Synthesis and Spectral Studies of Some Seven-Coordinated Rare Earth Metal Complexes

Abstract

N-(3,4-diaminobenzophenonimino)-2-benzamido-ethanamide, dabbe, has been synthesized and characterized. The ligand dabbe was found to coordinate with the trivalent lanthanide metal ions to give Ln(III) metal complexes of the type [Ln (dabbe)2Cl3].4H2O where Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy and Y. The complexes were studied by elemental analyses, electrical conductance, magnetic susceptibility, electronic, infrared and NMR (1H, 13C and 139La) spectral techniques. Various bonding parameters (β, b1/2, % δ and η) were calculated from the electronic spectra of the Pr(III), Nd(III), Sm(III) and Dy(III) complexes and suggest weak covalent bond formation in the complexes. The theoretical oscillator strengths (Pcalcd) and a set of three intensity parameters (Tλ-2,4,6) computed from the Judd-Ofelt equation are found to be in reasonable agreement with the experimental values. An approximate mean M-L distance, R(Ln-O) Å, in case of the Pr(III) complex was found to be 2.56 Å from the energy of the 3H4 → 3P0 transition. IR and NMR spectral data suggest a neutral bidentate nature of dabbe in the complexes. Low site molecular symmetry in the present complexes is proposed on the basis of 139La NMR spectra. Referee I: S. P. Nolan Referee II: G. J. Grant