Synthesis, structures and photoluminescence properties of mixed ligand divalent metal-organic frameworks

Three new metal-organic frameworks [Co-2(bmip)(bdc)(2)]center dot 2DMF (1), [Cu(bmip)(bdc)]center dot 6H(2)O (2) and [Zn-2(bmip)(bdc)(2)(H2O)(2)] (3) have been prepared using a solvothermal process, derived from a flexible N,N'-donor spacer 1,3-bis(2-methylimidazolyl)propane (bmip) and 1,4-benzenedicarboxylic acid (H(2)bdc) ligands. Whereas compound 1 shows a three-dimensional (3D) framework, exhibiting a pcu alpha-Po network topology, compound 2 displays a two-dimensional (2D) network structure lying parallel to the plane (1 1 -1) and shows a dia topology. The 2D layers in 2 are further linked by hydrogen bonding that involves water solvate molecules, which in turn results in an infinite 3D hydrogen bonded framework. Compound 3 on the other hand shows a three-dimensional (3D) complicated framework with zigzag chains having a ThSi2 topology. The structural features of 1-3 display diverse variations from 3D, 2D and 3D frameworks, respectively, that are entirely different for each transition metal [Co(II), Cu(II), and Zn(II)] with the same combination of mixed ligands under similar reaction conditions. The physical and chemical properties of 1-3 were investigated by single crystal X-ray diffraction, elemental analysis, FTIR spectroscopy (FTIR), thermogravimetric analysis (TGA) and photoluminescence properties.