Syntheses, molecular and crystalline architectures, and luminescence behaviour of terephthalate bridged heptacoordinated dinuclear lead(II) complexes containing a pentadentate N-donor Schiff base

Abstract

One-pot synthesis using a 2:2:1:2 molar ratio of Pb(OAc)2·3H2O, L, piperidinum terephthalate (ptp) and NaClO4/NH4PF6 at room temperature affords two dinuclear compounds of the type [Pb2(L)\(_{2}(\upmu \)-tp)](ClO4/PF6)2 (1/2) [L=N,N′-(bis-(pyridin-2-yl)benzylidene)diethylenetriamine and tp = terephthalate dianion]. The compounds are characterized by microanalytical, spectroscopic, thermal and other physicochemical results. X-ray structural analyses of 1 and 2 reveal that each heptacoordinated lead(II) centre with a PbN5O2 chromophore are bound by five N atoms of L and connected through O atoms of a bis(bidentate) tp bridge. The arrangements of L and tp suggest a gap around the metal centre due to occupation of a stereo-active lone pair of electrons reflecting a hemidirected coordination around the metal centre. The complexes exhibit reasonable thermal stabilities with the tolerate temperatures ca. 255°C for 1 and 263°C for 2. The complexes display intraligand (π-π*) fluorescence in the solid state and in DMF solutions at room temperature. Two dinuclear lead(II) compounds are isolated and X-ray crystallographically characterized. Each heptacoordinated metal(II) center adopts a hemidirected environment and connected through bis(bidentate) terephthalate bridge. The complexes exhibit intraligand 1(π-π*) fluorescence in the solid state and in DMF solutions at room temperature.