Substitution effect on the geometry and electronic structure of the ferrocene

The Renaissance of Ferrocene-Based Electrocatalysts: Properties, Synthesis Strategies, and Applications

The fascinating electrochemical properties of the redox-active compound ferrocene have inspired researchers across the globe to develop ferrocene-based electrocatalysts for a wide variety of applications. Advantages including excellent chemical and thermal stability, solubility in organic solvents, a pair of stable redox states, rapid electron transfer, and nontoxic nature improve its utility in various electrochemical applications. The use of ferrocene-based electrocatalysts enables control over the intrinsic properties and electroactive sites at the surface of the electrode to achieve specific electrochemical activities. Ferrocene and its derivatives can function as a potential redox medium that promotes electron transfer rates, thereby enhancing the reaction kinetics and electrochemical responses of the device. The outstanding electrocatalytic activity of ferrocene-based compounds at lower operating potentials enhances the specificity and sensitivity of reactions and also amplifies the response signals. Owing to their versatile redox chemistry and catalytic activities, ferrocene-based electrocatalysts are widely employed in various energy-related systems, molecular machines, and agricultural, biological, medicinal, and sensing applications. This review highlights the importance of ferrocene-based electrocatalysts, with emphasis on their properties, synthesis strategies for obtaining different ferrocene-based compounds, and their electrochemical applications.

The comparison of structure, nature of bond, and electronic transitions in [M(η5 -Cp)(η5 -C60 Me5 )] (M = Fe2+ , Ru2+ , Os2+ ) hybrids and corresponding metallocenes; a theoretical study

In this paper, metallocene-fullerene hybrid complexes, [M(η⁵ -Cp)(η⁵ -C₆₀ Me₅ )] (M = Fe²⁺ , Ru²⁺ , Os²⁺ ), as well as corresponding classical metallocenes have been studied theoretically at BP86/def2-SVP and M06L/def2-SVP levels of theory. With considering these metal complexes as an ABA' system (B is the central metal ion and A and A' are related η⁵ -ligands), the total interaction energies were calculated using common methods, as well as by calculating the interaction energies between the four defined pairs of fragments including A-B, B-A', A-BA', and AB-A'. The resulting data clearly showed that in all complexes there is a strong anticoopertivity between two metal-(η⁵ -ligand) bonds. In order to understand the origin of difference in values of various calculated interactions in above two types of complexes, the nature of metal-ligand bonds was also studied using energy decomposition analysis-natural orbital for chemical valence calculations. The results showed that in hybrid complexes, in contrast to metallocenes, the orbital interactions are considerably larger than electrostatic interactions.

Computational investigations of electronic structure modifications of ferrocene-terminated self-assembled monolayers: effects of electron donating/withdrawing functional groups attached on the ferrocene moiety

The electrochemical properties of chemically modified electrodes have long been a significant focus of research. Although the electronic states are directly related to the electrochemical properties, there have been only limited systematic efforts to reveal the electronic structures of adsorbed redox molecules with respect to the local environment of the redox center. In this study, density functional theory (DFT) calculations were performed for ferrocene-terminated self-assembled monolayers with different electron-donating abilities, which can be regarded as the simplest class of chemically modified electrodes. We revealed that the local electrostatic potentials, which are changed by the electron donating/withdrawing functional groups at the ferrocene moiety and the dipole field of coadsorbed inert molecules, practically determine the density of states derived from the highest occupied molecular orbital (HOMO) and its vicinities (HOMO-1 and HOMO-2) with respect to the electrode Fermi level. Therefore, to design new, sophisticated electrodes with chemical modification, one should consider not only the electronic properties of the constituent molecules, but also the local electrostatic potentials formed by these molecules and coadsorbed inert molecules.

Ferrocene Orientation Determined Intramolecular Interactions Using Energy Decomposition Analysis

Two very different quantum mechanically based energy decomposition analyses (EDA) schemes are employed to study the dominant energy differences between the eclipsed and staggered ferrocene conformers. One is the extended transition state (ETS) based on the Amsterdam Density Functional (ADF) package and the other is natural EDA (NEDA) based in the General Atomic and Molecular Electronic Structure System (GAMESS) package. It reveals that in addition to the model (theory and basis set), the fragmentation channels more significantly affect the interaction energy terms (ΔE) between the conformers. It is discovered that such an interaction energy can be absorbed into the pre-partitioned fragment channels so that to affect the interaction energies in a particular conformer of Fc. To avoid this, the present study employs a complete fragment channel—the fragments of ferrocene are individual neutral atoms. It therefore discovers that the major difference between the ferrocene conformers is due to the quantum mechanical Pauli repulsive energy and orbital attractive energy, leading to the eclipsed ferrocene the energy preferred structure. The NEDA scheme further indicates that the sum of attractive (negative) polarization (POL) and charge transfer (CL) energies prefers the eclipsed ferrocene. The repulsive (positive) deformation (DEF) energy, which is dominated by the cyclopentadienyle (Cp) rings, prefers the staggered ferrocene. Again, the cancellation results in a small energy residue in favour of the eclipsed ferrocene, in agreement with the ETS scheme. Further Natural Bond Orbital (NBO) analysis indicates that all NBO energies, total Lewis (no Fe) and lone pair (LP) deletion all prefer the eclipsed Fc conformer. The most significant energy preferring the eclipsed ferrocene without cancellation is the interactions between the donor lone pairs (LP) of the Fe atom and the acceptor antibond (BD*) NBOs of all C–C and C–H bonds in the ligand, LP(Fe)-BD*(C–C & C–H), which strongly stabilizes the eclipsed (D_5h) conformation by −457.6 kcal·mol⁻¹.

The d-electrons of Fe in ferrocene: the excess orbital energy spectrum (EOES)

The EOES (Δε_i=εE-Fci −εS-Fci) shows that the orbitals with significantly excess energies are Fe d-electron dominant.

Ferrocene analogues of sandwich M(CrB₆H₆)₂: a theoretical investigation

The stability and electronic structures of the new sandwich compounds M(CrB6H6)2 (M = Cr, Mn(+), Fe(2+)) are investigated by density functional theory. All the investigated sandwich complexes are in D(6d) symmetry and all of them are thermodynamically stable according to the large HOMO-LUMO gap, binding energy, vertical ionization potential and vertical electron affinity analyses, as well as Fe(C5H5)2 and Cr(C6H6)2, following the 18-electron principle. The natural bond orbital, detailed molecular orbitals and adaptive natural density partitioning analyses suggest that the spd-π interaction plays an important role in the sandwich compounds. This work challenges the traditional chemical bonding of the inorganic metal compound, investigates first the bonding style of the d atom orbital interacting with the π MO which was formed by p-d atomic orbitals, and indicates that the metal-doped borane ring can also be an ideal type π-electron donor ligand to stabilize the transition metal.

The one-electron oxidation of a dithiolate molecule: the importance of chemical intuition

A series of nine commonly used density functional methods were assessed to accurately predict the oxidation potential of the (C2H2S2(-2)/C2H2S2(•-)) redox couple. It was found that due to their greater tendency for charge delocalization the GGA functionals predict a structure where the radical electron is delocalized within the alkene backbone of C2H2S2(•-), whereas the hybrid functionals and the reference QCISD/cc-pVTZ predict that the radical electron remains localized on the sulfurs. However, chemical intuition suggests that the results obtained with the GGA functionals should be correct. Indeed, with the use of the geometries obtained at the HCTH/6-311++G(3df,3pd) level of theory both the QCISD and hybrid DFT methods yield a molecule with a delocalized electron. Notably, this new molecule lies at least 53 kJ mol(-1) lower in energy than the previously optimized one that had a localized radical. Using these new structures the calculated oxidation potential was found to be 2.71-2.97 V for the nine DFT functionals tested. The M06-L functional provided the best agreement with the QCISD/cc-pVTZ reference oxidation potential of 3.28 V.