Effect of interlayer anions on [NiFe]-LDH nanosheet water oxidation activity

We synthesized nickel–iron layered double hydroxide ([NiFe]-LDH) nanosheets with different interlayer anions to probe their role in water oxidation catalysis. In alkaline electrolyte in ambient air, carbonate rapidly replaced other interlayer anions and catalytic activity was highest. Electrocatalytic water oxidation in virtually carbonate-free alkaline electrolyte revealed that activity was a function of anion basicity. Our [NiFe]-LDH nanosheets, prepared by pulsed laser ablation in liquids, were regenerated in carbonate-containing aqueous KOH. Anion binding motifs were assessed by X-ray photoelectron spectroscopy in combination with density functional theory calculations, suggesting that nitrite species bound to edge-site Fe in the precatalyst correlated with higher water oxidation activity

Ammonia coordination introducing a magnetic moment in an on-surface low-spin porphyrin

Amazing ammonia: The molecular spin state of Ni(II) porphyrin, supported on a ferromagnetic Co surface, can be reversibly switched between spin-off (S = 0) and spin-on (S = 1) states upon coordination and decoordination of the gaseous ligand NH3, respectively (see picture). This finding clearly indicates the possible use of the system as a single-molecule-based magnetochemical sensor and in spintronics

Assessment of Various Density Functionals and Basis Sets for the Calculation of Molecular Anharmonic Force Fields

In a previous contribution (Mol. Phys. {\bf 103}, xxxx, 2005), we established the suitability of density functional theory (DFT) for the calculation of molecular anharmonic force fields. In the present work, we have assessed a wide variety of basis sets and exchange-correlation functionals for harmonic and fundamental frequencies, equilibrium and ground-state rotational constants, and thermodynamic functions beyond the RRHO (rigid rotor-harmonic oscillator) approximation. The fairly good performance of double-zeta plus polarization basis sets for frequencies results from an error compensation between basis set incompleteness and the intrinsic error of exchange-correlation functionals. Triple-zeta plus polarization basis sets are recommended, with an additional high-exponent $d$ function on second-row atoms. All conventional hybrid GGA functionals perform about equally well: high-exchange hybrid GGA and meta-GGA functionals designed for kinetics yield poor results, with the exception of of the very recently developed BMK functional which takes a middle position along with the HCTH/407 (second generation GGA) and TPSS (meta-GGA) functionals. MP2 performs similarly to these functionals but is inferior to hybrid GGAs such as B3LYP and B97-1.Comment: Int. J. Quantum Chem., in press (special issue on vibrational spectroscopies

Tailoring large pores of porphyrin networks on Ag(111) by metal-organic coordination

The engineering of nanoarchitectures to achieve tailored properties relevant for macroscopic devices is a key motivation of organometallic surface science. To this end, understanding the role of molecular functionalities in structure formation and adatom coordination is of great importance. In this study, the differences in formation of Cu-mediated metal–organic coordination networks based on two pyridyl- and cyano-bearing free-base porphyrins on Ag(111) are elucidated by use of low-temperature scanning tunneling microscopy (STM). Distinct coordination networks evolve via different pathways upon codeposition of Cu adatoms. The cyano-terminated module directly forms 2D porous networks featuring fourfold-coordinated Cu nodes. By contrast, the pyridyl species engage in twofold coordination with Cu and a fully reticulated 2D network featuring a pore size exceeding 3 nm2 only evolves via an intermediate structure based on 1D coordination chains. The STM data and complementary Monte Carlo simulations reveal that these distinct network architectures originate from spatial constraints at the coordination centers. Cu adatoms are also shown to form two- and fourfold monoatomic coordination nodes with monotopic nitrogen-terminated linkers on the very same metal substrate—a versatility that is not achieved by other 3d transition metal centers but consistent with 3D coordination chemistry. This study discloses how specific molecular functionalities can be applied to tailor coordination architectures and highlights the potential of Cu as coordination center in such low-dimensional structures on surfaces

First hyperpolarizability of a sesquifulvalene transition metal complex by time-dependent density-functional theory

The first hyperpolarizability and electronic excitation spectrum of sesquifulvalene and a sesquifulvalene ruthenium complex have been computed and analyzed with use of time-dependent density-functional theory. A new orbital decomposition scheme is introduced that allows the computed first hyperpolarizability to be related to the electronic structure of complex molecules. The analysis shows that the first hyperpolarizability of sesquifulvalene is not associated with the first intense absorption, with HOMO → LUMO+1 character, but is dominated by the lowest energy transition, with HOMO → LUMO character, despite its very low intensity. In the ruthenium complex, the analysis reveals that the strong enhancement of the nonlinear optical response compared to free sesquifulvalene should not be attributed to the effect of complexation on the hyperpolarizability of sesquifulvalene. The strong hyperpolarizability originates from MLCT transitions from ruthenium d-orbitals to an empty orbital located at the seven ring of sesquifulvalene, transitions that have no analogue in free sequifulvalene. © 2006 American Chemical Society

Response properties of furan homologues by time-dependent density functional theory

The electronic excitations and frequency-dependent electronic second hyperpolarizability γ(-ω,ω,ω,-ω) of the five-ring heterocycles furan, thiophene, selenophene, and tellurophene have been reinvestigated using time-dependent density functional theory. Aspects of basis set saturation, the performance of exchange-correlation potentials, and relativistic effects are discussed. Increased hyperpolarizabilities for molecular dimer species suggest that intermolecular interactions may provide a simple explanation for the large deviations between recent ab initio calculations and experimental condensed-phase data

In situ UPS study of the formation of FeSi films from cis-Fe(SiCl 3)2(CO)4

Organometallics17265825-5829ORGN

A computational study on possible active species in nickel(II)-catalyzed 1-butene dimerization in [BMIM]⁺[AlCl₄]⁻ ionic liquid solution

<div><p>The butene insertion step of nickel complex-catalyzed butene dimerization in the presence of a [BMIM]⁺[AlCl₄]⁻ ionic liquid has been studied using density functional theory. The possibility of anion coordination from the ionic liquid to the catalyst complex has explicitly been taken into account. The calculated relative energies of various possible active catalyst complexes suggest that anion coordination to the nickel center may be thermodynamically favorable. Phosphine-free complexes which are only coordinated by one or two anions are higher in energy and show higher activation barriers for butene insertion. The lowest activation barrier has been found for a mono-phosphine nickel complex. Explanations for the calculated barriers based on structural data are offered.</p></div

Mechanisms of the Water-Gas Shift Reaction Catalyzed by Ruthenium Pentacarbonyl: A Density Functional Theory Study

The mechanism of the water-gas shift reaction catalyzed by Ru­(CO)₅ is analyzed using density functional methods in solution within the conductor-like screening model. Four different mechanistic pathways have been considered. It turned out that the incorporation of solvent effects is very important for a reasonable comparison among the mechanistic alternatives. The explicit inclusion of a water solvent molecule significantly changes the barriers of those steps which involve proton transfer in the transition state. The corresponding barriers are either lowered or increased, depending on the structure of the corresponding cyclic transition states. The results show that protolysis steps become competitive due to solution effects. The formation of formic acid as an intermediate in another, alternative pathway is also found to be competitive