Lead(ii) supramolecular structures formed through a cooperative influence of the hydrazinecarbothioamide derived and ancillary ligands

In this work, we report on new heteroleptic coordination compounds, [Pb-2(L-I)(2)](NO3)(2)center dot 2MeOH (1), [Pb-2(L-II)(2)](NO3)(2) (2), [Pb-2(L-III)(2)](NO3)(2)center dot MeOH center dot H2O (3) and [Pb-2(L-III)(2)(H2O)](NCS)(2) (4), which were obtained through self-assembly of 2-(amino(pyridin-2-yl)methylene)hydrazine-1-carbothioamide (HLI), 2-(amino(pyrazin-2-yl)methylene)hydrazine-1-carbothioamide (HLII) or 2-(amino(pyridin-2-yl)methylene)-N-methylhydrazine-1-carbothioamide (HLIII) with Pb(NO3)(2) or a mixture of Pb(ClO4)(2) and KNCS, respectively. In all the obtained complexes, the lead(ii) cation is N,N ',S-chelated by the tridentate pincer type monodeprotonated ligand LI-III. In addition to the thiosemicarbazone chelation, the sulfur atom in each structure acts as a bridge connecting two [Pb(LI-III)](+) units to form a dinuclear dimeric species having a centrosymmetric geometry, so that the ligands are directed either at different, in 1 and 2, or the same, in 3 and 4, sides of the coplanar Pb2S2 core. In the latter structures, two metal centers are additionally linked with each other through the oxygen atom of the bridging water molecule. The dimeric units in 1-4 are further linked through the Pb-N tetrel bonds, yielding 1D supramolecular polymeric chains, which, in turn, are interlinked though a myriad of other intermolecular noncovalent interactions, including tetrel bonds, hydrogen bonds and pi-stacking. Counterions (NO3- and NCS-) and co-crystallized solvent molecules (MeOH and H2O) are also responsible in the further stabilization of the overall crystal packing of the obtained complexes as sources of either tetrel and/or hydrogen bonds. The observation of the recurrent tetrel bonds in compounds 1-4 has been rationalized using DFT calculations and molecular electrostatic potential (MEP) surface plots. Moreover, coordination bonds (covalent character) and tetrel bonds (noncovalent character) between the complexes and their counterions (and water molecules) have been differentiated using the quantum theory of atoms-in-molecules (QTAIM) and the noncovalent interaction index (NCI index) computational methods.

Automated summary

In this work, new heteroleptic coordination compounds were synthesized using various ligands and lead ions, forming complex structures with diverse intermolecular interactions. The observation and differentiation of tetrel bonds and coordination bonds in the complexes were analyzed through computational methods, providing insights into the structural and bonding characteristics of the compounds.