On the pivotal role of tetrel bonding in the supramolecular architectures of PbII–NCS complexes with chelating thiosemicarbazide derivatives

Abstract

Three new Pb^II complexes [Pb(L^I)(SCN)]_n, {[Pb(L^II)](SCN)}_n and {[Pb(HL^III)(SCN)](SCN)}_n (HL^I = N′-phenyl(pyridin-2-yl)methylene-N-phenylthiosemicarbazide, HL^II = N′-amino(pyrazin-2-yl)methylenethiosemicarbazide, HL^III = N′-amino(pyridin-2-yl)methylenethiosemicarbazide) have been synthesized and characterized by spectroscopic techniques and single crystal X-ray diffraction. In all complexes, the corresponding organic ligand behaves as a tridentate N,N′,S-chelating species. A 1D supramolecular polymeric aggregation in complex [Pb(L^I)(SCN)]_n is dictated by the Pb⋯NCS and Pb⋯SC tetrel bonds formed between the [Pb(L^I)(SCN)] species. 1D cationic coordination polymers ([Pb(L^II)])_nⁿ⁺ in the structure of complex {[Pb(L^II)](SCN)}_n are linked into a 2D supramolecular polymeric layer through the Pb⋯NCS tetrel bonds and Pb⋯π(NCS) interactions formed with the nitrogen atom and the conjugated system of the free SCN⁻ anions, respectively. The cationic species [Pb(HL^III)(SCN)]⁺ in the structure of complex {[Pb(HL^III)(SCN)](SCN)}_n produce a 1D supramolecular polymer due to the Pb⋯SCN and Pb⋯SC tetrel bonds, further stabilized by the Pb⋯π(NCS) interactions formed with the conjugated system of the coordinated NCS⁻ anion. The latter anions also link these 1D chains through the Pb⋯SCN tetrel bonds, yielding 1D supramolecular polymeric ribbons. The energetic relevance of the Pb⋯S and Pb⋯N tetrel bonds has been studied by DFT calculations. The tetrel bonds have been characterized using QTAIM and NCIplot analysis and rationalized using molecular electrostatic potential surface calculations.