Abstract
AbstractCarbon and oxygen NMR chemical shift tensors for Group 6 hexacarbonyl complexes M(CO)6 (M Cr, Mo, W) have been calculated by using a combination of quasirelativistic metal effective‐core potentials and density‐functional theory. Comparison with high‐resolution solid‐state shift tensors indicates excellent agreement between theory and experiment. The sensitivity of the shifts to the W‐C distance in W(CO)6 is discussed. A breakdown of the shielding tensor components into contributions from localized molecular orbitals allows the detailed interpretation of the trends on going down Group 6, and of differences to free CO. Group trends in the carbon shielding tensors are related largely to contributions from M‐C σ‐bonding orbitals. The presence of occupied metal (n–1)p and (n–1)d orbitals is partly responsible for the changes on going from free to metalbound CO. The origin of the less pronounced trends in the oxygen shielding tensors is more complicated. The influence of scalar relativistic effects on the shift tensors has been studied for W(CO)6 and is found to be relatively small, in spite of considerable changes in the W‐C distance.
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