Synthesis and Characterization of Binuclear Lanthanide Complexes of 1,4,7,10-Tetrakis(2-Pyridylmethyl)-1,4,7,10-Tetraazacyclododecane

Abstract

A series of new dinuclear lanthanide complexes with a macrocyclic tetramine ligand containing 4-pyridyl pendants has been synthesized by the reaction of 1,4,7,10-tetrakis-(2-pyridylmethyl)-1,4,7,10-tetraazacyclododecane (L) and lanthanide nitrates (where Ln = Ce, Nd, Eu, Gd, Tb, Ho, Yb). The complexes have the general formula [Ln2(L)(NO3)4](NO3)2. L acts as an octadentate donor ligand to bond two lanthanide(III) ions in these complexes. The electronic and steric requirements of the lanthanide ion appear to be fully satisfied by coordination of the two nitrogens of the macrocyclic ring, the two nitrogens of the pyridyl pendants of L, and the oxygens of two bidentate chelating nitrate ions. The coordination number of the metal ions is therefore 8. The electronic spectra of the Nd and Ho complexes in the visible region have been analyzed, and the spectral parameters (β, b1/2, δ, ωλ) have been calculated and discussed. The emission spectra of the Eu and Tb complexes show strong luminescence, and the spectra from methanol and aqueous solutions are obviously different. The variable-temperature magnetic susceptibility (4-300 K) of the Gd(III) complex reveals a weak antiferro-magnetic spin exchange with J = - 0.23 cm−1 between the Gd3+ ions.