Halide Ligated Iron Porphines: A DFT plus U and UB3LYP Study

Pooja M Panchmatia, M E Ali, B Sanyal, P M Oppeneer

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31 Citations (SciVal)


We apply the density functional theory + U (DFT+U) and unrestricted hybrid functional DFT-UB3LYP methods to study the electronic structure and magnetic properties of two prototypical iron porphines: porphine chloride (FePCl) and difluoro iron(III-IV) porphine. Plain DFT within the generalized gradient approximation (GGA) implementation fails in describing the correct high-spin ground state of these porphine molecules, whereas DFT+U and UB3LYP provide an improved description. For a range of U values (4-8 eV), we compare the results of the DFT+U approach to those obtained previously with the hybrid functional (B3LYP) and with the CASPT2 approach. The DFT+U and UB3LYP methods successfully predict the molecular high spin (S = 5/2) ground state of FePCl, and also provide the nontrivial S = 3 high spin ground state for FePF2. For the latter six-coordinated Fe porphine, our DFT+U calculations show that the S = 2, S = 5/2, and S = 3 states are energetically very close together (differences of 30 meV). Nonetheless, S = 3 is obtained as the ground state of the whole molecule, in accordance with the spin expected from the electron count. Our DFT+U calculations show furthermore that the Fe 3d occupancy is similar for FePF2 and FePCl, i.e., DET+U does not support Fe(IV) for FePF2, but rather an Fe(III) porphyrin pi-cation radical species, with an Fe high spin S-Fe = 5/2, and an additional S = 1/2 stemming from spin density distributed over the porphine ring. This observation is also supported by our UB3LYP calculations.
Original languageEnglish
Pages (from-to)13381-13387
Number of pages7
JournalThe Journal of Physical Chemistry A
Issue number51
Publication statusPublished - 30 Dec 2010


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