Capturing the spin state diversity of iron(III)-aryl porphyrins: OLYP is better than TPSSh

DFT calculations with a variety of exchange-correlation functionals, including PW91, OLYP, TPSSh, B3LYP and B3LYP*, have been carried out on the low-energy spin states of chloroiron(III) porphyrin and four aryliron(III) porphyrins, viz. FeIII(P)Ph (S = 1/2), FeIII(P)C6F5 (S = 5/2), FeIII(P)(3,4,5-C6F3H2) (S = 1/2), FeIII(P)(2,4,6-C6F3H2) (S = 5/2), where the expected spin states have been indicated within parentheses. Qualitatively, OLYP reproduces all the expected ground spin states. B3LYP appears to have some difficulty yielding the observed sextet ground states. B3LYP*, TPSSh and PW91 all fail to reproduce the sextet ground states, the latter two by rather large margins of energy. As far as this study is concerned, the overall performance of the functionals appears to be OLYP/OPBE > B3LYP > B3LYP* >> TPSSh > PW91/BLYP/BP86/TPSS.

Graphical AbstractFive-coordinate iron(III)-aryl porhyrins exhibit either high- or low-spin ground states, providing a stringent test for DFT vis-à-vis transition metal spin state energetics. For the complexes examined, the overall performance of the functionals appears to be (best to worst): OLYP/OPBE > B3LYP > B3LYP* >> TPSSh > PW91/BLYP/BP86/TPSS.Figure optionsDownload as PowerPoint slide