Cadmium O‐alkylxanthates as CVD precursors of CdS: a chemical characterization

Cadmium bis(O‐alkylxanthates) are potential single‐source molecular precursors for the chemical vapor deposition (CVD) of Cd(II) sulfide thin films. In this work, a multi‐technique characterization of Cd(O‐RXan)₂ compounds [where O‐RXan is CH₃CH₂OCS₂ (O‐EtXan) or (CH₃)₂CHOCS₂ (O‐ⁱPrXan)] is performed by means of several analytical methods (extended x‐ray absorption fine structure, Raman, Fourier transform infrared and optical absorption, spectroscopics ¹H and ¹³C NMR, thermal analysis and mass spectrometry) for a thorough investigation of their structure and chemical–physical properties. The most important results concerning the chemical behavior under different experimental conditions, with particular attention to relevant properties for CVD applications, are presented and discussed. Copyright © 2005 John Wiley & Sons, Ltd.     

Study of Complex Formation Between 18-Crown-6 and Pb2+, Tl+ and Cd2+ Cations in Binary Aqueous/Non-aqueous Solvents Using Polarographic Techniques (DPP and SWP)

The complexation of Pb²⁺, Tl⁺ and Cd²⁺ cationsby 18-crown-6 was studied in water/propanol (H₂O/PrOH),water/acetonitrile (H₂O/AN) and water/dimethylformamide(H₂O/DMF) binary systems at 20 °C using squarewave polarography (SWP) and differential pulse polarography (DPP).It was confirmed that the stoichiometry of each of the complexes formed between 18C6 and the respective cations is 1 : 1. The formation constants of the complexes were found to increase with increasing concentration of the non-aqueous solvent. In all cases, a stability order of Pb²⁺ > Tl⁺ > Cd²⁺ was observed. In general,the stabilities of individual complexes were found to decrease as the binary solvent mixture varied from H₂O/AN to H₂O/PrOH to H₂O/DMF.     

Salen impregnated silica gel as a new sorbent for on-line preconcentration of cadmium(II)

A new sorbent – salen impregnated silica gel – was prepared and characterised for application as a minicolumn packing for flow-injection on-line preconcentration of cadmium(II). The system was coupled with flame atomic absorption spectrometer (FI-FAAS). The optimal pH for Cd(II) sorption was in the range of 7.4–8.8 and nitric acid (1%, v/v) was efficient as eluent. Sorption was most effective within the sample flow rate up to 7?mL?min^?1. Sorption capacity of the sorbent found in a batch procedure was 26.3?µmol?g^?1 (2.95?mg?g^?1). Enrichment factor (EF) and limit of detection (LOD) obtained for 120-second loading time were 113 and 0.26?µg?L^?1, respectively. The sorbent stability in the working conditions was proved for at least 100 preconcentration cycles. The evaluated method was applied to Cd(II) determination in various water samples.     

A study of the glutathione metaboloma peptides by energy-resolved mass spectrometry as a tool to investigate into the interference of toxic heavy metals with their metabolic processes

To better understand the fragmentation processes of the metal-biothiol conjugates and their possible significance in biological terms, an energy-resolved mass spectrometric study of the glutathione conjugates of heavy metals, of several thiols and disulfides of the glutathione metaboloma has been carried out. The main fragmentation process of gamma-glutamyl compounds, whether in the thiol, disulfide, thioether or metal-bis-thiolate form, is the loss of the gamma-glutamyl residue, a process which ERMS data showed to be hardly influenced by the sulfur substitution. However, loss of the gamma-glutamyl residue from the mono-S-glutathionyl-mercury (II) cation is a much more energetic process, possibly pointing at a strong coordination of the carboxylic group to the metal. Moreover, loss of neutral mercury from ions containing the gamma-glutamyl residue to yield a sulfenium cation was a much more energetic process than those not containing them, suggesting that the redox potential of the thiol/disulfide system plays a role in the formal reduction of the mercury dication in the gas phase. Occurrence of complementary sulfenium and protonated thiol fragments in the spectra of protonated disulfides of the glutathione metaboloma mirrors the thiol/disulfide redox process of biological importance. The intensity ratio of the fragments is proportional to the reduction potential in solution of the corresponding redox pairs. This finding has allowed the calculation of the previously unreported reduction potentials for the disulfide/thiol pair of cysteinylglycine, thereby confirming the decomposition scheme of bis- and mono-S-glutathionyl-mercury (II) ions. Finally, on the sole basis of the mass spectrometric fragmentation of the glutathione-mercury conjugates, and supported by independent literature evidence, an unprecedented mechanism for mercury ion-induced cellular oxidative stress could be proposed, based on the depletion of the glutathione pool by a catalytic mechanism acting on the metal (II)-thiol conjugates and involving as a necessary step the enzymatic removal of the glutamic acid residue to yield a mercury (II)-cysteinyl-glycine conjugate capable of regenerating neutral mercury through the oxidation of glutathione thiols to the corresponding disulfides.     

Synthesis and crystal and molecular structure of mixed-ligand complexes Cd(2,2′-Bipy)(i-PrOCS2)2 and (2,2′-Bipy)(i-BuOCS2)2

Mixed-ligand complexes Cd(2,2′-Bipy)(i-PrOCS₂)₂ (I) and Cd(2,2′-Bipy)(i-BuOCS₂)₂ (II) have been prepared. Their structures were solved using the X-ray diffraction technique (X8 APEX diffractometer, MoK _α radiation, 1941 and 4244 F _hkl , R = 0.0188 and 0.0379). The crystals are orthorhombic with unit cell parameters a = 18.1404(4) Å, b = 6.9513(1) Å, c = 17.5835(4) Å; V = 2217.27(8) ų, Z = 4, space group Pccn (for complex I) and a = 11.7890(3) Å, b = 12.1859(3) Å, c = 17.5335(5) Å; V = 2518.9(1) ų, Z = 4, space group P2₁2₁2₁ (for complex II). The structures consist of isolated mononuclear molecules. The cadmium atoms have distorted octahedral N₂S₄ environments. Molecular packings and intermolecular interactions in the structures are considered. __________ Translated from Zhurnal Strukturnoi Khimii, Vol. 46, No. 6, pp.1064–1071, November–December, 2005. Original Russian Text Copyright ? 2005 by S. V. Larionov, L. A. Glinskaya, T. G. Leonova, and R. F. Klevtsova     

Use of unmodified silver nanoparticles (AgNPs) as colorimetric Hg(II) sensor: A new approach to sensitive and high sample throughput determination of Hg(II) under high influence of ionic suppression

Facile unmodified silver nanoparticles (AgNPs) as colorimetric sensor for determination of Hg(II) ions in aqueous samples were developed using UV-Vis spectrophotometry. Abrupt change in absorbance of the AgNPs was observed, which progressively decreased and slightly shifted to the blue wavelength as the concentration of Hg(II) increased. It appears that the AgNPs were oxidized by Hg(II), resulting in disintegration of the AgNPs and Hg(0). Deposition of Hg(0) on the surface of AgNPs also occurred, resulting in amalgam particles of mercury (Hg-Ag). Interestingly, the developed approach showed a significant enhancement in the Hg(II) analytical sensitivity when formic acid was doped onto the AgNPs, with the linearity range of 0.01–10 mg L^?1 (r² = 0.999) providing the quantitative detection limit of 0.007 mg L^?1 (3SD blank/slope of the calibration curve). Greater selectivity toward Hg(II) over other ions and colour dyes was also observed, likely a result of stabilization by polyvinylpyrrolidone (PVP), which kept the AgNPs well-stabilized and dispersed in the bulk aqueous environment making them resistant to ionic suppression. Under using a 96-well microplate and a smartphone equipped with homemade application as a colorimetric analyzer under controlled lighting, high sample throughput (128 sample h^?1, n = 4) was achieved, establishing its potential for practical analysis. The percentage recoveries of spiked aqueous samples obtained from the microplate-based system were in acceptable range, in agreement with the values obtained from the UV-Vis spectrophotometry-based system. The proposed colorimetric sensor has been shown to provide a rapid, simple, sensitive and selective detection of Hg(II) ions in various aqueous samples.     

Metallothionein as a biomarker for mercury in tissues of rat fed orally with cinnabar

Cinnabar, as one of the most widely used mineral drugs in traditional Chinese medicines, has been proven to have prominent curative effects in clinical use for more than 2000 years. But the safety and toxicity of the drug has been under constant debate in clinic usage. Metallothionein (MT) contains about 30% of cysteine in the molecule, and plays an important detoxification role against heavy metals. In this study, it was used as a biomarker to assess mercurial accumulation in rats fed orally with cinnabar. After feeding rats with cinnabar by gastric gavage at different dosages and at different times, the distribution of heavy metals (including mercury, copper and zinc) and MT was investigated among rat tissues, including liver, kidney, heart, brain, testis and blood. Metals and MT determinations were carried out using inductively coupled plasma mass spectrometry (ICP‐MS) and a modified mercury saturation assay technique respectively. The results indicated that mercury was easily accumulated in the tissues of rats exposed to cinnabar, especially in kidney. For example: at a feeding dosage of 5 g kg^?1 (bw) for 4 weeks, the mercury concentrations in kidney were 13, 8.7, 21.6 and 26 times those in liver, testis, brain and heart respectively; and at 2.5 g kg^?1 (bw) for 2 weeks, the mercury concentrations in kidney were 21, 2.1, 3 and 21 times those in liver, testis, brain and heart respectively. In addition, mercury in kidney and liver of all cinnabar groups was significantly higher than that of the control group (P < 0.01). A high positive correlation observed between MT concentrations and mercury levels in both liver and kidney (R² = 0.9299, P < 0.02 for liver; R² = 0.9923, P < 0.0008 for kidney) indicated that MT could be used as a biomarker for mercury in tissues. Copyright © 2004 John Wiley & Sons, Ltd.     

Syntheses,characterization and crystal structures of mixed-ligand Cu(II), Ni(II) and Mn(II) complexes of N-(1-phenyl-3-methyl-4-propenylidene-5-pyrazolone)-salicylidene hydrazide containing ethanol or pyridine as a co-ligand

Five new mixed-ligand complexes [CuL(EtOH)] (1), [NiL(EtOH)₃] (2), [Mn₂L₂(μ₂-EtOH)₂(EtOH)₂] (3), [CuL(Py)] · MeOH (4) and [NiL(Py)₃] (5) (L²⁻ = N-(1-phenyl-3-methyl-4-propenylidene-5-pyrazolone)-salicylidene hydrazide anion, Py = pyridine) have been synthesized and characterized by elemental analyses, IR spectra, thermal analyses and single crystal X-ray diffraction. The crystallographic structural analyses of these complexes reveal that the ligand (H₂L) itself undergoes isomerization from the keto form to the enol form in the reaction, then loses two protons and acts as a double negatively charged tridentate chelating agent coordinated to the metal ion in the solution. The final results show that when a co-ligand was present in the synthetic reaction, other coordination sites around the metal ions Cu²⁺ and Ni²⁺ were completed either by the ethanol or pyridine molecules under the common solvent reaction or solvothermal syntheses conditions, respectively. In the case of the Mn²⁺ ion, it was still coordinated with the solvent molecules regardless of whether it was synthesized under the common solvent reaction or solvothermal syntheses with pyridine. The reason for this difference might be attributed to the fact that the coordination modes and bonding effect of the co-ligand with the metal ions are different, the final complexes tend to form the most stable compound.     

Nickel(II) tri-tert-butoxysilanethiolates with N-heterocyclic bases as additional ligands: Synthesis, molecular structure and spectral studies

Three heteroleptic, neutral nickel(II) tri-tert-butoxysilanethiolates with monodentate heterocyclic bases (pyridine, 2-methylpyridine and 3,5-dimethylpyridine) serving as additional ligands have been prepared following the same synthetic procedure. The complexes were characterized by single crystal X-ray structure determination and elemental analysis. For complexes 1 and 2, FT-IR and UV-Vis spectroscopy have been additionally recorded.Three different coordination motifs have been observed in these complexes. Molecules building tetragonal crystals of [Ni{SSi(O^tBu)₃}₂(C₅H₅N)] (1) feature Ni(II) coordinated by two S,O-chelating tri-tert-butoxysilanethiolato residues and one N atom of pyridine in a strongly distorted trigonal bipyramidal environment. The complex [Ni{SSi(O^tBu)₃}₂(C₆H₇N)₂] (2) forms triclinic crystals and its core atoms adopt a planar geometry with Ni(II) in the middle of the N₂S₂ plane. Molecules of complex [Ni{SSi(O^tBu)₃}₂(C₇H₉N)₂(H₂O)] (3) form orthorhombic crystals with penta-coordinated Ni(II) in a distorted tetragonal pyramidal NiN₂OS₂ environment. Complex 2 roughly mimics one of the two metal centers in the active site of the ACS/CODH enzyme.     

Cage complexes as a molecular scaffold for assembling of polyfunctional and multicentered systems: Synthesis and structures of the first nitroxide clathrochelates

The reaction of the reactive clathrochelate FeBd₂(Cl₂Gm)(BF)₂ (Bd and Cl₂Gm are the α -benzyl dioxime and dichloroglyoxime dianions, respectively) with amino-substituted nitroxide TEMPO-NH₂ afforded new mono- and biradical iron(II) mono- and dinitroxide clathrochelate complexes. The complexes were characterized by X-ray diffraction and spectroscopic (UV-Vis, ESR, and ⁵⁷Fe Mossbauer) methods. Dedicated to Academician N. K. Kochetkov on the occasion of his 90th birthday. __________ Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 1097–1102, May, 2005.     

Two-dimensional molecular pattern in the structure of a calcium(II) complex with pyrazine-2,3-dicarboxylate and water ligands

The structure of di(aquo-O)(pyrazine-2,3-dicarboxylato-N,O; -O′,O′′) calcium(II) hydrate [Ca(2,3-PZDC)(H₂O)₂·;H₂O] contains molecular sheets in which Ca(II) ions are bridged by the carboxylate groups of the ligand molecules. Two bridging paths are evident. In the first, an N,O-bonding moiety formed by a hetero-ring nitrogen atom and the carboxylate oxygen atom nearest to it and both oxygen atoms of the second carboxylic group are active. The second path is formed by the other oxygen atom from the carboxylic group involved in the N,O-bonding moiety and an oxygen atom from the second carboxylic group. The latter atom is bidentate. A two-dimensional molecular pattern is formed. Each Ca(II) ion is also coordinated by two water oxygen atoms, making the number of coordinated atoms eight. The coordination polyhedron is a distorted pentagonal bipyramid with an oxygen atom at the apex on one side of the equatorial plane and two oxygen atoms forming the apices on the other side.     

Inclusion of the ligand field contribution in a polarizable molecular mechanics: SIBFA-LF

To account for the distortion of the coordination sphere that takes place in complexes containing open-shell metal cations such as Cu(II), we implemented, in sum of interactions between fragments ab initio computed (SIBFA) molecular mechanics, an additional contribution to take into account the ligand field splitting of the metal d orbitals. This term, based on the angular overlap model, has been parameterized for Cu(II) coordinated to oxygen and nitrogen ligands. The comparison of the results obtained from density functional theory computations on the one hand and SIBFA or SIBFA-LF on the other shows that SIBFA-LF gives geometric arrangements similar to those obtained from quantum mechanical computations. Moreover, the geometric improvement takes place without downgrading the energetic agreement obtained from SIBFA. The systems considered are Cu(II) interacting with six water molecules, four ammonia or four imidazoles, and four water plus two formate anions.     

pH-stat techniques in titrimetric analysis: Part 3. The principles of pH-stat chelatometric titrations

Chelatometric titrations can be effectively monitored by means of the pH-stat technique. During the addition of the primary titrant (the chelating agent), the pH of the titrated solution is kept at a pre-selected value by adding a strong base as the auxiliary titrant. The equivalence point is characterised by a sudden change in the ratio between the added volumes of auxiliary and primary titrant solutions, i.e. in the slope of the linearly segmented titration plot representing the volume of the base against the volume of the chelating agent. The slope of the linear segments depends on the reactions involving proton exchange, which accompany the primary complexation reaction. The dependence of the shape of the plots on the imposed pH for typical titrations (magnesium(II) and copper(II)) is examined and the conditions for the feasibility of pH-stat chelatometric titrations are discussed.     

Probing delocalisation across highly ethynylated mono and dinuclear Pt(II) tethers containing nitrogroups and organic models as redox active probes: X-ray crystal structure of trans-[Pt(CC-C6H4NO2)2(PPh3)2]

The electrochemical study on Pt(II) organometallic and organic ethynylated compounds bearing nitro substituents in the phenyl groups has been performed, demonstrating that the presence of severe chemical irreversibility accompanying the electron transfer, preclude an evaluation of the electronic communication between redox active centres. The X-ray structure of the complex trans-[Pt(CC-C₆H₄NO₂)₂(PPh₃)₂] is showed.     

The determination of some "toxic" metals in human liver as a guide to normal levels in New Zealand. Part II. Arsenic, mercury and selenium.

Results of analyses for arsenic, mercury and selenium in human livers considered to be representative of the population of New Zealand are reported. Procedures are described for the determination of the three elements in liver tissue by colorimetry, flameless atomic absorption spectrometry and spectrofluorimetry respectively.     

Complexation in a 5-acylpyrimidine-4-thione—aliphatic diamine—metal(II) chloride system (M = Ni or Co). The molecular structure of <Emphasis Type="Italic">fac</Emphasis>-tris(5-acetyl-2,4-dimethylpyrimidine-6-thiolato)cobalt(III)

The reactions of 5-acylpyrimidine-4-thiones with aliphatic diamines in the presence of Ni^II and Co^II salts were studied. New Ni^II and Co^III complexes with ligands of the pyrimidinethione series were synthesized. The results of the reactions of 5-acetyl-6-methyl-2-phenylpyrimidine-4-thione and 5-acetyl-2,6-dimethylpyrimidine-4-thione with ethylenediamine or 1,3-diaminopropane in the presence of NiCl₂· 6H₂O or CoCl₂·6H₂O depend on (1) the nature of the substituent at position 2 of the pyrimidine ring, (2) the length of the polymethylene bridge between the nitrogen atoms in the diamine molecule, (3) the nature of complex-forming metal, and (4) the pyrimidinethione: diamine ratio. The resulting complexes were studied by electrochemical methods. The mechanism of electrooxidation and electro-reduction of 5-acylpyrimidine-2-thiones and related nickel and cobalt complexes was proposed. The structures of the complexes were investigated by NMR, UV-Vis spectroscopy, and IR spectroscopy and mass spectrometry. The molecular structure of fac-tris(5-acetyl-2,4-dimethylpyrimidine-6-thiolato)cobalt(III) was established by X-ray diffraction. According to semiempirical quantum-chemical calculations by the PM3(tm) method, both the highest occupied and lowest unoccupied molecular orbitals in the molecules of the compounds under study have a π symmetry and are localized predominantly on the ligand fragments. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2666–2678, December, 2005.     

Multifrequency electron paramagnetic resonance and theoretical studies of a Mn(II) (S = 5/2) complex: The role of geometrical elements on the Zero Field Splitting parameters

The Zero Field Splitting (ZFS) parameters of the mononuclear Mn(II) (S = 5/2) compound [Mn(Ac4Ph)₂], where HAc4Ph stands for 4-phenyl-2-acetylpyridine thiosemicarbazone, are determined by dual mode X-band and high field/high frequency electron paramagnetic resonance spectroscopy. Density functional theory (DFT) calculations reproduce both the sign and absolute value of the axial parameter D of the ZFS tensor, whose distribution is quantitatively correlated to distribution on geometrical elements of the complex.     

Synthesis and characterization of 2,7-dihydro-1H-dinaphtho[c,e]tellurepin: a new heterocyclic telluride

Synthesis of the racemic cyclic telluride, i.e., 2,7-dihydro-1H-dinaphtho-[c,e]tellurepin (1), possessing a C₂ axis was based on the reaction of 2,2^′-bis(bromomethyl)-1,1^′-binaphthalene with potassium tellurocyanate in dry DMSO. Reaction of halogens with 1 gave the diiodo (2), dibromo (3) and dichloro (4) derivatives. Treatment of 1 with iodomethane and iodoethane gave the methyl- and ethyl tellurepinium iodides, 5 and 6, respectively.Compound 1 reduced the carbonyl groups in DDQ and TCQ to hydroxyl groups. Mononuclear palladium(II) complex, [(C₂₂H₁₆Te)₂PdCl₂], was prepared by reaction of 1 with [PdCl₂(NCPh)₂].All new compounds were characterized by elemental analysis and spectroscopic techniques.     

Synthesis,molecular and crystalline architectures,and magnetic properties of neutral nickel(II)dicyanamide coordination polymers containing a symmetrical/unsymmetrical 1,2-diamine as an end-capping ligand

Two neutral nickel(II) coordination polymers [Ni(en)(dca)₂]_n (1) and [Ni(dmen)(dca)₂]_n (2) (en = ethylenediamine; dmen = N,N-dimethylethylenediamine; dca = dicyanamide) have been synthesized and X-ray crystallographically characterized. Each nickel(II) center in 1/2 adopts a distorted octahedral coordination environment with a NiN₆ chromophore ligated by two amine N atoms of the bidentate amine (en/dmen) and four nitrile N atoms of μ_1,5 bridged dca. The metal(II) centers are connected with each other through single μ_1,5 M–NCNCN–M bridges, resulting in a 2D layer structure with a (4,4) topology in 1 and a 3D network of topology (6,6) in 2. Multiple lateral N–H···N and C–H···N hydrogen bondings promote dimensionality. The magnetic susceptibility results of 1 and 2 at very low temperature support the zero-field splitting effect of the nickel(II) ions.