Metal phosphides from the 3d period exhibit a range of structures and compositions. Many metal-rich phosphides and monophosphides function as heterogeneous electrocatalysts in the hydrogen evolution reaction. This paper describes the direct and tin flux-assisted synthesis of phosphorus-rich metal phosphides with MP2 or MP3 compositions. The facile synthesis of FeP2, CoP3, NiP2, and CuP2 is thermochemically driven by PCl3 formation from reactions of anhydrous metal halides and P4 vapor at 500 °C. Well-crystallized micrometer-sized particles result from these solvent-free reactions. A tin flux leads to more complete reactions at lower temperature for FeP2 and enables synthesis of a monoclinic polymorph of NiP2 rather than the kinetic cubic product formed by direct reaction. These crystalline metal phosphides are investigated as electrocatalyts for hydrogen evolution in acidic and buffered aqueous solutions. All phosphorus-rich products show very good stability in strongly acidic media. The catalytic activity for hydrogen evolution ordered by higher current at a fixed electrode geometric area and low onset potential is CoP3 > NiP2 (cubic and monoclinic) > FeP2 ≫ CuP2. At high applied potentials, CuP2 undergoes surface reactions and roughening that improve its electrocatalytic activity. Correlations of the observed electrocatalytic activity with electrochemically active surface area, particle size, metallic versus semiconducting properties, and local metal coordination environment are noted for these phosphorus-rich 3d metal phosphides.

Review of the literature on the currently recognized, thirteen vitamins yields an overview of the electrochemical properties that include estimates of the formal potentials at physiological pH and identification of the general classes of redox mechanisms. All vitamins are electroactive and map a range of formal potentials E 0 over a 3 V window. The vitamins are grouped as lipid soluble (vitamins A, D, E, and K) and water soluble (B vitamins and vitamin C). Mechanisms are grouped as single electron transfer agents (B3, B7, B2, C, and D), vitamins that can be both oxidized and reduced (B1, B5, B6, B9, and E), and vitamins that undergo two successive, distinct reductions (B12 and K). Vitamin A voltammetry is uniquely complex. Plot of the formal potentials on a potential axis allows assessment of mechanistic paths to vitamin recycling, antioxidant behavior, pH dependence, electrochemical stability in air, acid, and water, electrochemical instability of vitamin pairs, and cooperative interactions between vitamins in medicine. The potential axis is shown as an effective tool for mapping thermodynamically complex interactions. By modern standards, the US federal government identifies 13 vitamins.3 The water soluble vitamins are vitamin C and the eight B vitamins (B1, B2, B3, B5, B6, B7, B9, B12). The lipid or fat soluble vitamins are A, D, E, and K. The fat soluble vitamins can accumulate in the body whereas the water soluble vitamins do not. There are no current vitamins designated beyond E except for K because materials historically assigned the interposed letter designations either no longer fall under the modern definition of vitamin or several related materials were reclassified. Several vitamins exist in different but related chemical structures.Questions considered in this perspective include whether all vitamins are electroactive; what is the redox potential of the vitamins; what are the kinetics and mechanisms of vitamins on oxidation and reduction; when are vitamins antioxidants; are vitamins stable to water and oxygen; do vitamins interact cooperatively. Although papers are available on the electrochemistry and voltammetry of individual vitamins, no single resource summarizes the electrochemical data for all vitamins. This review compiles and critically assesses the available literature on vitamin voltammetry. The compiled data serve to develop perspective on the electrochemical properties of vitamins and the role of vitamins individually and collectively as electroactive species. This CRES 3 T review assimilates fundamentals of thermodynamics and estimated formal potentials, kinetics, and mechanisms as assessed voltammetrically for individual vitamins to provide perspective on the collective electrochemical properties of the thirteen vitamins. Perspective on vitamin electrochemical properties may contribute to assess yet more complex bioelectrochemical processes. * Electrochemical Society Student Member.* * Electrochemical Society Fellow. z E-mail: johna-leddy@uiowa.eduThe review contains two main sections....

Oligothiophene-substituted 1,1,4,4-tetracyanobutadienes (TCBDs) have been synthesized by [2 þ 2] cycloaddition reactions between tetracyanoethylene and oligothiophene alkynes. The TCBD moiety is compared to other electron acceptors attached to dibutylterthiophene including dicyanovinyl (DCV) and tricyanovinyl (TCV). These donor-acceptor molecules (TCBD-3T, DCV-3T, and TCV-3T) show red-shifted absorption spectra relative to the unsubstituted oligothiophene as a result of intramolecular charge-transfer (ICT). Monosubstituted terthiophenes bearing the electron acceptors show both oxidation and reduction processes as characterized by cyclic voltammetry. Density functional theory (DFT) calculations are used to explain the electronic and redox properties of the materials. Electrochemical oxidation of a bis(terthienyl)-substituted TCBD molecule (3T-TCBD-3T) yields a conducting polymer exhibiting balanced ambipolar redox conduction with similar values for the oxidized and reduced states of the polymer (1 Â 10 -3 S cm -1 ). Raman spectra of the asymmetric donor-acceptor materials are characterized by two intense bands characteristic of the aromatic and quinoidal regions in the conjugated π-system of the oligothiophene.

New stilbenoid and thiophenic compounds terminally functionalized with donor-donor, acceptor-acceptor, or donor-acceptor moieties and possessing a central [2.2]paracyclophane unit have been prepared, and their properties interpreted in terms of through-bond and through space π-electron delocalization (i.e., π-conjugations). Based on photophysical data, their excited-state properties have been described with a focus on the participation of the central [2.2]paracyclophane in competition with through-bond conjugation in the side arms. To this end, two-photon and one-photon absorption and emission spectroscopy, as a function of temperature, solvent polarity, and pressure in the solid state have been recorded. Furthermore, charge delocalization through the [2.2]paracyclophane in the neutral state and in the oxidized species (radical cations, dications and radical trications) has been investigated, allowing the elucidation of the vibrational Raman fingerprint of through-space charge delocalization. Thus, a complementary approach to both "intermolecular" excitation and charge delocalizations in [2.2]paracyclophane molecules is shown which can serve as models of charge and exciton migration in organic semiconductors.

Benzo[1,dithiophenes were oxidized under mild conditions with m-CPBA to yield the corresponding bis-sulfones (or tetraoxides). These sulfones possess redshifted absorption and emission spectra relative to the parent molecules. Electrochemical analyses reveal that the benzodithiophene molecules are transformed from electron donors to electron acceptors.