Oxalato-bridged oligonuclear complexes of cadmium(II)/lead(II) with bipyridine coligands: Synthesis, crystal structure, electronic spectra, density functional theory calculation and effect of organic compounds on the fluorescence property

A trinuclear [Cd3(ox)2(bipy)5](ClO4)2 (1) and a dinuclear [Pb2(ox)(bipy)2(NO3)2(H2O)2] (2) oxalato-bridged complex, where ox = oxalate dianion and bipy = 2,2′-bipyridine, have been synthesized and characterized by elemental analysis, IR spectroscopy and X-ray crystallography. Structural determination for complex 1 reveals a cationic species of C2 symmetry having two Cd(bipy)2 fragments connected through bridging oxalate to a central Cd(bipy) unit. Complex 2 is a neutral centrosymmetric species having two Pb(bipy)(NO3)(H2O) units connecting through the bridging oxalate. The dinuclear fragments through H-bonding as well as π–π interactions result in a 2D supramolecular network. Since complex 1 exhibits intense fluorescence (λex = 284 nm, λem = 315, 329 and 356 nm) in methanol at room temperature with a fluorescence quantum yield Фs = 0.41, it was tested in association with several aromatic compounds. The results show a pronounced fluorescence quenching and enhancement in presence of nitrobenzene and m-toluidine, respectively. The outcome from DFT calculations is discussed and compared with the experimental electronic, IR spectral and X-ray structural data.