Supramolecular coordination polymers, obtained from multidentate N′-benzoylpyrazine-2-carbohydrazonamide and a variety of salts PbX2 (X = Cl− , NO3 − , NO2 − , SCN− ), derived from tetrel and other noncovalent bonds

Abstract

Four lead(II) complexes, [Pb(HL)Cl2] (1), [Pb(HL)2(NO3)2] (2), [PbL(NO2)] (3) and [PbL(NCS)(H2O)]·H2O (4·H2O), were synthesized from PbX₂ salts and the ligand N′-benzoylpyrazine-2-carbohydrazonamide (HL). Spectroscopic characterization confirmed that complexes 1 and 2 contain the neutral ligand (HL), while 3 and 4·H2O feature its deprotonated form (L). In all structures, the Pb2+ center is N,N′,O-chelated by the ligand. Bond length analysis revealed the longest Pb–N/O bonds in 2 due to coordination of two neutral HL ligands, whereas the deprotonated L− in 3 and 4·H2O resulted in shorter Pb–Nimine and Pb–Ocarbonyl bonds. Secondary Pb⋯X tetrel bonds (X = Cl, N, O, S) form in complexes 1, 3, and 4·H2O due to coordination sphere gaps, leading to supramolecular 1D chains (1, 4·H2O) or a 2D sheet (3). These assemblies are further stabilized by extensive hydrogen bonding and π⋯π stacking interactions. The nature of the tetrel bonds was investigated using MEP surface analysis, dimerization energy calculations, and quantum chemical tools (QTAIM, NCIplot). Electron localization function (ELF) and Laplacian maps differentiated tetrel bonds from primary coordination bonds, and the energy contributions of coexisting tetrel and hydrogen bonds were quantified.