Tetracarboxylato-bridged copper(II) complexes with ancillary N-chelating ligands: Syntheses, crystal structures and effect of aromatic compounds on the fluorescence property

Two Cu(II) complexes [Cu2(1,10-phen)2(H2O)4(cbtc)].6H2O (1) and {[Cu2(2,20-bipy)2(cbtc)].6H2O}n (2) [1,10-phen = 1,10-phenanthroline; 2,20-bipy = 2,20-bipyridine; cbtc = 1,2,3,4-cyclobutane tetracarboxylate tetraanion], were synthesized and characterized by elemental analysis, IR, single crystal X-ray crystallography and thermal analysis. The structural determination reveals that complex 1 is dinuclear, while 2 is a 1Dpolymeric chain built by a bridging cbtc ligand. Hydrogen bonding interactions, formed by coordinated and/or lattice water molecules with cbtc oxygens, lead to a supramolecular architecture in both structures. Complex 1, which exhibits intense fluorescence (kex = 262 nm, kem = 358 and 373 nm) at room temperature, was tested with several aromatic compounds, such as m-toluidine, aniline, nitrobenzene, etc. in MeOH– CHCl3 (1:1) solution. The results show that a pronounced fluorescence quenching and enhancement is observed in the presence of nitrobenzene andm-toluidine, respectively. Thermogravimetric analysis shows that complex 2 undergoes a reversible deaquation–rehydration process.