Structural Study of Alkaline 1-Phenyl-1H-1, 2, 3, 4-tetrazole-5-thiolate Salts: An Example of Periodicity in Alkaline Cations

The alkaline 1-phenyl-1H-1, 2, 3, 4-tetrazole-5-thiolate salts, M[C₆H₅N₄CS] (M = Li ( 1 ), Na ( 2 ), K ( 3 ), Rb ( 4 ) and Cs ( 5 )) were obtained and characterized by means of mass spectrometry (FAB⁺) and NMR (¹H; ¹³C) spectroscopy. The structures of Na ( 2 ), K ( 3 ), Rb ( 4 ) and Cs ( 5 ) compounds were determined by X-ray diffraction methods. The ligand shows a rich variety of coordination patterns with the alkaline cations. The formation of a four-membered ring MSCN in the compounds with heavier alkali cations (K, Rb and Cs) is shown. In all the cations the coordination number around it increases with the ionic radius. Compounds with Cs⁺ and Rb⁺ exhibited the formation of Cs-C and Rb-C interactions with the phenyl group.     

Reduced-size polarized basis sets for calculations of molecular electric properties. IV. First-row transition metals

Recent studies of the perturbation-dependent basis sets have indicated the possibility of a significant reduction of the size of the usual CGTO sets without considerable loss of accuracy in calculations of molecular electric properties. The resulting (ZPolX) basis sets have been developed for several atoms of the first and second row of the Periodic Table. The same method of the ZPolX basis set generation is extended for the first-row transition metals and the corresponding contracted ZPolX basis sets of the size [6s5p3d1f] are determined for both nonrelativistic and scalar relativistic calculations. The performance of the ZPolX basis sets is verified in calculations on the first-row transition metal oxides at the level of the ROHF, ROHF/CASPT2, and ROHF/CCSD(T) approximations. Also the study of the dipole polarizability of TiCl₄ confirms the excellent features of these very compact basis sets. The ZPolX basis sets for nonrelativistic and relativistic calculations of molecular electric properties are available on the web page http://www.chem.uni.torun.pl/zchk/basis-sets.html.     

Catalytic olefination of carbonyl compounds. A new versatile method for the synthesis of alkenes

The review is devoted to a new catalytic olefination reaction (COR) discovered by the authors. This is the reaction between N-unsubstituted hydrazones of carbonyl compounds with dihalides CHal₂XY in the presence of copper(i) chloride to give substituted alkenes. Catalytic olefination is versatile. Variation of the carbonyl and olefinating components opens up the way for the synthesis of various classes of unsaturated compounds including those containing functional groups. The reaction mechanism is discussed and a catalytic cycle describing the process is proposed. A model for estimating and predicting the reactivity of halogen-containing compounds in the COR is developed. The relationship between the structure of the carbonyl substrates and their behavior in the title reaction is elucidated.     

Nanometer-sized zirconium dioxide microcolumn separation/preconcentration of trace metals and their determination by ICP-OES in environmental and biological samples

A new method is proposed using a microcolumn (20 mm × 2.0 mm) packed with nanometer-sized zirconia as solid-phase extractor for the separation/preconcentration of Mn, Cu, Cr, Zn, Ni and Co prior to their determination by inductively coupled plasma optical emission spectrometer (ICP-OES) in environmental samples. The factors affecting the separation and preconcentration of analytes such as pH, sample flow rate and volume, eluent concentration and volume were determined, interfering ions were studied, and the optimal experimental conditions were established. The adsorption capacity of nanometer-sized ZrO₂ for Mn, Cu, Cr, Zn, Ni and Co was found to be 1.3, 1.3, 1.7, 2.0, 3.9 and 1.5 mg g⁻¹, respectively. The detection limits of the method were 12, 58, 24, 2, 7 and 36 ng L⁻¹, respectively, with a preconcentration factor of 25. The precision of this method was 1.7% (Mn), 2.9% (Cu), 5.9% (Mn), 3.8% (Mn), 6.2% (Mn) and 4.3% (Mn) with 9 determinations of 10 ng mL⁻¹ of target analytes, respectively. The method was successfully applied to the determination of trace metals in lake water, dried fish samples, certified reference materials of human hair and milk, and provided satisfactory results.     

Crystal structures of the organic metals (ET)2[Hg(SCN)Cl2] and (ET)2[Hg(SCN)2Br]

The compositions and structures of two new organic metals based on ET [where ET = bis(ethylenedithio)tetrathiafulvalene], viz., (ET)₂[Hg(SCN)Cl₂], with a metal-dielectric transition temperature (T_m-d) of 35°K, and (ET)₂[Hg(SCN)₂Br], with T_m-d = 140°K, were established by x-ray diffraction analysis. The crystal structures of the investigated compounds are similar to the structure of the previously studied organic metal (ET)₂[Hg(SCN)₂Cl] with T_m-d = 50°K. The principal crystallographic data for (ET)₂[Hg(SCN)Cl₂] are as follows: a = 36.64(1), b = 8.300(4), c = 11.798(1) Å, = 89.91(3)°, V = 3588.1(9) ų, space group Cc, Z = 4, d_calc = 2.05 g/cm³. The principal crystallographic data for (ET)₂[Hg(SCN)₂Br] are as follows: a = 37.088(14), b = 8.338(3), c = 11.738(5) Å, = 89.71(3)°, V = 3629.6(8) ų, space group C2/c, Z = 8, d_calc = 2.15 g/cm³. A characteristic feature of the crystal structure of the investigated compounds is alternation of the anion and cation layers along the a axis of the crystal. In the cation layer of the k type the ET are interconnected by shortened S...S intermolecular contacts (3.39–3.58 Å). The [Hg(SCN)_3–nX_n]^– anions (X = Cl, Br; n = 1, 2) form polymeric chains with one or two bridged SCN groups. A tendency for a decrease in the metal-dielectric transition temperature with a decrease in the volume of the anion is detected in the (ET)₂[Hg(SCN)_3–nX_n] salts, where X = Cl and Br, and n = 1 and 2.Institute of Chemical Physics, Russian Academy of Sciences, 142432 Chernogolovka. Translated from Izvestiya Akademii Nauk, Seriya Khimicheskaya, No. 10, pp. 2323–2331, October, 1992.     

Stripping voltammetry of copper and lead using gold electrodes modified with self-assembled monolayers

One problem associated with using bare solid metal electrodes, such as gold and platinum, in stripping analysis to determine heavy metal ions such as lead and copper ions in dilute solutions is that underpotential deposition (UPD) gives multiple stripping peaks in the analysis of mixtures. These peaks are often overlapped and cannot be conveniently used for analytical purposes. Bifunctional alkylthiols, such as 3-mercaptopropionic acid, with an ionizable group on the other terminal end of the thiol can form self-assembled monolayers (SAMs) on the surface of the gold electrode. It is shown that such an SAM-modified gold electrode minimizes the UPD effects for the stripping analysis of lead and copper. The anodic peak potential shifts and the peak shape changes, indicating that the SAM changes the deposition and stripping steps of these heavy metal ions. Thus, the sensitivity levels for both single species and mixtures can be significantly improved for the conventional solid electrodes. The mechanism of the deposition reaction at the SAM-modified gold electrodes is discussed. Received: 29 May 1997 / Accepted: 24 June 1997     

Bis(phosphinimino)methanides as ligands in divalent lanthanide and alkaline earth chemistry - synthesis, structure, and catalysis

Divalent bis(phosphinimino)methanide lanthanide complexes of composition [{(Me₃SiNPPh₂)₂CH}EuI(THF)]₂ and [{(Me₃SiNPPh₂)₂CH}YbI(THF)₂] have been prepared by a salt metathesis reactions of K{CH(PPh₂NSiMe₃)₂} and LnI₂. Further reactions of these complexes with [K(THF)_nN(PPh₂)₂] led selectively to the heteroleptic amido complexes [{(Me₃SiNPPh₂)₂CH}Ln{(Ph₂P)₂N}(THF)] (Ln = Eu, Yb). The ytterbium complex can also be obtained by reduction of [{CH(PPh₂NSiMe₃)₂}Yb{(Ph₂P)₂N}Cl] with elemental potassium. The single crystals of [{(Me₃SiNPPh₂)₂CH}Ln{(Ph₂P)₂N}(THF)] contain enantiomerically pure complexes. As a result of the similar ionic radii of the divalent lanthanides and the heavier alkaline earth metals some similarities in coordination chemistry of the bis(phosphinimino)methanide ligand were anticipated. Therefore, MI₂ (M = Ca, Sr, Ba) was reacted with K{CH(PPh₂NSiMe₃)₂} to give [{(Me₃SiNPPh₂)₂CH}CaI(THF)₂], [{(Me₃SiNPPh₂)₂CH}SrI(THF)]₂, and [{(Me₃SiNPPh₂)₂CH}BaI(THF)₂]₂, respectively. As expected the Sr and Eu complexes and the Ca and Yb complexes are very similar, whereas for the Ba compound, as a result of the large ion radius, a different coordination sphere is observed. For all new complexes the solid-state structures were established by single crystal X-ray diffraction. In the solid-state the {CH(PPh₂NSiMe₃)₂}⁻ ligand acts as tridentate donor forming a long methanide carbon metal bond. Thus, all complexes presented can be considered as organometallic compounds. [{(Me₃SiNPPh₂)₂CH}YbI(THF)₂] was also used as precatalyst for the intramolecular hydroamination/cyclization reaction of different aminoalkynes and aminoolefines. Good yields but moderate activities were observed.     

Determination of trace elements in seawater samples by on-line column extraction/graphite furnace atomic absorption spectrometry

An innovative procedure for the on-line coupling of ion chromatography with graphite furnace atomic absorption spectrometry is described, which is particularly effective for the determination of trace metals in seawater samples. The Capillary Injection Device (CID) is used as an interface which allows the eluent to be transferred from the chromatographic column into the graphite tube at a flow rate of as high as 2 ml/min. The analytical procedure is based on the metal complex formation with 8-hydroxyquinoline in the sample solution, followed by the preconcentration of the complexes in a chromatographic column packed with XAD-2 resin. The complexes were then eluted from the column with methanol, and quantitatively injected into the furnace. The procedure was validated by determining cadmium and lead in certified reference seawater samples at a level of 30–40 pg/g, with a typical reproducibility of 10% and an accuracy of better than 5%. Finally, it was tested on a real sample of seawater. Due to the high reproducibility, a pg/g concentration level can be measured.     

Determination of physiological noble metals in human urine using liquid-liquid extraction and Zeeman electrothermal atomic absorption spectrometry

An extremely sensitive, reliable and simple procedure is described for the determination of physiological palladium, platinum and gold in human urine. The urine samples were adjusted to pH 4 (Pd, Au) or pH 5 (Pt), followed by conversion of the analytes to their pyrrolidinedithiocarbamate complexes. These complexes were separated from the matrix by liquid-liquid extraction into 4-methyl-2-pentanone resulting in a 25-fold enrichment. Determination was by electrothermal atomic absorption spectrometry (ET-AAS) using longitudinal inverse alternating current Zeeman-effect background correction. The limits of detection calculated from three standard deviations of the blank values were 20 ng l⁻¹ for Pd and Au and 70 ng l⁻¹ Pt. Within-day precision (n = 10, 5 μg l⁻¹) ranged 5.2%–7.7%. The procedure is successfully applied to determine urinary palladium, platinum and gold in nine unexposed persons. Palladium levels in urine ranged < 20–80 ng l⁻¹ (arithmetical MEAN=38.7 ng l⁻¹), while gold levels ranged < 20–130 ng l⁻¹ (36.0 ng l⁻¹). Physiological platinum levels in urine were all < 70 ng l⁻¹. The accuracy of the procedure was checked by analyzing a series of urine samples by a second independent method (magnetic sector field inductively-coupled plasma-mass spectrometry) in combination with UV photolysis.     

Fullerene C60 as a η5- and η6-ligand in sandwich-type π-complexes with transition metals

The molecular and electronic structures of some hypothetical sandwich-type -complexes of transition metals with fullerene C₆₀ were modeled. The M-C₆₀ bonds in ⁵-C₆₀MCp⁺ complexes (M = Fe, Ru, Os) are less strong than the M-Cp bonds in ferrocene, ruthenocene, and osmocene, respectively. The ⁶-C₆₀MC₆H₆ complexes (M = Cr, Mo, W) should be less stable than their classical analogs (C₆H₆)M(C₆H₆). The coordination of a metal atom with the fullerene at its pentagonal face is more energetically favorable than at a hexagonal face.Translated fromIzyestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 598–601, April, 1994.We are grateful to V. I. Sokolov for discussion of the results obtained. This study was supported by the Russian Foundation for Basic Research (grants 93-03-4101 and 93-03-18725).