| dc.description | The carbon chemical shift (CS) tensors for several unsaturated-carbon ligands and their platinum complexes have been investigated by solid-state 13C NMR spectroscopy. The magnitudes of the principal components and their orientations relative to the 13C,13C dipolar vector were determined using the dipolar-chemical shift NMR method. Orientations for the CS tensors in the molecular framework are proposed, based on the results from first principles calculations of the magnetic shielding tensors, using restricted Hartree-Fock theory with gauge-independent atomic orbitals (GIAO). The isotropic shielding of the alkenyl carbon nuclei increases significantly upon coordination with Pt(0). For example, the ethylene carbon nuclei of Pt(C 2H4)(PPh3)2 are shielded by approximately 85 ppm compared to those for uncoordinated ethylene. The increased isotropic shielding is a consequence of increased shielding in the directions of delta 11 and delta22; the shielding in the direction of delta 33 is relatively insensitive to coordination with platinum. In contrast, the alkynyl carbon shielding for diphenylacetylene decreases following coordination with Pt(0). The alkynyl carbon CS tensors for Pt(eta2-diphenylacetylene)(PPh 3)2 are similar to those for uncoordinated trans -stilbene. Deuterium NMR studies of Pt(C22H 4)(PPh3)2 and Zeise's salt-2H 4 indicate that motion of the ethylene ligand is not significant for these samples in the solid state at room temperature. Ab initio calculation of the carbon magnetic shielding for some nickel and palladium complexes suggest that the effect on the carbon CS tensors of coordination with these metals is comparable to that observed experimentally for platinum. | en_US |
