## The ground states of iron(III) porphines: Role of entropy–enthalpy compensation, Fermi correlation, dispersion, and zero-point energies

Publication: Research - peer-review › Journal article – Annual report year: 2011

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**The ground states of iron(III) porphines: Role of entropy–enthalpy compensation, Fermi correlation, dispersion, and zero-point energies.** / Kepp, Kasper Planeta.

Publication: Research - peer-review › Journal article – Annual report year: 2011

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*Journal of Inorganic Biochemistry*, vol 105, no. 10, pp. 1286-1292., 10.1016/j.jinorgbio.2011.07.012

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*Journal of Inorganic Biochemistry*,

*105*(10), 1286-1292. 10.1016/j.jinorgbio.2011.07.012

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*Journal of Inorganic Biochemistry*. 2011, 105(10). 1286-1292. Available: 10.1016/j.jinorgbio.2011.07.012

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TY - JOUR

T1 - The ground states of iron(III) porphines: Role of entropy–enthalpy compensation, Fermi correlation, dispersion, and zero-point energies

AU - Kepp,Kasper Planeta

PY - 2011

Y1 - 2011

N2 - Porphyrins are much studied due to their biochemical relevance and many applications. The density functional TPSSh has previously accurately described the energy of close-lying electronic states of transition metal systems such as porphyrins. However, a recent study questioned this conclusion based on calculations of five iron(III) porphines. Here, we compute the geometries of 80 different electronic configurations and the free energies of the most stable configurations with the functionals TPSSh, TPSS, and B3LYP. Zero-point energies and entropy favor high-spin by ~4kJ/mol and 0–10kJ/mol, respectively. When these effects are included, and all electronic configurations are evaluated, TPSSh correctly predicts the spin of all the four difficult phenylporphine cases and is within the lower bound of uncertainty of any known theoretical method for the fifth, iron(III) chloroporphine. Dispersion computed with DFT-D3 favors low-spin by 3–53kJ/mol (TPSSh) or 4–15kJ/mol (B3LYP) due to the attractive r−6 term and the shorter distances in low-spin. The very large and diverse corrections from TPSS and TPSSh seem less consistent with the similarity of the systems than when calculated from B3LYP. If the functional-specific corrections are used, B3LYP and TPSSh are of equal accuracy, and TPSS is much worse, whereas if the physically reasonable B3LYP-computed dispersion effect is used for all functionals, TPSSh is accurate for all systems. B3LYP is significantly more accurate when dispersion is added, confirming previous results.

AB - Porphyrins are much studied due to their biochemical relevance and many applications. The density functional TPSSh has previously accurately described the energy of close-lying electronic states of transition metal systems such as porphyrins. However, a recent study questioned this conclusion based on calculations of five iron(III) porphines. Here, we compute the geometries of 80 different electronic configurations and the free energies of the most stable configurations with the functionals TPSSh, TPSS, and B3LYP. Zero-point energies and entropy favor high-spin by ~4kJ/mol and 0–10kJ/mol, respectively. When these effects are included, and all electronic configurations are evaluated, TPSSh correctly predicts the spin of all the four difficult phenylporphine cases and is within the lower bound of uncertainty of any known theoretical method for the fifth, iron(III) chloroporphine. Dispersion computed with DFT-D3 favors low-spin by 3–53kJ/mol (TPSSh) or 4–15kJ/mol (B3LYP) due to the attractive r−6 term and the shorter distances in low-spin. The very large and diverse corrections from TPSS and TPSSh seem less consistent with the similarity of the systems than when calculated from B3LYP. If the functional-specific corrections are used, B3LYP and TPSSh are of equal accuracy, and TPSS is much worse, whereas if the physically reasonable B3LYP-computed dispersion effect is used for all functionals, TPSSh is accurate for all systems. B3LYP is significantly more accurate when dispersion is added, confirming previous results.

KW - Spin states

KW - DFT

KW - Complexes

KW - Spin crossover

KW - Metal–ligand bonds

KW - Entropy

U2 - 10.1016/j.jinorgbio.2011.07.012

DO - 10.1016/j.jinorgbio.2011.07.012

M3 - Journal article

VL - 105

SP - 1286

EP - 1292

JO - Journal of Inorganic Biochemistry

T2 - Journal of Inorganic Biochemistry

JF - Journal of Inorganic Biochemistry

SN - 0162-0134

IS - 10

ER -