Tetrel bonding and other non-covalent interactions assisted supramolecular aggregation in a new Pb(II) complex of an isonicotinohydrazide

A new supramolecular Pb(II) complex [PbL(NO₂)]_n was synthesized from Pb(NO₃)₂, N’-(1-(pyridin-2-yl)ethylidene)isonicotinohydrazide (HL) and NaNO₂. [PbL(NO₂)]_n is constructed from discrete [PbL(NO₂)] units with an almost ideal N₂O₃ square pyramidal coordination environment around Pb(II). The ligand L⁻ is coordinated through the 2-pyridyl N-atom, one aza N-atom, and the carbonyl O-atom. The nitrite ligand binds in a κ²-O,O coordination mode through both O-atoms. The Pb(II) center exhibits a hemidirected coordination geometry with a pronounced coordination gap, which allows a close approach of two additional N-atoms arising from the N=C(O) N-atom of an adjacent molecule and from the 4-pyridyl N-atom from the another adjacent molecule, yielding a N₄O₃ coordination, constructed from two Pb–N and three Pb–O covalent bonds, and two Pb· · · N tetrel bonds. Dimeric units in the structure of [PbL(NO₂)]_n are formed by the Pb· · · N=C(O) tetrel bonds and intermolecular electrostatically enforced π⁺· · · π⁻ stacking interactions between the 2- and 4-pyridyl rings and further stabilized by C–H· · · π intermolecular interactions, formed by one of the methyl H-atoms and the 4-pyridyl ring. These dimers are embedded in a 2D network representing a simplified uninodal 3-connected fes (Shubnikov plane net) topology defined by the point symbol (4·8²). The Hirshfeld surface analysis of [PbL(NO₂)] revealed that the intermolecular H· · · X (X = H, C, N, O) contacts occupy an overwhelming majority of the molecular surface of the [PbL(NO₂)] coordination unit. Furthermore, the structure is characterized by intermolecular C· · · C and C· · · N interactions, corresponding to the intermolecular π· · · π stacking interactions. Notably, intermolecular Pb· · · N and, most interestingly, Pb· · · H interactions are remarkable contributors to the molecular surface of [PbL(NO₂)]. While the former contacts are due to the Pb· · · N tetrel bonds, the latter contacts are mainly due to the interaction with the methyl H-atoms in the π· · · π stacked [PbL(NO₂)] molecules.

www.mdpi.com/journal/molecules to both the Pb· · · N tetrel bonds and the dimer forming π⁺· · · π⁻ stacking interactions. Quantum theory of atoms in molecules (QTAIM) analyses underlined the tetrel bonding character of the Pb· · · N interactions. The manifold non-covalent interactions found in this supramolecular assembly are the result of the proper combination of the polyfunctional multidentate pyridine-hydrazide ligand and the small nitrito auxiliary ligand.