Construction of a PbII coordination polymer from a semi-rigid ditopic 2,2-biimidazole derivative: synthesis, crystal structure and characterization

<!?tlsb=-0.04pt>A new Pb^II coordination polymer, poly[0.75(aqua)[μ₃-4,4'-(1H,1'H-[2,2'-biimidazole]-1,1'-diyl)dibenzoato-κ⁵O,O';N;O'',O''']]lead(II)] 1.25-hydrate], {[Pb(C₂₀H₁₂N₄O₄)(H₂O)_0.75]·1.25H₂O}_n or {[Pb(L)(H₂O)_0.75]·1.25H₂O}_n (1) [H₂L = 4,4'-(1H,1'H-[2,2'-biimidazole]-1,1'-diyl)dibenzoic acid], was synthesized under solvothermal reaction conditions and characterized using microanalysis, IR spectroscopy and thermogravimetric analysis. Single-crystal structure analysis reveals that a two-dimensional corrugated layer structure is formed in 1 and that neighbouring layers are further extended into a three-dimensional structure by hydrogen-bonding interactions. In addition, a fluorescence sensing experiment towards Cu²⁺ based on the polymeric Pb^II complex was carried out.

The tetrel bonding role in supramolecular aggregation of lead(II) acetate and a thiosemicarbazide derivative

A new Pb^II coordination complex [PbL(OAc)], which was readily synthesized from a mixture of Pb(OAc)₂·3H₂O and 1-(pyridin-2-yl)benzylidene-4-phenylthiosemicarbazide (HL) is reported. The crystal structure analysis of [PbL(OAc)] showed that the Pb^II cation is N,N',S-chelated by the tridentate pincer-type ligand L and by the oxygen atoms of the acetate anion. In addition, the metal centre forms Pb...O and Pb...S tetrel bonds with an adjacent complex molecule, yielding a 1D zigzag polymeric chain, which is reinforced by N-H...O hydrogen bonds and π...π interactions. These chains are interlinked by C-H...py non-covalent interactions, realized between one of the acetate hydrogen atoms and the pyridine rings. According to the Hirshfeld surface analysis, the crystal packing is mainly characterized by intermolecular H...H, H...C and H...O contacts, followed by H...N, H...S, C...C, C...N, Pb...H, Pb...O and Pb...S contacts. The FTIR and ¹H NMR spectra of [PbL(OAc)] testify to the deprotonation of the parent ligand HL, while the acetate ligand exhibits an anisobidentate coordination mode as established by means of single-crystal X-ray diffraction and FTIR spectroscopy. Lastly, theoretical calculations at the PBE0-D3/def2-TZVP level of theory have been used to analyze and characterize the Pb...O and Pb...S tetrel bonds observed in the crystal of [PbL(OAc)], using a combination of QTAIM (Quantum Theory of Atoms in Molecules) and NCIPlot (Non-Covalent Interaction Plot) computational tools.

A three-dimensional metal-organic polymer: poly[bis(μ₂-pyrimidine-2-thiolato-κ⁴N¹,S:S,N³)lead(II)]

The title compound, [Pb(C4H3N2S)2]n, was prepared by the reaction of [Pb(OAc)2]·3H2O (OAc is acetate) with pyrimidine-2-thione in the presence of triethylamine in methanol. In the crystal structure, the Pb(II) atom has an N4S4 coordination environment with four ligands coordinated by N- and S-donor atoms. This compound shows that the pyrimidine-2-thiolate anion can lead to a three-dimensional network when the coordination number of the metal ion can be higher than 6, as is the case with the Pb(II) ion. This compound presents only covalent bonds, showing that despite the possibility of the hemidirected geometries of Pb(II), the eight-coordinated ion does not allow the formation of an isolated molecular structure with pyrimidine-2-thiolate as the ligand.

A one-dimensional lead(II) coordination polymer with terminal and bridging 5-carboxy-2-(pyridin-3-yl)-1H-imidazole-4-carboxylate ligands

In the coordination polymer catena-poly[[[diaqua[5-carboxy-2-(pyridin-3-yl)-1H-imidazole-4-carboxylato-κ(2)N(3),O(4)]lead(II)]-μ-5-carboxy-2-(pyridin-3-yl)-1H-imidazole-4-carboxylato-κ(3)N(3),O(4):N(2)] dihydrate], {[Pb(C10H6N3O4)(H2O)2]·2H2O}n, the two 5-carboxy-2-(pyridin-3-yl)-1H-imidazole-4-carboxylate ligands have different coordination modes, one being terminal and the other bridging. The bridging ligand links Pb(II) cations into one-dimensional coordination polymer chains. The structure is also stabilized by intra- and interchain π-π stacking interactions between the pyridine rings, resulting in the formation of a two-dimensional network. Extensive hydrogen-bonding interactions lead to the formation of a three-dimensional supramolecular network.