Synthesis, crystal structures, photophysics and computational study of a series of luminescent Pb2+ compounds bearing various functionalized diimine ligands

A series of luminescent Pb2+ complexes, [Pb(L1)(N3)2]n (1), [Pb(L2)(OAc)2]2 (2), [Pb(L3)]n (3), [Pb(L4)(H2O)]n(4), [Pb(L5)(Cl)(H2O)]2 (5), where L1 = pyrazino[2,3-f][1,10]phenanthroline, L2 = dipyrido[3,2-a:2′,3′-c]phenazine, H2L3 = 1,10-phenanthroline-2,9-dicarboxylic acid, H2L4 = 2,2′-bipyridine-6,6′-dicarboxylic acid, HL5 = 2,2′-bipyridine-6-carboxylic acid, have been synthesized by treatment of the polydentate ligands with various hydrated Pb2+ salts. These complexes have been characterized by IR, TGA and elemental analysis. Their crystal structures have been determined by X-ray crystallography and the phase purity of the bulk samples were further confirmed by PXRD. Different architectures, including discrete, linear, layer and 3-D supramolecular networks, are observed in these compounds. The solid-state UV–visible reflectance spectra and luminescence of these complexes have been investigated in detail at room temperature. The emissions of these compounds have different origins, which are dependent on the coordination modes, coordination number and the ancillary ligands. To decipher the emission origin, DFT calculations have also been carried out based on the asymmetric units in the crystal structures of these compounds.