Pseudocontact contribution to the isotropic chemical shifts of protons in octahedral paramagnetic complex ions

Abstract

Following the formalism of Kurland and McGarvey, it is shown that transferred spin densities onto ligands can give rise to pseudocontact shifts even for protons in octahedral complexes. In the case of ammonia as a ligand the pseudocontact shift of the protons originates from the spin density on the p orbitals of the nitrogen as well as spin density on the s orbitals on the neighboring hydrogen atoms. Using LCAO-MO wavefunctions for the Ru(NH 3) 3+ 6 ion the contact and pseudocontact shifts were estimated to contribute about 75% and 25% of the total shift of the amine protons respectively. Based on experimental paramagnetic NMR shifts, the covalency parameter in the Ru(NH 3) 3+ 6 ion was recalculated to be λ = 0.325.