Platinum-195 magnetic resonance spectra of some platinum(II) and platinum(IV) complexes

Abstract

The 195Pt magnetic resonance spectra of fourteen symmetrical, substitutionally inert octahedral Pt(IV) and square-planar Pt(II) complexes have been measured at 9.75 MHz using Fourier transform techniques. Chemical shifts observed in aqueous solutions of the PtL 6 m complexes cover a range of 6033 ppm and the shielding of the 195Pt nucleus is in the order Cl > 1 2 en > Br > SCN > CN > I. For aqueous solutions of the PtL 4 m complexes, the chemical shifts cover a range of 3876 ppm and the order of shielding is CI > NO 2 > NH 3 > Br > 1 2 en > SCN > CN > I. These results are interpreted in terms of covalency effects in the σ p contribution to shielding. Relaxation times T 1 and T 2 have been measured in several cases where the signal to noise was favorable. In addition the temperature dependence of T 1 has been investigated for H 2PtCl 6 and H 2PtCl 4 in aqueous HCl. The relaxation process for these two complexes appears consistent with a spin-rotation mechanism. The solvent dependence of the 195Pt resonance in PtCl 6 2− and PtCl 4 2− has also been measured for solutions tetra- n-butylammonium salts in a variety of nonaqueous solvents. Some proton and 13C NMR spectra have also been obtained for Pt(en) 3 4+ and Pt(en) 2 2+ in aqueous solution and some 13C spectra for Pt(CN) 6 2− and Pt(CN) 4 2− in D 2O/H 2O. Platinum-195 spin-coupling constants have been determined and some of the factors affecting coupling are discussed.