Extraction of vanadium(V) chelates with N-benzohydroxamic acid (BHA) and ammonium thiocyanate and its application in steel and rock analyses

A mixed-ligand complex of vanadium(V) with N-benzohydroxamic acid and thiocyanate formed at various acidities can be extracted into methyl isobutyl ketone, and used for photometric determination of trace amounts of vanadium in materials such as alloy steels and rocks. The absorption maximum of the violet mixed-ligand complex is at 535 nm. The values for the simple complex are 505 nm and molar absorptivity 7.4 x 10(3)l.mole(-1).cm(-1).     

Extraction-spectrophotometric determination of vanadium with 5,5′-dithiodisalicylhydroxamic acid (DTDSHA)

A new method for the extraction-spectrophotometric determination of V(V) is proposed. The violet complex V(V)-5,5′-dithiodisalicylhydroxamic acid formed in aqueous medium (pH 5.0) is extracted into a solution of trioctylmethylammonium chloride (Adogen 464) in toluene, and its spectrophotometric characteristics are studied. The stoichiometry of the complexes formed is 1:1 and 2:1 (reagent:vanadium), and 1:3 for the ionic association complex (2:1):trioctylmethylammonium ion. The system follows Beer's law at pH 5.0 (λ = 550 nm) over the concentration range 0.4 to 2.0 ppm (ε = 7.34 × 10³ liter · mol⁻¹ · cm⁻¹). The method is applied for the determination of vanadium in steel.     

Competitive Substitution and Electron Transfer in Reactions between Haloamminegold(III) and Halocyanoaurate(III) Complexes and Thiocyanate

Kinetics for reactions between thiocyanate and trans-Au(CN)(2)Cl(2)(-), trans-Au(CN)(2)Br(2)(-), and trans-Au(NH(3))(2)Cl(2)(+) in an acidic, 1.00 M perchlorate aqueous medium have been studied by use of conventional and diode-array UV/vis spectroscopy and high-pressure and sequential-mixing stopped-flow spectrophotometry. Initial, rapid formation of mixed halide-thiocyanate complexes of gold(III) is followed by slower reduction to Au(CN)(2)(-) and Au(NH(3))(2)(+), respectively. This is an intermolecular process, involving attack on the complex by outer-sphere thiocyanate. Second-order rate constants at 25.0 degrees C for reduction of trans-Au(CN)(2)XSCN(-) are (6.9 +/- 1.1) x 10(4) M(-)(1) s(-)(1) for X = Cl and (3.1 +/- 0.7) x 10(3) M(-)(1) s(-)(1) for X = Br. For reduction of trans-Au(CN)(2)(SCN)(2)(-) the second-order rate constant at 25.0 degrees C is (3.1 +/- 0.1) x 10(2) M(-)(1) s(-)(1) and the activation parameters are DeltaH() = (55 +/- 3) x 10(2) kJ mol(-)(1), DeltaS() = (-17.8 +/- 0.8) J K(-)(1) mol(-)(1), and DeltaV() = (-4.6 +/- 0.5) cm(3) mol(-)(1). The activation volume for substitution of one chloride on trans-Au(NH(3))(2)Cl(2)(+) is (-4.5 +/- 0.5) cm(3) mol(-)(1), and that for reduction of trans-Au(NH(3))(2)(SCN)(2)(+) (4.6 +/- 0.9) cm(3) mol(-)(1). The presence of pi-back-bonding cyanide ligands stabilizes the transition states for both substitution and reductive elimination reactions compared to ammine. In particular, complexes trans-Au(CN)(2)XSCN(-) with an unsymmetric electron distribution along the X-Au-SCN axis are reduced rapidly. The observed entropies and volumes of activation reflect large differences in the transition states for the reductive elimination and substitution processes, respectively, the former being more loosely bound, more sensitive to solvational changes, and probably not involving any large changes in the inner coordination sphere. A transition state with an S-S interaction between attacking and coordinated thiocyanate is suggested for the reduction. The stability constants for formation of the very short-lived complex trans-Au(CN)(2)(SCN)(2)(-) from trans-Au(CN)(2)X(SCN)(-) (X = Cl, Br) by replacement of halide by thiocyanate prior to reduction can be calculated from the redox kinetics data to be K(Cl,2) = (3.8 +/- 0.8) x 10(4) and K(Br,2) = (1.1 +/- 0.4) x 10(2).     

Mononuclear and dinuclear monoperoxovanadium(v) complexes with a hetero ligand. 1.(1) Self-decomposition reaction, detection of reactive oxygen species, and oxidizing ability

A mononuclear peroxovanadium(V) complex with histamine-N,N-diacetate (histada), K[VO(O(2))(histada)], and a dinuclear peroxovanadium(V) complex with 2-oxo-1,3-diaminopropane-N,N,N',N'-tetraacetate (dpot), Cs(3)[(VO)(2)(O(2))(2)(dpot)], were prepared and characterized. The self-decomposition reaction was examined for these peroxovanadium(V) complexes as well as for K[VO(O(2))(cmhist)] (cmhist = N-carboxymethylhistidinate). The reaction profiles depicted by the absorbance change in the UV-vis spectrum show a sigmoid shape with an induction period. The induction period is reduced by the addition of acid, fluoride, thiocyanate, VO(2+), VO(2)(+), and trolox compared to the solution containing perchlorate. On the other hand, the induction period was elongated by the addition of chloride, bromide, and 2-tert-butyl-p-cresol. These behaviors are discussed on the basis of a radical chain mechanism. The self-decomposition reactions have also been followed by the (1)H and (51)V NMR and EPR spectra. These spectral studies as well as the UV-vis spectral study indicate that vanadium(V) is partly reduced to vanadium(IV) in the self-decomposition process. The histada complex yields a mixed-valence dinuclear complex in a concentrated solution, and the dpot complex yields a mixed-valence tetranuclear complex. The reduction of vanadium ion suggests that the peroxo ligand may act as a reducing agent. In order to know the fate of the peroxo ligand, we tried to detect superoxide anion and hydroxyl radical, which were anticipated to be produced in the self-decomposition process. The formation of superoxide anion was spectrophotometrically confirmed using two independent methods, including the reduction of cytochrome c and the reduction of sodium 4-[3-(iodophenyl)-2-(4-nitrophenyl)-2H-5-tetrazolio]-1,3-benzene disulfonate (WST-1). The formation of hydroxyl radical was confirmed by an EPR spin trapping technique. The oxidizing abilities of the peroxovanadium(V) complexes toward bovine serum albumin (BSA) were also evaluated. In the protein carbonyl assay, it was found that the total amount of protein carbonyl in BSA was increased by the reaction with the peroxovanadium complexes in the concentration-dependent manner. In addition, the oxidation of sulfhydryl group in BSA induced by the peroxovanadium complexes was confirmed.     

Structural and spectroscopic evidence for the formation of trinuclear and tetranuclear vanadium(III)/carboxylate complexes of acetate and related derivatives in aqueous solution

The formation of vanadium(III) complexes with nuclearity greater than two is believed to occur in aqueous solution on the basis of potentiometric, electrochemical, and/or UV-vis spectroscopy titration measurements, although structural evidence for this is limited. Upon the addition of 1-2 equiv of acetate, propionate, chloroacetate, trifluoroacetate, or bromoacetate to an aqueous, acidic solution of vanadium(III), trinuclear and tetranuclear complexes are formed. The structures of [V4(mu-OH)4(mu-OOCCF3)4(OH2)8]Cl4.7.5H2O (1), [V4(mu-OH)4(mu-OOCCH3)4(OH2)8]Cl4.CH3COOH.12H2O (2), [V4(mu-OH)4(mu-OOCCH3)4(OH2)8]Cl4.3H2O (3), [V3(mu3-O)(mu-OOCCH2Br)6(OH2)3]CF3SO3.H2O (4), [V3(mu3-O)(mu-OOCCH2CH3)6(OH2)3]Cl.2H2O (5), [V3(mu3-O)(mu-OOCCH3)6(OH2)3]Cl.3.5H2O (6), and [V3(mu3-O)(mu-OOCCH2Cl)6(OH2)3]CF3SO3.H2O (7) have been determined by X-ray diffraction. Importantly, electrospray mass spectrometry and 1H NMR measurements suggest that these complexes are not purely solid-state phenomena but are also present in solution. For the vanadium(III)/acetate and vanadium(III)/propionate systems, two paramagnetic 1H NMR signals corresponding to two distinct complexes (species A and B) are observed in the 40-55 ppm region for 0.20 mol equiv of acetate or propionate, at pD 3.44. No corresponding signals are observed for the vanadium(III)/bromoacetate and vanadium(III)/chloroacetate systems under the same conditions or for the vanadium(III)/ trifluoroacetate system using 19F NMR spectroscopy. UV-vis spectra suggest that species B are structurally analogous for the vanadium(III)/acetate and vanadium(III)/propionate systems, whereas structurally different complexes are the major species for the other systems. Diffusion coefficients of species B for the vanadium(III)/acetate and vanadium(III)/propionate systems determined by pulsed-field-gradient spin-echo NMR spectroscopy measurements are (3.0 +/- 0.1) x 10-6 and (3.23 +/- 0.01) x 10-6 cm2 s-1, respectively, and are most consistent with species B being trimeric, rather than tetranuclear, complexes.     

Spectrophotometric determination of vanadium(V) as a mixed thiocyanate-4-pyridone complex

The spectrophotometric determination of vanadium(V) as a mixed thiocyanate-3-hydroxy-2-methyl-1-phenyl-4-pyridone (HX) complex and as a mixed thiocyanate-3-hydroxy-2-methyl-1-(4-tolyl)-4-pyridone (HY) complex is described. The extracted complexes in chloroform have a maximum absorbance at 450 and 650 nm. The optimal conditions for the extraction and spectrophotometric determination of vanadium(V) are determined. The solutions of the V-SCN-HX and V-SCN-HY complexes in chloroform obey Beer's law in the range 1–10 ppm of vanadium, and are stable for at least 24 hr. The molar absorptivity of the method is 6.8 × 10³ liters mol^?1 cm^?1. The molar ratio V:SCN:HX (HY) of the extracted complex is 1:1:2.     

Selective extraction and photometric determination of trace vanadium with cinnamohydroxamic acid in MIBK and its application to steel and rock ore analysis

A sensitive and selective photometric method for the trace determination of vanadium with cinnamohydroxamic acid extracted from 1.8 M HCl in methyl isobutyl ketone is described. The wine-red chelate formed under an optimum acidity of 1.3-2.6 M HCl absorbs with a maximum at 525 nm. Beer's law is obeyed in the range 0-8 ppm of vanadium(V) and the optimum range of determination of vanadium is found to be 1-8 ppm. The molar absorptivity and Sandell's sensitivity are 6.0 x 10(3) l mol(-1) cm(-1) and 0.0086 mug cm(-2) of vanadium(V) at 525 nm. The photometric determination of trace amounts of vanadium in materials such as alloys, minerals and rock ores is also reported. The solvent extraction methods are simple, rapid and highly selective with fluoride used as a masking agent for Fe and Ti. The standard deviations are minimal and the mean error is only 0.015%.     

The solvent extraction and spectrophotometric determination of vanadium (V) with 4-(2-thiazolylazo)resorcinol and tetrazolium salts

The formation and extraction of ion-associate complexes between the vanadium(V)-4-(2-thiazolylazo)resorcinol (TAR) anionic chelate and the cations of some mono-and ditetrazolium salts {3-(4,5-dimethyl-2-thiazol)-2,5-diphenyl-2H-tetrazolium bromide (Thiazolyl blue, MTT), 3-(2-naphtyl)-2,5-diphenyl-2H-tetrazolium chloride (Tetrazolium violet), 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride (Iodonitrotetrazolium chloride), 3,3′-[3,3′-dimetoxy(1,1′-biphenyl)-4,4′-diyl]-bis[2,5-diphenyl-2H-tetrazolium] chloride (Tetrazolium blue chloride) and 3,3′-(3,3′-dimetoxy-4,4′-biphenylene)bis[2-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride] (Nitro blue tetrazolium chloride)} have been studied. The optimum extraction conditions have been found. The composition of the V-TAR-monotetrazolium and V-TAR-ditetrazolium complexes extracted into chloroform has been determined to be 1:2:3 and 2:4:3 respectively. The extraction, distribution and association constants, and the recovery factors have been calculated. The relationship between the molecular weight of tetrazolium cations, and the association constants of their complexes has been discussed. The special behavior of the tetrazolium cations, containing-NO₂ groups has been noticed. The effects of foreign ions and reagents on the extraction of vanadium with TAR and the best tetrazolium salt-MTT have been studied. A sensitive, selective, simple and fast method for the determination of vanadium has been developed.      

Vanadium(IV,V) complexes of D-saccharic and mucic acids in aqueous solution

The vanadium(IV,V) complexes formed with two aldaric acids (D-saccharic or D-glucaric acid, and mucic or galactaric acid) in aqueous solution were characterised by employing pH-potentiometry, EPR, multinuclear NMR and UV-VIS spectroscopy. The stoichiometry and stability constants of the complexes formed were determined at 25 degrees C and ionic strength I= 0.2 mol dm(-3)(KCl). The spectral measurements revealed that vanadium(IV,V) coordinates first at the terminal COO(-) functions, forming mononuclear complexes. At pH > 3, through the metal ion-induced deprotonation and coordination of the neighbouring alcoholic functions, (COO(-), O(-)) coordinated dinuclear complexes are formed, which predominate in the pH range 4-8. In the basic pH range, the ligand molecules are displaced and binary metal hydroxo and oxo complexes are present. EPR measurements at room temperature and at 140 K proved that formation of the VO(iv) dimers is more enhanced at room temperature, but at 140 K their dissociation is favoured. An interesting pH-dependent cis-trans isomeric equilibrium was assumed and analysed by EPR and molecular modelling in the case of the complexes [(VO)(2)L(2)H(x)](x=-2 and -4). Joint evaluation of the pH-potentiometric and (51)V NMR measurements revealed that both aldaric acids are able to bind an excess of vanadium(V), through the formation of oligomeric 2:1 and 3:2 species, besides the 2:2 species formed with VO(IV).     

Separation via flotation, spectrophotometric speciation, and determination of vanadium(IV) in wastes of power stations.

1-(2-Hydroxy-4-methoxybenzophenone)-4-phenylthiosemicarbazone (HMBPT) was investigated as a new reagent for the flotation of vanadium(IV). At pH approximately 1.5, vanadium(IV) forms a 1:1 pale-violet complex with HMBPT in aqueous solution. An intense clear violet layer was formed after flotation, by adding an oleic acid (HOL) surfactant. The composition of the float was 1:1 [V(IV)]:[HMBPT]. A highly selective and sensitive spectrophotometric procedure was proposed for the determination of microamounts of V(IV) as its floated complex. The molar absorptivities of the V(IV)-HMBPT and V(IV)-HMBPT-HOL systems were 0.4 x 10(4) and 0.12 x 10(5) L mol(-1) cm(-1) at 560 nm, respectively. The formation constants of the species formed in the presence and absence of HOL were 4.6 x 10(7) and 8.7 x 10(5) L mol(-1), respectively. Beer's law was obeyed up to 1 x 10(-4) mol L(-1) in the aqueous layer as well as in the oleic acid layer. The HMBPT-V(IV) complexes formed in the aqueous solution and scum layer were characterized by elemental analysis, infrared and UV spectrophotometric studies. The mode of chelation between V(IV) and HMBPT is proposed to be due to a reaction between the protonated bidentate HMBPT ligand and V(IV) through the S=C and N=C groups. Interferences from various foreign ions were avoided by adding excess HMBPT and/or Na2S2O3 as a masking agent. The proposed flotation method was successfully applied to the analysis of V(IV) in synthetic mixtures, wastes of power stations, simulated samples and in real ores. The separation mechanism is discussed.     

Extraction of palladium with tri-isobutylphosphine sulphide (cyanex 471) in toluene from chloride solutions containing thiocyanate

The extraction of PD(II) by tri-isobutylphosphine sulphide, TIBPS (Cyanex 47 1x), in toluene from aqueous chloride solutions (containing small amounts of thiocyanate) has been investigated. The extraction is enhanced by the presence of thiocyanate, owing to formation of mixed-ligand Pd(II)-Cl(-)-SCN(-)-TIBPS complexes. Analysis of the metal distribution suggests the formation of PdCl(SCN).TIBPS, PdCl(SCN).2TIBPS, Pd(SCN)(2).TIBPS and Pd(SCN)(2).2TIBPS in the organic phase. The equilibrium constants are logK(111) =9.56, logK(112) =12.70, logK(121) =14.73 and logK(122) =17.17, respectively. The ultraviolet absorption spectra of the organic phase support the hypothesis of formation of mixed-ligand complexes.     

Vanadium complexes possessing N2O2S2-based ligands: highly active procatalysts for the homopolymerization of ethylene and copolymerization of ethylene/1-hexene

The family of ligands containing an N2O2S2 core, namely, 1,2-di(3-Me-5-t-Bu-salicylaldimino-o-phenylthio)ethane (H2L1), 1,3-di(3-Me-5-t-Bu-salicylaldimino-o-phenylthio)propane (H2L2), 1,4-di(3-Me-5-t-Bu-salicylaldimino-o-phenylthio)butane (H2L3), and 1,2-di(3-Me-5-t-Bu-salicylaldamino-o-phenylthio)ethane (H2L4), have been prepared and complexed with a variety of vanadium chlorides and alkoxides to afford complexes of the form [V(X)L1] (X = O (1), Np-tol (2), Cl (3)), [V(O)(L2,3)] (L2 (4), L3 (5)), and [V(L4)] (6). Crystal structure determinations of H2L1 and H2L4 show the molecule to be centrosymmetric about the bridging ethane moiety, with structural determination of 1 and 3 revealing isostructural monomeric complexes in which the ligand chelates in such a way as to afford pseudo-octahedral coordination at the vanadium center. Prolonged reaction of H2L1 with [V(Np-tol)(OEt)3] led, via oxidative cleavage of the C-S bond, to the bimetallic complex [V2L1(3-Me,5-t-Bu-salicylaldimino-o-phenylthiolate)2] [VL'] (7), as characterized by single-crystal X-ray crystallography. 7 was also isolated from the reaction of H2L4 and [VO(On-Pr)3]. The ability of 1-7 to catalyze the homopolymerization of ethylene and the copolymerization of ethylene/1-hexene in the presence of dimethylaluminum chloride (DMAC) has been assessed: screening reveals that for ethylene homopolymerization 1-7 are all highly active (>1000 g/mmol.h.bar), with the highest activity (ca. 11 000 g/mmol.h.bar) observed using catalyst 3; the use of trimethyl aluminum (TMA) or methylaluminoxane (MAO) as the cocatalyst led only to poorly active systems producing negligible polymer. Analysis of the polyethylene produced showed high molecular weight linear polymers with narrow polydispersities. For ethylene/1-hexene copolymerization, activities as high as 1,190 g/mmol.h.bar were achieved (4); analysis of the copolymer indicated an incorporation of 1-hexene in the range of 5-13%.     

Vanadium-Komplexe mit dreizähnigen diaciden Liganden. Die Kristallstrukturen von Bis[acetylacetonthiobenzoylhydrazonato(2-)]vanadium(IV), Methoxo-oxo-[salicylaldehydthiobenzoylhydrazonato(2-)]vanadium(V) und Methoxo-oxo-[salicylaldehydbenzoylhydrazonato(2-)]methanolvanadium(V)

Vanadium Complexes with Tridentate Diacidic Ligands. The Crystal Structures of Bis[acetylacetonato-thiobenzoylhydrazonato(2-)]vanadium(IV), Methoxo-oxo-[salicylaldehyd-thiobenzoylhydrazonato(2-)]vanadium(V), and Methoxo-oxo-[salicylaldehydbenzoylhydrazonato(2-)]methanol Vanadium(V) By template reactions of bis(acetylacetonato)oxovanadium(IV) and bis(salicylaldehydato)oxo-vanadium(IV), respectively, with benzoylhydrazine, thiobenzoylhydrazine, and 2-aminophenol the vanadium(IV) complexes V(LLL)₂ of tridentate azomethine ligands LLL were synthesized. The complexes were characterized by EPR spectroscopy and by absorption spectroscopy. From the complex V(LLL)₂ ( 1 ), in which LLL is acetyl-aceton-thiobenzoydrazonate(2-), the crystal structure analysis was solved. The vanadium atom in 1 is coordinated trigonal-prismatically by two N, 0 and S atoms. Furthermore, the 0x0 vanadium(V) complexes[VO(LLL)(OCH,)] (6) with LLL = salicylaldehyd-thio-benzoylhydrazonato(2-) and [VO(LLL)(OCH₃)· -CH₃OH] (7) with LLL = salicylaldehydbenzoylhydrazonato(2-) were identified by X-ray diffraction and by IR spectroscopy in the reaction products. Crystallographic data for 1, 6 , and 7 see ?Inhaltsübersicht”?.     

Nonoxovanadium(IV) and oxovanadium(V) complexes with mixed O, X, O-donor ligands (X = S, Se, P, or PO)

Ligating properties of four potentially tridentate bisphenol ligands containing [O, X, O] donor atoms (X = S 1, Se 2, P 3, or P=O 4) toward the vanadium ions in +IV or +V oxidation states have been studied. Each ligand with different heterodonor atoms yields as expected nonoxovanadium(IV) complexes, V(IV)L(2), whose structures have been determined by X-ray diffraction methods as having six-coordinate V(IV), VO(4)X(2), core. Compounds 1-4 have also been studied with electrochemical methods, variable-temperature (2-295 K) magnetic susceptibility measurements, X-band electron paramagnetic resonance (EPR) (2-60 K) spectroscopy, and magnetic circular dichroism (MCD) (5 K) measurements. Electrochemical results suggest metal-centered oxidations to V(V) (i.e., no formation of phenoxyl radicals from the coordinated phenolates). A combination of density functional theory calculations and experimental EPR investigations indicates a dramatic effect of the heteroatoms on the electronic structure of 1-4 with consequent reordering of the energy levels; 1 and 3 possess a trigonal ground state (d(z)()(2))(1), but 4 with the phosphoryl oxygen as the heterodonor atom in contrast exhibits a tetragonal ground state, (d(xy)())(1). On the basis of the intense electronic transitions in absorption spectra, all electronic transitions observed for 4 have been assigned to ligand-to-metal charge-transfer transitions, which have been confirmed by preliminary resonance Raman measurements and C/D ratios obtained from low-temperature MCD spectroscopy. Moreover, diamagnetic complexes 5 and 6 containing mononuclear and dinuclear oxovanadium(V) units have also been synthesized and structurally and spectroscopically ((51)V NMR) characterized.     

Theoretical Studies on the Fe-M Interactions and 31P NMR in Fe(CO)3(EtPhPpy)2MX2 (X=NCS,SCN, Cl; M=Zn,Cd, Hg)

To study the Fe?M interactions and their effects on 31P NMR, the structures of Fe(CO)3(EtPhPpy)2 1,Fe(CO)3(EtPhPpy)2M(NCS)2 (2: M=Zn, 3: M=Cd, 4: M=Hg) and Fe(CO)3(EtPhPpy)2CdX2 (5: X=Cl,6: X=SCN) were investigated by density functional theory (DFT) PBE0 method. The stabilities S of complexes follow S(2)>S(3)>S(4) and S(3)≈S(6)>S(5), indicating that 6 is stable and may be synthesized.The complexes with thiocyanate are more stable than that with chloride in Fe(CO)3(EtPhPpy)2CdX2.The strength I of Fe-M interactions follows I(2)≈I(3)相似文献   

Vanadium complexes of the N(CH2CH2S)3(3-) and O(CH2CH2S)2(2-) ligands with coligands relevant to nitrogen fixation processes

Vanadium(III) and vanadium(V) complexes derived from the tris(2-thiolatoethyl)amine ligand [(NS3)3-] and the bis(2-thiolatoethyl)ether ligand [(OS2)2-] have been synthesized with the aim of investigating the potential of these vanadium sites to bind dinitrogen and activate its reduction. Evidence is presented for the transient existence of (V(NS3)(N2)V(NS3), and a series of mononuclear complexes containing hydrazine, hydrazide, imide, ammine, organic cyanide, and isocyanide ligands has been prepared and the chemistry of these complexes investigated. [V(NS3)O] (1) reacts with an excess of N2H4 to give, probably via the intermediates (V(NS3)(NNH2) (2a) and (V(NS3)(N2)V(NS3) (3), the V(III) adduct [V(NS3)(N2H4)] (4). If 1 is treated with 0.5 mol of N2H4, 0.5 mol of N2 is evolved and green, insoluble [(V(NS3))n] (5) results. Compound 4 is converted by disproportionation to [V(NS3)(NH3)] (6), but 4 does not act as a catalyst for disproportionation of N2H4 nor does it act as a catalyst for its reduction by Zn/HOC6H3Pri2-2,6. Compound 1 reacts with NR1(2)NR2(2) (R1 = H or SiMe3; R2(2) = Me2, MePh, or HPh) to give the hydrazide complexes [V(NS3)(NNR2(2)] (R2(2) = Me2, 2b; R2(2) = MePh, 2c; R2(2) = HPh, 2d), which are not protonated by anhydrous HBr nor are they reduced by Zn/HOC6H3Pri2-2,6. Compound 2b can also be prepared by reaction of [V(NNMe2)(dipp)3] (dipp = OC6H3Pri2-2,6) with NS3H3. N2H4 is displaced quantitatively from 4 by anions to give the salts [NR3(4)][V(NS3)X] (X = Cl, R3 = Et, 7a; X = Cl, R3 = Ph, 7b; X = Br, R3 = Et, 7c; X = N3, R3 = Bu(n), 7d; X = N3, R3 = Et, 7e; X = CN, R3 = Et, 7f). Compound 6 loses NH3 thermally to give 5, which can also be prepared from [VCl3(THF)3] and NS3H3/LiBun. Displacement of NH3 from 6 by ligands L gives the adducts [V(NS3)(L)] (L = MeCN, nu CN 2264 cm-1, 8a; L = ButNC, nu NC 2173 cm-1, 8b; L = C6H11NC, nu NC 2173 cm-1, 8c). Reaction of 4 with N3SiMe3 gives [V(NS3)(NSiMe3)] (9), which is converted to [V(NS3)(NH)] (10) by hydrolysis and to [V(NS3)(NCPh3)] (11) by reaction with ClCPh3. Compound 10 is converted into 1 by [NMe4]OH and to [V(NS3)NLi(THF)2] (12) by LiNPri in THF. A further range of imido complexes [V(NS3)(NR4)] (R4 = C6H4Y-4 where Y = H (13a), OMe (13b), Me (13c), Cl (13d), Br (13e), NO2 (13f); R4 = C6H4Y-3, where Y = OMe (13g); Cl (13h); R4 = C6H3Y2-3,4, where Y = Me (13i); Cl (13j); R4 = C6H11 (13k)) has been prepared by reaction of 1 with R4NCO. The precursor complex [V(OS2)O(dipp)] (14) [OS2(2-) = O(CH2CH2S)2(2-)] has been prepared from [VO(OPri)3], Hdipp, and OS2H2. It reacts with NH2NMe2 to give [V(OS2)(NNMe2)(dipp)] (15) and with N3SiMe3 to give [V(OS2)(NSiMe3)(dipp)] (16). A second oxide precursor, formulated as [V(OS2)1.5O] (17), has also been obtained, and it reacts with SiMe3NHNMe2 to give [V(OS2)(NNMe2)(OSiMe3)] (18). The X-ray crystal structures of the complexes 2b, 2c, 4, 6, 7a, 8a, 9, 10, 13d, 14, 15, 16, and 18 have been determined, and the 51V NMR and other spectroscopic parameters of the complexes are discussed in terms of electronic effects.     

Spectrophotometric determination of vanadium in different oxidation states with pyrogallol

Determination of vanadium at low concentrations is easily performed with pyrogallol as a ligand which forms a bluish-violet complex with vanadium(III), (IV) or (V). The colour of the bluish-violet complex (lambda(max) = 580 nm) contrasts well with the colour of both pyrogallol and vanadium. The complexes are stable for several hours. Beer's law is obeyed over the range 0-14 mug/ml vanadium at pH 6. The apparent molar absorptivity at 580 nm is (7.75 +/- 0.25) x 10(3)1.mole(-1).cm(-1). The effects of diverse ions on the determination of vanadium have been fully studied. Only Mo(VI) and W(VI) interfere seriously. The method is selective, sensitive and can be applied to the determination of total vanadium in a variety of samples.     

Mechanism of CO exchange on cis-[M(CO)2X2]- complexes (M=Rh,Ir;X=Cl, Br, or I)

The CO exchange on cis-[M(CO)2X2]- with M = Ir (X = Cl, la; X = Br, 1b; X = I, 1c) and M = Rh (X = Cl, 2a; X = Br, 2b; X = I, 2c) was studied in dichloromethane. The exchange reaction [cis-[M(CO)2X2]- + 2*CO is in equilibrium cis-[M(*CO)2X2]- + 2CO (exchange rate constant: kobs)] was followed as a function of temperature and carbon monoxide concentration (up to 6 MPa) using homemade high gas pressure NMR sapphire tubes. The reaction is first order for both CO and cis-[M(CO)2X2]- concentrations. The second-order rate constant, k2(298) (=kobs)[CO]), the enthalpy, deltaH*, and the entropy of activation, deltaS*, obtained for the six complexes are respectively as follows: la, (1.08 +/- 0.01) x 10(3) L mol(-1) s(-1), 15.37 +/- 0.3 kJ mol(-1), -135.3 +/- 1 J mol(-1) K(-1); 1b, (12.7 +/- 0.2) x 10(3) L mol(-1) s(-1), 13.26 +/- 0.5 kJ mol(-1), -121.9 +/- 2 J mol(-1) K(-1); 1c, (98.9 +/- 1.4) x 10(3) L mol(-1) s(-1), 12.50 +/- 0.6 kJ mol(-1), -107.4 +/- 2 J mol(-1) K(-1); 2a, (1.62 +/- 0.02) x 10(3) L mol(-1) s(-1), 17.47 +/- 0.4 kJ mol(-1), -124.9 +/- 1 J mol(-1) K(-1); 2b, (24.8 +/- 0.2) x 10(3) L mol(-1) s(-1), 11.35 +/- 0.4 kJ mol(-1), -122.7 +/- 1 J mol(-1) K(-1); 2c, (850 +/- 120) x 10(3) L mol(-1), s(-1), 9.87 +/- 0.8 kJ mol(-1), -98.3 +/- 4 J mol(-1) K(-1). For complexes la and 2a, the volumes of activation were measured and are -20.9 +/- 1.2 cm3 mol(-1) (332.0 K) and -17.2 +/- 1.0 cm3 mol(-1) (330.8 K), respectively. The second-order kinetics and the large negative values of the entropies and volumes of activation point to a limiting associative, A, exchange mechanism. The reactivity of CO exchange follows the increasing trans effect of the halogens (Cl < Br < I), and this is observed on both metal centers. For the same halogen, the rhodium complex is more reactive than the iridium complex. This reactivity difference between rhodium and iridium is less marked for chloride (1.5: 1) than for iodide (8.6:1) at 298 K.     

Synthesis of (1-adamantylimido)vanadium(V) complexes containing aryloxo, ketimide ligands: effect of ligand substituents in olefin insertion/metathesis polymerization

A series of (1-adamantylimido)vanadium(V) complexes containing anionic donor ligands of the type, V(NAd)Cl2(L) [Ad = 1-adamantyl; L = O-2,6-Me2C6H3 (2), O-2,6-(i)Pr2C6H3 (3), NC(t)Bu2 (5), NC((t)Bu)CH2SiMe3 (6), NC((t)Bu)Ph (7), NCPh2 (8)], have been prepared from V(NAd)Cl 3, which was in turn prepared from VOCl3 by treatment with 1-adamantylisocyanate in octane, by treatment with the corresponding lithium salts (lithium phenoxides, lithium ketimides) in Et2O. These complexes (2, 3, 5-8) were identified by NMR spectroscopy and elemental analysis, and the structures for 2 and 5 were determined by X-ray crystallography. The reaction of V(NAd)Cl3 with 2,6-dimethylphenol in n-hexane afforded the tris(aryloxo) analogue V(NAd)(O-2,6-Me2C6H3)3 (4), the structure of which was determined by X-ray crystallography. 8 gradually decomposed in toluene to give a dimeric species, [N(Ad)H3](+)[V2(mu2-Cl)3Cl2(NAd)2(NCPh2)2](-) (10), but 8 was stabilized as a PMe 3 coordinated species, V(NAd)Cl2(NCPh2)(PMe3)2 (9): the structures for 9 and 10 were determined by X-ray crystallography. These complexes were evaluated as catalyst precursors for ethylene polymerization in the presence of MAO. The ketimide analogues, especially 5, exhibited moderate catalytic activity, and the activity with a series of V(NAd)Cl2(L)-MAO catalyst systems increased in the order: L = NC(t)Bu2 (5, 516 kg-PE/mol x V x h) > NC((t)Bu)Ph (7, 300) > NCPh2 (8, 105) > NC((t)Bu)CH2SiMe3 (6, 70.8). These complexes (2, 3, 5, 6) were found to be effective as catalyst precursors for the ring-opening metathesis polymerization (ROMP) of norbornene (NBE) in the presence of MeMgBr and PMe3.     

EPR, magnetic and spectral studies of copper(II) and nickel(II) complexes of schiff base macrocyclic ligand derived from thiosemicarbazide and glyoxal

A new macrocylic Schiff base 1,2,5,6,8,11-hexaazacyclododeca-7,12-dithione-2,4,8,10-tetraene(H(2)L(4)) containing thiosemicarbazone moiety is readily prepared and characterized for the first time with fairly good yield. Macrocylic ligand (H(2)L(4)) is prepared from the mesocyle 6-ethoxy-4-thio-2,3,5-triazine(H(2)L(3)) in ethanol with copper chloride acting as template using high dilution technique. The complexes of macrocylic ligand with a general composition M(H(2)L(4))X(2) [where M=Cu(II) or Ni(II); H(2)L(4)=1,2,5,6,8,11-hexaazacyclo dodeca-7,12-dithione-2,4,8,10-tetraene; X= Cl(-), NO(3)(-), (1)/(2)SO(4)(2-)] and ML(4) (where metal salt used to synthesize complex is copper acetate and nickel thiocyanate) have been synthesized. The complexes were characterized on the basis of elemental analysis, molar conductance, magnetic susceptibility, IR, electronic, 1H NMR, mass and EPR spectral studies. The complexes from H(2)L(4) show different stoichiometry ratio and with a variable grade of deprotonation in the ligand, depending upon the salt used and working conditions.