A structural versatility of the lead(II) coordination compounds with N′-(pyridin-2-ylmethylene)isonicotinohydrazide

Abstract

We report on the reaction of Pb(NO 3 ) 2 or PbI 2 or Pb(SCN) 2 with an equimolar amount of the dipyridyl compound N′ -(pyridin-2-ylmethylene)isonicotinohydrazide ( HL ) in methanol or a mixture of methanol and acetonitrile, which yielded novel heteroleptic coordination polymers [Pb(HL)X 2 ] n (X = NO 3 − , 1 ; I − , 2 ) and [PbL(SCN)(H 2 O)] n ( 3 ). Furthermore, it was established that using an equimolar mixture of Pb(ClO 4 ) 2 and KSCN as a source of the metal cation also leads to the formation of complex 3 . The structures of the resulting complexes 1 and 2 each comprise a neutral ligand HL , while complex 3 contains a monodeprotonated anionic form L of the parent organic ligand. Both forms, HL and L , exhibit an N , N′ , O -chelated coordination mode formed by the 2-pyridine and imine nitrogen atoms, and the carbonyl oxygen atom. This resulted in mononuclear doubly charged [Pb(HL)] 2+ (in complexes 1 and 2 ) or monocharged [PbL] + (in complex 3 ) cations as the primary building blocks of the resulting coordination polymers. The latter structures are formed primarily due to the additional coordination of the metal cation to the 4-pyridine nitrogen atom arising from the other building block, thus, yielding 1D supramolecular chains of a zig-zag-like structure. These chains are linked into 3D supramolecular aggregates due to the formation of the tetrel bonds with the center-of-gravity of the nitrate O–N–O and the thiocyanate C≡N fragments in the structures of complexes 1 and 3 , respectively. In complex 2 , one of the iodide anions links two metal cations, thus, exhibiting a μ-bridging coordination mode. This allowed for the production of a 2D double-layered sheet in the structure of complex 2 . 3D supramolecular aggregates in the crystal structures of 1 – 3 are stabilized by π⋯π interactions formed between the pyridine rings, and by the corresponding hydrogen bonds formed due to the NH functionality (in complexes 1 and 2 ) or due to the water ligand (in complex 3 ). Complexes 1 – 3 were established to be emissive in a solution of DMSO due to intraligand transitions. In addition, density functional theory (DFT) calculations were performed to elucidate the nature of key noncovalent interactions, namely hydrogen bonds, tetrel bonds and π-stacking interactions, within the supramolecular assemblies observed in the crystal structures of complexes 1 and 3 . Using molecular electrostatic potential (MEP) surfaces, QTAIM and NCIplot analyses, we characterized the role of the Pb 2+ center as an electrophilic σ-hole donor. Moreover, combined ELF and RDG calculations were used to distinguish between covalent and ionic Pb⋯I interactions in complex 2 . Novel Pb(II) coordination polymers synthesized via one-pot reactions exhibit diverse 1D/2D/3D supramolecular architectures. These assemblies are stabilized by crucial Pb(II)-activated tetrel bonds and complementary noncovalent interactions. Advanced DFT reveals ionic character of elongated Pb⋯I bonds and highlights unique solution-phase dynamics. • Novel one-pot synthesis of 3 heteroleptic Pb(II) coordination polymers. • DFT reveals Pb(II) as σ-hole donor for structure-directing tetrel bonds. • Advanced analyses confirm ionic nature of elongated Pb⋯I interactions. • Complex 2 shows unique solution-phase dynamic coordination behavior.

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