Syntheses, structures, and characterizations of four new lead(II) 5-sulfosalicylate complexes with both chelating and bridging neutral ligands

Four structurally diverse complexes, {[Pb(Hssal)(2,2'-bipy)](4,4'-bipy)(0.5)}(n) (1), [Pb-2(Hssal)(2)(2,2'-bipy)(2)(4,4'-bipy)(H2O)(2)] (2), [Pb(Hssal)(phen)(4,4'-bipy)(0.5)](n) (3), and [Pb(Hssal)(2,2'-bipy)(bpe)(0.5)](n) (4), have been synthesized and characterized by elemental analyses, IR, thermogravimetric analyses, fluorescent spectra, and single-crystal X-ray analyses, where Hssal(2-) is doubly deprotonated 5-sulfosalicylate, 2,2'-bipy is 2,2'-bipyridine, phen is 1,10-phenanthroline, 4,4'-bipy is 4,4'-bipyridine, and bpe is trans-1,2-bis(4-pyridyl)ethylene. The structure of complex 1 possesses a one-dimensional ladderlike chain with guest 4,4'-bipy molecules, while the molecular structure of complex 2 is a dimeric species with a coordinating 4,4'-bipy ligand. Complex 3 consists of a one-dimensional ladderlike chain with monodentate 4,4'-bipyridine but somewhat different from that of complex 1. Complex 4 is a two-dimensional layer structure. In 1-4, all 5-sulfosalicylates are doubly deprotonated, and all carboxylate groups of Hssal(2-) chelate to Pb-II ions; however, the coordination modes of sulfonyl groups are different: syn-syn bridging in 1, noncoordinating in 2, syn-skew bridging in 3, and one-atom bridging in 4. The noncoordinating mode of sulfonate in Pb-II complexes containing 5-sulfosalicylate is first reported in this presentation. The 4,4'-bipy ligands act as guest molecules in 1, dimeric linkers in 2, and monodentates in 3. The pi-pi stacking interactions can be observed in complexes 1-3, whereas there is no such interaction in complex 4. The coordination spheres of Pb-II ions in 1-4 are controlled by three factors: the activity of a lone pair of electrons, weak Pb-O interactions, and pi-pi stacking interactions. The Pb-II lone pair in 4 is inactive, whereas in 1-3, they are stereochemically active. The thermal stability and fluorescent property of complexes 1-4 are different from those of Pb-II complexes only containing chelating ligands, [Pb(Hssal)(2,2'-bipy)(DMF)](n) (5), and [Pb(Hssal)(2,2'-bipy)(H2O)](n) (6), and [Pb(Hssal)(phen)(DMF)](n) (7).