-coordinate vanadium(V) complexes. The X-ray crystal structures of Na[VO(2)dipic-NH2]center dot 2H(2)O (2) and K[VO(2)dipic-NO2] (3) show the vanadium adopting a distorted, trigonal-bipyramidal coordination environment similar to the parent coordination complex, [VO(2)dipic](-) (1), reported previously as the Cs+ salt. The observed differences in the chemical shifts of the complexes both in the H-1 (ca. 0.7-1.4 ppm) and V-51 (ca. 1-11 ppm) NMR spectra were consistent with the electron-donating or electron-withdrawing properties of the substituent groups, respectively. Stoichiometric addition of a series of hydroxylamine ligands (H2NOH, MeHNOH, Me2NOH, and Et2NOH) to complexes 1-3 led to the formation of seven-coordinate vanadium(V) complexes. The X-ray crystal structure of [VO(dipic)(Me2NO)(H2O)]center dot 0.5H(2)O (1C) was found to be similar to the previously characterized complexes [VO(dipic)(H2NO)(H2O)] (1a) and [VO(dipic)(OO-Bu-1)(H2O)]. While only slight differences in the H-1 NMR spectra were observed upon addition of the hydroxylamido ligand, the signals in the V-51 NMR spectra change by up to 100 ppm. The addition of the hydroxylamido ligand increased the complex stability of complexes 2 and 3. Evidence for a nonstoichiometric redox reaction was found for the monoalkyl hydroxylamine ligand. The reaction of an unsaturated five-coordinate species with a hydroxylamine to form a seven-coordinate vanadium complex will, in general, dramatically increase the amounts of the vanadium compound that remain intact at pH values near neutral.