Structural characterization and luminescence studies of new lanthanide(III) complexes with nicotinic and isonicotinic acid N-oxides

Four new polymeric lanthanide(III) complexes of nicotinic acid N-oxide and isonicotinic acid N-oxide have been synthesized and structurally determined. In the isomorphous compounds [{Ln(L1)3 (H2O)2}n] · 4nH2O (HL1 = nicotinic acid N-oxide; Ln = Eu, 1; Ln = Er, 2) the lanthanide(III) ions form infinite double chains along the b direction through the coordination of bridging carboxylate and N-oxide groups. The chains are cross-linked through hydrogen bonds between aqua ligands and uncoordinated N-oxide groups and between aqua ligands and lattice water molecules, to form a three-dimensional network. [{Eu(L2)2(H2O)4}n](NO3)n · nH2O (HL2=isonicotinic acid N-oxide, 3) has a polymeric structure in which the europium (III) ions are connected into infinite chains by pairs of syn–syn carboxylate groups. Adjacent chains are inter-linked by hydrogen bonds between aqua ligands and N-oxide groups to form a layer parallel to the (100) plane, and such layers are connected by hydrogen bonds between nitrate anions and aqua ligands, and between oxide groups and lattice water molecules, into a three-dimensional network. In [{Er2(L2)4(H2O)10}](NO3)2 · H2O, 4, dinuclear units are inter-linked into a three-dimensional network through hydrogen bonding between aqua ligands and N-oxide groups of both bidentate bridging and unidentate L2 ligands. Factors affecting the formation of coordination chains and dinuclear units are discussed. Luminescence properties of 1 and 3 have also been studied.