Nuclear magnetic resonance study of transition metal—pyridine complexes in aqueous solutions

• Published in: Chemical physics Vol. 15; no. 2; pp. 261 - 267
• Main Authors: Mignot, P., Grivet, J.Ph
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.07.1976
• ISSN: 0301-0104
• DOI: 10.1016/0301-0104(76)80159-0

We have investigated by NMR the structure and dynamics of cobalt and nickel complexes of pyridine in water solutions. At high temperatures, fast exchange previals and the geometry of the complexes can be derived from the spin—lattice relaxation times. At low temperatures, slow exchange obtains and the contact and dipolar shifts may be found from the spectrum of bound pyridine. In the intermediate range, the exchange kinetics may be studied. We find a value of ca. 3A for the metal pyridine distance, an average number of 3.5 bound molecules in the complex, and activation energies for chemical exchange of 16 kcal/mole for nickel and 22 kcal/mole for cobalt. The ligand molecules undergo free rotation about the metal nitrogen bond.