Rational synthesis and functionalization of metal assemblies using a new unsymmetric bridging ligand

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In this research, hexanuclear cyclic assemblies have been prepared by a new bridging ligand having factors of structural restriction.A new unsymmetric bridging ligand 3-[1-(2-pyridyl)-3, 5-dimethylpyrazole-4-yl]-3, 5-pentane-dione (HL) was prepared. This ligand has two dissimilar metal-binding sites ('acac' and 'pypz' sites) which are forced to be perpendicular to each other due to steric hindrance of four methyl groups and the binding angle is nonlinear to form an angle of ca. 120°. Reaction of HL and CuX_2・nH_2O (X= ClO_4^-, BF_4^-) in the 1 : 1 molar ratio has given copper (II) assemblies {[Cu (L)(H_2O)] X・nH_2O}_6. These complexes have essentially same structure where the Cu (II) adopts a square-pyramidal geometry with a N_2O_2 equatorial plane formed by the 'acac' site of one ligand and the 'pypz' site of another ligand and coordination water at the axial site. And the hexanuclear cyclic structure was constructed by the six times repeat of the asymmetric unit having a cavity of di … More ameter of 17.2 Å. In the bulk, 1-D channel structure was formed by stacking of the hexagonal units. Counter anion and lattice water molecules were located between hexanuclear units, which formed an alternate arrangement of two kinds of phases. However, their packing structure was so fragile against a dehydration treatment owing to the phase structure. Although PXRD results showed that the packing arrangement was reconstructed by hydration and the hexagonal cyclic structure was maintained even after dehydration, gas adsorption ability of these complexes was not so remarkable.In order to reinforce the channel structure and to improve the gas adsorption ability, trimethoxybenzene (TMB) adduct, {[Cu (L)(H_2O)] ClO_4・4H_2O・1/3TMB}_6 was prepared. This compound maintained the original 1-D channel structure with mostly similar lattice parameters. TMB molecules were located on three-screw axis and filled the gap between hexanuclear cyclic units PXRD results showed stability against dehydration treatment, which suggests that TMB molecules sustained the packing structure as pillars. The estimation of gas adsorption ability of the TMB adduct is now in progress. Less