Estimation of πd-interactions in magnetic molecular conductors

In order to investigate molecular conductors containing magnetic anions, πd-interactions Jπd and dd-interactions Jd, have been estimated from the overlap of molecular orbitals by using the relation J = −2t2/U. In the present paper this method is applied to a new antiferromagnetic superconductor (BDA-TTP)2FeCl4, a semiconducting ferrimagnet (EDT-TTF-VO)2FeBr4, and a β′-type semiconductor (BEDT-TTF)3(MnCl4)2. The dd interaction of (BDA-TTP)2FeCl4 is as large as λ-(BETS)2FeCl4, guaranteeing the relatively high TN. The small Jπd of this compound is related to the steric effect of the outer trimethylene groups of the donor. The observed ferrimagnetism in (EDT-TTF-VO)2FeBr4 is related to the localization of the π-electrons associated with the charge order, as well as the fairy large πd-interactions bridging different anions. (BEDT-TTF)3(MnCl4)2 is a characteristic compound due to the extraordinarily large πd-interactions to the donors incorporated in the anion layer.