Lanthanide complexes of tetradentate macrocyclic ligand: synthesis and spectroscopic investigation

In the present paper, the lanthanide complexes derived from (1,5,8,12-tetraaza-2,4,9,11-tetramethyl cyclotetraaza-1,4,8,11-tetraene) were synthesized. The general composition of the complexes is (Ln(L)X2.H2O)X, where Ln = La, Ce, Nd, Sm and Eu and X = NO3- and CI-. The ligand was characterized on the basis of elemental analyses, IR, Mass and 1H NMR spectral studies. All the complexes were characterized by elemental analyses, molar conductance measurements, magnetic susceptibility measurements, IR, Mass, electronic spectral techniques and thermal studies. The Iigand acts as a tetradentate chelate and coordinates through four nitrogen atoms of azomethine groups. The lanthanum complexes are diamagnetic while the other Lnlll complexes are paramagnetic due to the presence of 4fn unpaired electrons. The spectral parameters i.e. nephelauxetic effect (β), covalency factor (b1/2), Sinha parameter (δ%) and covalency angular overlap parameter (η) have been calculated from absorption spectra of Ndlll and Smlll complexes. These parameters suggest the metal-Iigand covalent bonding. In the present study, the complexes show the co- ordination number seven. (author)