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), [Pb2(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 Hssal2- 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 Hssal2- chelate to PbII 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 PbII 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 π−π stacking interactions can be
observed in complexes 1−3, whereas there is no such interaction in complex 4. The coordination spheres of PbII
ions in 1−4 are controlled by three factors:  the activity of a lone pair of electrons, weak Pb−O interactions, and
π−π stacking interactions. The PbII 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 PbII 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).