Molecular antiferromagnets based on TTF-type radical ion salts

We investigate the structure and the magnetic properties of the radical ion salts of C1TET-TTF and M(dddt)(2) (M = Ni, Pt, Au) with FeX4- (X = Cl, Br) anion. Despite the isolated, chain or sheet structure of the magnetic anion within these salts, the magnetic susceptibility shows the three dimensional behavior for all of these salts. This is regarded as a consequence of the coexistence of Fe-X ... X-Fe and Fe-X ...(donor)(n) ... X-Fe exchange paths, the latter of which exchange is mediated by the pi-electrons on the donor molecules. These salts show the antiferromagnetic transition around liquid helium temperature if FeBr4- is adopted as a counter anion, and their transition temperature is also affected by the central atom (M) substitution. These sensibility can be qualitatively understood as the difference in the magnitudes of the MO coefficients on the halogen and the sulfur atoms at the Fe-X ...(donor)(n) contacts.