THEORETICAL-STUDY OF SPIN INTERACTIONS IN STACKED ACETYLENE RADICAL IONS

The search for organic ferromagnets has so far focused on radical ions of cyclic conjugated systems which have a doubly degenerate highest-occupied molecular orbital. However, recent theoretical studies on dimers of such systems have shown that the ground state is a singlet and not a triplet as expected. In this paper, we demonstrate that an acetylenic radical ion system possesses a high-spin ground state which is stable with respect to different geometries of packing and substitutions. The stability of the high-spin state is attributed to the degeneracy of the atomic orbitals involved in conjugation. We suggest that these systems are prime candidates for observing organic ferromagnetism.