Mixed-ligand coordination polymers from 1,2-bis(1,2,4-triazol-4-yl)ethane and benzene-1,3,5-tricarboxylate: Trinuclear nickel or zinc secondary building units for three-dimensional networks with crystal-to-crystal transformation upon dehydration

摘要

The hydrothermal reaction of M(NO3)(2)center dot 6H(2)O (M = Ni and Zn) with benzene-1,3,5-tricarboxylic acid (H(3)btc) and 1,2-bis(1,2,4-triazol-4-yl)ethane (btre) produced the mixed-ligand coordination polymers (MOFS)(3)(infinity) {[Ni-3(mu(3)-btC)(2)(mu(4)-btre)(2)(mu-H2O)(2)]center dot similar to 22H(2)O} (1) and (3) (infinity){[Zn-3(mu(4)-btC)(2)(mu(4)-btre)(H2O)(2)]center dot 2H(2)O} (3). The compounds, characterized by single-crystal X-ray diffraction, X-ray powder diffraction and thermoanalysis feature trinuclear secondary building units (SBU) within the three-dimensional frameworks. The trinuclear nickel unit in 1 exhibits an intra-trimer together with some weak inter-trimer antiferromagnetic coupling with J = - 13.88(8) cm(-1) from the magnetic susceptibility measurement between 1.9-300 K. The zinc coordination polymer 3 shows a strong fluorescence at 423 nm upon excitation at 323 nm (not seen in the free btre ligand). Compound 3 is thermally robust until 200 degrees C (ambient pressure) where loss of the water molecules starts. Careful control of the dehydration procedure (freeze-drying) for 1 and (heating to 280 degrees C) for 3 allowed for a solid-state reaction with single-crystal-to-single-crystal structural transformations in obtaining the largely dehydrated products (3)(infinity){[Ni-3(mu(2)-btc)(2)(mu(4)-btre)(2)(mu-H2O)(2)(H2O)(2)]center dot 4H(2)O} (2) and (3)(infinity){[Zn-3(mu(6)-btC)(2)(mu(4)-btre)(2)]center dot similar to 0.67H(2)O} (4), respectively. In the transformation from 1 to 2 the unit cell volume is reduced to about 60%. The transition from 3 to 4 involves breakage and formation of new Zn-O bonds.