Modeling Transition Metal Complexes in the Framework of the Spin-Crossover Phenomenon: A DFT Perspective

Using the study of the low-spin complex [Fe(bpy)3]2+ in the gas phase and in condensed phases as a guideline, we examine different aspects of the application of DFT to the study of transition metal complexes in the framework of spin crossover or related phenomena

Redox behavior of the iron-sulfur cluster [Fe4Cp4S5][PF6]2 in protic organic solvents and aqueous micellar solutions

The structural and electronic stabilities of the title compound have been investigated in CH3CN---CH3OH (100-0% to 0-100%) and in aqueous Triton X-100 micelles, by cyclic voltammetry and electronic absorption and EPR spectroscopies. The iron-sulfur cluster has been located in the peripheral polar zone of the micelle, where H2O molecules are also present. When incorporated in the micelle, the cluster shows satisfactory stability and appears to react, at its most reduced state, with the unsaturated substrate 4-methyl-l-cyclohexene

Ab Initio Molecular Dynamics Study of an Aqueous Solution of [Fe(bpy)3](Cl)2 in the Low-Spin and in the High-Spin States

The mechanism of the photoinduced low-spin → high-spin spin crossover is actively being investigated in Fe(II) complexes in solution using ultrafast spectroscopies. These studies accurately inform on the reaction coordinate of the Fe(II) chromophore upon photoexcitation. However, they leave open questions regarding the role of the solvent. Here, we report the description from a fully ab initio molecular dynamics study of the structure of [Fe(bpy)3]2+ in water and of the organization of its solvation shell in the low-spin and the high-spin states. In particular, the low-spin → high-spin change of states is shown to be accompanied (i) by a 0.191 Å lengthening of the Fe−N bond, in agreement with experiment, and (ii) by an increased thermal fluctuation of the molecular edifice, which both result from the weakening of the Fe−N bond. Furthermore, our results suggest that about two water molecules are expelled from the first solvation shell of [Fe(bpy)3]2+, which consists of water molecules intercalated between the bpy ligands

First-principles study of the pressure dependence of the structural and vibrational properties of the ternary metal hydride Ca2RuH6

The influence of pressure on the structural and vibrational properties of Ca2RuH6 has been investigated using periodic density functional theory calculations performed at the local density approximation (LDA) and generalized gradient approximation (GGA) levels. At ambient pressure, the calculated structure and vibrational frequencies are in satisfactory agreement with experimental data. The calculated P-V curves could be fitted with the Vinet equation of state, yielding B0=67.6 and B0=58.5 GPa at the LDA and GGA levels, respectively, and B=4.0 at both theoretical levels. The unit cell parameter is found to decrease faster with increasing pressure than the Ru–H bond length. The calculated pressure dependence of the vibrational frequencies agrees well with experiment for 5(T2g) but not for 9(A1g)

Influence of Guest−Host Interactions on the Structural, Energetic, and Mössbauer Spectroscopy Properties of Iron(II)tris(2,2'-bipyridine) in the Low-Spin and High-Spin States: A Density-Functional Theory Study of the Zeolite-Y Embedded Complex

Density functional theory is applied within a supramolecular approach to the study of the guest−host interactions in [Fe(bpy)3]2+@Y and their influence on the structural, energetic, and 57Fe Mssbauer spectroscopy properties of the encapsulated [Fe(bpy)3]2+ complex in the low- and high-spin states. The structures of the isolated complex and the supramolecular model used for [Fe(bpy)3]2+@Y were optimized in both spin-states using different generalized gradient approximation (PBE, HCTH, OLYP) and hybrid (B3LYP*, O3LYP) functionals. The results obtained are consistent with one another and show that, in either spin-state, the structure of [Fe(bpy)3]2+ shrinks and distorts upon encapsulation. Still, the structural changes experienced by the complex in a given spin-state remain limited, especially in that they do not lead to a substantial variation of the 57Fe quadrupole splitting, whose calculated values are in very good agreement with avalaible experimental data. The decomposition of the guest−host interaction energy into its electrostatic, Pauli and orbital contributions shows that the bonding between the complex and the supercage is more electrostatic than covalent. The ability of modern functionals to accurately describe the interactions explains the remarkable consistency of the results obtained with the various functionals. In particular, although the functionals perform very differently for the determination of the high-spin/low-spin energy difference ΔEHLel in [Fe(bpy)3]2+ and [Fe(bpy)3]2+@Y, they consistently predict that the encapsulation entails a destabilization of the high-spin state with regard to the low-spin state of Δ(ΔEHLel) = 2500 cm−1. Using for [Fe(bpy)3]2+ the CASPT2 value of ΔEHLel = 3700 cm−1 [ Pierloot, K.; Vancoillie, S. J. Chem. Phys. 2006, 125, 124303; Pierloot, K.; Vancoillie, S. J. Chem. Phys. 2008, 128, 034104], we obtain for the high-spin/low-spin energy difference in [Fe(bpy)3]2+@Y, a best ab initio estimate of ΔEHLel = 6200 cm−1

A theoretical study of the spectroscopic properties of B₂H₆ and of a series of B_xHyz- species (x = 1-12, y = 3-14, z = 0-2): From BH₃ to B₁₂H122-

The characterization of boron-hydrogen compounds is an active research area which encompasses subjects as diverse as the chemistry and structures of closoboranes or the thermal decomposition mechanism of the borohydrides. Due to their high gravimetric hydrogen content, borohydrides are considered as potential hydrogen storage materials. Their thermal decompositions are multistep processes, for which the intermediate products are not easily identified. To help address this issue, we have extensively investigated the vibrational and NMR properties of 21 relevant BmHnz− boron-hydrogen species (m = 1–12; n = 1–14; z = 0–2) within density functional theory. We could thus show that the B3LYP-D2 dispersion-corrected hybrid can be used in combination with the large cc-pVTZ basis set for the reliable prediction of the 11B and 1H NMR spectra of the boron-hydrogen species, and also for the reliable prediction of their IR and Raman spectra while taking into account the anharmonicity of their molecular vibrations

Ab Initio Molecular Dynamics Study of an Aqueous Solution of [Fe(bpy)₃](Cl)₂ in the Low-Spin and in the High-Spin States

The mechanism of the photoinduced low-spin → high-spin spin crossover is actively being investigated in Fe(II) complexes in solution using ultrafast spectroscopies. These studies accurately inform on the reaction coordinate of the Fe(II) chromophore upon photoexcitation. However, they leave open questions regarding the role of the solvent. Here, we report the description from a fully ab initio molecular dynamics study of the structure of [Fe(bpy)₃]²⁺ in water and of the organization of its solvation shell in the low-spin and the high-spin states. In particular, the low-spin → high-spin change of states is shown to be accompanied (i) by a 0.191 Å lengthening of the Fe−N bond, in agreement with experiment, and (ii) by an increased thermal fluctuation of the molecular edifice, which both result from the weakening of the Fe−N bond. Furthermore, our results suggest that about two water molecules are expelled from the first solvation shell of [Fe(bpy)₃]²⁺, which consists of water molecules intercalated between the bpy ligands

Computational study of the vibrational spectroscopy properties of boron-hydrogen compounds: Mg(B₃H₈)₂, CB₉H₁₀⁻ and CB₁₁H₁₂⁻

We report the DFT study of the vibrational spectroscopy properties of Mg(B3H8)2, a potential intermediate in the decomposition of Mg(BH4)2, as well as those of CB11H12− and CB9H10−, whose salts can exhibit high ionic conductivities. Because the inclusion of anharmonicity is key to the accurate description of the vibrational properties of BH species [D. Sethio, L. M. Lawson Daku, H. Hagemann. Int. J. Hydrogen Energy, 41 (2016) 6814], the calculations were performed both in the harmonic and in the anharmonic approximation. The IR and Raman spectra of Cs(CB11H12) and Na2(B10H10) have also been measured. The calculated and experimental spectra are in good agreement. A comparative analysis of the vibrational spectroscopy properties is made for B3H8− and Mg(B3H8)2, B12H122− and CB11H12−, and for B10H102− and CB9H10−