Computational ⁵⁹Co NMR Spectroscopy:  Beyond Static Molecules

Abstract

GIAO-B3LYP computations of (59)Co NMR chemical shifts are reported for CoH(CO)4, Co(CO)4(-), CoCp(C2H4)2, Co(CN)6(3)(-), Co(NH3)3(CN)3, Co(NH3)6(3+), Co(NH3)4(CO3)(+), Co(acac)3, and Co(H2O)6(3+), employing both static calculations for equilibrium geometries as well as methods which include zero-point and classical thermal effects. The zero-point effects were computed by applying a perturbational approach, and the classical thermal effects were evaluated using Car-Parrinello molecular dynamics simulations. Both methods lead to a downfield shift of δ((59)Co) with respect to the equilibrium values, which can be attributed to a large extent to cobalt-ligand bond elongation. In some cases the zero-point and classical thermal corrections improve the agreement between computed and experimental values, but especially for complexes where the experimental NMR data were obtained in aqueous solution, the error increases somewhat. Mean absolute deviations between averaged and experimental δ((59)Co) values are on the order of 500-760 ppm over a chemical shift range of almost 20 000 ppm. The computed structures and properties of three Co2(CO)8 tautomers reproduce the experimental data very well. Two transition states for interconversion of these tautormers were located: low barriers are obtained, consistent with the observed fluxionality on the NMR time scale. Two model cobaloximes were taken as test cases to study the change of δ((59)Co) upon deuteration three bonds away from the metal. The sizable downfield shift of δ((59)Co) observed on going from H to D is attributed to a changed vibrational wave function, which causes a noticeable cobalt-ligand bond elongation.

Computational, electrochemical, and spectroscopic studies of two mononuclear cobaloximes: the influence of an axial pyridine and solvent on the redox behaviour and evidence for pyridine coordination to cobalt(i) and cobalt(ii) metal centres

“…The five coordinate py and CH 3 CN complexes have DFT-GIAO 59 Co chemical shifts that are much larger than the observed values, which may be attributed to an effect of large variations in the weak Co–L bond that calculations on static molecules cannot recover. 97–99 Taken together, the results of the TD-DFT calculations and DFT-GIAO chemical shifts cannot definitively assign the species observed experimentally, but suggest that the Co(I) complex is five-coordinate in the presence of py, but forms the [Co(dmgBF 2 ) 2 ] − ion when water and acetonitrile, are present as solvents.…”

Nuclear magnetic resonance spectroscopic studies of the trihexyl (tetradecyl) phosphonium chloride ionic liquid mixtures with water

“…Long-range effects and dynamic averaging should be taken into account, such as the works in Refs [31][32][33][34]. In particular, it is expected that such dynamic calculations would lead to a larger average distance between cation and the anion center in the liquid phase than in our gas phase calculations [31].…”

Quantum chemistry-based NMR spin Hamiltonian parameters of GABA for quantitation in magnetic resonance spectroscopy

“…Going beyond such a static picture may increase the accuracy of theoretical NMR parameters. 23 Such investigations are now in progress for GABA.…”