Syntheses, structures and luminescent properties of lanthanide complexes with 6-hydroxynicotinic acid

Two types of novel lanthanide complexes with the 6-hydroxynicotinic acid (OHnicH) {[Ln(OHnic)(Onic)(H2O)5·(OHnicH)]·H2O}n [Ln = La(1), Ce(2), Gd(3)] and {[Ln(OHnic)3(H2O)]·3H2O}n [Ln = La(4), Pr(5)] have been synthesized and characterized by elemental analyses, IR spectra, UV absorption spectra and single crystal X-ray diffraction. The structures of the as-prepared complexes vary with the different coordination modes of the ligands. In complexes 1–3, the adjacent metal centers are linked by the chelating-bridging tridentate modes of the ligands to form 1D chains; while in 4 and 5, the adjacent metal ions are bridged by the ligands in the chelating-bridging bidentate modes to form dinuclear units, then linked into 1D chains through the ligands in the bridging bidentate modes, and further linked to form 2D plane structures via the bridging tridentate modes of the ligands. Thermostabilities and luminescent properties of the complexes have been discussed in detail.