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

Three new metal-organic frameworks [Co₂(bmip)(bdc)₂]·2DMF (1), [Cu(bmip)(bdc)]·6H₂O (2) and [Zn₂(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 (H₂bdc) ligands. Whereas compound 1 shows a three-dimensional (3D) framework, exhibiting a pcuα-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.