Patrizia R. Mussini

Silver as a powerful electrocatalyst for organic halide reduction: The critical role of molecular structure

Abstract The remarkable electrocatalytic properties of silver for organic halide reductions, related to its strong specific interactions with halide ions, and therefore modulated by the surface state and by the nature of the supporting electrolyte, have been shown by us recently. The key role played by the molecular structure is now described together with its effect on the reaction pathway, in terms of not only the intrinsic R⋯X reactivity modification but also of elements connected to the heterogeneous nature of the process, including the accessibility of the leaving group and the possible presence of adsorption auxiliary groups stabilizing the postulated R⋯X⋯Me intermediate. The present discussion is supported by: (a) cyclovoltammetric investigations on a wide set of aliphatic and aromatic halides performed on silver, mercury and glassy carbon; and (b) a systematic program of preparative electroreductions carried out on variously configurated haloadamantanes in different operating conditions. The haloadamantane case, yielding a mixture of adamantane and dimers in a ratio heavily affected by the operating conditions, is very appropriate for an elucidation of the factors favouring monoelectronic dimerisation versus bielectronic halogen replacement by hydrogen.

Electrocatalytic potentialities of silver as a cathode for organic halide reductions

The peculiar halide affinity for silver results in an extraordinary electrocatalytic activity for the reduction of halides (either glycosyl halides or, more generally, aryl and alkyl halides). The most striking features are: (a) a reduction potential shift in the positive direction of about 1000 mV with respect to glassy carbon and 500 mV with respect to mercury; (b) a cage effect, evidenced in previous synthetic work concerning bromosugars, promoted by the halide acting as a bridge between the electrode surface and the reacting substrate, which mainly results in dimerization and/or addition products. The above electrocatalytic effect is here investigated by means of a systematic reactivity study on Ag, Hg and glassy carbon cathodes, with a variety of substrates. The effect of the supporting electrolyte is also analysed in detail, providing a first inspection on specific halide/silver interactions in acetonitrile media.

Reference value standards and primary standards for pH measurements in D2O and aqueousorganic solvent mixtures: New accessions and assessments (Technical Report)

Recommended Reference Value Standards based on the potassium hydrogenphthalate buffer at various temperatures are reported for pH measurements in various binary solvent mixtures of water with eight organic solvents: methanol, ethanol, 2-propanol, 1,2-ethanediol, 2-methoxyethanol (“methylcellosolve”), acetonitrile, 1,4-dioxane, and dimethylsulphoxide, together with Reference Value Standards based on the potassium deuteriumphthalate buffer for pD measurements in D2O. In addition are reported Primary Standards for pH based on numerous buffers in various binary solvent mixtures of water with methanol, ethanol, and dimethylsulphoxide, together with Primary Standards for pD in D2O based on the citrate, phosphate and carbonate buffers.

Relevance of electron transfer mechanism in electrocatalysis: the reduction of organic halides at silver electrodes

The mechanism of dissociative electron transfer (ET) to a series of organic chlorides has been investigated both at an inert electrode and at a catalytic surface such as Ag; electrocatalysis is important only when breaking of the carbon-halogen bond is concerted with the ET.

Microcrystalline cellulose powders: structure, surface features and water sorption capability

Characterization of an Avicel PH 102 MCC powder through polymerization degree determination, X‐ray diffraction and N2 adsorptions at subcritical temperatures is described. Specific characterizations of MCC/H2O exchange in different environments were performed by means of thermogravimetric weight losses on time/temperature scale and analyses of water adsorption/absorption from saturated vapors at 310 K. The reversibility of MCC/H2O interactions and the influence of different ‘surface area probes’ on the specific surface area are discussed.

A new class of luminescent tricarbonyl rhenium(I) complexes containing bridging 1,2-diazine ligands: electrochemical, photophysical, and computational characterization.

A novel class of luminescent tricarbonyl rhenium(I) complexes of general formula [Re2(mu-X)2(CO)6(mu-diaz)] (X=halogen and diaz=1,2-diazine) was prepared by reacting [ReX(CO)5] with 0.5 equiv of diazine (seven different ligands were used). The bridging coordination of the diazine in these dinuclear complexes was confirmed by single-crystal X-ray analysis. Cyclic voltammetry in acetonitrile showed for all the complexes (but the phthalazine derivative) a chemically and electrochemically reversible ligand-centered reduction, as well as a reversible metal-centered bielectronic oxidation. With respect to the prototypical luminescent [ReCl(CO)3(bpy)] complex, the oxidation is more difficult and the reduction easier (about +0.3 V), so that a similar highest occupied molecular orbital-lowest unoccupied molecular orbital gap is observed. All of the complexes exhibit photoluminescence at room temperature in solution, with broad unstructured emission from metal-to-ligand charge-transfer states, at lambda in the range 579-620 nm. Lifetimes (tau=20-2200 ns) and quantum yields (Phi up to 0.12) dramatically change upon varying the bridging ligand X and the diazine substituents: in particular, quantum yields decrease in the series Cl, Br, and I and in the presence of substituents at the alpha positions of the pyridazine ring. A combined density functional and time-dependent density functional study of the geometry, relative stability, electronic structure, and photophysical properties of all the pyridazine derivatives was performed. The nature of the excited states involved in the electronic absorption spectra was ascertained, and trends in the energy of the highest occupied and lowest unoccupied molecular orbitals upon changing the pyridazine substituents and the bridging halogen ligands were discussed. The observed emission properties of these complexes were shown to be related to a combination of steric and electronic factors affecting their ground-state geometry and their stability.

The Electrocatalytic Performance of Silver in the Reductive Dehalogenation of Bromophenols

The remarkable electrocatalytic properties of silver for organic halide reduction have been applied to obtain quantitative direct dehalogenation of mono and polyphenols in acetonitrile and in water/acetonitrile 1:1 mixed solvent. Structure effects on the reaction pathways observed by electrolysis monitoring are discussed with the support of systematic cyclovoltammetric experiments on silver, mercury, and glassy carbon. The process, environmentally friendly as based on a nontoxic electrocatalytic material, also appears highly competitive on account of its mildness of operating conditions, selectivity, and current efficiency.

Thiocyanate-Free Ruthenium(II) Sensitizer with a Pyrid-2-yltetrazolate Ligand for Dye-Sensitized Solar Cells

The synthesis of the new complex [Ru(Tetrazpy)(dcbpy)2]Cl is reported, along with its spectroscopical, electrochemical, and theoretical characterization. The first dye-sensitized solar cell device with this complex has been prepared, leading to a 3% of conversion efficiency, promising data considering the simplicity of the Tetrazpy ligand.

Tetraaryl ZnIIPorphyrinates Substituted at β-Pyrrolic Positions as Sensitizers in Dye-Sensitized Solar Cells: A Comparison withmeso-Disubstituted Push-Pull ZnIIPorphyrinates

A facile and fast approach, based on microwave-enhanced Sonogashira coupling, has been employed to obtain in good yields both mono- and, for the first time, disubstituted push-pull Zn(II) porphyrinates bearing a variety of ethynylphenyl moieties at the β-pyrrolic position(s). Furthermore, a comparative experimental, electrochemical, and theoretical investigation has been carried out on these β-mono- or disubstituted Zn(II) porphyrinates and meso-disubstituted push-pull Zn(II) porphyrinates. We have obtained evidence that, although the HOMO-LUMO energy gap of the meso-substituted push-pull dyes is lower, so that charge transfer along the push-pull system therein is easier, the β-mono- or disubstituted push-pull porphyrinic dyes show comparable or better efficiencies when acting as sensitizers in DSSCs. This behavior is apparently not attributable to more intense B and Q bands, but rather to more facile charge injection. This is suggested by the DFT electron distribution in a model of a β-monosubstituted porphyrinic dye interacting with a TiO2 surface and by the positive effect of the β substitution on the incident photon-to-current conversion efficiency (IPCE) spectra, which show a significant intensity over a broad wavelength range (350-650 nm). In contrast, meso-substitution produces IPCE spectra with two less intense and well-separated peaks. The positive effect exerted by a cyanoacrylic acid group attached to the ethynylphenyl substituent has been analyzed by a photophysical and theoretical approach. This provided supporting evidence of a contribution from charge-transfer transitions to both the B and Q bands, thus producing, through conjugation, excited electrons close to the carboxylic anchoring group. Finally, the straightforward and effective synthetic procedures developed, as well as the efficiencies observed by photoelectrochemical measurements, make the described β-monosubstituted Zn(II) porphyrinates extremely promising sensitizers for use in DSSCs.

Near‐IR Emitting Iridium(III) Complexes with Heteroaromatic β‐Diketonate Ancillary Ligands for Efficient Solution‐Processed OLEDs: Structure–Property Correlations

Three NIR-emitting neutral Ir(III) complexes [Ir(iqbt)2 (dpm)] (1), [Ir(iqbt)2 (tta)] (2), and [Ir(iqbt)2 (dtdk)] (3) based on the 1-(benzo[b]thiophen-2-yl)-isoquinolinate (iqtb) were synthesized and characterized (dpm=2,2,6,6-tetramethyl-3,5-heptanedionate; tta=2-thienoyltrifluoroacetonate; dtdk=1,3-di(thiophen-2-yl)propane-1,3-dionate). The compounds emit between λ=680 and 850 nm with high luminescence quantum yields (up to 16 %). By combining electrochemistry, photophysical measurements, and computational modelling, the relationship between the structure, energy levels, and properties were investigated. NIR-emitting, solution-processed phosphorescent organic light-emitting devices (PHOLEDs) were fabricated using the complexes. The devices show remarkable external quantum efficiencies (above 3 % with 1) with negligible efficiency roll-off values, exceeding the highest reported values for solution-processible NIR emitters.