Synthesis of novel luminous lanthanide complexes, crystal structure, thermal decomposition mechanism and fluorescence properties

Abstract

Nine novel lanthanide complexes with 2-chlorobenzoic acid and 2,2′:6,2′'-terpyridine was synthesized in the ethanol solution. The structural formulae are [Ln (2-ClBA)3(terpy)(H2O)]2, Ln = La(1), Pr(2), Nd(3) and Ln (2-ClBA)3(terpy)(H2O), Ln = Sm(4), Eu(5), Gd(6), Tb(7), Dy(8), Ho(9), 2-ClBA= 2-chlorobenzoate, terpy= 2,2′:6′2’’-terpyridine. X-ray diffraction shows that these compounds form two types of structures: mononuclear and dimeric. Surprisingly, the complexes 4–9 have pseudo-dimeric supramolecular structures. The complexes were characterized by infrared and Raman spectroscopy. The thermal decomposition mechanism of nine complexes was studied by TG-DTG-DSC/FTIR coupling technique. Finally, the fluorescence of solid complexes 4, 5, 7, and 8 was tested, and the fluorescence lifetimes of complexes 5 and 7 are 637(6) and 331(5) μs, respectively. The fluorescence quantum yield of complex 5 is 14.3(8)%. The luminescence mechanism in terms of energy transfer is discussed.