Diversified architectures of one-dimensional zinc(II) and cadmium(II) coordination polymers incorporating bipyridyl ligands: Syntheses, structures, theoretical studies, fluorescent and nonlinear optical properties

Reactions of Zn(II)/Cd(II) salts with two bipyridyl ligands afforded four coordination polymers (CPs), [Zn(mu(2)-4,4'-pytz)(NO2)(2)](n) (1), [Cd(mu(2)-4,4'-pytz)(mu(t)-4,4'-pytz)(NO2)(2)](n) (2), [Zn(mu(2)-3,3'-pytz)(NO2)(2)](n) (3), and {[Cd(mu(2)-3,3'-pytz)(1.5)(NO2)(2)]center dot CH2Cl2}(n) (4), (4,4'-pytz = 3,6-bis(4-pyridyl)-1,2,4,5-tetrazine, and 3,3'-pytz = 3,6-bis(3-pyridyl)-1,2,4,5-tetrazine). The identities of 1-4 have been unambiguously established by single-crystal X-ray diffraction, and further characterized by Fourier-transform infrared and UV-Vis spectroscopies, elemental analysis, powder X-ray diffraction, electrospray ionization-mass spectrometry (ESI-MS) and fluorescence analysis. CPs 1 and 3 exhibit similar one-dimensional (1-D) zigzag chains containing an octahedral [ZnO4N2] unit bridged by N-donor ligands in the crystal lattice. Among them, 1 and 3 are supramolecular isomers attributing positional isomeric ligands (4,4'-pytz vs 3,3'-pytz). 2 reveals an uncommon 1-D herringbone chain, in which Cd atoms are coordinated by two chelating NO2 ligands and three 4,4'-pytz ligands, one terminal and two bridged, resulting in a pentagonal bipyramid [CdO4N3] structural motif. In 4, the 3,3'-pytz ligands adopt a trans arrangement around the Cd atom, giving a 1D ladder-like chain structure. Density functional theory and time-dependent density functional theory calculations at the B3LYP/LanL2DZ+6-31G/level were performed on compounds 1-3 to rationalize their experimental absorption spectra. The fluorescent properties of the two ligands 4,4'-pytz, 3,3'-pytz, 1-4 and also the mixture with corresponding stoichiometry between the metal salts and ligands of CPs 14 have been studied in dimethylformamide (DMF) solutions at room temperature, which revealed that CPs 1-4 exhibit blue emissions. The third-order nonlinear optical (NLO) property of 3 were also investigated. (C) 2015 Published by Elsevier B.V.