Giovanna Battistuzzi Gavioli

Bimetallic cyclooligosiloxanolate complexes of copper and nickel

The bimetallic cyclosiloxanolate cluster complexes Na[PhSiO 2 ) 6 Cu 4 Ni 2 ( μ 6 -Cl)(PhSiO 2 ) 6 ] ( 1 ) and Na[(PhSiO 2 ) 6 Cu 3 Ni 3 ( μ 6-Cl)(PhSiO 2 ) 6 ] ( 2 ) were prepared by Na + and Ni 2+ ion exchange from in situ generated Na 2 {[(PhSiO 2 ) 6 ] 2 Na 4 Ni 4 (OH) 2 }. Complexes 1 and 2 were characterized by analytical, spectroscopic and electrochemical methods as well as complex 2 by single-crystal X-ray diffraction. The X-ray structure shows a sandwich-type array comprising two superimposed cyclosiloxanolate rings and an M 6 Cl unit in between. For the first time the regioselectivity of the metal ion exchange could be deduced from the X-ray structural parameters.

The effect of a dansyl group on the co-ordinative ability of N-protected amino acids. Part 1. Behaviour of the copper(II) ion–N-dansylglycinate system in aqueous and methanolic solution

Polarographic, potentiometric, and spectrophotometric measurements show that copper(II) and N-dansylglycine (5-dimethylaminonaphthalene-1-sulphonylglycine) form the same complexes in aqueous and methanolic solution. Mixed-hydroxy complexes are the prevailing species. In aqueous (methanolic) solution up to pH 5(5) no formation of complexes is observed; in the pH range 7–8.5 (8.5–11) a change in the ligand co-ordination from O-co-ordination through the carboxylate group to N,O-bidentate co-ordination through the carboxylate oxygen and the deprotonated amide nitrogen is revealed. There is a low tendency for two N-dansylglycine ligand molecules to coordinate to the CuII ion, probably due to the steric hindrance of the dansyl group. The equilibria in which the prevailing complexes are involved and the reduction processes at the electrode are proposed. The nucleophilic and electrophilic properties of the two solvents are used to explain the solvent effect on the polarographic parameters and on the stability constants of the complexes.

Bimetallic siloxane cluster of higher valent transition metals: Na{[η6-cyclo-(PhSiO2)6]2Co2Ni4(μ6-Cl)}

Abstract The bimetallic siloxane cluster / cage compound Na{[η 6 -cyclo-(PhSiO 2 ) 6 ] 2 Co 2 Ni 4 (μ 6 -Cl)} was preparred and characterized by single crystal X-ray diffraction, spectroscopic, magnetic and electrochemical methods.

Siloxane clusters of higher valence transition metals: Redox properties

Abstract Cyclic voltammetric behaviour of polymetallic complexes of hexaphenylyclohexasiloxane-hexaol with Ni, Mn and dodecaphenyl-cyclododecasiloxane-dodecaol with Cu was studied. The complexes react electrochemically as a unit assembly of the complexed metals

Electrochemistry of 4,6-dimethyl-2-thiopyrimidine and 4,6-dimethyl-1-phenyl-2-thiopyrimidine in dimethylformamide

Abstract The electrochemical behaviour of 4,6-dimethyl-2-thiopyrimidine (LH) and 4,6-dimethyl-1-phenyl-2-thiopyrimidine (LΦ) and their protonated forms was investigated in dimethylformamide on Hg electrodes. Adsorption processes affect the oxidation mechanism of both the compounds and the formation of Hg(I) complexes was observed. The electrochemical reduction of LH provides an example of the so-called “father—son reaction” but this kind of mechanism cannot occur with LΦ. Only in the species LH is a proton present which can be abstracted by the product of the first electron transfer LH · − while LΦ can be protonated by the solvent. However, in the presence of strong acids, for both molecules LH and LΦ the formation of the dimer from the radical anion obtained in the first electron transfer is kinetically preferred to the father—son reaction.

Cyclosiloxane sandwich complexes of a lanthanide metal: Na6{[(C6H5SiO2)8]2Nd4(μ4-O)}☆

Abstract The oligocyclosiloxane cluster (‘sandwich’) complex of Nd3+, Na6{[(C6H5SiO2)8]2Nd4(μ4-O)} has been prepared and characterized by analyses, infrared spectra, single crystal X-ray diffraction, magnetic susceptibility, conductivity and cyclic voltammetry. The μ4-O2− anion is in a square planar coordination environment. Electrochemical studies identify the cluster core as a moiety with a delocalized electron system.

Electrosorption of ‘hard’ and ‘soft’ aromatic derivatives on mercury

An ‘intrinsic’ value of the adsorption Gibbs energy (ΔG°int)∥, not directly proportional to the measured ΔG∥ads, has been evaluated for a set of 28 aromatic, heterocyclic and naphthalenic derivatives. The structural feature of (ΔG°int)∥ is rationalised in terms of a ‘soft’ interaction with mercury at the point of zero charge, on the basis of the parr and Pearson concept, accounting on a quantitative basis for the different adsorbability of the compounds. Moreover, the partial charge-transfer coefficient, λ, has been related in a satisfactory way to ΔN(the fractional number of electrons transferred) calculated taking into account the absolute electronegativitiy, χ, and the hardness, η, both of the adsorbate and of mercury.

Catalytic polarographic currents in aqueous solutions of phenylmethyl sulphoxide

Summary The polarographic behaviour of phenylmethyl sulphoxide has been studied in aqueous sulphuric acid. The study has been carried out using two different methods: the first, an analytical investigation involving coulometric, polarographic and spectrophotometric measurements to investigate the reaction products; the second, an accurate study of the nature of the polarographic wave and of the reaction mechanism, effected by analysing the influence of pH, sulphoxide concentration, temperature and drop-time on the experimental values of current and potential. At pH φ−SO−CH3 + H+ ⇄ φࢤSOHCH3+ φ−SOHCH3+ + e ⇄ φࢤSOHCH3⋅ 2φ−SOH−CH3⋅ → 2φࢤSOࢤCH3 + H2 Chemical reduction of -SO−CH3 to sulphide accompanies this electrochemical process.

Theoretical study of the electroreduction of halogenated aromatic compounds. Part 2.—Bromine and chlorine derivatives in different organic solvents

The electrochemical dehalogenation of a variety of halogenated aromatic compounds is studied by means of semiempirical (AM1) and ab initio(ROHF 3-21G*) calculations. Comparison of the electrochemical half-wave potential values (E1/2) and calculated theoretical indices indicates the formation of a π radical following the electron uptake. Moreover, the relationship observed between the half-wave potential, in dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), and the electron affinity suggests that the reduction potential is determined by the first electron uptake and that kinetic factors play a minor role, their influence being constant or negligible.

Heterobimetallic Cyclosiloxanolate Sandwich Clusters: Na[η6-cyclo(PhSiO2)6]2[Fe(OR)]2Ni4(μ6-Cl) (R = H, Me)

The heterobimetallic cyclosiloxanolate sandwich clusters Na[η6-cyclo (PhSiO2)6]2[Fe(OR)]2Ni4(μ6-Cl) (R = H, Me) (1) were prepared from Na2[(PhSiO2)6]2Na4Ni4(OH)2 in the form of solvates. The new clusters 1 were characterized by spectra (UV-VIS, IR, 1H-NMR), cyclic voltammetry. conductivity, magnetic susceptibility, and single-crystal X-ray diffraction.