Relevance of the DFT method to study expanded porphyrins with different topologies

Abstract

Meso-aryl expanded porphyrins present a structural versatility that allows them to achieve different topologies with distinct aromaticities. Several studies appeared in the literature studying these topological switches from an experimental and theoretical point of view. Most of these publications include density functional theory calculations, being the B3LYP the most used methodology. In this work, we show that the selection of the functional has a critical role on the geometric, energetic, and magnetic results of these expanded porphyrins, and that the use of an inadequate methodology can even generate spurious stationary points on the potential energy surface. To illustrate these aspects, in this article we have studied different molecular distortions of two expanded porphyrins, [32]-heptaphyrin and [26]-hexaphyrin using 11 DFT functionals and performing single point energy calculations at the local pair natural orbital coupled cluster DLPNO-CCSD(T) method, which have been carried out for benchmarking purposes. For some selected functionals, the dispersion effects have also been evaluated using the D3-Grimme's dispersion correction with Becke-Johnson damping. Our results let us to conclude that the CAM-B3LYP, M05-2X, and M06-2X functionals are the methodologies that provide a more consistent description of these topological switches, while other methods, such as B3LYP, BPE, and BP86, show a biased description. © 2017 Wiley Periodicals, Inc.

Vorticity: Simplifying the analysis of the current density

“…The geometry of all systems was optimized with the method PBE0/Def2TZVP . It is known that PBE0 functional could overestimate aromaticity but in the present study, we analyze trends that should not be affected by this issue . Moreover, recent studies have shown that PBE0 is one of the functional that does not have large errors in the calculation of atomic densities.…”

Aromaticity of N‐heterocyclic carbene and its analogues: Magnetically induced ring current perspective

“…Several previous studies have demonstrated that functionals with a high percentage of Hartree‐Fock (HF) exchange (eg, M06‐2X, CAM‐B3LYP, becke‐half‐and‐half‐LYP (BHandHLYP), etc.) give better results for the conjugated (and, therefore, aromatic) systems . Hence, functional with higher Hartree‐Fock exchange: BH and HLYP and M06‐2X are also considered to check the consistency.…”

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The N-heterocyclic carbene, imidazole-2-ylidene, and its main group (13)(14)(15) analogues contain cyclically conjugated 6π electrons. Experimental 1 H nuclear magnetic resonance (NMR) spectra suggest an increase in aromaticity along a period from left to right.

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“…Thus, it is essential to discuss the aromatic character of the NHC and its main group analogues by some modern and reliable theoretical methods. Moreover, the recent two papers [8,10] do not consider all the species (group [13][14][15] to make a periodic trend.…”

“…Herein the aromaticity of group 13 to 15 carbene analogues are quantitively analyzed using magnetically induced ring current perspective. First, the NMR data ( 1 H, 13 C, and 15 N) of the related species from literature are summarized, and the order of aromaticity has been constructed based on the 1 H NMR chemical shift. Then, a structural characterization based on natural bond orbital (NBO) has been illustrated, and the NMR results have been rationalized.…”