Metallic coordination selectivity effect in the trinuclear M3(RCOO)6 secondary building units of three layer metal–carboxylate frameworks

摘要

Three two-dimensional metal–carboxylate frameworks (MCFs), namely Zn _(3) (BDC) _(3) (py) _(2) ·2DMF ( 1 ), Mn _(3) (BDC) _(3) (DMF) _(4) ( 2 ) and Co _(3) (BDC) _(3) (DMF) _(2) (py) _(2) ( 3 ) [H _(2) BDC = 1,4-benzene dicarboxylic acid, py = pyridine, DMF = N , N ′-dimethylformamide], have been synthesized by reaction of the M(NO _(3) ) _(2) and H _(2) BDC with py as base and DMF as solvent, under the microwave-assisted solvo-thermal conditions. Three MCFs were characterized by single crystal X-ray diffraction and mensurated its fluorescent or magnetic behaviors. The structural analyses reveal that 1–3 are constructed of the slightly dissimilar carboxylate bridged linear M _(3) (RCOO) _(6) (L _(T) ) _(2/4) clusters where the coordination terminal ligand (L _(T) ) are py in 1 , DMF in 2 and py/DMF in 3 , respectively. The results demonstrated the different metal ions in two side of every SBU inclined to coordinate their respectively selected L _(T) . The time-dependent density functional theory (TDDFT) calculations of 1 show that the emission peak of 423–428 nm (the experimental value is 425 nm) might be derived from the energy transition on the ligand-to-ligand charge transfer (LLCT) where electron densities residing on the π-bonding orbital of BDC ~(2?) are transferred to the π*-anti-bonding orbital of pyridine. Variable-temperature magnetic susceptibility studies indicate the presence of antiferromagnetic exchange coupling within the M _(3) -units of 2 and 3 .