H-1 NMR properties of trinuclear transition-metal complexes [M-3 O-square(OOCR)(6)L-3](+) (M = Cr, Fe, Mn; R = CH3, C2H5,CH2NH2; L = C5H5N, H2O)

A series of oxo-centered trinuclear transition-metal complexes with general formula [(M3O)-O-II(OOCR)(6)L-3](+) (M = Cr, Fe, Mn; R = CH3, C2H5, CH2NH2 ; L = C5H5N, H2O) were studied by H-1 NMR spectra. The investigation was fo cussed on the change of H-1 chemical shifts with various factors such as me tals, ligands, temperatures and solvents. The experimental results show tha t the main effect on chemical shifts comes from skeleton metals and there i s antiferromagnetic exchange interaction among the three metal ions within M3O core, For manganese complexes, the influence mechanisms of paramagnetic centers on chemical shifts and peak widths were discussed. It shows that t heir H-1 NMR isotropic shifts are mostly contributed by contact interaction s.