CASSCF and CASPT2 calculations of hole-doped polycarbenes. Possibilities of organic ferromagnetic conductors and metals

Ab initio CASSCF and CASPT2 calculations were carried out for hole-doped polycarbenes such as monocations of bis(methylene)ethylene and phenylene bis(methylene) in order to confirm previous spin polarization and delocalization rules for ion-radicals. The ground state was calculated to be quartet for the hole-doped meta-phenylene bis(methylene). The high- and low-spin crossover by hole doping did not occur, being consistent with the ESR and ENDOR experiments for the monocation of meta-phenylene bis(phenylmethylene) by the Shida and Itoh-Takui groups. On the other hand, spin crossover by hole doping is concluded for bis(methylene)ethylene and para-phenylene bis(methylene) in accord with the previous spin delocalization effect. The implications of these results are discussed in relation to the possibilities of organic ferromagnetic conductors and metals.