Adding two electrons to conjugated hydrocarbons usually reverses their aromaticity, so it is not surprising that 1 Ti(IV) 4+ P 4-shows behavior consistent with an aromatic compound. Table . Classification of Metalloporphenes. To emphasize electron transfer, formulas of metalloporphenes in groups -1, 1, and 2 in are written as in the example above. In Figure , minimal band structures for each metalloporphene group are shown, alongside analogous frontier MO diagrams. Throughout the text, metallic conductors are shown in orange and semiconductors in blue. The next section provides an overview of metalloporphene groups with a few examples; data for all systems can be found in the SI. Members of 0 t are formed with metals which have at least a half-filled d-shell (Mn-Cu). They undergo a Peierls distortion to D2h, which breaks the band degeneracy at the M point (Figure ), but which is insufficiently large to open a band gap. This may be attributed to a slightly larger U/t ratio compared to 0 tt , resulting a marginally more localized electronic structure. An analogous annulene would be cyclobutadiene with very slight BLA (Figure bottom), in which both open-shell character and antiaromaticity are slightly reduced relative to 0 tt . Compared to other metalloporphenes, members of 0 tt and 0 t tend to have relatively high work functions and conductivities (Table ).