The solution state of nickel(II) and nickel(I) in the presence of diphosphines in acetonitrile. A combined electroanalytical and spectrophotometric approach

The equilibria involving nickel(II), nickel(I) and nickel(0) in the presence of bidentate phosphine ligands in acetonitrile solution have been investigated by cyclic voltammetry, controlled-potential electrolysis, and spectrophotometry. The obtained results show that when both cone angles and PP distance make the diphosphine well-suited to act as a chelating ligand, only bis-chelate complexes of the type NiL₂ are formed by nickel in all the three achieved oxidation states. Longer methylene chains interposed between the phosphorus atoms make the diphosphine less suited to act in a bidentate fashion, thus allowing lower-order complexes, e.g. NiLS₂ (S = solvent), to be obtained for nickel in the +2 and +1 oxidation states. Evidence for the poor stability of the [Ni^ILS₂]⁺ complexes and for a higher-order complex of the type NiL₃ for nickel(II) have also been obtained. The dependence of the reduction potentials on the nature of the diphosphine employed is discussed.     

The preparation and characterisation of some complexes of iron(II) with amino acids

The following complexes of iron(II) with the amino acids glycine, alanine, phenylglycine, phenylalanine, leucine, serine, aspartic acid, glutamic acid, glutamine, tryptophan, histidine, methionine, S-methylcysteine, cystine, and glycylglycine have been isolated: Fe(Gly)₂, Fe(Ala)₂, Fe(Phegly)₂, Fe(Phe)₂·2H₂0, Fe(Leu)₂·2H₂0, Fe(Ser)₂, Fe(Asp)·2H₂0, Fe(Glu)·2H₂0, Fe(Gln)₂, Fe(Trp)₂, Fe(His)₂·H₂0 and 2H₂0, Fe(Met)₂, Fe(MeCys)₂, Fe(CysCys) and Fe(GlyGly)₂. Their magnetic behaviour, reflectance spectra, and Mössbauer parameters are consistent with high spin, hexacoordinate iron(II), and imply extended structures involving carboxylate bridges.     

The syntheses and properties of cobalt(II), nickel(II) and copper(II) complexes with some heterocyclic dithiocarbamates

New cobalt(II), Nickel(II) and copper(II) dithiocarbamato complexes of the type M(Rdtc)₂ (Rdtc = 4-phenylpiperidinedithiocarbamate and N-phenylpiperazinedithiocarbamate) have been prepared and characterized through elemental analyses, conductivity measurements, spectral (electronic and IR) studies, magnetic moment measurements at different temperatures, e.p.r. techniques and thermal analyses (TG and DTG). The dithioligands exhibit bidentate behaviour in all the complexes. The magnetic moments studies suggest that there is no significant interaction between copper ions, and the e.p.r. data provide parameters typical of sulphur coordination in planar CuS₄ chromophores.     

The copper(II) catalyzed reaction of L-ascorbinc acid with tris(oxalato)cobaltate(III) ion in aqueous solution

The kinetics of the reaction between tris(oxalato)cobaltate(III) ion and L-ascorbic acid were studied in aqueous solution over a range of copper(II) ion concentrations, ascorbic acid concentrations, pH values and temperatures. A rate law of the type rate = k[HA^?][Cu²⁺][Co³⁺], where HA^? = ascorbate, is suggested by the experimental results. A mechanism involving a copper-ascorbate complex is proposed.     

A polarimetric study of the reaction of bis(L-serinato)copper(II) with formaldehyde

Polarimetric data have shown that the base-catalyzed reaction of bis(L-serinato)copper(II) with excess formaldehyde proceeds via the initial dissociation of the proton on the nitrogen atom of the amino acid chelate. A bis(oxazolidine)copper(II) complex appears as an intermediate but this species is not detected polarimetrically at 50°C and above.     

The direct electrochemical synthesis of neutral and anionic halogen complexes of uranium(IV) and uranium(VI)

The electrochemical oxidation of anodic uranium into acetonitrile solutions of X₂ (X = Cl, Br) under nitrogen gives rise to UCl₄·4CH₃CN or UBr₄·2CH₃CN in good yield. These compounds are easily converted to other UX₄ adducts. In the presence of oxygen, solutions of UO₂X₂ are produced by the electrolysis, and the parent halide, or neutral addition compounds, are readily obtained from these. Addition of R₄NX to the cell results in the direct synthesis of (R₄N)₂UX₆ under nitrogen, or (R₄N)₂UO₂X₄ under oxygen. The only iodo compound which could be formed by electrolysis into N,N- dimethylformamide (=dmf) was UI₄·4dmf.     

Kinetic studies on the reaction of ethylenediaminetetraacetatochromium(III) complex with hydrogen peroxide

The rate of reaction of [Cr(III)Y]_aq (Y is EDTA anion) with hydrogen peroxide was studied in aqueous nitrate media [μ = 0.10 M (KNO₃)] at various temperatures. The general rate equation, Rate = $\text{k}{}_1\text{+}\text{k}{}_2\text{K}{}_1\text{[H}{}^{\mathrm{+}}\text{]}{}^{\mathrm{?1}}\text{1 +}\text{K}{}_1\text{[H}{}^{\mathrm{+}}\text{]}{}^{\mathrm{?1}}$ [Cr(III)Y]_aq[H₂O₂] holds over the pH range 5–9. The decomposition reaction of H₂O₂ is believed to proceed via two pathways where both the aquo and hydroxo-quinquedentate EDTA complexes are acting as the catalyst centres. Substitution-controlled mechanisms are suggested and the values of the second-order rate constants k₁ and k₂ were found to be 1.75 × 10^?2 M^?1 s^?1 and 0.174 M^?1 s^?1 at 303 K respectively, where k₂ is the rate constant for the aquo species and k₂ is that for the hydroxo complex. The respective activation enthalpies (ΔH^*₁ = 58.9 and ΔH^*₂ = 66.5 KJ mol^?1) and activation entropies (ΔS^*₁ = ?85 and ΔS^*₂ = ?40 J mol^?1 deg^?1) were calculated from a least-squares fit to the Eyring plot. The ionisation constant pK₁, was inferred from the kinetic data at 303 K to be 7.22. Beyond pH 9, the reaction is markedly retarded and ceases completely at pH ? 11. This inhibition was attributed in part to the continuous loss of the catalyst as a result of the simultaneous oxidation of Cr(III) to Cr(VI).     

The chemistry of rhenium and technetium. Part III. The synthesis and characterisation of oxo-bis-(tetrathiomolybdenato)-technetium(V) and its reduction by triphenylphosphine

The Complexes (Bu₄N)[TcO(MoS₄)₂] and Tc- (PPh₃)₂(MoS₄)₂ were prepared. The former complex has a much lower Tc-O stretching frequency than is generally found gor the TcO³⁺. moiety. The latter technetium(IV) Complex was obtained by the reduction of Tc^(v) O(MoS₄)₂^? with triphenylphosphine and also by the substitution reaction of TcCl₄(PPh₃)2 with MoS₄^2-. Previous reductions of this nature have led to the isolation of species that differ by two formal oxidation state numbers from the oxidant.     

Complexes of binucleating ligands. XVII. Some 3-atom N,C bridged palladium(II) complexes

The acetate-bridged complex, LPd₂(CH₃CO₂), in which L^3? is a binucleating ligand, reacts with 2-vinylpyridine in the presence of methanol or ethanol to generate the 3 atom N,C bridged complexes LPd₂(2-C₅H₄N·CH·CH₂OR) (R = Me or Et) whose ¹H and ¹³C nmr spectra indicate the presence in solution of two slowly interconverting forms at room temperature. The ¹H and ¹³C nmr spectra of two closely related pairs of 3 atom N,C bridged complexes of the form LPd₂(2-C₅H₄N·CH·X) and LPd₂ (HN = C(CH₃)·CH·X) (where X = COCH₃ or COOCH₃) show that the complexes with pyridine-containing bridges exist in solution at room temperature in two distinguishable forms whilst the corresponding imine-bridged complexes behave as single species. The existence of two forms of the complexes with pyridine-containing 3 atom N,C bridges, the natures of which are discussed in this paper, appears to be a consequence of steric interaction between the pyridine α hydrogen atom and the closely adjacent oxygen donor of L.     

Mononuclear Ni(II) and Zn(II) complexes of some potentially binucleating Schiff base ligands

Mononuclear Zn(II) and Ni(II) complexes have been prepared from two new Schiff base ligands in which two alternative co-ordination sites (N₂O₂ or O₂O₂) occur. The first ligands is the Schiff base derived from 1,2-diaminobenzene and 2-hydroxy-3-carboxyl-1-napthaldehyde (bopaH₄). The complexes of this ligand contain the metal ions in the N₂O₂ coordination site as a result of the steric requirements of the co-ordinated ligand. The second ligand series are derivatives of X-substituted 1,2-diaminobenzenes, 2-hydroxy-3-carboxy-1-naphthaldehyde and 2-hydroxy-5-methyl isophthaldehyde (X-bolaH₃). In this case Ni(II) occupies the N₂O₂ site in its complexes with the X-bolaH₃ ligands, whereas the Zn(II) complexes are co-ordinate through the O₂O₂ site since the steric restrictions are less severe.     

Cisplatin analogues. cis-Dichloroaminoacid-tert-butylamineplatinum(II) complexes and their adducts with guanosine

A series of compounds of formula cis-[PtCl₂- (aaH)(tba)] (1) (aaH, N-coordinate amino acid; tba, tert-butylamine) were synthesized. The circular dichroism spectra of these compounds show that the phenylalanine and proline derivatives have an anomalous conformation in water solution. By reaction with guanosine (guo) compounds 1 give cis- [Pt(aaH)(tba)(guo)₂]Cl₂ (2), in which infrared and nuclear magnetic resonance evidence suggest N(7) coordination of guo. NMR and circular dichroism data suggest that in 2 the two guanosine ligands are arranged head-to-head and form a right-hand helix. The bulkiness of the other ligands make rotation around the PtN(7) bonds a slow process on the NMR time scale. The chiroptical properties of 2 are not greatly influenced by the absolute configuration of the amino acid, the right-hand screw probably arising by some guo-guo interaction since the derivatives of 9-methylguanine with chiral amino acids do not possess this conformation.Preliminary results on the reaction between 1 and calf thymus DNA are also briefly reported. They show that the interaction of 1 with DNA is of a lower extent than in the case of cisplatin and its diamine analogues, and that it is independent on the configuration of the amino acids.All these results are briefly discussed and tentatively correlated with the low antitumor activity of 1 reported in a previous paper.     

The synthesis and structural characterization of (2-pyridyldiphenylphosphine oxide)platinum(IV)tetrabromide. A chelating phosphine oxide with a substantially bent PtOP angle

The complex (pyPh₂PO)PtBr₄ (pyPh₂PO is 2-pyridyldiphenylphosphine oxide) has been synthesized by three different pathways, and its structure has been established by X-ray crystallography. C₁₇H₁₄Br₄NOPPt crystallizes in the space group P2₁/c (no. 14) with cell dimensions (at 140 K) of a = 13.696(7), b= 16.653(5), c = 17.612(7) Å, β = 92.23(4)°, Z = 8 and V = 3993(3) ų. The structure was refined by block-cascade least-squares to a conventional R value of 0.048 using 3647 significant data. The structure involves a six-coordinate platinum((IV) ion with the chelated ligand bound through its nitrogen and oxygen atoms. The two crystallography independent molecules in the asymmetric unit have very similar dimensions. To our knowledge this is the first reported structure of a chelating phosphine oxide. The PtOP angles within the rings are 114.4(6)° and 117.4(6)°.     

Group IIB metal chloride complexes with some 2-(methylpyridyl or -quinolyl)benz-X-azoles

The complexes formed by Zn(II), Cd(II) and Hg(II) chlorides with benzimidazole, benzoxazole and benzothiazole linked to 4-methylpyridine and 4-methylquinoline have been prepared and characterized by chemical analysis, infrared spectra and conductivity data.The coordination behaviour of these ligands toward the metal salts and the stereochemistry of the obtained complexes have been investigated.     

The reactions of zirconium(IV) bromide and zirconium(III) bromide and chloride with ammonia and zirconium(IV) bromide with ammonium cyanide

Unlike ZrCl₄, ZrBr₄ is not ammonolysed in liquid ammonia at temperatures up to −33 °C. The existence of ammoniates ZrBr₄nH₃ (n = 17, 12 and 9) at −36 °C has been established; at room temperature, the hexammine ZrBr₄ · 6NH₃ is the stable species which becomes ZrBr₄ · 2NH₃ at 200 °C. When treated with an excess of NH₄CN in liquid ammonia, complete replacement of bromide ions by cyanide occurs to give an inseparable mixture of Zr(CN)₄ · 2NH₃ and NH₄Br. The chloride and bromide of zirconium(III) also undergo no ammonolysis in liquid ammonia; the ammoniates stable at room temperature are ZrCl₃ · 2.5NH₃ and ZrBr₃ · 6NH₃.     

Preparation of heterocyclic thialato ligands and their Copper(II) complexes

A number of different heterocyclic aldehydes substituted in the β-position with the t-butylthio moiety were converted into new S₂N₂ ligands containing protected thiol groups. Reaction of the protected ligands 2 with copper(II) salts resulted in elimination of isobutene and formation of copper(II) complexes of mercaptoimines 3.     

New acyclic and cyclie Schiff bases derived from 2,6-diformyl-4-chlorophenol and their interaction with uranyl(Vl), copper(II) and nickel(Il) ions

A new heptadentate compartmental ligand has been synthesized by condensation of 3-formylsalicylic acid and 1,5-diamino-3-thiapentane in methanol (H₄L_a). This Schiff base contains an inner N₂SO₂ and an outer O₂O₂ site and gives, by reaction with copper(II), nickel(II) and uranyl(VI) diacetate, mononuclear, homo- and heterobinuclear complexes. In the mononuclear copper and nickel complexes, the metal ion is in the inner N₂SO₂ site, while it is in the outer O₂O₂ for uranyl; a solvent molecule fills the fifth equatorial coordination position in this last complex. The physico-chemical properties of the compounds are discusscd on the basis of infrared, electronic and magnetic data and by comparison with the analogous complexes with the ligand obtained by reaction of 3- formylsalicylic acid and diethylenetriamine (H₄L_b). The mononuclear copper and the heterodinuclear copper-uranyl complexes show anomalously low magnetic moments.     

Metal complexes of the schiff bases 2-pyridinylhydrazine and 2-quinolinyl-hydrazine with 2-pyridinecarboxaldehyde N-oxide,including some N-oxide-bridged antiferromagnetic complexes of cobalt(II) and nickel(II)

Metal complexes of 2-pyridine carboxaldehyde 2′-pyridinylhydrazone 1-oxide (poph) and 2-pyridinecarboxaldehyde 2′-quinolinylhydrazone 1-oxide (poqh) are reported with copper(II), nickel(II), cobalt(II), iron(II) and manganese(II). Each ligand appears to function as an ONN donor, via the pyridine N-oxide oxygen, the imine nitrogen, and a pyridine or quinoline nitrogen. The complexes have been characterised by magnetic susceptibility measurements to liquid nitrogen temperature, and also by electronic, infrared, X-ray powder diffraction, and Mössbauer spectra. No magnetic interaction was detected with the copper(II) complexes. All the complexes of metal nitrates appear to be monomers.The complexes of poph with the halides and thiocyanates of nickel(II) and cobalt(II) appear to be six-coordinate and N-oxide-bridged; they exhibit varying degress of antiferromagnetic interaction and the magnetic data for the nickel(II) complexes have been fitted to various models. In contrast, the bulky ligand poqh produces halide-bridged six-coordinate nickel(II) complexes and monomeric five-coordinate cobalt(II) complexes.This behaviour by poqh resembles that of the related NNN ligands paphy and paqhy, which are the Schiff bases of 2-pyridinecarboxaldehyde with 2-pyridinylhydrazine and 2-quinolinylhydrazine, respectively.     

The complex formation of copper(II) with GHL and HSA

The formation constants for complexes of copper(II) with GHL have been determined by means of pH titrations and ESR spectroscopy in aqueous solutions. GHL has an extremely high affinity for copper(II) and forms very stable 1:1 complexes and a comparatively weak 1:2 complex. The ? amino group of GHL seems not to be involved in complex formation as can be deducted from both equilibrium constants and ESR spectroscopy. The ternary system copper(II)-GHL-HSA was investigated by ESR spectroscopy and optical absorption spectroscopy in aqueous solution at physiological pH (7.4). At equimolar concentrations, copper(II), HSA and GHL form a ternary complex.