Coexistence of one-electron- and monoprotonated two-electron-reduced species of the K-5[PMo2VW9O40]center dot 24H(2)O heteropolyoxometalate identified by EPR

The simulation of the room-temperature experimental electron paramagnetic r esonance spectrum of K-2[PMo2VW9O40] . 24H(2)O heteropolyoxometalate indica tes the presence of equal amounts of a one-electron-reduced species (g(para llel to) = 1.922, g(perpendicular to) = 1.972, A(parallel to) = 181 G, A(pe rpendicular to) = 63 G) and a monoprotonated two-electron-reduced species w ith mixed-valence V-IV, Mo-V and Mo-VI ions (g(iso) = 1.972, DeltaB(ISO)(p- p) = 450 G). Two unprotonated one-electron-reduced isomers are identified i n dimethylsulfoxide-H2O solution of the sample at T = 100 K (g(parallel to) (1) = 1.929, g(perpendicular to)(1) = 1.990, A(parallel to)(1) = 179 G, A(p erpendicular to)(1) = 65 G and g(parallel to)(2) = 1.918, g(perpendicular t o)(2) = 2.000, A(parallel to)(2) = 187 G, A(perpendicular to)(2) = 80 G, re spectively). The values of the in-plane pi (V-O) bond beta (2)(2) coefficie nt for the one-electron-reduced species (0.87 at room temperature and 0.83 and 0.74 for the species in frozen solution) suggests the delocalization of the vanadium unpaired electron towards the molybdenum ions via O-b atoms.