Simulation of Co-59 NMR chemical shifts in aqueous solution

Co-59 chemical shifts were computed at the GIAO-B3LYP level for [Co(CN)(6)](3-), [Co(H2O)(6)](3+), [Co- (NH3)(6)](3+), and [Co(CO)(4)](-) in water. The aqueous solutions were modeled by Car-Parrinello molecular dynamics (CPMD) simulations, or by propagation on a hybrid quantum-mechanical/ molecular-mechanical Born-Oppenheimer surface (QM/MM-BOMD). Mean absolute deviations from experiment obtained with these methods are on the order of 400 and 600 ppm, respectively, over a total delta(Co-59) range of about 18000 ppm. The effect of the solvent on delta(Co-59) is mostly indirect, resulting primarily from substantial Metal-ligand bond contractions on going from the gas phase to the bulk. The simulated solvent effects on geometries and delta(Co-59) values are well reproduced by using a polarizable continuum model (PCM), based on optimization and perturbational evaluation of quantum-mechanical zero-point corrections.