While a direct, quantitative comparison between calculated gas phase-geometries should only be made with gas-phase experimental structures, researchers routinely use solid-state diffraction data to assess the reliability of computed geometries. Therefore, this work does not seek to assign error bars to the XMS-CASPT2 or DFT geometries based on experiment. However, comparisons with experiment are valuable and should be made when possible, particularly for cases where the methods result in different electronic structures. For the copper corroles studied herein, the XMS-CASPT2 S 0 ground state has significant multiconfigurational and open-shell character (vide infra), while the DFT S 0 state is the closed-shell singlet. In other words, the optimizations are for qualitatively different electronic structures. To the authors' knowledge, no empirical structure of the bare copper corrole has been reported, in the solid-state or otherwise, due to the instability of unsubstituted corroles that can easily undergo oxidative coupling at the meso positions. The unsubstituted corrole is included since it has been widely studied as a model system for the larger functionalized corroles and to provide electronic structure insights. However, the 5,10,15-triphenyl copper corrole has been characterized by solid-state diffraction experiments. The average Cu-N bond distances in the S 0 structures are reported in Table . For the unsubstituted corrole, all of the bond distances are within 0.038 Å of one another. Although these are very small differences, the BLYP-D3 geometry contains the longest bond distance on average (1.906 Å) while the PBE0-D3 geometry exhibits the shortest (1.868 Å). The hy- D3 computed distances are also consistent with prior work. A similar pattern emerges for the Cu-N distances in the triphenyl complex (Table ). In the saddled geometry of the triphenyl copper corrole, the XMS-CASPT2 computed average Cu-N distances are in good agreement with those determined experimentally with differences of only +0.007 Å. The The degree of saddling is more sensitive to method choice than bond distances. While saddling can be seen visually, it is quantified via two types of dihedral angles labeled Ω and χ (Figure ). Ω is a Cu-N-C-C angle where the two carbon atoms are on the same pyrrole ring as the nitrogen atom. This angle shows how the Cu atom deviates from the plane of the ligand. On the other hand, when the ligand itself is buckled, an angle between two of the pyrrole rings can demonstrate how they relate to one another; therefore, χ is a C-C-C-C