Syntheses, structures, and luminescence behavior of terephthalate bridged lead(II) complexes with tetradentate N-donor Schiff bases

Three dinuclear compounds of the types [Pb2(L1)2(μ-tp)](ClO4)2 (1) and [Pb2(L2)2(μ-tp)](ClO4/PF6)2 (2/3) [L1 = N,N′-(bis-(pyridin-2-yl)formylidene)-1,2-ethanediamine; L2 = N,N′-(bis-(pyridin-2-yl)benzylidene)-1,2-ethanediamine and tp = terephthalate dianion] have been synthesized using one-pot reactions of 2:2:1:2 M ratio of Pb(OAc)2⋅3H2O, L1/L2, piperidinium terephthalate (ptp) and appropriate counter anions in MeOH at room temperature. Compounds 1–3 are characterized on the basis of microanalytical, spectroscopic, thermal and other physicochemical results. X-ray structural analyses of 1–3 reveal each six-coordinated lead(II) center with PbN4O2 chromophore to be bound by four N atoms of L1 in 1 and L2 in 2 and 3 and connected through O atoms of a bis(bidentate) tp bridge. The arrangements of L1/L2 ligand and the tp dianion suggest a void around the metal center presumably occupied by a stereoactive lone pair of electrons that reflect a hemidirected coordination around the metal center. The complexes exhibit reasonable thermal stabilities. In solid states, L1, L2, ptp and 1 display intraligand π → π* fluorescence and 1–3 show ligand-to-metal charge transfer at room temperature.