Mercury Coordination Polymers Research Articles

New Hg(II) coordination polymers based on a thioimidazole ligand with good performance to detoxify Hg(II) and reversibly capture iodine.

In the current paper, we have successfully synthesized three new mercury coordination polymers with fascinating structures and properties via a flexible sulfur donor ligand, namely, {[Hg(μ2-Cl)(μ2-Ls)]}n[BF4]n(1), {[Hg(μ2-Cl)(μ2-Ls)]}n[ClO4]n(2), and [Hg(SCN)2(μ2-Ls)]n(3) [Ls = 1,1-bis(3-methyl-4-imidazoline-2-thione)methane]. These complexes have been characterized by means of different techniques such as single crystal X-ray crystallography, FT-IR, elemental analysis (CHNS), UV-Vis, PXRD, BET, and TGA. Suitable single crystals of all complexes were obtained using the branch tube method with a very high yield and good stability due to the high affinity of mercury to bind to the thione groups. The cationic moieties of polymers 1 and 2 were isostructural, with a HgCl2S2 coordination core structure. The voids of the quasi-hexagonal packing of the columnar chains were occupied by unbonded tetrahedral BF4- ions in 1 and perchlorate anions in polymer 2. Polymer 3 has a less distorted tetrahedral geometry than 1 and 2, with a HgS4 core structure. By considering the thiophilicity of mercury, a thioamide-based Ls ligand was used to detoxify Hg(II) into insoluble polymers 1-3. The results of an MTT assay for (HepG2) liver cells confirmed the excellent cytoprotective effect of this ligand against mercury. Based on IC50 calculations, their toxicity was in order of polymer 1 > polymer 2 > polymer 3. These polymers were also considered as adsorbents for the reversible removal of iodine from solution and the kinetics of the process has been studied in detail. Interestingly, all of them showed an excellent stability and high capacity, in order of 763.53 mg g-1, 877.10 mg g-1, and 905.31 mg g-1 for polymers 1-3, respectively.

Synthesis, structure and properties of a multifunctional inorganic–organic hybrid mercury(II) coordination polymer: [Hg2Cl2(mtz)2(H2O)

A new mercury coordination polymer was successfully prepared from HgCl2 and 5-methyltetrazole (Hmtz) and characterized by elemental analysis, thermal analysis, luminescence, theoretical calculation, powder X-ray diffraction and single-crystal X-ray diffraction. Complex 1 is a three-dimensional (3D) hybrid framework constructed from 1D double mercury halide chains and mtz−, and it has an unprecedented ‘AFUQOH’ topological network. Time-dependent density functional theory (TDDFT) calculations reveal that the mechanisms of the fluorescence emission of 1 are dominantly resulted from the metal-to-ligand charge transfer (MLCT) and ligand-to-metal charge transfer (MLCT). Impressively, acentric complex 1 displays not only second harmonic generation (SHG) response but also ferroelectric behaviors.

Synthesis, structures and properties of three mercury coordination polymers based on 5-methyltetrazolate ligand

Three new mercury coordination polymers, [HgCl2(Hmtz)]n (1), (2) and [Hg2(mtz)4]n (3), were successfully prepared from HgCl2 and 5-methyltetrazole (Hmtz) and characterized by elemental analysis, thermal analysis, luminescence, theoretical calculation, powder X-ray diffraction and single-crystal X-ray diffraction. The results reveal that 1 and 2 are isomers resulted from different one dimensional (1D) mercury halides chains, and they are all 3D supramolecular structures. Complex 3 possesses a 2-fold interpenetrated diamondoid network with intersecting channels. Time-dependent density functional theory (TDDFT) calculations reveal that the mechanisms of the fluorescence emission are dominantly resulted from the ligand-to-metal charge transfer (LLCT) and partial ligand-to-ligand charge transfer (LLCT) for 1 and 2, but ligand-to-metal charge transfer (LMCT) for 3, which is in good agreement with their different fluorescence spectra and crystal structures. Optical absorption spectra indicate that complexes 1–3 have wide optical band-gaps and can be probably used as wide optical band-gap semiconductor materials.

Syntheses, structures and investigation of the properties of mercury coordination polymers based on 5-amino-tetrazolate ligands

Four new mercury coordination polymers were successfully synthesized under solvothermal conditions and characterized by elemental analysis, IR spectroscopy, thermal analysis, powder X-ray diffraction and single-crystal X-ray diffraction. In these complexes, the chemical valence of mercury is +2, except for complex 1 which is +1. 1 contains [Hg2]2+ metal–metal bonded cores which are bounded by atz− (Hatz = 5-amino-tetrazolate) ligands and features a two-dimensional (2D) uninodal 3-connected ‘hcb’ network. 2 exhibits a trinodal 3D (3,6)-connected ‘apo/alpha-PbO2’ topological net in which 2D [HgCl]nn+ inorganic cation layers are pillared by atz− ligands. In 3, the 2D [HgCl]nn+ cation layers are interconnected by atz− ligands, affording a trinodal 3D (3,6)-connected ‘flu/fluorite’ topological net. 4 is a 3D pillared-layer metal–organic framework based on mixed atz− and isonicotinic ligands, showing a binodal (4,6)-connected ‘fsc’ coordination network. In this work, 1 and 4 were synthesized from an in situ generated tetrazolate ligand, while 2 and 3 were prepared from a commercially available tetrazolate ligand. These results indicate that the final structures of the target complexes will highly depend on the synthetic conditions as well as the preparation methods. Moreover, the photoluminescence properties of these complexes were investigated. Impressively, the non-centrosymmetric complex 3 displays not only a second harmonic generation (SHG) response but also a ferroelectric behavior.

Synthesis and Structure of a Polymeric Homobimetallic Mercury Compound Constructed from (E)-Acetyloxy{4-[(pyridin-2-ylmethylene)amino]phenyl}mercury(II)

A two-dimensional homobimetallic mercury coordination polymer (2-{[4-(acetyloxymercuryl)phenyl]iminomethyl}pyridine-κ2N,N′)dithiocyanatomercury(II) (1) was synthesized and characterized by FT-IR, 1H-NMR spectroscopic and single crystal X-ray diffraction techniques. Crystallographic results reveal that the primary structural building unit in the structure is a centrosymmetric tetranuclear entity, where long Hg–N bonds link a thiocyanate ligand of the dinuclear asymmetric unit to the acetate coordinated Hg-atom of its neighbor. These tetranuclear units are then linked into extended chains and the chains are cross-linked by weaker Hg···O interactions to give a two-dimensional polymeric structure. Part of the structure of the 2-D bimetallic mercury coordination polymer constructed from the reaction of (E)-acetyloxy{4-[(pyridin-2-ylmethylene)amino]phenyl}mercury(II) with Hg(SCN)2 is reported.

Mercury coordination polymers with flexible ethane-1,2-diyl-bis-(pyridyl-3-carboxylate): Synthesis, structures, thermal and luminescent properties

The reaction of the flexible ligand, ethane-1,2-diyl-bis-(pyridyl-3-carboxylate), (L) with HgI2 and HgBr2 salts under the same experimental conditions leads to the formation of two coordination polymers with different motifs: {[Hg(L)(Br2)]}n(1) and {[Hg(L)(I2)]}n(2).In both compounds, the ligand, (L) acts in a μ2-N:N′-bidentate fashion to link HgBr2 and HgI2 units to form a linear and helical chain motif, along [100] for (1) and [001] for (2). The ethylene moiety of (L) has gauche and trans conformation in compounds (1) and (2), respectively. The flexible conformation of L produces differences in the optical and crystal properties of the two compounds.

Microwave-assisted template synthesis of diazacyclam-based macrocyclic copper complex and forming octahedral, square planar and square pyramidal geometries by ion exchanging and introducing a novel 2D square-grid copper–mercury coordination polymer

The microwave-assisted template reaction of copper(II) nitrate with N-(2-aminoethyl)-1,3-diaminopropane and formaldehyde yields the macrocyclic copper complex of 1,3,6,10,12,15-hexaazatricyclo[13.3.1.16,10]eicosane (L), [CuL(NO3)2] (1), with octahedral geometry. Replacement of nitrate with bromide and iodide ions gives [CuL]Br2 (2) and [CuLI][CuLI]′I2·H2O (3) complexes respectively with square planar and distorted square pyramidal geometry. The reaction between 1 and HgCl2 forms the 2D square-grid coordination polymer, {[CuL(NO3)]2[Hg5(μ-Cl)8(μ3-Cl)2]Cl2} (4). The complexes were characterized by FT-IR and Raman spectroscopies, electronic absorption, cyclic voltammetry and X-ray crystallography. Photoluminescent properties of 1 were also investigated. Cyclic voltammetry experiments show two one-electron waves corresponding to CuII/CuIII and CuII/CuI processes. In the structure of 4, expansion of the Hg–Cl bonds in two directions gives rise to a 2D polymeric chain. The [CuL(NO3)]+ unit is coordinated to main chain as a lateral branch by its nitrogen atom. There are two different geometries around the mercury atoms including octahedral and distorted square pyramidal. The chains are linked by N–H⋯Onitrate hydrogen bonds between two [CuL(NO3)]+ units belonging to the parallel chains. Hydrogen bonds including N–H⋯A and C–H⋯A (A: N, O, Br, I) present in the crystal networks of 1–3.

Isostructural Mercury Coordination Polymers with Amide Junction: Interplay of Coordination and π–π Stacking

Two coordination polymers [Hg2Cl4L·2(DMF)]n, 1, and [Hg2Br4L·2(DMF)]n, 2, where L is the N,N′-(1,2-diphenylethane-1,2-diyl)diisonicotinamide ligand, have been synthesized and characterized. X-ray single crystal diffraction reveals that both coordination polymers are isostructural and that mercury adopts square based pyramid coordination geometry. Our results show that interplay between the coordination of the carbonyl group and π···π interaction of adjacent pyridine rings leads to the formation of 2D structures.

Mercury(II) metal–organic coordination polymers with pyrazine derivatives

Eight mercury coordination polymers of the three pyrazine ligands 2,6- and 2,5-dimethylpyrazine and pyrazine itself {2,5-dmpyr, 2,6-dmpyr, and pyr, respectively} were prepared from reactions with mercury(II) chloride, bromide, iodide and thiocyanate under thermal gradient conditions using the branched tube method and by simple solvent evaporation from the reactant mixtures. All eight compounds, namely [Hg(µ-pyr)(µ-Br)2]n (1), [Hg2(µ-pyr)(µ-I)2I2]n (2), [Hg(µ-pyr)(µ-SCN)2]n (3), [Hg2(µ-2,5-dmpyr)(µ-Cl)4]n (4), [Hg2(µ-2,5-dmpyr)(µ-Br)4]n (5), [Hg2(µ-2,5-dmpyr)(µ-SCN)2(SCN)2]n (6), [Hg(2,6-dmpyr)(µ-Br)2]n (7) and [Hg(µ-2,6-dmpyr)(µ-SCN)2]n (8), were structurally characterized by single-crystal X-ray diffraction. The results indicate that the substitution pattern of the pyrazine derivatives and the counter ions play important roles in the framework formation of the mercury(II) polymers and reveal that there are two general types of mercury(II) pyrazine derivatives: coordination complexes with HgX2L stoichiometry with usually no holes, and (HgX2)2L complexes with one or two holes or vacant sites at the mercury atoms. X-Ray powder diffraction patterns and thermal properties of compounds 1–8 are discussed.