Spodium bonding and other non-covalent interactions assisted supramolecular aggregation in a new mercury(II) complex of a nicotinohydrazide derivative

Abstract In this work we report a new Hg(II) coordination compound [Hg(HL)(SCN)2], which was readily obtained from a mixture of Hg(SCN)2 and N'-(1-(pyridin-2-yl)ethylidene)nicotinohydrazide (HL). The metal cation is chelated by the organic ligand in a N,N',O tridentate manner through the 2-Py and amide nitrogen donors, and carbonyl oxygen atom. The coordination sphere is filled by the sulfur donors of two thiocyanate anions, thus yielding a pentacoordinated geometry, which is best described as being about 64% along the pathway of distortion from the ideal square pyramidal toward trigonal bipyramidal structure. In addition, the metal center forms two types of the Hg∙∙∙N spodium bonds, which are formed with the 3-Py nitrogen atom of a symmetry related molecule and with the nitrogen atom of one thiocyanate ligand of another molecular unit. These Hg∙∙∙N spodium bonds enlarge the coordination environment of the metal cation in between a capped trigonal prism close to pentagonal bipyramid. In addition 1D zig-zag-like polymeric chain is formed, which is further reinforced by bilateral C–H∙∙∙O hydrogen bonds. These chains are interlinked through N–H∙∙∙N hydrogen bonds and additionally glued by π∙∙∙π interactions between the 2-Py rings. Thus, considering all the Hg∙∙∙N spodium and N–H∙∙∙N hydrogen bonds, a supramolecular 2D layer is formed with a binodal 3,4-connected hcb topology. The 2D layers are interlinked through a myriad of π∙∙∙π interactions. According to the Hirshfeld surface analysis, the crystal packing of [Hg(HL)(SCN)2] is mainly characterized by intermolecular H∙∙∙H, H∙∙∙C, H∙∙∙N and H∙∙∙S contacts comprised from 15.9 to 22.3%, followed by less significant H∙∙∙O, C∙∙∙C, C∙∙∙N, N∙∙∙S and Hg∙∙∙N contacts comprised from 2.8 to 6.3%. The intermolecular H∙∙∙C, H∙∙∙N, H∙∙∙O, H∙∙∙S and C∙∙∙C contacts are highly favoured in the molecular surface of [Hg(HL)(SCN)2], while the N∙∙∙S contacts are less favoured, and remaining contacts are significantly impoverished. Finally, density functional theory (DFT) calculations at the PBE0/def2-TZVP level of theory have been used to evaluate and characterize the Hg∙∙∙N spodium bonds, including molecular electrostatic potential (MEP), quantum theory of atoms in molecules (QTAIM) and noncovalent interaction plot (NCIPlot) computational tools.