Angular Overlap Studies of Mono-(Aminodiphosphonato)Copper(II) Complexes in Aqueous Solutions

Electronic absorption spectra of copper(II) complexes with iminodimethylenephosphonates R-N(CH₂PO₃H₂)₂ type (L, R-dmp), in aqueous solution have been characterized and quantitatively interpreted. The geometry of species in aqueous solution at pH 7–8 has been assumed on the basis of our previous combination of UV spectrophotometric measurements and ESR spectra, as well as data obtained from potentiometric titration. The ligand-field spectra (d–d transitions) of the [CuL(H₂O)_x]^2– chromophores (where x = 2, 3) have been treated by the angular overlap model (AOM) and C_2v symmetry. Low-symmetry splittings of the broad asymmetric bands in the spectra of solutions at room temperature were resolved by Gaussian analysis. The effect of the and bonding of the tridentate (and tetradentate) ligands (with oxygen-donor and nitrogen-donor ligators) on the central metal ion has been described in the ligand-field framework.