Metallic coordination selectivity effect in the trinuclear M-3(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)center dot 2DMF (1), Mn-3(BDC)(3)(DMF)(4) (2) and Co-3(BDC)(3)(DMF)(2)(py)(2) (3) [H2BDC = 1,4-benzene dicarboxylic acid, py = pyridine, DMF = N,N'-dimethylformamide], have been synthesized by reaction of the M(NO3)(2) and H2BDC 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)(LT)(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 pi-bonding orbital of BDC2- are transferred to the pi*-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.