Solid-State Nuclear Magnetic Resonance Spectroscopic and Quantum Chemical Investigation of 13C and 17O Chemical Shift Tensors, 17O Nuclear Quadrupole Coupling Tensors, and Bonding in Transition-Metal Carbonyl Complexes and Clusters

Abstract

The carbon-13 and oxygen-17 nuclear magnetic resonance spectroscopic shielding behavior, as well as the oxygen-17 nuclear quadrupole coupling constants (NQCC), in the four metal−CO systems Fe(CO)5, Fe2(CO)9, Ni2(η5-C5H5)2(CO)2, and Rh6(CO)16 have been investigated both experimentally and by density functional calculations. Characteristics of the spectroscopic observables and bonding for the most common types of metal−carbonyl coordination, μ1-, μ2-, and μ3-CO, may thus be compared in detail. There is generally very good agreement between the theoretical predictions and the experimental measurements, including the 17O shift predictions for Fe2(CO)9 and Rh6(CO)16 made previously. Interestingly, the bridging oxygen shift tensor in Fe2(CO)9 has its most deshielded component parallel to the C−O axis. This is highly unusual for carbonyl ligands, but is the normal behavior seen in organic carbonyl groups. To explain this and other observations, the computed shielding tensors and electric field gradients have bee...