Fluoride ion detection by 8-hydroxyquinoline-Zr(IV)-EDTA complex

A simple fluorescent detection based on the ligand exchange mechanism is proposed for the fluoride ion in aqueous media. This procedure is based on the exchange of 8-hydroxyquinoline (oxine) coordinated to Zr(IV) by fluoride ion without interference from other common anions. The ternary complex of oxine with [Zr(H(2)O)(2)EDTA].2H(2)O formed by replacing two water molecules in aqueous solution provides a sensitive signalling system for fluoride ion in the concentration range from 6 x 10(-7)M to 8 x 10(-4)M. The green fluorescence (lambda(max)=532 nm) exhibited by the complex upon excitation at 247 nm decreases in intensity with fluoride addition with a detection limit of 12 ppb. The complexation reaction between oxine and Zr(IV)-EDTA and the ligand exchange reaction with fluoride ion has been investigated by UV-vis and fluorescence spectroscopies combined with the PM3 semi-empirical quantum chemical calculations. Job's method of continuous variation and the molar ratio method ascertain a 1:1 stoichiometry composition of the chelate in aqueous media.     

Simultaneous determination of Zr(IV) and Hf(IV) by CE using precolumn complexation with a [PW(11)O(39)](7-) ligand

A CE method was developed for the simultaneous determination of Zr(IV) and Hf(IV) at trace levels. A lacunary Keggin-type [PW(11)O(39)](7-) ligand reacted quantitatively with a mixture of trace amounts of Zr(IV) and Hf(IV) to form the so-called ternary Keggin-type anions [P(Zr(IV)W(11))O(40)](5-) and [P(Hf(IV)W(11))O(40)](5-) in 0.010 M monochloroacetate buffer (pH 2.2). Since both ternary anions possessed different electrophoretic mobilities and high molar absorptivities in the UV region, Zr(IV) and Hf(IV) were determined simultaneously with direct UV detection at 258 nm. Each peak height was linearly dependent on the concentration of Zr(IV) or Hf(IV) in the range of 5.0x10(-7)-1.0x10(-5) M; a detection limit of 2x10(-7) M was achieved. The utility of the proposed CE method was demonstrated for the simultaneous determination of Zr(IV) and Hf(IV) in natural water samples with satisfactory results.     

Structure and dynamics of dinuclear zirconium(IV) complexes

We have determined by X-ray crystallography the structures of three dinuclear zirconium(IV) complexes containing the heptadentate ligand dhpta (where H(5)dhpta = 1,3-diamino-2-propanol-N,N,N',N'-tetraacetic acid, 1) and different countercations: K(2)[Zr(2)(dhpta)(2)].5H(2)O (2.5H(2)O), Na(2)[Zr(2)(dhpta)(2)].7H(2)O.C(2)H(5)OH (3.7H(2)O.C(2)H(5)OH), and Cs(2)[Zr(2)(dhpta)(2)].H(5)O(2).Cl.4H(2)O (4.H(5)O(2).Cl.4H(2)O). In the K(I) complex 2, crystallized from water, the two Zr(IV) ions are 3.5973(4) A apart and bridged via two alkoxo groups (average Zr-O 2.165 A). Each Zr(IV) is eight-coordinate and also bound to two N atoms (average Zr-N 2.448 A), and four carboxylate O atoms (average Zr-O 2.148 A). The two dhpta ligands in the dinuclear unit have different conformations. One face of the complex contains an array of 14 oxygen atoms and interacts strongly with the two K(I) ions, one of which is 6-coordinate, the other 8-coordinate, which are 3.922(4) A apart and bridged by a carboxylate O and by two water molecules. The structures of the dinuclear anion [Zr(2)(dhpta)(2)](2-) in the Na(I) complex 3 and in the Cs(I) complex 4 are essentially identical to that found in complex 2, although the alkali metal ions coordinate differently to the oxygen-rich face. All Zr(IV) ions have a distorted triangulated dodecahedral geometry. Although the crystal structure of complex 2 does not indicate the presence of acidic protons, in 4 an [H(5)O(2)](+) unit is strongly H-bonded to an oxygen atom of a coordinated carboxylate group. 1D and 2D (1)H and (13)C NMR spectroscopic and potentiometric studies reveal two deprotonations with pK(a) values of 9.0 and 10.0. At low pH, two carboxylate groups appear to undergo protonation accompanied by chelate ring-opening, and the complex exhibits dynamic fluxional behavior in which the two magnetically nonequivalent dhpta ligands exchange at a rate of 11 s(-1) at pH 3.30, 298 K, as determined from 2D EXSY NMR studies. Ligand interchange is not observed at high pH (>11). The same crystals of complex 2 were obtained from solutions at pH 3 or 12. The dynamic configurational change is therefore mediated by the aqueous solvent.     

Two-phase reactions of tin(IV)–tetraphenylporphine complexes as carrier of anion selective electrodes

Two-phase reactions of [Sn(OH)₂(tpp)] with lipophilic anions and inorganic acids were studied and compared with those of [Zr(OH)₂(tpp)] having the same oxidation state of the central metal ion but different structural characteristics. The reaction with tetrakis[3,5-bis(trifluoromethyl)phenyl]borate formed a 2:1 cationic dimer and 1:1 and 1:2 ion-pairs, while the reaction with dodecyl sulfate formed 1:1 and 1:2 ion-pairs. The 1:1 and 1:2 species formed concomitantly in the reaction with HCl and CH₃COOH having higher coordination abilities, while forming in stepwise manner in the reaction with HClO₄ and HNO₃ having lower coordination abilities. The 2:1 cationic dimer of Sn(IV) had significantly lower stability than that of Zr(IV). The affinity of Sn(IV) for Cl⁻ relative to OH⁻ was much higher, compared with Zr(IV). Except in extremely acidic media, [SnCl₂(tpp)] working as a carrier in PVC membranes hydrolyzed to give [Sn(OH)Cl(tpp)] or [Sn(OH)₂(tpp)], which showed stronger but less-selective potential responses at lower pH and weaker but more-selective responses to salicylate at higher pH. The affinities and responses of Sn(IV) complexes to oxygen-containing anions were weaker than those of Zr(IV) complexes.     

Spectrophotometric determination of vanadium(IV) with nitrilotriacetic acid

A new and convenient spectrophotometric method for the estimation of vanadium(IV) with NTA is described. The minimum ratio of metal ion to ligand, working pH, wavelength for maximum absorbance of the complex ion, and the effect of various cations and anions are described. The complex ion obeys Beer's law in the concentration range 1–32 mmol/liter of the vanadium(IV) ion. It is observed that iron(II), cobalt(II), nickel(II), copper(II), and oxidizing anions such as chromate and nitrite interfere in this determination, whereas managanese(II), chromium(III), iron(III), and anions like nitrate, chloride, bromide, iodide, thiocyanate, sulfate, and sulfite do not have any effect. Excessive amounts of acetate, phosphate, oxalate, tartrate and thiosulfate must also be avoided in this determination. Anions and cations which interfere in the determination of vanadium(IV) by NTA should not be present in the system.     

Diorganotin(IV) dithiocarbamate complexes as chromogenic sensors of anion binding

One dinuclear chlorodiphenyltin (IV) dithiocarbamate complex (1) and four mononuclear complexes of general formula Ph₂Sn(S₂CNR)Cl (2, 3, 5, and 6) have been synthesized and characterized both in solid-state and solution. X-ray structures for complexes 1, 3 and 6 demonstrated a five-coordination geometry around of tin atoms, in which dithiocarbamate ligand chelates asymmetrically the metal center. As shown by ¹¹⁹Sn NMR spectroscopy, five-coordination geometry observed in the solid-state remains in solution. The stability of these chlorodiphenyltin(IV) dithiocarbamate complexes in the presence of biologically relevant anions such as acetate, dicarboxylates of general formula ^?OOC-(CH₂)_n-COO^? (n = 2–8), dihydrogenphosphate, hydrogensulfate, and halides has been examined in acetonitrile solutions. For all of these organotin(IV) complexes the displacement of the coordinated ligands (i.e., chloride and dithiocarbamate) from the organotin(IV) moiety occurred in the presence of monoanions like acetate, dihydrogenphosphate, hydrogensulfate and fluoride. A stepwise mechanism for ligand exchange is proposed based on UV–Vis, ¹H, ¹³C and ¹¹⁹Sn spectroscopic data, as well as mass spectrometry. From UV–Vis titration experiments it was found that dicarboxylates with small spacers like malonate and succinate, acted differently in the exchange of the dithiocarbamate group in comparison to other monoanionic O donor ligands or dicarboxylates with longer chains, perhaps by following an intramolecular displacement of the coordinated ligand.The lability of these organotin(IV) dithiocarbamate compounds in solution hampers their use as stably host for anions, however, by taking advantage of the intrinsic chromogenic properties of free dithiocarbamate anions, or by attaching dithiocarbamate groups to well-known fluorescent moieties such as antracene, these complexes can sense the presence of O-donor anions at very low concentrations by displacement of the metal-coordinated dithiocarbamate.     

Consecutive thin-layer chromatographic separation of Zr(IV), Hf(IV) and many other ions on silica gel in nitric acid-hydrogen peroxide media

The thin-layer chromatographic (TLC) behaviour of 64 ions including Zr(IV) and Hf(IV) has been surveyed on systems composed of silica gel and of nitric acid and nitric acid-hydrogen peroxide media. In the 0.5 mol 1(-1) HNO(3)-3% (w/v) H(2)O(2) solution, only Hf(IV) adsorbed very strongly, whereas Zr(IV) and many other ions showed no or weak adsorption. Stepwise development with diluted nitric acid and subsequently with nitric acid-hydrogen peroxide solution allowed the consecutive separation of three-component mixtures consisting of Zr(IV), Hf(IV) and one of many other accompanying elements, such as Mo(VI), Nb(V), Th(IV), Ti(IV), U(VI) and rare earths(III), to be conducted simply and effectively.     

A Comparative Study of the Synthesis and Ion Exchange Properties of Iodophosphates of Tin(IV), Zirconium(IV) and Iron(III): Separations of Metal Ions on Tin(IV)-iodophosphate Columns

Abstract

Iodates and iodophosphates of tin(IV), zirconium(IV) and iron(III) have been synthesized under varying conditions and studied their ion exchange behaviour. Among the various ion exchangers synthesized, tin(IV)-iodophosphate is chosen for detailed study owing to its highest ion exchange capacity and highest chemical stability. The most stable sample is prepared by mixing 0.1M stannic chloride, 0.1M potassium iodate and 0.1M potassium dihydrogen orthophosphate solutions in the volume ratio 1:1:2 respectively at pH 0–1. It is a monofunctional weak cation exchanger. Its ion exchange capacity for K⁺ is 1.6 meq/dry g. The thermal and chemical stabilities of this material have been determined and compared with Zr(IV)-phosphoiodate. Effect of heating on the properties of tin(IV)-iodophosphate has been determined. To explore the separation potential of tin(IV)-iodophosphate Kd values of different metal ions have been determined in organic solvents. A number of important separations of metal ions of industrial utility have been successfully achieved on the columns of tin(IV)-iodophosphate.     

Visible-light induced oxo-bridged Zr(IV)-O-Ce(III) redox centre in tetragonal ZrO2-CeO2 solid solution for degradation of organic pollutants

Tetragonal ZrO(2)-CeO(2) solid solutions with composition Zr(1-x)Ce(x)O(2) (x = 0.1, 0.2, and 0.3) were synthesized in a citrate complexation route and characterized by XRD, XPS, UV-vis diffuse reflectance and ESR measurements. The formation of the homogeneous solid solution Zr(1-x)Ce(x)O(2) constructed the oxo-bridged bimetallic Zr(IV)-O-Ce(III) linkage between two neighboring flattened tetrahedrons of the structural framework. As compared to their parent oxides, the ZrO(2)-CeO(2) solid solutions exhibited optical absorption extending to longer wavelengths in the visible region. The red shift in the absorption spectrum was demonstrated to be partially due to a metal-to-metal charge transfer (MMCT) transition of the oxo-bridged Zr(IV)-O-Ce(III) linkage. The visible-light induced MMCT transition of Zr(IV)-O-Ce(III)→ Zr(III)-O-Ce(IV) resulted in the generation of the additional Ce(IV) and superoxide anion radical formed by the interaction of Zr(III) with adsorbed O(2). Catalytic activity evaluation revealed that the photoexcitation of the MMCT over the solid solution can initiate the degradation of RhB and 2,4-DCP upon visible-light irradiation, whereby Zr(III) and Ce(IV) act as a site-specific reducing and oxidizing center, respectively. The structure of the solid solution Zr(1-x)Ce(x)O(2) and the oxidation states of Zr and Ce species are also discussed in detail.     

Solid state and aqueous solution characterization of rectangular tetranuclear V(IV/V)-p-semiquinonate/hydroquinonate complexes exhibiting a proton induced electron transfer

Reaction of the non-innocent dinucleating ligand 2,5-bis[N,N-bis(carboxymethyl) aminomethyl]hydroquinone (H 6bicah) with VO (2+) and VO 4 (3-) salts in water in the pH range 2 to 4.5 provides a series of novel tetranuclear V (IV) and/or V (V) macrocycles with the main core consisting of the anions [V (V) 4O 4(mu-O) 2(mu-bicah) 2] (4-) isolated at pH = 2.5 and [V (IV) 2V (V) 2O 4(mu-O) 2(mu-bicas)(mu-bicah)] (5-) and [V (IV) 4O 4(mu-O) 2(mu-bicas) 2] (6-) isolated at pH = 4.5 (bicas (*5-) = 2,5-bis[N,N-bis(carboxymethyl) aminomethyl]- p-semiquinonate), whereas at pH = 2 the dinuclear [(V (IV)O) 2(OH 2) 2(mu-bicah)] (2-) was obtained. All vanadium compounds have been characterized, and the charge of the ligand has been assigned in solid state by X-ray crystallography and infrared spectroscopy. The structures of the tetranuclear anions consist of four vanadium atoms arranged at the corners of a rectangle with the two bridging bicas (*5-) and/or bicah (6-) ligands on the long and the two V (IV/V)-O-V (IV/V) bridges on the short sides of the rectangle. UV-vis, (51)V and (1)H NMR spectroscopy and electrochemistry showed that these complexes interconvert to each other by varying the pH. This pH induced redox transformation of the tetranuclear anions has been attributed to the shift of the reduction potential of the bicas (*5-) to higher values by decreasing the pH. The electron is transferred intramolecularly from the metal ion to the electron accepting semiquinones resulting in reduction of bicas (*5-) to bicah (6-) and concurrent oxidation of the V (IV) to V (V). The resulting complexes are further oxidized by atmospheric oxygen. This system as a model for the H (+) coupled redox reactions in metalloenzymes and its relevance is discussed briefly.     

"Oxidative addition" to a Zirconium(IV) redox-active ligand complex

A strategy to enable reactivity analogous to oxidative addition is presented for d(0) transition-metal complexes. The reaction of the redox-active ligand 2,4-di-tert-butyl-6-tert-butylamidophenolate (ap) with ZrCl(4)(THF)(2) affords the new complex Zr(IV)(ap)(2)(THF)(2). This compound is formally zirconium(IV) and contains no d electrons; however, exposure of Zr(IV)(ap)(2)(THF)(2) to chlorine gas results in swift chlorine addition at the zirconium metal center via one-electron oxidation of each ap ligand. The diradical product, Zr(IV)Cl(2)(isq)(2) (isq = 2,4-di-tert-butyl-6-tert-butyliminosemiquinone), has been characterized by X-ray crystallography, electron paramagnetic resonance spectroscopy, and SQUID magnetometery.     

Complexes of Pt(II) and Pt(IV) with disubstituted purines

Mixed-ligand complexes of Pt(II) and Pt(IV) with 2,6-diaminopurine and 6-thioguanine were synthesized and characterised. The complexes were prepared in acidic and basic media. The binding of the ligands to the metal ion varies according to the pH of the medium. Thus, in the complexes of 6-thioguanine, the ligand acts as a monodentate ligand coordinating through the neutral C₆-SH group in the acidic medium and in the basic medium as a bidentate ligand binding to the metal ion through C₆S^? and N₇, forming a five-membered chelate ring. In an acidic medium 2,6-diaminopurine forms mononuclear complexes with Pt(II) and Pt(IV) binding through N₇. In a basic medium binuclear hydroxobridged complexes are formed with Pt(IV) and the ligand is monodentate, coordinating through N₇.     

Adsorption of metal anions of vanadium(V) and chromium(VI) on Zr(IV)-impregnated collagen fiber

The metal anions of vanadium (V) and chromium (VI) in aqueous solution can be effectively adsorbed by Zr(IV)-impregnated collagen fiber (ZrICF). The maximum adsorption capacity of V(V) takes place within the pH range of 5.0 to 8.0, while that of Cr(VI) is within the pH range of 6.0 to 9.0. When the initial concentration of metal ions was 2.00 mmol L⁻¹ and the temperature was 303 K, the adsorption capacity of V(V) on Zr-ICF was 1.92 mmol g⁻¹ at pH 5.0, and the adsorption capacity of Cr(VI) was 0.53 mmol g⁻¹ at pH 7.0. As temperature increased, the adsorption capacity of V(V) increased, while that of Cr(VI) was almost unchanged. The adsorption isotherms of the anionic species of V(V) and Cr(VI) can be fit by the Langmuir equation. The adsorption rate of V(V) follows the pseudo-first-order rate model, while the adsorption rate of Cr(VI) follows the pseudo-second-order rate model. Furthermore, ZrICF shows high adsorption selectivity to V(V) in the mixture solution of V(V) and Cr(VI). Practical applications of ZrICF could be expected in consideration of its performance in adsorption of V(V) and Cr(VI).     

Application of modified multiwall carbon nanotubes as a sorbent for zirconium (IV) adsorption from aqueous solution

Modified multiwall carbon nanotubes (MWCNTs) by nitric acid solution were used to investigate the adsorption behavior of zirconium from aqueous solution. Pristine and oxidized MWCNTs were characterized using nitrogen adsorption/desorption isotherm, Boehm’s titration method, thermogravimetry analysis, transmission electron microscopy and Fourier transform infrared spectroscopy. The results showed that the surface properties of MWCNTs such as specific surface area, total pore volume, functional groups and the total number of acidic and basic sites were improved after oxidation. These improvements are responsible for their hydrophobic properties and consequently an easy dispersion in water and suitable active sites for more adsorption of zirconium. The adsorption of Zr(IV) as a function of initial concentration of zirconium, contact time, MWCNTs dosage, HCl and HNO₃ concentration and also ionic strength was investigated using a batch technique under ambient conditions. The experimental results indicated that sorption of Zr(IV) was strongly influenced by zirconium concentrations, oxidized MWCNTs content and acid pH values. The calculated correlation coefficient of the linear regressions values showed that Langmuir model fits the adsorption equilibrium data better than the Freundlich model. Kinetic data of sorption indicated that equilibrium was achieved within 60 min and the adsorption process can be described by the pseudo second-order reaction rate model. Based on the experimental results, surface complexation is the major mechanism for adsorption of Zr(IV) onto MWCNTs. Also, Study on the desorption process of zirconium showed that the complete recovery can be obtained using nitric or hydrochloric acids of 4 M.     

A chromogenic calixarene hydroxamic acid for the sequential separation of Ti(IV) and Zr(IV)

A new chromogenic calixarene with hydroxamic acid as chelating agent was synthesized by partial reduction of nitrocalixarene which was subsequently coupled with coumarin chloride. The reagent showed selective and quantitative extraction of Ti(IV) into chloroform at 6 M HCl and that of Zr(IV) at 0.5 M HCl. A facile liquid-liquid extraction method for the separation and spectrophotometric determination of Ti(IV) and Zr(IV) has been proposed. The validity of the method was checked by separating several synthetic mixtures. The method was successfully applied to the analysis of piezoelectric lead-zirconium-titanate (PZT) samples. The method shows remarkable simplicity and selectivity. The method can also be used for the determination of Ti(IV) and Zr(IV) in various environmental samples. The article is published in the original.     

Importance of platinum(II)-assisted platinum(IV) substitution for the oxidation of guanosine derivatives by platinum(IV) complexes

Guanosine derivatives with a nucleophilic group at the 5' position (G-5') are oxidized by the Pt (IV) complex Pt( d, l)(1,2-(NH 2) 2C 6H 10)Cl 4 ([Pt (IV)(dach)Cl 4]). The overall redox reaction is autocatalytic, consisting of the Pt (II)-catalyzed Pt (IV) substitution and two-electron transfer between Pt (IV) and the bound G-5'. In this paper, we extend the study to improve understanding of the redox reaction, particularly the substitution step. The [Pt (II)(NH 3) 2(CBDCA-O,O')] (CBDCA = cyclobutane-1,1-dicarboxylate) complex effectively accelerates the reactions of [Pt (IV)(dach)Cl 4] with 5'-dGMP and with cGMP, indicating that the Pt (II) complex does not need to be a Pt (IV) analogue to accelerate the substitution. Liquid chromatography/mass spectroscopy (LC/MS) analysis showed that the [Pt (IV)(dach)Cl 4]/[Pt (II)(NH 3) 2(CBDCA-O,O')]/cGMP reaction mixture contained two Pt (IV)cGMP adducts, [Pt (IV)(NH 3) 2(cGMP)(Cl)(CBDCA-O,O')] and [Pt (IV)(dach)(cGMP)Cl 3]. The LC/MS studies also indicated that the trans, cis-[Pt (IV)(dach)( (37)Cl) 2( (35)Cl) 2]/[Pt (II)(en)( (35)Cl) 2]/9-EtG mixture contained two Pt (IV)-9-EtG adducts, [Pt (IV)(en)(9-EtG)( (37)Cl)( (35)Cl) 2] and [Pt (IV)(dach)(9-EtG)( (37)Cl)( (35)Cl) 2]. These Pt (IV)G products are predicted by the Basolo-Pearson (BP) Pt (II)-catalyzed Pt (IV)-substitution scheme. The substitution can be envisioned as an oxidative addition reaction of the planar Pt (II) complex where the entering ligand G and the chloro ligand from the axial position of the Pt (IV) complex are added to Pt (II) in the axial positions. From the point of view of reactant Pt (IV), an axial chloro ligand is thought to be substituted by the entering ligand G. The Pt (IV) complexes without halo axial ligands such as trans, cis-[Pt(en)(OH) 2Cl 2], trans, cis-[Pt(en)(OCOCF 3) 2Cl 2], and cis, trans, cis-[Pt(NH 3)(C 6H 11NH 2)(OCOCH 3) 2Cl 2] ([Pt (IV)(a,cha)(OCOCH 3) 2Cl 2], satraplatin) did not react with 5'-dGMP. The bromo complex, [Pt (IV)(en)Br 4], showed a significantly faster substitution rate than the chloro complexes, [Pt (IV)(en)Cl 4] and [Pt (IV)(dach)Cl 4]. The results indicate that the axial halo ligands are essential for substitution and the Pt (IV) complexes with larger axial halo ligands have faster rates. When the Pt (IV) complexes with different carrier ligands were compared, the substitution rates increased in the order [Pt (IV)(dach)Cl 4] < [Pt (IV)(en)Cl 4] < [Pt (IV)(NH 3) 2Cl 4], which is in reverse order to the carrier ligand size. These axial and carrier ligand effects on the substitution rates are consistent with the BP mechanism. Larger axial halo ligands can form a better bridging ligand, which facilitates the electron-transfer process from the Pt (II) to Pt (IV) center. Smaller carrier ligands exert less steric hindrance for the bridge formation.     

Sorption of [Fe(CN)6]3− and [Fe(CN)6]4− ions on the surface of Fe(III), Cr(III), and Zr(IV) oxyhydroxide hydrogels from aqueous solutions

The sorption of [Fe(CN)₆]^3? and [Fe(CN)₆]^4? anions on the surface of Fe(III), Cr(III), and Zr(IV) oxyhydroxide hydrogels at various pH values of hydrogel precipitation from solutions without a support electrolyte and from NaCl and Na₂SO₄ solutions with an ionic strength of 0.5 was studied. It was found that isotherms of sorption of [Fe(CN)₆]^3? and [Fe(CN)₆]^4? anions from solutions without a support electrolyte and from NaCl solutions and those of sorption of [Fe(CN)₆]^4? from Na₂SO₄ solutions are described by the Langmuir equation. It was established that the sulfate background suppresses the sorption of [Fe(CN)₆]^3? on Fe(III) and Zr(IV) oxyhydroxides. Both anions are sorbed only when the surface of the oxyhydroxides is charged positively; the Langmuir equation parameters A _max and K tend to decrease to the point of zero charge as the pH value of oxyhydroxide precipitation increases. An electrostatic mechanism of the sorption of [Fe(CN)₆]^3? and [Fe(CN)₆]^4? anions was suggested.     

New anionic species of tellurium(IV)

Tetrahaloaryltellurates(IV) were prepared by refluxing aryltellurium trihalides with phosphonium, tropylium and telluronium halides in CHCl₃. These compounds, which contain the ArTeX^?₄ anion, may be also prepared from aryltellurium trihalides and aqueous halogen hydride solutions. The phosphonium derivatives can be considered as potential precursors of tellurophosphoranes for Wittig reactions. Halogen exchange reactions allow the interconversion of the complex anions. The ionic nature of the compounds is supported by ion exchange reactions utilizing ion exchange resins, and by conductance measurements. Far infrared and Raman spectral data suggest a square pyramidal configuration for the ArTeX^?₄ anions.     

Kinetische Untersuchungen zum Ligandenaustausch an Chloro-Bromo-Osmaten(IV)

Kinetic Studies on Ligand Exchange of Chloro-Bromo-Osmates(IV) The 18 ligand exchange reactions in the system [OsCl_nBr_6?n]^2?, n = O–6, are investigated by radiometric measurements with regard to the dependence of temperature and concentrations of substituents. The kinetic stability increases with the number of more electronegative Cl ligands. The reactions proceed partly via aquo complexes as intermediates. The rate constants of isomers indicate that the trans-effect of Br is only slightly higher compared to that of Cl. Therefore ligand exchange does not run stereospecifically. Corresponding to the higher kinetic stability of the chloro-bromo-osmates(IV) activation energies are higher than those of chloro-iodo-osmates(IV).     

Catalytic ester-amide exchange using group (IV) metal alkoxide-activator complexes

A process for preparation of amides from unactivated esters and amines has been developed using a catalytic system comprised of group (IV) metal alkoxides in conjunction with additives including 1-hydroxy-7-azabenzotriazole (HOAt). In general, ester-amide exchange proceeds using a variety of structurally diverse esters and amines without azeotropic reflux to remove the alcohol byproduct. Initial mechanistic studies on the Zr(Ot-Bu)4-HOAt system revealed that the active catalyst is a novel, dimeric zirconium complex as determined by X-ray crystallography.