Short Hg Research Articles

Hg(II)⋅d8 [M] Interactions: Are they Metallophilic Interactions or Spodium Bonds?

Some literature reports have shown the existence of short Hg(II)⋅⋅⋅d8 [M] (M=Pd, Pt) contacts between linear Hg(II) and square planar d8 [M] complexes that have been defined as heterometallophilic interactions. Linear L-Hg(II)-L complexes exhibit a π-hole or positive belt of electrostatic potential at the Hg atom, whereas late transition metals can serve as effective electron donors through their filled dz 2 orbitals. This study provides compelling evidence that Hg(II)⋅⋅⋅d8 [M] interactions should be more appropriately termed spodium bonds.

Study on low methoxyl pectin (LMP) with varied molecular structures cross-linked with calcium inducing differences in the gel properties

The gel properties of pectin are significantly connected with its molecular structure. In this paper, we investigated the relationship between low methoxyl pectin (LMP) molecular structure and gel strength in the same degree of esterification (DE) range. LMP with DE of 31% ± 2% was prepared from citrus peels by acid, alkaline, enzymatic, and citric acid/sodium citrate solution methods. And based on data from monosaccharide composition, Mw, and NMR spectroscopy, the proportion of structural regions was speculated. The result revealed that C-LMP (pectin de-esterified by citric acid/sodium citrate solution method) was a highly branched macromolecular polysaccharide with short HG and enriched RG-I, with HG and RG-I proportions of 19.37% and 76.96%. According to the gel property investigation, of all the LMP samples, A-LMP-0.7 (pectin de-esterified by acid method at pH 0.7), which possessed lengthy HG and enriched RG-I domain, exhibited the best gel strength. C-LMP, A-LMP-0.5 (pectin de-esterified by acid method at pH 0.5), and B-LMP (pectin de-esterified by alkaline) failed to form a complete gel due to the low HG linearity, sparse RG-I and low Mw, respectively.

A New Mineral Hanauerite, AgHgSI, and Common Crystal Chemical Features of Natural Mercury Sulphohalides

A new mineral, hanauerite, ideally AgHgSI, was found in the oxidation zone of Ag- and Hg-bearing ores at two old, abandoned mines in Rhineland-Palatinate, Germany. In a holotype specimen originating from the Schöne Aussicht Mine, Dernbach, Westerwald, it is associated with plumbogummite–hinsdalite series of minerals and goethite. In cotype from the Friedrichssegen Mine, Bad Ems, it is associated with perroudite, goethite, and quartz. At both localities, hanauerite occurs as a prismatic crystal up to 0.15 mm long and up to 0.02 mm thick. The mineral is yellow, transparent, with an adamantine lustre. It is brittle, and cleavage was not observed. The calculated density values are 6.671 and 6.575 g cm−3 for holotype and cotype, respectively. The empirical formulae calculated (from electron microprobe data) based on the sum of all atoms = 4 apfu are Ag0.95Hg1.00S1.01(I0.83Br0.19Cl0.03)Σ1.05 for holotype and Ag0.97Hg0.97S1.05(I0.76Br0.25)Σ1.01 for cotype. Hanauerite is orthorhombic, space group Pmma; the unit cell parameters (from single-crystal X-ray diffraction data; holotype/cotype) are: a = 9.932(2)/9.9256(8), b = 4.6219(19)/4.6209(2), c = 9.891(4)/9.9006(4) Å, V = 454.0(3)/454.19(5) Å3, and Z = 4. The crystal structure was studied on single crystals extracted from both holotype and cotype specimens; R1 = 0.0416 (holotype) and =0.0544 (cotype). In hanauerite, Hg2+ cations centre strongly distorted octahedra with two short Hg–S bonds (Hg and S atoms build “crankshaft-type” chains) and four strongly elongated Hg–I bonds. The Hg-centred octahedra are connected via common edges and faces to form corrugated layers; Ag+ cations are located between these layers. Hanauerite is named in honour of the German mineral collector Dr. Alfred Hanauer (1912–1988). The common crystal chemical features of mercury sulphohalide minerals are discussed.

Hg···Hg···Hg Interaction Stabilizes Unusual Trinuclear Double Sandwich Structure of Mercury(II) Porphyrins.

For the first time, fully characterized and stable trinuclear "double sandwich" molecules are reported with Hg(II) ion using a highly flexible porphyrin dimer. The molecules display interesting and intense luminescence properties at room temperature. The present investigation clearly demonstrates that attractive mercurophilic interactions do play an essential role in bringing two porphyrin macrocycles exactly on top of each other with an unfavorable fully eclipsed geometry to produce short Hg···Hg distances. Interactions between Hg(II) dz2 orbitals provide the directionality with a linear Hg3 core having short Hg···Hg distances despite the fact that ligand framework is highly flexible.

On the structure of monohalomercury(II) complexes in dimethylsulfoxide, pyridine and N,N-dimetylthioformamide solution

The structures of the monohalomercury(II) complexes, [HgX]+, in dimethylsulfoxide (dmso), pyridine and N,N-dimethylthioformamide (dmtf) solution have been studied by means of EXAFS. All complexes in the Hg2+-X− systems, X = Cl, Br and I, in dmso and pyridine have the unique property with wide range of predominance of all individual complexes. This means that all complexes can be individually characterized in solution. The previously reported complex formation thermodynamics in dmso and pyridine predicted a substantial desolvation at the formation of the first complex. This study shows that the dmso and pyridine solvated [HgX]+ complexes have one solvent molecule strongly bound “trans” to the halide ion and another two weakly bound solvent molecules in the remaining positions of linearly distorted tetrahedra. This shows that a substantial desolvation of the hexasolvated mercury(II) ions takes place at the formation of the [HgX]+ complexes. The strongly bound dmso molecule binds through its oxygen atom to mercury(II) in the [HgCl]+ and [HgBr]+ complexes, while in the [HgI]+ complex through its sulfur atom. The Hg–X bonds are slightly shorter in the [HgX]+ complexes than in corresponding [HgX2] complexes, and the short Hg–O and Hg–N bond distances are ca. 0.35 and 0.25 Å shorter than in the octahedral hexakis(dmso)- and -(pyridine)mercury(II) solvates, respectively. In dmtf solution, the dmtf solvated mercury(II) ion is four-coordinate in tetrahedral fashion. The structures of the dmtf solvated [HgX]+ complexes show the same basic tetrahedral configuration as the mercury(II) solvate. This shows that a simple substitution reaction takes place at the formation of the [HgX]+ complexes in dmtf.

Structure of 2,2'-(5-tert-butyl-1,3-phenyl-ene)bis-(1-pentyl-1H-benzimidazol-3-ium) tetra-chlorido-mercurate(II).

In the title salt, (C34H44N4)[HgCl4], the [C34H44N4]2+ cations and [HgCl4]2- anions are linked by N-H⋯Cl hydrogen bonds. One of the two n-pentyl side chains was refined as disordered over two sets of sites, with occupancies of 0.733 (18) and 0.267 (18). The geometry around the HgII atom in the [HgCl4]2- anion is distorted tetra-hedral, with bond angles ranging from 98.16 (3) to 120.68 (3)°. In the [HgCl4]2- anion, there are two short Hg-Cl bonds [2.4120 (9) and 2.4171 (11) Å], one inter-mediate Hg-Cl bond [2.4716 (12) Å] and one long Hg-Cl bond [2.6579 (13) Å] for the Cl atom involved in a trifurcated hydrogen bond as an acceptor, including two N-H⋯Cl⋯H-N interactions as well as one C-H⋯Cl inter-action. There are several C-H⋯Cl inter-actions, with C⋯Cl distances ranging from 3.492 (3) to 3.796 (3) Å. These link the cations and anions into a zigzag chain along the c-axis direction. In addition, there are Cl⋯Cl halogen bonds, as well as π-π inter-actions, with centroid-to-centroid distances of 3.4765 (18) Å, which link one of the two benzimidazole moieties into dimeric units.

Polar protic solvent-trapping polymorphism of the HgII-hydrazone coordination polymer: experimental and theoretical findings

A novel series of HgII coordination polymers with a general formula [HgL(N)3]n·n(solv) (HL = 2-pyridinecarbaldehyde isonicotinoylhydrazone; n(solv) = 0.5H2O (1), 2MeOH (2), EtOH (3), PrOH (4) and 0.5BuOH (5)) was prepared and characterized by elemental analysis, IR spectroscopy and single crystal X-ray diffraction. The crystal structure of HL, elucidated by X-ray diffraction, comprises two independent molecules in the asymmetric unit cell, each of which is stabilized by an intramolecular hydrogen bond formed between the carbohydrazide hydrogen atom and the 2-pyridyl nitrogen atom. Crystal structures of 1–5 each reveal a similar 1D zigzag metal–organic chain [HgL(N)3]n, where the organic ligands bridge metal centers. These chains are extended into distinct 2D supramolecular nets by strong hydrogen bonds with the solvent molecules and/or short Hg⋯N supramolecular contacts. These networks were topologically classified as the hcb in 1 and fes in 2–5 underlying nets. On comparing the H-bonding patterns, it can be concluded that the lattice water molecules in 1 and methanol molecules in 2 form H-bonding interactions with the O and amide N atoms of L in the former structure and the O atom of L in the latter structure. In the remaining coordination compounds, the lattice solvent prefers the azide N atom for H-bonding. Furthermore, the existence of Hg⋯N interactions in 2–5 and their absence in 1 clearly highlights the importance of the size and polarity of the solvents on the self-assembly generation of HgII coordination polymers. A broad network of intermolecular π⋯π stacking interactions, formed between the pyridyl fragments, provide further reinforcement of crystal packing patterns in the structures of HL and 2–5. DFT based charge and energy decomposition scheme (ETS-NOCV) was applied to characterize the obtained polymers.

Mercurophilic interactions: a theoretical study on the importance of ligands

In this work, a theoretical analysis of intermolecular HgHg contacts in the presence of different ligands is presented. A survey of structural databases to explore the geometrical preferences among experimental structures presenting short Hg(ii)Hg(ii) contacts reveals the main interaction topologies depending on the nature of the ligand. A benchmark study of several dispersion corrected-density functional methods is carried out to determine the optimal computational methodology for the theoretical study of such interaction. This methodology is later used in the study of several dimers of dicoordinated mercury compounds [HgX2]2 (X = Cl, Br, I, CN, CH3, CF3, SiH3, SiMe3) as well as to evaluate the stability of different interacting topologies in such dimers. It is found that, whenever possible, two mercury-containing molecules will preferentially join through intermolecular HgX donor-acceptor interactions and only ligands devoid of atoms with lone pairs available for such interactions can form dimers attached predominantly via mercurophilic interactions.

In situ generation of functionalized 1,2,4-triazole-5-thiones containing pyridine or pyrazine moieties and their coordination to HgII

The reaction of 2-cyanopyridine or 2-cyanopyrazine with N-methylthiosemicarbazide afforded (Z)-2-(amino(pyridin-2-yl)methylene)-N-methylhydrazinecarbothioamide (HPyAm4M) and (Z)-2-(amino(pyrazin-2-yl)methylene)-N-methylhydrazinecarbothioamide (HPzAm4M), respectively. Prolonged heating under reflux in methanol in the synthesis of these thiosemicarbazones led to the formation of 4-methyl-5-pyridin-2-yl-2,4-dihydro-[1,2,4]triazole-5-thione (HMPytat, 1) and 4-methyl-5-pyrazin-2-yl-2,4-dihydro-[1,2,4]triazole-5-thione (HMPztat, 2) by oxidative cyclization of the starting thiosemicarbazones. Reactions of thiosemicarbazones with mercury(II) salts gave new complexes of general formulae [Hg(tat)X] (3, 4) and [Hg(Htat)2X2] (5, 7, 9–11), along with [Hg3(HEPytat)2(EPytat)2Cl4]·3H2O (6) and [Hg(EPytat)(HEPytat)I]·H2O (8) (Htat = general 1,2,4,-triazole-5-thione). The complexes were isolated as solids and were characterized by elemental analysis, mass spectrometry and IR, 1H NMR and 13C NMR spectroscopy. Recrystallization of the complexes from DMSO gave the compounds [Hg(MPytat)2]n (3a), [Hg(HMPytat)2Br2]·H2O (4a), [{Hg(HEPytat)(μ2-NS-EPytat)Cl2}2Hg] (6a), [Hg(EPytat)2]n (6b), [Hg(MPztat)2]n (10a) and [Hg(EPztat)2]n (11a) (HEPytat = 4-ethyl-5-pyridin-2-yl-2,4-dihydro-[1,2,4]triazole-5-thione and HEPztat = 4-ethyl-5-pyrazin-2-yl-2,4-dihydro-[1,2,4]triazole-5-thione). These complexes were studied by single-crystal X-ray diffraction. The structural analysis revealed the versatility of heterocyclic functionalized 1,2,4-triazole-5-thiones to coordinate to mercury(II) in the thione and thiolate forms through the use of various donor atoms to give different and interesting crystalline packings. The supramolecular assemblies observed in the solid state were analysed. These elegant assemblies are formed by a combination of several noncovalent interactions, including intermolecular hydrogen-bonding supramolecular synthons and aromatic–aromatic interactions. The short Hg⋯Hg distance of 3.660 A indicates the presence of a probable mercurophilic interaction in 6a.

Crystal structure of metallo-DNA duplex containing T-Hg(II)-T base pairs

The DNA duplex containing mercury-mediated base pairs (T-Hg(II)-T) is an attractive biomacromolecular nanomaterials. In a recent study, it was confirmed that the Hg(II) ion significantly stabilizes a DNA duplex by binding selectively to a T-T mispair [1]. Based on the phenomenon observed, a DNA-based sensing system that selectively and sensitively detects Hg(II) ions in aqueous solution was developed [2]. In the present study, we have solved the first crystal structure of a B-form DNA duplex containing two consecutive T-Hg(II)-T base pairs [3]. The Hg(II) ion occupies the center between two T residues. The geometry of the T-Hg(II)-T base pair is very similar to that of the canonical Watson-Crick base pairs. The distance of N3-Hg(II) bond is 2.0 Å, suggesting that the N3 nitrogen releases an imino-proton even at neutral pH (pKa of N3 position of T is 9.8) and directly bonds to Hg(II). In the B-form DNA, the helical axis runs through the center of base pairs, and the Hg(II) ions are therefore aligned along the helical axis. The distance between the two neighboring Hg(II) ions is 3.3 Å. The relatively short Hg(II)-Hg(II) distance indicates that the metallophilic attraction could exit between them and may stabilize the B-form duplex. To support this, the DNA duplex is largely distorted and adopts an unusual non-helical conformation in the absence of Hg(II). In conclusion, the Hg(II) ion is essential for maintaining the B-form conformation of the DNA duplex containing T-T mispairs. The structure of the Hg(II)-DNA hybrid duplex itself and the Hg(II)-induced structural switching from the non-helical form to the B-form provide the basis for the structure-based design of metal-conjugated nucleic acid nanomaterials.

Role of Fluorophore–Metal Interaction in Photoinduced Electron Transfer (PET) Sensors: Time-Dependent Density Functional Theory (TDDFT) Study

The origins of fluorescence quenching by Hg(II) ion chelation and fluorescence enhancement by Zn(II) ion chelation to a PET sensor are investigated. Specifically, the fluorescence quenching and enhancing mechanisms associated with the ligand ADPA (N-(9-anthracenylmethyl)-N-(2-pyridinylmethyl)-2-pyridinemethanamine), protonated ADPA and metal bound (Zn(II) and Hg(II)) ADPA are studied via density functional theory (DFT) and time-dependent DFT (TDDFT) methods. The study found that a structural change in the excited state of ADPA induces reordering of the frontier molecular orbitals, and the S1 → S0 transition becomes a charge transfer transition from the fluorophore to the tertiary nitrogen of the dipicolylamine (DPA) unit, which is forbidden. Protonation on the tertiary amine or chelation of Zn(II) prevents such changes, and the HOMO-LUMO transition is contained within the fluorophore. Therefore, fluorescence is restored. The chelation of Hg(II), on the other hand, promotes extensive interaction between the Hg(II) ion and the fluorophore, which is reflected in the short Hg(II)-fluorophore distance (3.11 Å). A noticeable structural change upon the S0 → S1 transition is observed in the Hg(II)-ADPA system as well, where the resulting S1 → S0 transition becomes a charge transfer transition from mercury to the fluorophore and the fluorescence is thus quenched. Therefore, the present DFT/TDDFT calculations reproduce the fluorescence on-off behavior associated with the entire ADPA family of complexes, which illustrates that the combination of DFT and TDDFT calculations, including excited state geometry optimization, can be a valuable tool to uncover the detailed fluorescence sensing mechanisms.

Lewis acid enhancement by juxtaposition with an onium ion: the case of a mercury stibonium complex

While diarylmercury derivatives (Ar2Hg) are usually not Lewis acidic, we have recently observed that bis(μ-1,8-naphthalenediyl)mercury(II)(bisphenylstibonium(V)) ([2]+), a compound that possesses a Ar2Hg moiety flanked on one of its sides by a stibonium unit, readily binds bromide or iodide ligands at the mercury center. To further investigate this behavior and understand its origin, we now report a series of results dealing with the coordination chemistry of [2]+. In particular, we show that this cation interacts with neutral donor ligands such as THF and DMAP to afford [2-THF]+ and [2-DMAP3]+, respectively, which have been isolated as [PF6]− salts. 1H and 199Hg NMR titration experiments carried out in DMSO-d6 indicate that the mercury center of [2]+ engages heavy halide anions to afford the corresponding complexes 2-Cl, 2-Br and 2-I whose stability constants are equal to 1890 (±10) M−1, 500 (±10) M−1, and 145 (±5) M−1, respectively. In the case of chloride, binding of a second halide ligand at antimony is observed leading to [2-Cl2]− which has been characterized as a [nBu4N]+ salt. Results obtained from titrating [2]+ against F− also indicate the formation of a complex, albeit with antimony as the primary anion binding site. Although the short Hg–Sb distances observed in these complexes (3.04–3.09 Å) remains essentially invariant, NBO calculations show a distinct strengthening of a 6s(Hg)→σ*(Sb–C) donor–acceptor interaction upon coordination of a halide to the mercury center. These NBO results also reveal weak 5d(Hg)→σ*(Sb–C) dative interactions which, as suggested by Hg L3 and Sb K-edge XANES measurements, are too weak to induce a measurable oxidation of the mercury center. In turn, we conclude that the enhanced Lewis acidity of the diarylmercury unit of [2]+ results from the presence of the stibonium moiety which provides a Coulombic pull for the coordination of Lewis bases while also drawing electron density away from the mercury atom via relatively weak orbital interactions.

Aurophilicity versus Mercurophilicity: Impact of d10–d10 Metallophilic Interactions on the Structure of Metal‐Rich Supramolecular Assemblies

Treatment of U-shaped, binuclear Cu(I) complexes 1,1' (1, counterion: BF(4)(-); 1', counterion: PF(6)(-)) with metal cyanide linear linkers K[Au(CN)(2)] (3) and Hg(CN)(2) (4) lead to formation of new supramolecular assemblies 5,5' and 6,6', respectively, in good yield. These derivatives have been characterized by NMR spectroscopy, IR, and X-ray diffraction studies. Derivative 5,5' are supramolecular metallacycles in which intramolecular aurophilic interactions between the Au(I) metal centers of the linkers are observed. Derivative 5 crystallizes as a single solid phase, whereas derivative 5' is characterized in the solid state as four different pseudo-polymorphs (5'a-d). Notably in the case of phase 5'd, a dimer of supramolecular metallacycles bounded by intermolecular aurophilic interactions is formed. Conversely, derivatives 6,6' present large structural diversity depending on the nature of the counterion. Derivative 6 is a supramolecular rectangle in which the Hg(II)-Hg(II) metal distance suggests mercurophilic interaction, whereas 6' crystallizes as two different pseudo-polymorphs 6'a,b, that is, a one-dimensional coordination polymer and one oligomer with no short Hg(II)-Hg(II) metal contacts, respectively. In derivatives 6,6', short contacts between the Hg(II) metal centers and fluorine atoms of the counterions are also observed, which may explain the counterion structural dependence of these supramolecular assemblies based on Hg(II) metal cyanide linker. Comparison of the different solid-state structures characterized highlights the importance of weak secondary interactions between the linkers for the formation supramolecular metallacycles from molecular clips 1,1' and suggests the range of energies required for these interactions to form metallacycles and to induce self-aggregation.

Synthesis, Characterization, Crystal and Molecular Structure Analysis of Di-μ-chlorido-bis{[(4-bromobenzoylmethylene) triphenyl-λ5-phosphorane]chloridomercury(II)}

The reaction of phosphorus ylide Ph3PCHC(O)C6H4–4–Br with HgCl2 in equimolar ratios using methanol as a solvent is reported. This reaction led to binuclear complex C-Coordination of ylide and trans-like structure of complex [Br–BPPY HgCl2]2·2CHCl3(1) is demonstrated by single crystal X-ray analyses and IR, 1H and 31P NMR spectroscopy. Elemental analyses indicate a 1:1 stoichiometry between the ylide and Hg(II) in the product two Hg atoms are four-coordinate in the form of a tetrahedral. The title molecule [Hg2Cl4(C26H29BrOP)2]·2CHCl3(1) has a crystallographic inversion centre at the centroid of the four-membered ring formed by the two Hg atoms and two Cl atoms, with one short Hg–Cl(2.393A°) bond, one Hg–C bond and two asymmetric bridging Hg–Cl (bonds at distances o 2.7345 and 2.2.7090A. The crystal packing is stabilized by C–H…O hydrogen bonds. The reaction of phosphorus ylide Ph3PCHC(O)C6H4–4–Br with HgCl2 in equimolar ratios using methanol as a solvent is reported. This reaction led to binuclear complex C-Coordination of ylide and trans-like structure of complex [Br–BPPY HgCl2]2·2CHCl3(1) is demonstrated by single crystal X-ray analyses and IR, 1H and 31P NMR spectroscopy. Elemental analyses indicate a 1:1 stoichiometry between the ylide and Hg(II) in the product two Hg atoms are four-coordinate in the form of a tetrahedral. The title molecule [Hg2Cl4(C26H29BrOP)2]·2CHCl3(1) has a crystallographic inversion centre at the centroid of the four-membered ring formed by the two Hg atoms and two Cl atoms, with one short Hg–Cl(2.393A°) bond, one Hg–C bond and two asymmetric bridging Hg–Cl (bonds at distances o 2.7345 and 2.2.7090A. The crystal packing is stabilized by C–H…O hydrogen bonds.

Mercury and methylmercury concentrations in high altitude lakes and fish (Arctic charr) from the French Alps related to watershed characteristics

Total mercury (THg) and methylmercury (MeHg) concentrations were measured in the muscle of Arctic charr ( Salvelinus alpinus) and in the water column of 4 lakes that are located in the French Alps. Watershed characteristics were determined (6 coverage classes) for each lake in order to evaluate the influence of watershed composition on mercury and methylmercury concentrations in fish muscle and in the water column. THg and MeHg concentrations in surface water were relatively low and similar among lakes and watershed characteristics play a major role in determining water column Hg and MeHg levels. THg muscle concentrations for fish with either a standardized length of 220 mm, a standardized age of 5 years or for individualuals did not exceed the 0.5 mg kg − 1 fish consumption advisory limit established for Hg by the World Health Organization (WHO, 1990). These relatively low THg concentrations can be explained by watershed characteristics, which lead to short Hg residence time in the water column, and also by the short trophic chain that is characteristic of mountain lakes. Growth rate did not seem to influence THg concentrations in fish muscles of these lakes and we observed no relationship between fish Hg concentrations and altitude. This study shows that in the French Alps, high altitude lakes have relatively low THg and MeHg concentrations in both the water column and in Arctic charr populations. Therefore, Hg does not appear to present a danger for local populations and the fishermen of these lakes.

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

A dimercury(I) 18-crown-6 complex is isolated, and its possible role in the hydrothermal preparation of the mercuric nitrite complex is discussed. The reported structures are of [Hg(2)(18-crown-6)(2)(H(2)O)(2)](ClO(4))(2) (1), monoclinic, C2/c, a = 21.0345(9), b = 12.1565(5), c = 16.8010(7) A, beta = 113.2000(10) degrees , V = 3948.7(3) A(3), Z = 16, R = 0.0230; [Hg(18-crown-6)](NO(2))(2) (2), monoclinic, P2(1)/c, a = 8.027(5), b = 14.437(9), c = 7.827(5) A, beta = 95.165(11) degrees , V = 905.6(10) A(3), Z = 2, R = 0.0175. The complex cation in compound 1 consists of a mercurous dimer exhibiting a Hg-Hg bond length of 2.524(2) A. Non-bonding interactions between adjacent crown ether macrocycles across the Hg-Hg bond result in large variations in mercury to oxygen distances within equatorial coordination sites. At low pH compound 1 is proposed to be preferentially formed under hydrothermal conditions affording compound 2 upon disproportionation. Nitrite ions ligate via a unidentate nitrito (cis to metal) coordination mode as interpreted using vibrational (infrared) spectroscopy. The conformation adopted by 18-crown-6 in compounds 1 and 2 is closely related to a D(3d) conformation as evidenced by X-ray crystallography. Band splitting readily observed in vibrational spectra of the metal free crown ether, attributed to vibrational modes of oxyethylene fragments, is absent in spectra of 1 and 2 confirming a regular D(3d) macrocyclic orientation. Short Hg-O bonds observed for axially coordinated water molecules in 1 and coordinated nitrite ligands in 2, illustrate the prevalence of relativistic effects commonly observed in mercury complexes.

Hg(II)···Pd(II) Metallophilic Interactions

Reaction of bis(pentafluorophenyl)mercury (1) with the Pd(II) complexes [Pd(salophen)] (I, salophen = N,N'-disalicylidene-o-phenylenediaminate) and [Pd(N--C)(OAc)]2 (II, N--C = (2-(2-pyridyl)phenyl-C,N)) leads to the formation of the supramolecular complexes [1-(I)2] and [1-(II)2] in which the mercury synthon is sandwiched by two molecules of the palladium complex. These complexes, whose formation can be observed in solution by UV-vis spectroscopy, have been fully characterized. The short Hg-Pd distances of 3.2841(2) A in [1-(I)2] and 3.1065(8) A in [1-(II)2] indicate the presence of a Hg-Pd metallophilic interaction which, at least for [1-(II)2], is complemented by a Pd(II)-->Hg(II) donor-or component.

Enhanced Metal Ion Selectivity of 2,9-Di-(pyrid-2-yl)-1,10-phenanthroline and Its Use as a Fluorescent Sensor for Cadmium(II)

The metal ion complexing properties of the ligand DPP (2,9-di-(pyrid-2-yl)-1,10-phenanthroline) were studied by crystallography, fluorimetry, and UV-visible spectroscopy. Because DPP forms five-membered chelate rings, it will favor complexation with metal ions of an ionic radius close to 1.0 A. Metal ion complexation and accompanying selectivity of DPP is enhanced by the rigidity of the aromatic backbone of the ligand. Cd2+, with an ionic radius of 0.96 A, exhibits a strong CHEF (chelation enhanced fluorescence) effect with 10(-8) M DPP, and Cd2+ concentrations down to 10(-9) M can be detected. Other metal ions that cause a significant CHEF effect with DPP are Ca2+ (10(-3) M) and Na+ (1.0 M), whereas metal ions such as Zn2+, Pb2+, and Hg2+ cause no CHEF effect with DPP. The lack of a CHEF effect for Zn2+ relates to the inability of this small ion to contact all four donor atoms of DPP. The structures of [Cd(DPP)2](ClO4)2 (1), [Pb(DPP)(ClO4)2H2O] (2), and [Hg(DPP)(ClO4)2] (3) are reported. The Cd(II) in 1 is 8-coordinate with the Cd-N bonds to the outer pyridyl groups stretched by steric clashes between the o-hydrogens on these outer pyridyl groups and the central aromatic ring of the second DPP ligand. The 8-coordinate Pb(II) in 2 has two short Pb-N bonds to the two central nitrogens of DPP, with longer bonds to the outer N-donors. The coordination sphere around the Pb(II) is completed by a coordinated water molecule, and two coordinated ClO4(-) ions, with long Pb-O bonds to ClO4(-) oxygens, typical of a sterically active lone pair on Pb(II). The Hg(II) in 3 shows an 8-coordinate structure with the Hg(II) forming short Hg-N bonds to the outer pyridyl groups of DPP, whereas the other Hg-N and Hg-O bonds are rather long. The structures are discussed in terms of the fit of large metal ions to DPP with minimal steric strain. The UV-visible studies of the equilibria involving DPP and metal ions gave formation constants that show that DPP has a higher affinity for metal ions with an ionic radius close to 1.0 A, particularly Cd(II), Gd(III), and Bi(III), and low affinity for small metal ions such as Ni(II) and Zn(II). The complexes of several metal ions, such as Cd(II), Gd(III), and Pb(II), showed an equilibrium involving deprotonation of the complex at remarkably low pH values, which was attributed to deprotonation of coordinated water molecules according to: [M(DPP)(H2O)]n+ <==> [M(DPP)(OH)](n-1)+ + H+. The tendency to deprotonation of these DPP complexes at low pH is discussed in terms of the large hydrophobic surface of the coordinated DPP ligand destabilizing the hydration of coordinated water molecules and the build-up of charge on the metal ion in its DPP complex because of the inability of the coordinated DPP ligand to hydrogen bond with the solvent.

Synthesis, structures, and luminescence properties of ternary supramolecular hydrogen‐bonded complexes involving [(o‐C6F4)Hg]3, carbazole, and a Lewis base

AbstractThe interaction of trimeric perfluoro‐ortho‐phenylene mercury (1) with carbazole in dichloromethane, THF, and THF/NEt3 leads to the crystallization of [1·C12H8NH] (2), [1·(C12H8NH·THF)] (3), and [1·(C12H8NH·NEt3)] (4), respectively. Adducts 3 and 4 have been characterized by elemental analysis, IR spectroscopy, and luminescence spectroscopy. The crystal structures of 3 and 4 have also been determined. Both adducts have extended structures that exhibit supramolecular binary stacks, where molecules of 1 and the carbazole–Lewis base complex alternate. Short Hg–C contacts involving molecules of 1 and carbazole indicate the presence of secondary Hg–π interactions. In addition, adducts 3 and 4 display hydrogen‐bonding interactions between the acidic NH moiety of carbazole and the heteroatom of the Lewis base. The presence of this hydrogen bond is also confirmed by IR spectroscopy, which shows that the νNH of 3 and 4 is lower than that of 2. The luminescence spectra of these adducts correspond to the phosphorescence of carbazole, which is induced by the mercury heavy atom effect. In the case of 3 and 4, additional low‐energy bands are observed at 578 and 567 nm. © 2007 Wiley Periodicals, Inc. Heteroatom Chem 18:195–201, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20329

Short-term high glucose exposure induces monocyte-endothelial cells adhesion and transmigration by increasing VCAM-1 and MCP-1 expression in human aortic endothelial cells

Acute, short-term hyperglycemia is becoming recognized as an important risk factor for several diseases. In the present study, using human aortic endothelial cells (HAECs), we investigated whether short-term high glucose exposure, either on the scale of hours, could enhance the monocyte adhesion and migration to the subendothelium via increasing expression of adhesion molecules and release of chemotactic factors. HAECs stimulated with 25 mM d(+)glucose (HG) for not more than 12 h, exhibited rapid up-regulation of vascular cell adhesion molecule-1 (VCAM-1) and monocyte chemoattractant protein-1 (MCP-1) mRNA and protein. Although intercellular adhesion molecule-1 (ICAM-1) is considered as a marker of the activation of the atherogenic process, early up-regulation was not observed, and VCAM-1 and MCP-1 protein enhance was sufficient to increase the adhesiveness of human monocytes U-937 to HAECs and their transmigration into the subendothelial space after 4 h HG stimulation; both effects were prevented by interfering with monoclonal antibodies against VCAM-1, CD11b, and MCP-1. An increased intracellular oxidative stress, a translocation of NF-κB to the nucleus and a prevention of adhesion and transmigration of U-937 by interfering with NF-κB inhibitors was also observed after a short HG treatment. Taken together, these results suggest that either acute hyperglycemic spikes could exert an influence on the onset of diabetic complications and on the development of the atherogenic profile on diabetic and non-diabetic subjects.