Mixed-valence state of symmetric diruthenium complexes: synthesis, characterization, and electron transfer investigation

Complexes of the type {[(pyS)Ru(NH3)(4)](2)-mu-L}(n), where pyS = 4-mercaptopyridine, L = 4,4'-dithiodipyridine (pySSpy), pyrazine (pz) and 1,4-dicyanobenzene (DCB), and n = +4 and +5 for fully reduced and mixed-valence complexes, respectively, were synthesized and characterized. Electrochemical data showed that there is electron communication between the metal centers with comproportionation constants of 33.2, 1.30 x 10(8) and 5.56 x 10(5) for L = pySSpy, pz and DCB, respectively. It was also observed that the electronic coupling between the metal centers is affected by the p-back-bonding interaction toward the pyS ligand. Raman spectroscopy showed a dependence of the intensity of the vibrational modes on the exciting radiations giving support to the assignments of the electronic transitions. The degree of electron communication between the metal centers through the bridging ligands suggests that these systems can be molecular wire materials.CNPqCNPqFAPESPFAPESPFUNCAP [PRONEM PRN-0040-00065.01.00/10, 10582696-0]FUNCAPCAPESCAPE

Cation‐dependent stabilization of electrogenerated naphthalene diimide dianions in porous polymer thin films and their application to electrical energy storage

Porous polymer networks (PPNs) are attractive materials for capacitive energy storage because they offer high surface areas for increased double-layer capacitance, open structures for rapid ion transport, and redox-active moieties that enable faradaic (pseudocapacitive) energy storage. Here we demonstrate a new attractive feature of PPNs--the ability of their reduced forms (radical anions and dianions) to interact with small radii cations through synergistic interactions arising from densely packed redox-active groups, only when prepared as thin films. When naphthalene diimides (NDIs) are incorporated into PPN films, the carbonyl groups of adjacent, electrochemically generated, NDI radical anions and dianions bind strongly to K(+), Li(+), and Mg(2+), shifting the formal potentials of NDI's second reduction by 120 and 460 mV for K(+) and Li(+)-based electrolytes, respectively. In the case of Mg(2+), NDI's two redox waves coalesce into a single two-electron process with shifts of 240 and 710 mV, for the first and second reductions, respectively, increasing the energy density by over 20 % without changing the polymer backbone. In contrast, the formal reduction potentials of NDI derivatives in solution are identical for each electrolyte, and this effect has not been reported for NDI previously. This study illustrates the profound influence of the solid-state structure of a polymer on its electrochemical response, which does not simply reflect the solution-phase redox behavior of its monomers.Porous polymer networks (PPNs) are attractive materials for capacitive energy storage because they offer high surface areas for increased double‐layer capacitance, open structures for rapid ion transport, and redox‐active moieties that enable faradaic (ps54451322513229FAPESP - FUNDAÇÃO DE AMPARO À PESQUISA DO ESTADO DE SÃO PAULO2013/25527‐1This research was supported by an NSF GRFP (DGE‐1144153) award to C.R.D. W.R.D. acknowledges support from the Alfred P. Sloan and Camille and Henry Dreyfus Foundations. This work was supported in part (K.H.B., H.D.A.) through grant DE‐FG02‐87ER45298, by

Release of Cyanopyridine from a Ruthenium Complex Adsorbed on Gold: Surface-Enhanced Raman Scattering, Electrochemistry, and Density Functional Theory Analyses

The results presented in this work definitely show that the stability of the SAM formed with [Ru­(NH₃)₄(CNpy)­(pyS)]²⁺ on gold, where CNpy = 4-cyanopyridine and pyS = 4-mercaptopyridine, is dependent on the applied potential and on the chemical properties of the solution in the solid/liquid interface. By means of SERS spectroscopy, it was found that CNpy ligand is released from the coordination sphere if no reducing condition is imposed to the system, i.e., citrate solution or applied potential lower than the formal potential of the complex. Theoretical Raman spectra obtained from DFT presented reasonable correlation with the experimental spectra and gave support for the assignments. The relative intensities of the bands in the SERS spectra showed to be dependent on the applied potential as well as on the wavelength of the exciting radiation, indicating the contribution of a charge transfer process to the SERS intensification. In fact, the shift of the potential of maximum SERS intensity (<i>E</i>_max) to negative values as the radiation energy increases indicates a charge transfer process from the HOMO orbitals of the complex to the Fermi level