SYNTHESIS AND CHARACTERIZATION OF BINUCLEAR LANTHANIDE COMPLEXES OF IS(2-PYRIDYLMETHYL)-1,4,7,10-TETRAAZACYCLODODECANE

A series of new dinuclear lanthanide complexes with a macrocyclic tetr amine ligand containing 4-pyridyl pendants has been synthesized by the reaction of is(2-pyridylmethyl)-1,4,7,10-tetraazacyclododecane (L) an d lanthanide nitrates (where Ln = Ce, Nd, Eu, Gd, Tb, Ho, Yb). The com plexes have the general formula [Ln(2)(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 io n 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 coordina tion number of the metal ions is therefore 8. The electronic spectra o f the Nd and Ho complexes in the visible region have been analyzed, an d the spectral parameters (beta, b(1/2), delta, Omega(lambda)) have be en calculated and discussed. The emission spectra of the Eu and Tb com plexes show strong luminescence, and the spectra from methanol and aqu eous solutions are obviously different. The variable-temperature magne tic susceptibility (4-300 K) of the Gd(III) complex reveals a weak ant iferromagnetic spin exchange with J = - 0.23 cm(-1) between the Gd3+ i ons.