The tetrel bonding role in supramolecular aggregation of lead(II) acetate and a thiosemicarbazide derivative

Abstract

A new PbII coordination complex [PbL(OAc)], which was readily synthesized from a mixture of Pb(OAc)2·3H2O and 1-(pyridin-2-yl)benzylidene-4-phenylthiosemicarbazide (HL ) is reported. The crystal structure analysis of [PbL(OAc)] showed that the PbII cation is N,N′,S-chelated by the tridentate pincer-type ligand L and by the oxygen atoms of the acetate anion. In addition, the metal centre forms Pb...O and Pb...S tetrel bonds with an adjacent complex molecule, yielding a 1D zigzag polymeric chain, which is reinforced by N—H...O hydrogen bonds and π...π interactions. These chains are interlinked by C—H...py non-covalent interactions, realized between one of the acetate hydrogen atoms and the pyridine rings. According to the Hirshfeld surface analysis, the crystal packing is mainly characterized by intermolecular H...H, H...C and H...O contacts, followed by H...N, H...S, C...C, C...N, Pb...H, Pb...O and Pb...S contacts. The FTIR and 1H NMR spectra of [PbL(OAc)] testify to the deprotonation of the parent ligand HL , while the acetate ligand exhibits an anisobidentate coordination mode as established by means of single-crystal X-ray diffraction and FTIR spectroscopy. Lastly, theoretical calculations at the PBE0-D3/def2-TZVP level of theory have been used to analyze and characterize the Pb...O and Pb...S tetrel bonds observed in the crystal of [PbL(OAc)], using a combination of QTAIM (Quantum Theory of Atoms in Molecules) and NCIPlot (Non-Covalent Interaction Plot) computational tools.

Transition between the Noncovalency and Covalency of σ–Hole Bonds

“…Whereas the interaction energies with the anions exceed 20 kcal/mol with ρ BCP as high as 0.03 au, those involving neutral NH 3 were limited to 6 kcal/mol, and the density was well below 0.02 au. Within the framework of observed crystal structures, when placed within a tetracoordinated framework that includes one O of a carboxylate group, the Pb atom keeps the second O atom of the carboxylate group 0.25 Å further than the first . The BCP density of this noncovalent bond is 0.025 au, compared to 0.059 au for the closer O, and the energy density H is positive compared to a negative H for the latter.…”

“…Within the framework of observed crystal structures, when placed within a tetracoordinated framework that includes one O of a carboxylate group, the Pb atom keeps the second O atom of the carboxylate group 0.25 Å further than the first. 74 The BCP density of this noncovalent bond is 0.025 au, compared to 0.059 au for the closer O, and the energy density H is positive compared to a negative H for the latter. The same sort of longer Pb••N distance occurs also 75 when all four covalent substituents around the Pb are close together, all in the same hemisphere.…”

An extended supramolecular coordination compound produced from PbCl2 and N′-isonicotinoylpicolinohydrazonamide

“…With all this in mind and in continuation of our comprehensive studies in the coordination chemistry of the hemidirected Pb 2+ architectures as well in shedding light on the role of noncovalent interactions in the formation of extended structures, [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53] herein we have focused our attention on the coordination properties of N′isonicotinoylpicolinohydrazonamide (HL), 54 which was intentionally designed to serve as a potential bridging ligand, in the reaction with PbCl 2 .…”

Factors contributing to halogen bond strength and stretch or contraction of internal covalent bond

“…The halogen bond (XB) [52][53][54][55][56][57] is one of a family of noncovalent bonds, including also chalcogen, pnicogen, and tetrel bonds, [58][59][60][61][62][63][64][65] in which the bridging proton of the HB is replaced by any of a large group of other elements. Because most of the halogen atoms are more electronegative than H, one cannot assign an overall positive charge to X as one can for H. Nonetheless, there is a high degree of anisotropy of electron density around X, which leads in turn to a positive region of the electrostatic potential that is focused along the extension of the A-X bond.…”