Lead(II) compounds with 2-acetylpyridine benzoylhydrazone: synthesis and molecular structure – arene η2-C2 and tetrel bonding

Four Pb(II) complexes with a hydrazone ligand obtained from 2-acetylpyridine and benzhydrazide were prepared by using Pb(II) acetate, nitrate and carbonate salts: [Pb(HL)2(NO3)2] (1), [Pb(L)(CH3CO2)]n (2), [Pb(L)2]n (3), and [Pb(L)(NO2)]n (4). Compound 4 was obtained from reaction of Pb(II) nitrate and addition of nitrite. Pb(II) carbonate reacts only by heating in N,N-dimethylformamide, producing compound 3. Structural analysis by single-crystal X-ray diffraction reveals that compound 1 exhibits a holodirected geometry with the ligand coordinated in its neutral form, whereas compounds 2–4 display hemidirected geometries with stereochemically active lone pairs and anionic hydrazonate ligands. The supramolecular architectures of these complexes are stabilized by non-covalent interactions, including hydrogen bonds and tetrel bonds. DFT calculations (MEP, QTAIM, and NCIplot) were employed to analyze the self-assembled dimers of the homoleptic complex 3 and its polymorph 3A. The theoretical results corroborate the existence of Pb•••N(azomethine) tetrel bonds in compound 3 and uncover a novel Pb•••η2-C2(arene) interaction in polymorph 3A and 4. For compound 4, the analysis additionally identifies the formation of strongly bound antiparallel π-stacked dimers driven by electrostatic complementarity. Energetic analysis indicates significant dimerization energies for these assemblies, highlighting the crucial role of these specific non-covalent interactions in the crystal packing. The compounds were further characterized by elemental analysis, FT-IR, NMR and diffuse reflectance spectroscopies.