To correctly model electron correlation effects in BS-DFT, three hybrid functionals (TPSSh, 31 B3LYP, 32 and PBE0 33 ) were evaluated. These functionals have been shown to reliably predict the electronic structures of transition metal complexes. Although the geometries of the copper complex showed minimal sensitivity to the choice of functional, minor variations in the M -O -M angles were noted for the nickel and iron complexes. In the end, the PBE0-optimized geometries were chosen for unrelaxed angle scans, as they showed greater alignment with the anticipated Mulliken spin populations on the metal centers. Information on all geometries acquired using the different functionals are provided in the SI.