In group -1 (25 π electrons per unit cell), an electron is transferred from the π system into a low-energy d orbital, while in group 1 (27 π e -) an electron is donated from a high-energy d orbital into the π system. Members of both -1 and 1 are halfmetals, which may be compared to open-shell radical cations (group -1) or anions (1) of annulenes.