Trifluoroacetate complexes of cobalt(II), nickel(II), and copper(II) with pyridine-type ligands. Part III. Nuclear magnetic resonance studies of cobalt(II) complexes in solution

Abstract

Complexes of cobalt(II) trifluoroacetate with pyridine and alkylpyridine ligands of stoicheiometries ML₄T₂ and ML₂T₂ have been investigated in solution by ¹H and ¹⁹F n.m.r. spectroscopy. In deuteriochloroform solution, cis–trans isomeric equilibria were detected for both series of complexes. Rapid cis–trans exchange occurred at ambient temperatures but became slow on the n.m.r. time scale below ca. 0 °C for ML₂T₂ complexes and below ca. –50 °C for ML₄T₂ complexes. In the ML₄T₂ series, intermediate species were detected between ca. 0 °C and ca. –40 °C. In hexadeuterioacetone solution, a number of polymeric species were detected. Some evidence has also been obtained for a rapid intramolecular scrambling of ligands occurring in these complexes even at temperatures below –60 °C.