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

•Two oxalato-bridged oligonuclear complexes of Cd(II)/Pb(II) have been synthesized and structurally characterized.•Electronic and IR spectral results compared with DFT and TD-DFT results.•Effects of aromatic compounds on fluorescence property have been investigated.

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.

Graphical abstractTwo oxalato-bridged oligonuclear Cd(II)/Pb(II) complexes with N donor neutral ligand have been synthesized and characterized. The IR and electronic spectral properties of complexes are explained by DFT computation using optimized geometries. Cd(II) compound is fluorescent when dissolved in MeOH and the effects of various organic compounds on its fluorescence property has been investigated.Figure optionsDownload full-size imageDownload as PowerPoint slide