Structure and stability of carboxylate complexes. Part XII. The location of co-ordination sites in copper(II) carboxylates in solution by proton magnetic resonance
Differential proton relaxation has been used to locate binding sites for copper(II) in 35 carboxylate ligands with distinguishable proton magnetic resonance signals. Relaxation rates in aqueous solution have been shown to decrease with increasing distance from the co-ordinated cation in a series of unequivocally unidentate mono-carboxylate ligands. 2- and 3-Hydroxy- and 2-alkoxy-carboxylates are predominantly bidentate towards copper-(II), whereas 4-hydroxy- and 3-alkoxy-carboxylates are predominantly unidentate. The dicarboxylates malonate, succinate, 2-metnyimalate, and diglycollate all appear to be bidentate.The relative dipolar and scalar contributions to the proton spin–spin relaxation have been assessed in the acetate and butyrate systems.