Exploring the ground and excited state potential energy landscapes of the mixed-valence biferrocenium complex

Density functional theory (DFT) and time-dependent DFT (TDDFT) have been used to explore the potential energy landscapes in the class II (in Robin and Day classification) mixed-valence biferrocenium mono-cation (BF^+) in an effort to evaluate factors affecting optical and thermal intramolecular electron transfer rates. Both energy- and spectroscopy-based benchmarks were used to explore the adiabatic potential energy surfaces (PESs) of the mixed-valence BF^+ cation along with the optimization of appropriate ground-, excited-, and transition-state geometries. The calculation of Mossbauer isomer shifts and quadrupole splittings, UV-vis excitation energies, and the electronic coupling matrix element, H_(ab), corroborate the PES analyses. The adiabatic electron transfer pathway is also analyzed with respect to several possible vibronic coordinates. The degree of the electronic coupling between iron sites, the value of H_(ab), and the nature of the electron transfer pathway correlate with the amount of Hartree-Fock exchange involved in the DFT calculation with hybrid (approximately 20% of Hartree-Fock exchange) methods providing the best agreement between theory and experiment. DFT (B3LYP) predicted values of H_(ab) (839, 1085, and 1265 cm^(-1)) depend on the computational method and are in good agreement with experimental data

Influence of Hartree-Fock exchange on the calculated Mössbauer isomer shifts and quadrupole splittings in ferrocene derivatives using density functional theory

Influence of molecular geometry, type of exchange-correlation functional, and contraction scheme of basis set applied at the iron nuclei have been tested in the calculation of ^(57)Fe Mössbauer isomer shifts and quadrupole splittings for a wide range of ligand types, as well as oxidation and spin states, in inorganic and organometallic systems. It has been found that uncontraction of the s-part of Wachter's full-electron basis set at the iron nuclei does not appreciably improve the calculated isomer shifts. The observed correlations for all tested sets of geometries are close to each other and predominantly depend on the employed exchange-correlation functional with B3LYP functional being slightly better as compared to BPW91. Both hybrid (B3LYP) and pure (BPW91) exchange-correlation functionals are suitable for the calculation of isomer shifts in organometallic compounds. Surprisingly, it has been found that the hybrid B3LYP exchange-correlation functional completely fails in accurate prediction of quadrupole splittings in ferrocenes, while performance of the pure BPW91 functional for the same systems was excellent. This observation has been explained on the basis of relationship between the amount of Hartree-Fock exchange involved in the applied exchange-correlation functional and the calculated HOMO-LUMO energy gap in ferrocenes. On the basis of this explanation, use of only pure exchange-correlation functionals has been suggested for accurate prediction of Mössbauer spectra parameters in ferrocenes

Interpretation of the UV-vis spectra of the meso(ferrocenyl)-containing porphyrins using a TDDFT approach: is Gouterman's classic four-orbital model still in play?

The vertical excitation energies of H_2TPP [TPP = 5,10,15,20-tetraphenylporphyrin(2-)], H_2FcPh_3P [FcPh_3P = 5-ferrocenyl-10,15,20-triphenylporphyrin(2-)], cis-H_2Fc_2Ph_2P [cis-Fc_2Ph_2P = 5,10-bisferrocenyl-15,20-diphenylporphyrin (2-)], trans-H_2Fc_2Ph_2P [trans-Fc_2Ph_2P = 5,15-bisferrocenyl-10,20-diphenylporphyrin(2-)], H_2Fc_3PhP [H_2Fc_3PhP = 5,10,15-trisferrocenyl-20-phenylporphyrin(2-)], and H_2TFcP [TFcP = 5,10,15,20-tetraferrocenylporphyrin(2-)] were investigated using a time-dependent density functional theory (DFT) approach and compared to their experimental UV-vis spectra in the 10,000-30,000 cm^(-1) region. It was shown that the lowest energy transitions in meso(ferrocenyl)-containing porphyrins have predominantly ferrocene-to-porphyrin charge transfer character, while the porphyrin-centered π-π* transitions predicted by the Gouterman's classic four-orbital model still have the largest intensities in the UV-vis region. The number of predominantly ferrocene-to-porphyrin charge transfer transitions increases with the number of ferrocene substituents and becomes dominant in H_2TFcP

3H-2,1-Benzoxaborole-1-spiro-4′-(5-oxa-3a-aza-4-borapyrene)

In the title compound, C20H14BNO2, the B atom has a tetra­hedral geometry with two short B—O and two long B—C and B—N bonds, revealing a significant difference between Car—O—B and Calk­yl—O—B bond distances. Inter­molecular Ar—H⋯O hydrogen bonds and strong π–π inter­actions (3.368 Å) between aromatic cores of neighbouring mol­ecules result in hexa­gonal channels along the crystallographic c axis, which are potentially accessible for small mol­ecules

Influence of Hartree-Fock exchange on the calculated Mössbauer isomer shifts and quadrupole splittings in ferrocene derivatives using density functional theory

Influence of molecular geometry, type of exchange-correlation functional, and contraction scheme of basis set applied at the iron nuclei have been tested in the calculation of ^(57)Fe Mössbauer isomer shifts and quadrupole splittings for a wide range of ligand types, as well as oxidation and spin states, in inorganic and organometallic systems. It has been found that uncontraction of the s-part of Wachter's full-electron basis set at the iron nuclei does not appreciably improve the calculated isomer shifts. The observed correlations for all tested sets of geometries are close to each other and predominantly depend on the employed exchange-correlation functional with B3LYP functional being slightly better as compared to BPW91. Both hybrid (B3LYP) and pure (BPW91) exchange-correlation functionals are suitable for the calculation of isomer shifts in organometallic compounds. Surprisingly, it has been found that the hybrid B3LYP exchange-correlation functional completely fails in accurate prediction of quadrupole splittings in ferrocenes, while performance of the pure BPW91 functional for the same systems was excellent. This observation has been explained on the basis of relationship between the amount of Hartree-Fock exchange involved in the applied exchange-correlation functional and the calculated HOMO-LUMO energy gap in ferrocenes. On the basis of this explanation, use of only pure exchange-correlation functionals has been suggested for accurate prediction of Mössbauer spectra parameters in ferrocenes

Interpretation of the UV-vis spectra of the meso(ferrocenyl)-containing porphyrins using a TDDFT approach: is Gouterman's classic four-orbital model still in play?

The vertical excitation energies of H_2TPP [TPP = 5,10,15,20-tetraphenylporphyrin(2-)], H_2FcPh_3P [FcPh_3P = 5-ferrocenyl-10,15,20-triphenylporphyrin(2-)], cis-H_2Fc_2Ph_2P [cis-Fc_2Ph_2P = 5,10-bisferrocenyl-15,20-diphenylporphyrin (2-)], trans-H_2Fc_2Ph_2P [trans-Fc_2Ph_2P = 5,15-bisferrocenyl-10,20-diphenylporphyrin(2-)], H_2Fc_3PhP [H_2Fc_3PhP = 5,10,15-trisferrocenyl-20-phenylporphyrin(2-)], and H_2TFcP [TFcP = 5,10,15,20-tetraferrocenylporphyrin(2-)] were investigated using a time-dependent density functional theory (DFT) approach and compared to their experimental UV-vis spectra in the 10,000-30,000 cm^(-1) region. It was shown that the lowest energy transitions in meso(ferrocenyl)-containing porphyrins have predominantly ferrocene-to-porphyrin charge transfer character, while the porphyrin-centered π-π* transitions predicted by the Gouterman's classic four-orbital model still have the largest intensities in the UV-vis region. The number of predominantly ferrocene-to-porphyrin charge transfer transitions increases with the number of ferrocene substituents and becomes dominant in H_2TFcP

Exploring the ground and excited state potential energy landscapes of the mixed-valence biferrocenium complex

Density functional theory (DFT) and time-dependent DFT (TDDFT) have been used to explore the potential energy landscapes in the class II (in Robin and Day classification) mixed-valence biferrocenium mono-cation (BF^+) in an effort to evaluate factors affecting optical and thermal intramolecular electron transfer rates. Both energy- and spectroscopy-based benchmarks were used to explore the adiabatic potential energy surfaces (PESs) of the mixed-valence BF^+ cation along with the optimization of appropriate ground-, excited-, and transition-state geometries. The calculation of Mossbauer isomer shifts and quadrupole splittings, UV-vis excitation energies, and the electronic coupling matrix element, H_(ab), corroborate the PES analyses. The adiabatic electron transfer pathway is also analyzed with respect to several possible vibronic coordinates. The degree of the electronic coupling between iron sites, the value of H_(ab), and the nature of the electron transfer pathway correlate with the amount of Hartree-Fock exchange involved in the DFT calculation with hybrid (approximately 20% of Hartree-Fock exchange) methods providing the best agreement between theory and experiment. DFT (B3LYP) predicted values of H_(ab) (839, 1085, and 1265 cm^(-1)) depend on the computational method and are in good agreement with experimental data

Comparative calculation of EPR spectral parameters in [Mo^VOX_4]^-, [Mo^VOX_5]^(2-), and [Mo^VOX_4(H_2O)]^- complexes

The EPR spectral parameters, i.e. g-tensors and molybdenum hyperfine couplings, for several d^1 systems of the general formula [Mo^VEX_4]^(n-), [Mo^VOX_5]^(2-), and [Mo^VOX_4(H_2O)]^- (E = O, N; X = F, Cl, Br; n = 1 or 2) were calculated using Density Functional Theory. The influence of basis sets, their contraction scheme, the type of exchange-correlation functional, the amount of Hartree-Fock exchange, molecular geometry, and relativistic effects on the calculated EPR spectra parameters have been discussed. The g-tensors and molybdenum hyperfine coupling parameters were calculated using a relativistic Hamiltonian coupled with several LDA, GGA, and 'hybrid' exchange-correlation functionals and uncontracted full-electron DGauss DZVP basis sets. The calculated EPR parameters are found to be sensitive to the Mo=E distance and E=Mo-Cl angle, and thus the choice of starting molecular geometry should be considered as an important factor in predicting the g-tensors and hyperfine coupling constants in oxo-molybdenum compounds. In the present case, the GGA exchange-correlation functionals provide a better agreement between the theory and the experiment

3-De­oxy-1,2-di-O-isopropyl­idene-5-O-tosyl-d-threo-pentofuran­ose

In the crystal structure of the title compound, C15H20O6S, the two independent mol­ecules crystalllize in a chiral setting with two different conformations, twisted 4 T 3 and envelope 4 E, for the furan­ose rings. Weak C—H⋯O contacts strengthen the crystal structure

Influence of molecular geometry, exchange-correlation functional, and solvent effects in the modeling of vertical excitation energies in phthalocyanines using time-dependent density functional theory (TDDFT) and polarized continuum model TDDFT methods: can modern computational chemistry methods explain experimental controversies?

A time-dependent density functional theory (TDDFT) approach coupled with 14 different exchange-correlation functionals was used for the prediction of vertical excitation energies in zinc phthalocyanine (PcZn). In general, the TDDFT approach provides a more accurate description of both visible and ultraviolet regions of the UV-vis and magnetic circular dichroism (MCD) spectra of PcZn in comparison to the more popular semiempirical ZINDO/S and PM3 methods. It was found that the calculated vertical excitation energies of PcZn correlate with the amount of Hartree-Fock exchange involved in the exchange-correlation functional. The correlation was explained on the basis of the calculated difference in energy between occupied and unoccupied molecular orbitals. The influence of PcZn geometry, optimized using different exchange-correlation functionals, on the calculated vertical excitation energies in PcZn was found to be relatively small. The influence of solvents on the calculated vertical excitation energies in PcZn was considered for the first time using a polarized continuum model TDDFT (PCM-TDDFT) method and was found to be relatively small in excellent agreement with the experimental data. For all tested TDDFT and PCM-TDDFT cases, an assignment of the Q-band as an almost pure a_(1u) (HOMO)-->e_g (LUMO) transition, initially suggested by Gouterman, was confirmed. Pure exchange-correlation functionals indicate the presence of six ^1_Eu states in the B-band region of the UV-vis spectrum of PcZn, while hybrid exchange-correlation functionals predict only five ^1E_u states for the same energy envelope. The first two symmetry-forbidden n-->pi* transitions were predicted in the Q0-2 region and in the low-energy tail of the B-band, while the first two symmetry-allowed n-->π* transitions were found within the B-band energy envelope when pure exchange-correlation functionals were used for TDDFT calculations. The presence of a symmetry-forbidden but vibronically allowed n-->π* transition in the Q_(0-2) spectral envelope explains the long-time controversy between the experimentally observed low-intensity transition in the Q_(0-2) region and previous semiempirical and TDDFT calculations, which were unable to predict any electronic transitions in this area. To prove the conceptual possibility of the presence of several degenerate ^1E_u states in the B-band region of PcZn, room-temperature UV-vis and MCD spectra of zinc tetra-tert-butylphthalocyanine (Pc^tZn) in non-coordinating solvents were recorded and analyzed using band deconvolution analysis. It was found that the B-band region of the UV-vis and MCD spectra of Pc^tZn can be easily deconvoluted using six MCD Faraday A-terms and two MCD Faraday B-terms with energies close to those predicted by TDDFT calculations for ^1E_u and ^1A_(2u) excited states, respectively. Such a good agreement between theory and experiment clearly indicates the possibility of employing a TDDFT approach for the accurate prediction of vertical excitation energies in phthalocyanines within a large energy range