1 1 3Cd and 13C chemical shielding tensors in a single crystal of cadmium (II) acetate dihydrate

Abstract

Both the carbon-13 and cadmium-113 chemical shielding tensors in a single crystal of cadmium (II) acetate dihydrate have been determined by solid state proton-enhanced NMR at 1.32 T. The 13C shielding tensors of a carboxyl group bound to a metal ion is determined quantitatively and unambiguously. The most shielded direction lies perpendicular to the O–C–O plane and the least shielded principal value is along C⋅⋅⋅Cd direction. The influence of carbon–cadmium dipolar interaction on the observed spectra is discussed and used to make unique assignments of the carboxyl carbon tensors. The CP-MAS spectrum exhibits resolved resonances for the two chemically distinct carboxyl carbons and these are assigned based on single crystal analysis. The methyl carbon tensors exhibit significant deviation from axial symmetry. The most shielded direction is along the C3 symmetry axis and the least shielded direction is perpendicular to the C(H3)–COO plane. It is demonstrated that the orientation dependence of 13C–1H dipolar interaction is useful in assigning 13C resonances of the two chemically similar methyl groups in the asymmetric unit. The 113Cd results show that the cadmium shielding tensor is not axially symmetric and the most shielded direction lies approximately perpendicular to the plane formed by cadmium and the two water oxygens.