Extended networks generated from the interaction of rare-earth(III) ions and pyridine-2-carboxamide-based ligands

The reaction of the ligand 1,4-bis(pyridine-2-carboxamido)butane (L) with RECl3 afforded complexes of general formula [RE(L)(1.5)Cl-2(CH3OH)]Cl center dot nS (RE = Pr, Nd, Eu, Tb; n = 4, S = H2O; n = 5, S = CH3OH). The structural determination reveals that complexes [RE(L)(1.5)Cl-2(CH3OH)]Cl center dot 5CH(3)OH (RE = Nd 2b, Eu 3b) are isomorphous, crystallizing in the monoclinic system, space group P2(1)/n; they possess a 2D architecture with the rare-earth ion in an eight-coordination geometry. By exposure to air, the lattice methanol molecules are easily replaced by water molecules to form the analogues [RE(L)(1.5)Cl-2(CH3OH)]Cl center dot 4H(2)O (RE = Pr 1, Nd 2a, Eu 3a, Tb 4) as indicated by elemental analysis, IR, and thermogravimetric analysis. Photophysical studies on the Eu-III, and Tb-III complexes showed that excitation into the ligand-centered pi ->pi* transition results in the characteristic visible luminescence from Eu-III at 614 nm and Tb-III at 545 nm. The magnetic properties were also investigated and show that crystal field effects are dominant. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).