New lead(II) complexes with N,S-ligands, including a lead pyrazolonate with unusual packing flexibility

The reaction of lead(II) acetate in methanol with thiosemicarbazones derived from β-keto esters and β-keto amides (HTSCs) afforded two lead(II) thiosemicarbazonates and numerous homoleptic ([PbL2]) and/or heteroleptic ([Pb(OAc)L]) complexes containing deprotonated pyrazolones L− formed by metal-induced cyclization of the starting HTSC ligands. All the complexes isolated were characterized by IR spectroscopy in the solid state and by 1H and 13C NMR spectroscopy in DMSO solution; in addition, crystals containing [Pb(L6)2] and [Pb(L7)2] were examined by X-ray crystallography. [Pb(L6)2] · 0.5H2O · 0.3MeOH (HL6 = 4-ethyl-2,5-dihydro-3-methyl-5-oxo-1H-pyrazole-1-carbothiamide) showed three types of molecule with significant structural differences that appear to be determined by packing interactions. In all three molecules the Pb⋯Pb distances are very short [3.6096(8)–3.7562(8) Å], but density-functional-theoretic calculations at the B3LYP level do not support the existence of Pb–Pb bonds. In [Pb(L7)2] (HL7 = N-ethyl-2,5-dihydro-3-methyl-5-oxo-1H-pyrazole-1-carbothiamide) all the molecules are of a single type, and they are linked in a three-dimensional network by weak intermolecular Pb⋯O bonds.

New lead(II) complexes with N,S-ligands including a lead pyrazolonate with unusual packing flexibility Lead(II) pyrazolonate complexes obtained from thiosemicarbazone ligands are reported. An X-ray study on a lead(II) pyrazolonate complex suggests that the crystal packing forces can decisively influence the primary and secondary metal–ligand interactions.Figure optionsDownload as PowerPoint slide