Anion driven tetrel bonding dictated supramolecular architectures of lead(ii) with a zwitterionic form of polydentate N′-(piperidine-1-carbonothioyl)picolinohydrazonamide

Abstract

Two novel supramolecular heteroleptic complexes [Pb₂L₂(NO₃)₂]_n (1) and {[Pb₃L₃](ClO₄)₃}_n·3.25nH₂O (2·3.25nH₂O), obtained from N′-(piperidine-1-carbonothioyl)picolinohydrazonamide (HL) and Pb(NO₃)₂ or Pb(ClO₄)₂ in aqueous methanol are reported. A crucial role of the auxiliary ligand (NO₃⁻vs. ClO₄⁻) was revealed as a driving force for the formation of the resulting architecture of complexes, which, in turn, are dictated by the formation of tetrel bonds. Complex 1 is constructed from heteroleptic dinuclear centrosymmetric species [Pb₂L₂(NO₃)₂], which, in turn, are formed from the heteroleptic mononuclear symmetry related [PbL(NO₃)] units, linked through a pair of bonds formed between the metal cations and the thioamide nitrogen atoms. The metal cations form a weaker tetrel bond with the symmetry related nitrate atoms, yielding a 1D polymeric chain structure. These chains are interlinked through N–H⋯O hydrogen bonds, formed between the covalently coordinated nitrate oxygen atom and the NH₂ hydrogen atom, yielding a 2D supramolecular architecture. Complex 2·3.25nH₂O is constructed from the trinuclear species [Pb₃L₃](ClO₄)₃. The trinuclear cation is constructed from three [PbL]⁺ cations interlinked through two Pb–S and two Pb–N bonds, formed with the thiocarbonyl sulfur atoms and the amide nitrogen atoms. The cations [Pb₃L₃]³⁺ are interlinked through two Pb–N and two Pb–S bonds yielding a 1D supramolecular polymeric cationic chain {[Pb₃L₃]³⁺}_n. The two metal cations corresponding to two [PbL]⁺ units, linked through a pair of the Pb–S bonds, are additionally bridged by two oxygen atoms of one of the perchlorate anions with the formation of two Pb⋯O tetrel bonds. The coordination spheres of the metal cations are filled by one of the oxygen atoms of two different perchlorate anions with the formation of tetrel bonds. One of these perchlorates also forms the N–H⋯O hydrogen bond within the trinuclear unit [Pb₃L₃](ClO₄)₃. 1D supramolecular chains {[Pb₃L₃]³⁺}_n are interlinked through a myriad of hydrogen bonds formed by the perchlorate anions and crystallized water molecules. The tetrel bonds involving the counterions (Pb⋯O) have been also analysed by DFT calculations via a MEP surface plot and 2D maps of electron localization function (ELF), Laplacian of electron density (∇²ρ) and reduced density gradient (RDG), confirming their noncovalent nature.