First principles determination of 99Ru chemical shifts using moderately sized basis sets

The use of moderately sized basis sets for ab initio and density functional theory calculations of 99Ru chemical shifts is investigated. Six different levels of theory are used for molecular geometry optimization. Isotropic shielding constants for 99Ru are determined using eight different levels of theory combined with four choices for the gauge origin. The best combination of methods uses a DFT geometry optimization followed by GIAO-B3PW91 shielding calculations (using a combined basis set of 3-21G(*) and 6-31G(d)). The correlation with experimental data using this method is excellent (R2=0.99). The effects of changes in molecular geometry, choice of gauge origin, and choice of basis set on the results are also investigated.