Effects of applied voltage on water at a gold electrode interface from ab initio molecular dynamics

Electrode–water interfaces under voltage bias demonstrate anomalous electrostatic and structural properties that are influential in their catalytic and technological applications. Mean-field and empirical models of the electrical double layer (EDL) that forms in response to an applied potential do not capture the heterogeneity that polarizable, liquid-phase water molecules engender. To illustrate the inhomogeneous nature of the electrochemical interface, Born–Oppenheimer ab initio molecular dynamics calculations of electrified Au(111) slabs interfaced with liquid water were performed using a combined explicit–implicit solvent approach. The excess charges localized on the model electrode were held constant and the electrode potentials were computed at frequent simulation times. The electrode potential in each trajectory fluctuated with changes in the atomic structure, and the trajectory-averaged potentials converged and yielded a physically reasonable differential capacitance for the system. The effects of the average applied voltages, both positive and negative, on the structural, hydrogen bonding, dynamical, and vibrational properties of water were characterized and compared to literature where applicable. Controlled-potential simulations of the interfacial solvent dynamics provide a framework for further investigation of more complex or reactive species in the EDL and broadly for understanding electrochemical interfaces in situ.

Ab initio molecular dynamics of an aqueous electrode interface reveal the electrostatic, structural, and dynamic effects of quantifiable voltage biases on water.     

Triethylphosphine—carbgn disulfide zwitterion as a bridging six-electron donor ligand in [Mo(CO)2(PEt3)(μ-S2CPEt3)]2; synthesis and x-ray crystal structure

The zwitterion Et₃PCS₂ reacts with Mo(CO)₆ or Mo(C₇H₈)(CO)₃ to give the dinuclear complex [Mo(CO)₂(PEt₃)(μ-S₂CPEt₃)]₂. An X-ray crystal structure determination has showed that both zwitterions coordinate one metal through an η³-S₂C linkage and the second metal through a single sulphur atom.     

Role of molecular conjugation in the surface radical reaction of aldehydes with H-Si(111): first principles study

Within the current effort to understand and develop the organic functionalization of silicon surfaces, recent experiments have identified the radical chain reaction of unsaturated organic molecules with H-terminated silicon surfaces as a particularly promising route for controlled formation of such functionalized surfaces. Using periodic density functional theory calculations, we theoretically study and characterize the basic steps of the radical chain reaction mechanism for different aldehyde molecules (formaldehyde, benzaldehyde, propanaldehyde, propenaldehyde) reacting with the H-Si(111) surface, under the assumption that a Si dangling bond is initially present on the surface. Molecular conjugation is found to play a crucial role in the viability of the reaction, by controlling the delocalization of the spin density at the reaction intermediate. Interesting differences between our present results for aldehydes and our previous study for the reactions of alkene/alkyne molecules with H-Si(111) are observed and discussed (Takeuchi et al. J. Am. Chem. Soc. 2004, 126, 15890).     

Electronic structure of the (111) ideal and relaxed surface of silicon by the chemical pseudopotential method

The electronic energy structure for the (111)ideal and relaxed surfaces of silicon is calculated by the chemical pseudopotential method. We use a minimal basis set of localized orbitals and an atomic-like crystal potential to compute the interaction parameters and include self-consistency. Results are compared with other more involved theoretical calculations with satisfactory agreement.     

Stepwise electron-induced demolition of the Ni-I σ-bond in complexes with tetradentate tripodal ligands: A theoretical rationalization of structural and electrochemical results

The X-ray structural analysis of the compound [(pp₃)Nil]BPh₄ (complex d), pp₃ = P(CH₂CH₂PPh₂)₃, is presented. The complex cation has an almost regular trigonal bipyramidal geometry (TBP) with distances Ni-I and Ni-P_ax of 2.546(2) and 2.142(3) Å, respectively. This structure completes a series of strictly related nickel complexes, namely [(np₃)Nil]I, complex a; (np₃)Nil, complex b; (np₃)Ni, complex c; [(pp₃)NiHClO₄), complex e; [np₃ = N(CH₂CH₂PPh₂)₃] The complexes are redox derivatives [Ni(II), Ni(I), Ni(O)] that can be isolated via chemistry and/or electrochemistry. In the solid state complexes c and e have a trigonal pyramidal (TP) structure, whereas, electrochemical measurements suggest that in solution the TBP structure with a very elongated Ni-I bond can also have a finite lifetime. EHMO calculations offer a satisfying interpretation of the main structural trends in complexes a e, in particular, those relative to axial bond stretching, and clarify the different roles of phosphine vs. the amine axial donor. Moreover, the correlation is discussed between the electrode potentials and the nature of the Ni-I ^* MO that accepts or releases the electrons exceeding thed ⁸ configuration of Ni(II).