EPR of substituted halo Ru(III) and Os(III) complexes

The interaction of chloro and bromo Ru and Os complexes with a number of re agents (L = DMSO, Thio, PPh3, CH3CN, py, Sn X-3(-); X = Cl, Br) in aqueous solutions of HX and Me2CO is studied by EPR. Twenty-nine new complexes form ulated as [MLX5](n-) (n = 3, 2), trans-[ML2X4](n-) (n = 2, 1), and mer-[ML3 X3] (M = Ru(III), Os(III)) are identified. Comparative analysis of EPR and ligand-field parameters of 60 related ruthenium and osmium compounds is car ried out. The energy of splitting the d(pi) levels Delta/lambda decreases i n the series L = CO > DMSO similar to Thio > PPh3 similar to AsPh3 greater than or equal to PEt3 > CH3CN > H2O > py > SnX3- > X-, which correlates wit h the trend in the pi-acceptor properties of the ligands. The orbital reduc tion factor k decreases when going from Ru(III) compounds to analogous Os(I II) compounds and from bromo to corresponding chloro complexes. The effect of solvation in solution and the effect of crystal lattice on symbatic chan ges in Delta/lambda and k are assessed. Analysis of hyperfine coupling indi cates that, in halo Ru complexes with a large axial distortion, the unpaire d electron is almost completely localized into the d(xy) metal-centered orb ital.