Synthesis, structural diversities and properties of a series of transition metal-organic frameworks based on asymmetric dicarboxylic acid and N-donor auxiliary ligand

Four new metal-organic frameworks, namely, [Zn(pimb)(hpht)]·H2O (1), Cd(pimb)0.5(hpht)(H2O) (2), [Co(pimb)(hpht)(H2O)2]·H2O (3) and [Ni(pimb)(hpht)(H2O)2]·H2O (4), (pimb = 1,4-bis(imidazol-1-yl-methyl)benzene, H2hpht = homophthalic acid) have been synthesized by using hydrothermal method based on mixed ligands of asymmetric dicarboxylate and N-donor auxiliary ligand. The networks show diverse structures and coordination modes at the metal ions. Complex 1 is a 2D corrugated network bridged by Csingle bondH···O hydrogen bond to generate a 3D framework, whereas the complex 2 features rare (3,4)-connected V2O5 topological net and stacks to give a 3D structure by Csingle bondH···π interactions. Complexes 3 and 4 are isomorphous and isostructural, where the X–H···π (X = C, O) interactions exist and stabilize the stack of their (4,4)-topological network. The factors causing structural diversities are discussed. The TGA and XPRD patterns as well as photoluminescent properties of complexes 1 and 2 are also studied in the solid state at room temperature.