A lead(ii) supramolecular coordination polymer, obtained from polydonor N′-(amino(pyrazin-2-yl)methylene)thiosemicarbazide, stabilized by tetrel bonds and other non-covalent interactions

Abstract

We report on a new tetranuclear lead(II) complex [Pb₄L₄(NO₂)₂(MeOH)₂](ClO₄)₂ (1), which was obtained by reacting an aqueous mixture of Pb(ClO₄)₂·3H₂O and NaNO₂ with a methanolic solution of N′-(amino(pyrazin-2-yl)methylene)thiosemicarbazide (HL), yielding orange prism-like crystals suitable for single-crystal X-ray diffraction. Elemental analysis confirmed the composition of the isolated solid, while the FTIR and ¹H NMR spectroscopy data supported the structural characterization. The parent organic ligand was found to be deprotonated to L under the applied synthetic procedure. The crystal structure of complex 1 revealed a centrosymmetric tetranuclear [Pb₄L₄(NO₂)₂(MeOH)₂]²⁺ cation, comprising two distinct Pb²⁺ cations, which are N,N′,S-chelated by one monodeprotonated ligand L. The DFT calculations, combined with QTAIM analysis, suggest that the tetranuclear core is best described as a self-assembled dimer of dinuclear units linked by Pb⋯N tetrel bonds. The substantial stability of this assembly is rationalized by the MEP surface, which reveals that the ClO₄⁻ anions act as a supramolecular “glue”, bridging the cationic units via a synergistic combination of tetrel bonds and electrostatically driven N–H⋯O hydrogen bonds. Furthermore, ELF and RDG analyses unequivocally confirm the σ-hole nature of the intra- and intermolecular Pb⋯S tetrel interactions. These tetranuclear cations further self-assemble into 1D supramolecular chains through Pb⋯S and Pb⋯O_nitrite tetrel bonds. The ClO₄⁻ anions “glue” these chains via Pb⋯O tetrel bonds. The coordination polyhedra of the two crystallographically independent Pb²⁺ cations are best described as capped cube J8 or spherical-relaxed capped cube, and spherical capped square antiprism. The structure of complex 1 is reinforced by a rich variety of N–H⋯N, N–H⋯O and O–H⋯O hydrogen bonds involving NH₂ and methanol OH hydrogen atoms, forming 2D supramolecular layers.