Spectroscopic and electrochemical investigations of the K8[P2VMoW16O62]•31H2O heteropolyoxometalate

The K-8[P2VMoW16O62]. 31H(2)O heteropolyoxometalate complex was synthesized and investigated by electrochemistry measurements and IR, UV-Vis and EPR spectroscopy. The substitution of one W = O-d unit by the VO2+ group was inferred from the shift of the nu(as)(M = O-a,O-d) and nu(as)(M-O-b,O-c-M) vibrational bands (M = W, Mo) and the appearance of nu(as)(V = O-d) approximate to 960 cm(-1) vibration in the IR spectrum of the complex and from the electrochemistry studies. The three transitions in the electronic spectra were assigned to B-2(2) --> E-2 (13 700 cm(-1)), B-2(2) --> B-2(1) (16 490 cm(-1)) and B-2(2) --> (2)A(1) (23 140 cm(-1)), indicating a six coordination of the vanadium(IV) ion in an axial C-4 nu environment. EPR spectrum of the complex obtained at room temperature shows resolved hyperfine features in the parallel and perpendicular regions typical for monomeric V4+ ion. EPR parameters (g(parallel to) = 1.940, g(perpendicular to) = 1.982, A(parallel to) = 178.5, A(perpendicular to) = 62.9 G) and the values of LCAO-MO coefficients (beta(1)(2) = 0.863, beta(2)(2) = 0.875 and beta(3)(2) = 0.935) correspond to a dominant ionic character of the sigma and pi V-O bondings and to an important delocalization of the electrons towards the O-b,O-c atoms. (C) 2000 Elsevier Science Ltd. All rights reserved.