Chemical shifts for proton signals of an imidazole ring coordinated to Co(III) move downfield as the total complex charge increases. However, the C(2)-H chemical shift of the imidazole ring in cis[Co(en)(2)(N-mIm) OPO3H]degrees, which has no charge compared to those of cis-[Co(en)(2)(N-mIm) OPO3H](+) and cis-[Co(en)(2)(N-mIm) OPO3H2](2+), moves downfield. These unexpected phenomena could be attributed to an intramolecular interaction between the phosphate anion group and C(2)-H of the imidazole ligand.