Complexation of Mercury(I) and Mercury(II) by 18-Crown-6: Hydrothermal Synthesis of the Mercuric Nitrite Complex

(1-(4-(5-Phenyl-1,3,4-oxadiazol-2-yl)phenyl)-1H-1,2,3-triazol-4-yl)-methylenyls α,ω-Bisfunctionalized 3- and 4-PEG: Synthesis and Photophysical Studies

Two new azaheterocycle-based bolas, such as (1-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenyl)-1H-1,2,3-triazol-4-yl)-methylenyls α,ω-bisfunctionalized PEGs, were prepared via Cu-catalyzed click reaction between 2-(4-azidophenyl)-5-(aryl)-oxadiazole-1,3,4 and terminal ethynyls derived from PEG-3 and PEG-4. Due to the presence of two heteroaromatic cores and a PEG linker, these bola molecules are considered as promising fluorescent chemosensors for electron-deficient species. As a result of a well-pronounced "turn-off" fluorescence response towards common nitro-explosive components, such as 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT), hard-to-detect pentaerythritol tetranitrate (PETN), as well as Hg²⁺ cation was observed.

A Hg(i) corrugated sheet assembled by auxiliary dioxole groups and Hg⋯π interactions

Comproportionation between Hg0 and Hg2+ resulted in the formation of [Hg2(Pip)2] supported by Hg⋯Odioxole and Hg⋯π interactions. Structural and computational assessment determined the tendency of Hg(i) to partake in Hg⋯π interactions.

Steric and Electronic Effects on the Structure and Photophysical Properties of Hg(II) Complexes

Since many factors influence the coordination around a metal center, steric and electronic effects of the ligands mainly determine the connectivity and, thus, the final arrangement. This is emphasized on Hg(II) centers, which have a zero point stabilization energy and, thus, a flexible coordination environment. Therefore, the unrestricted Hg(II) geometry facilitates the predominance of the ligands during the structural inception. Herein, we synthesized and characterized a series of six Hg(II) complexes with general formula (Hg(Pip)₂(dPy)) (Pip = piperonylate, dPy = 3-phenylpyridine (3-phpy) (1), 4-phenylpyridine (4-phpy) (2), 2,2′-bipyridine (2,2′-bipy) (3), 1,10-phenanthroline (1,10-phen) (4), 2,2′:6′,2′-terpyridine (terpy) (5), or di(2-picolyl)amine (dpa) (6)). The elucidation of their crystal structures revealed the arrangement of three monomers (3, 5, and 6), one dimer (4), and two coordination polymers (1 and 2) depending on the steric requirements of the dPy and predominance of the ligands. Besides, the study of their photophysical properties in solution supported by TD-DFT calculations enabled us to understand their electronic effects and the influence of the structural arrangement on them.

Six Hg(II) complexes containing 1,3-benzodioxole-5-carboxylic acid and pyridine derivatives bearing N-, N^N′-, and N^N^N-donor sites have been characterized and their crystal structure elucidated. Steric crowding defined the predominance of the linkers in the structural arrangement, varying from monomers to coordination polymers. Their photophysical properties were analyzed through experimental and TD-DFT calculations, identifying the character and regions involved on each electronic transition. In addition, seclusion of the HOMO from the LUMO defined them as appropriate to selective band gap tuning.

A Chemodosimetric Approach for Fluorimetric Detection of Hg2+ Ions by Trinuclear Zn(II)/Cd(II) Schiff Base Complex: First Case of Intermediate Trapping in a Chemodosimetric Approach

The present work discloses the application of two fluorescent zinc and cadmium complexes (1 and 2) for sensing of Hg(II) ions through a chemodosimetric approach. The ligand under consideration in this work is a N₂O donor Schiff base ligand (E)-4-bromo-2-(((2-morpholinoethyl)imino)methyl)phenol (HL), which has been harnessed to generate complexes [Zn₃L₂(OAc)₄] (1) and [Cd₃L₂(OAc)₄] (2). X-ray single crystal diffraction studies unveil the trinuclear skeleton of complexes 1 and 2. Both complexes have been found to be highly fluorescent in nature. However, the quantum efficiency of Zn(II) complex (1) dominates over the Cd(II) analogue (2). The absorption and emission spectroscopic properties of the complexes have been investigated by density functional theory. Complexes 1 and 2 can detect Hg²⁺ ions selectively by fluorescence quenching, and it is noteworthy to mention that the mechanism of sensing is unique as well as interesting. In the presence of Hg²⁺ ions, complexes 1 and 2 are transformed to mononuclear mercuric intermediate complex (3) and finally to a trinuclear mercuric complex (4) by hydrolysis. We have successfully trapped the intermediate complex 3, and we characterized it with the aid of X-ray crystallography. Transformation of complexes 1 and 2 to intermediate complex 3 and finally to 4 has been established by UV-vis spectroscopy, fluorescence spectroscopy, ESI-MS spectroscopy, ¹H NMR spectroscopy, and X-ray crystallography. The spontaneity of the above conversion is well supported by thermodynamic aspects as reflected from density functional theoretical calculations.

The first coordination polymers with an [O]2[N]P(S)-Hg segment: a combined experimental, theoretical and database study

The study of one-dimensional coordination polymers {Hg₂Cl₄L₁}_n (1), {HgBr₂L₁}_n (2) and {Hg₂Cl₄L₂}_n (3) (L₁ = (S)P(OC₂H₅)₂NHC₆H₄NHP(S)(OC₂H₅)₂ and L₂ = (S)P(OC₂H₅)₂NC₄H₈NP(S)(OC₂H₅)₂) is the first such structural study of Hg(ii) coordination polymers with (O)₂(N)PS-based ligands. The mercury atoms adopt a distorted trigonal pyramidal environment, Hg(Cl)₃(S) for 1 and 3 and Hg(Br)₂(S)₂ for 2, and the difference observed in the stoichiometry of mercury halide to the thiophosphoramide ligand in 1 and 3 with respect to the one in 2 is a result of the formation of the Hg₂Cl₂ ring, however, the molar ratio 2 : 1 of HgX₂ (X = Cl and Br) to ligand was used for the preparation of all three complexes. The strengths of mercury-sulfur and mercury-halide covalent bonds are evaluated by theoretical calculations (QTAIM and NBO) which show their principally electrostatic nature with a partial covalent contribution. The energies of interactions building supramolecular assemblies and intramolecular interactions, i.e. NHCl, NHBr, CHCl, CHBr, CHO, CHS and CHπ, are theoretically evaluated. The characteristic structural features arising from the aromatic/aliphatic linkers in the ligands and chloride/bromide attached to mercury are investigated by Hirshfeld surface analysis and fingerprint plots.

Phase transition and switchable dielectric behaviours in an organic-inorganic hybrid compound: (3-nitroanilinium)2(18-crown-6)2(H2PO4)2(H3PO4)3(H2O)

An organic-inorganic hybrid compound with an extensive three-dimensional (3D) crystal structure, (3-nitroanilinium)₂(18-crown-6)₂(H₂PO₄)₂(H₃PO₄)₃(H₂O) (1), was synthesized under slow evaporation conditions. Differential scanning calorimetry measurements indicated that 1 underwent a reversible phase transition at ca 231 K with a hysteresis width of 10 K. Variable-temperature X-ray single-crystal diffraction revealed that the phase transition of 1 can be ascribed to coupling of pendulum-like motions of its nitro group with proton transfer in O-H···O hydrogen bonds of the 3D framework. The temperature dependence of its dielectric permittivity demonstrated a step-like change in the range of 150-280 K with remarkable dielectric anisotropy, making 1 a promising switchable dielectric material. Potential energy calculations further supported the possibility of dynamic motion of the cationic nitro group. Overall, our findings may inspire the development of other switchable dielectric phase transition materials by introducing inorganic anions into organic-inorganic hybrid systems.

Crystal structures of three mercury(II) complexes [HgCl2 L] where L is a bidentate chiral imine ligand

The crystal structures of three complexes [HgCl2 L] were determined, namely, (S)-(+)-di-chlorido-[1-phenyl-N-(pyridin-2-yl-methyl-idene)ethyl-amine-κ(2) N,N']mercury(II), [HgCl2(C14H14N2)], (S)-(+)-di-chlorido-[1-(4-methyl-phen-yl)-N-(pyridin-2-yl-methyl-idene)ethyl-amine-κ(2) N,N']mercury(II), [HgCl2(C15H16N2)], and (1S,2S,3S,5R)-(+)-di-chlorido-[N-(pyridin-2-yl-methyl-idene)isopino-camph-eyl-amine-κ(2) N,N']mercury(II), [HgCl2(C16H22N2)]. The complexes consist of a bidentate chiral imine ligand coordinating to HgCl2 and crystallize with four independent mol-ecules in the first complex and two independent mol-ecules in the other two. The coordination geometry of mercury is tetra-hedral, with strong distortion towards a disphenoidal geometry, as a consequence of the imine bite angle being close to 70°. The Cl-Hg-Cl angles span a large range, 116.0 (2)-138.3 (3)°, which is related to the aggregation state in the crystals. For small Cl-Hg-Cl angles, complexes have a tendency to form dimers, via inter-molecular Hg⋯Cl contacts. These contacts become less significant in the third complex, which features the largest intra-molecular Cl-Hg-Cl angles.

On the coordination chemistry of the dimercury(I) ion with O-donor ligands

An overview of published crystalline dimercury(I) hydrates, solvates, and complexes/compounds with O-donor ligands shows that there is virtually no correlation between the Hg—Hg bond distance and the overall Hg—O bonding conditions. Additionally, many structures feature different configurations for the individual mercury atoms in the dimercury(I) ion, Hg2 2+. To supplement these findings, the crystal structures of the perchlorate salts of hydrated and dimethylsulfoxide (dmso) solvated mercury(I), [Hg2(OH2)2](ClO4)2 (1) and [Hg10(OS(CH3)2)16](ClO4)10 (2), respectively, have been determined by single crystal X-ray diffraction. In compound 1, the perchlorate ions act as bridges between the almost linear [Hg2(OH2)2]2+ units forming infinite chains. The Hg—Hg bond distance is 2.500(1) Å and the Hg—O distance to the water molecule is 2.231(19) Å. Additional much weaker Hg—O bonds to the bridging perchlorate oxygens lie in the range 2.78–3.15 Å. Compound 2 consists of five crystallographically independent [Hg—Hg]2+ units solvated and bridged by dmso oxygens. These larger entities form chains through much weaker bridging perchlorate ions at longer distances, 3.0–3.3 Å, with a few remaining perchlorate ions isolated in the lattice. The mean Hg—Hg bond distance is 2.500(1) Å, while the Hg—Odmso bond distances are in the range of 2.15–2.92 Å. The dmso molecules are grouped into three types of coordination, strong κO-terminal, medium μ2 O-bridging, or medium/weak μ3 O-bridging, depending on which dimercury(I) ion(s) in the entity they coordinate to.