Syntheses, structures and photophysical properties of Ni/Co-Ln coordination polymers

The new Ni/Co-Ln coordination polymers (CPs), {[LnNi0.5(2,5-pydc)(ox)(H2O)x]& sdot;yH2O}n (Ln = Pr 1, Nd 2, x = 4, y = 2; Gd 3, Tb 4, Dy 5, x = 3, y = 1; 2,5-H2pydc = pyridine-2,5-dicarboxylic acid, H2ox = oxalic acid); {[Er2Ni (2,5-pydc)3(ox)(H2O)4]& sdot;2H2O}n 6; {[LnCo0.5(2,5-pydc)(ox)(H2O)x]& sdot;yH2O}n (Ln = Pr 7, Nd 8, x = 4, y = 2; Tb 9, x = 3, y = 5) were successfully synthesized by the hydrothermal methods, and their crystal structures were characterized by single-crystal X-ray diffraction. With the participation of the auxiliary ligands (ox2-), the main ligands (2,5-pydc2-) adopt four coordination modes and make these polymers exhibit three kinds of crystal structures. CPs 1, 2, 7 and 8 are isomorphous and exhibit 2D layers which are further connected to form the 3D structure by hydrogen bonds. The other four CPs are bridged into the 3D network structure by 2,5-pydc2- and ox2-. All the polymers are characterized by IR spectro, Roman spectro, thermogravimetric analysis and X-ray powder diffraction. The UV-vis-NIR absorption spectra and Vis fluorescence excitation and emission spectra of nine coordination polymers are measured and analyzed. All the CPs show ligand-to-metal charge transfer (LMCT) transition emission of NiII/CoII-ligands, while some of the CPs show weak characteristic luminescence of LnIII ions.