Journal of the American Chemical Society, Vol.121, No.5, 1030-1036, 1999
A DFT and Co-59 solid-state NMR study of the second-sphere interaction in polyammonium macrocycles cobalt cyanide supercomplexes
The second-sphere interaction for a series of supercomplexes formed from the binding of [Co(CN)(6)](3-), photochemical active metal complex, with preorganized protonated polyammonium macrocyclics has been studied with Co-59 solid-state NMR and ab initio quantum chemical methods at the DFT level. For the supercomplexes studied in this work, the Co-59 NMR chemical shift of [Co(CN)(6)](3-) has been successfully computed, demonstrating that the hybrid XC functional method is equally powerful in rationalizing small adjustments in structural and electronic modification at the metal center. This success has confirmed that the entire Co-59 chemical shift range may be predicted with reasonable confidence. The charge-transfer mechanism has also been established on the basis of the correlations between the Co-59 chemical shifts and the relative contribution of cobalt-3d orbitals to second-order interaction energies, as well as structure parameters. The shielding tensor results confirmed that the structure distortions occurring in these supercomplexes are the direct consequence of the second-sphere interaction resulting from site-symmetry being lowered at cobalt. Thus, the degeneracy of the electron energy state (T-1(1g)) at cobalt has been lifted, resulting in splitting of the energy levels.
Keywords:NUCLEAR-MAGNETIC-RESONANCE;DENSITY-FUNCTIONAL THEORY;SHIELDING TENSOR ELEMENTS;MOLECULAR-ORBITAL METHODS;GAUSSIAN-BASIS SETS;CHEMICAL-SHIFTS;PERTURBATION-THEORY;RECEPTORMOLECULES;CO(III) COMPLEXES;RECOGNITION