Zinc and cadmium metal-directed coordination polymers: in situ flexible tetrazole ligand synthesis, structures, and properties

Seven zinc and cadmium coordination frameworks, {[Zn-2(TE)(2)]center dot H2O} (1a); {[Cd-2(TE)(SO4)(OH)(H2O)]} (1b); TE = 2-(1H-tetrazol-5-yl)-ethanol, {[Zn-1.5(TA).INA)]center dot 4H(2)O} (2a); {[Cd-4.5(TA)(3)(N-3)(OH)(2)(H2O)(2)]center dot H2O} (2b); {[Zn(MT)(INA)]center dot H2O} (2c); TA = (1H-tetrazol-5-yl)-acetic acid, MT = 5-methyl-tetrazole, INA = isonicotinic acid, {[Cd(BTMA)]center dot H2O} (3a); [Cd-2(TTMA)(OH)] (3b); BTMA = bis-(1H-tetrazol-5-ylmethyl)-amine; TTMA = tris-(1H-tetrazol-5-ylmethyl)-amine, were obtained through in situ tetrazole synthesis and have been structurally characterized by single crystal and powder X-ray diffraction, as well as elemental analyses, FTIR spectroscopy and thermal studies. Interestingly, by varying the reaction conditions of hydrothermal synthesis, the unprecedented in situ generation of TA and MT for 2 based on cyanoacetamide or BTMA and TTMA for 3 based on iminodiacetonitrile was observed, respectively. Compound 1a represents a very interesting example of three-dimensional (3D) frameworks containing hexagonal channels and meso-helical chains (P + M) alternately trapped by Zn-TE coordination interactions; compound 1b possesses a two-dimensional (2D) layered structure constructed from infinite organic chains and sulfate anions. Compounds 2a and 2b both crystallize in 3D frameworks containing infinite rod-shaped SBUs; compound 2c displays a two-fold diamondoid network constructed by the interconnection of Zn-MT-INA honeycomb layers and INA ligands. Compound 3a shows a 3D framework consisting of cyclic [Cd-2(BTMA)(2)] dimer subunits, possessing an 8-connected network topology. Compound 3b shows a 3D binodal (4,8)-connected net based on tetranuclear [Cd4O2] polyoxometalates (POMs) as nodes. Furthermore, the luminescence properties of these compounds were investigated. Notably, compound 1b crystallizes in an acentric space group representing significant second harmonic generation (SHG) efficiencies.