Three solid materials, [Pb(HL)(SCN)2 ]⋅CH3 OH (1), [Pb(HL)(SCN)2 ] (2), and [Pb(L)(SCN)]n (3), were obtained from Pb(SCN)2 and an unsymmetrical bis-pyridyl hydrazone ligand that can act both as a bridging and as a chelating ligand. In all three the lead center is hemidirectionally coordinated and is thus sterically optimal for participation in tetrel bonding. In the crystal structures of all three compounds, the lead atoms participate in short contacts with thiocyanate sulfur or nitrogen atoms. These contacts are shorter than the sums of the van der Waals radii (3.04-3.47 Å for Pb⋅⋅⋅S and 3.54 Å for Pb⋅⋅⋅N) and interconnect the covalently bonded units (monomers, dimers, and 2D polymers) into supramolecular assemblies (chains and 3D structures). DFT calculations showed these contacts to be tetrel bonds of considerable energy (6.5-10.5 kcal mol(-1) for Pb⋅⋅⋅S and 16.5 kcal mol(-1) for Pb⋅⋅⋅N). A survey of structures in the CSD showed that similar contacts often appear in crystals of Pb(II) complexes with regular geometries, which leads to the conclusion that tetrel bonding plays a significant role in the supramolecular chemistry of Pb(II) .
In this study, neutral mercuryIJII) complexes of the composition ijHgIJL1)IJμ-Cl) 2 Hg 3 Cl 6 ] n (1), ijHgIJL1)IJμ-Br) 2 HgBr 2 ] (2), ijHgIJL3)Br 2 ] (2a), ijHgIJL1)I 2 ] (3), ijHgIJL2)Cl 2 ]ĴCH 3 OH (4) and ijHgIJL2)IJμ-Br)HgBr 3 ] 2 (5) (L1 = benzilbisIJ(pyridin-2-yl)methylidenehydrazone); L2 = benzilbisIJ(acetylpyridin-2-yl)methylidenehydrazone)) are described. Single-crystal X-ray crystallography showed that the molecular complexes can aggregate into larger entities depending upon the anion coordinated to the metal centre. Iodide gives discrete monomeric complexes, bromide generates a 1D coordination polymer formed through Hg-Br-Hg bridges and chloride gives rise to an inorganic-organic hybrid material. The significant differences in the reaction conditions indicate that the anions exert a substantial influence on the formation of the compoundssmaller anions show a larger potential for bridging metal ions and forming coordination polymers. A minute increase in the bulkiness of the ligand (two extra methyl substituents in L2) dramatically changes the coordination architectures, and leads to the formation of monomeric (chloride and iodide) and oligomeric (bromide) structures, rather than polymeric structures. The noncovalent C-H/π and π-hole interactions observed in the solid state architecture of some complexes have been rationalized by means of theoretical DFT calculations.CrystEngComm, 2015, 17, 3493-3502 | 3493This journal is
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