In virtually all cases, we found that the bands close to the Fermi level have a dominant π character (Figures and), indicating that the analogy between metalloporphenes and annulenes may be generally valid. This motivated us to classify the metalloporphenes according to the number of π electrons in their unit cell (Table ). Chart 1 displays a "periodic table" of first transition row metalloporphenes, showcasing a variety of open-and closed-shell metallic conductors and semiconductors.