The electron spin resonance spectra of copper(II)- tris(hydroxymethyl)amino-methane complexes in aqueous solution provides evidence of the formation of dimeric species. These species are found to be different from those postulated by previous investigations. In dimethylformamide dimeric species are formed at room temperature and frozen solution in 1 : 1 and 1 : 2 metal-to-ligand mole ratios, though the formation of the dimer is critically dependent on the addition of base. Low field, ΔM = 2, signals observed for these systems have been interpreted in terms of dipole-dipole coupling between pairs of copper(II) ions. Structures for the copper(II) dimers have been proposed which are compatible with the copper-copper separation estimated by computer simulation of the spectra.

Boyd, P., Pilbrow, J., & Smith, T. (1971). An electron spin resonance study of the copper(II) complexes of Tris(hydroxymethyl) aminomethane formed in aqueous and non-aqueous solution. Australian Journal of Chemistry, 24(1), 59.