Novel supramolecular architecture of high-spin aggregates? The comparison of ferromagnetic coupling through space and through hydrogen bond Original Research Article

Intermolecular ferromagnetic interactions in various stacking models of the dimers of high-spin molecules with triazine coupling unit and cationic amino radical spin centers were calculated and finally compared with the intermolecular interactions through hydrogen bonds in one plane. AM1 including configuration interaction (C.I.) was used. It is shown that the ferromagnetic coupling through space depends on the distance and alignment of the radicals. When dimers are placed in stacking fashion, the increase of intermolecular vertical distance can only reduce the stability of the ground state but not the sign of the exchange coupling Jij. The stability of high-spin ground state versus low-spin state can be simply traced back to the number of atoms with reversed signs of π-spin density in neighboring molecules coupled to each other. In general, ferromagnetic coupling through space between stacked radicals under proper conformation is larger than the one through hydrogen bonds in one plane. Calculated results were interpreted by the splitting of high-spin ground state and first low-spin state, together with the splitting of partially occupied MOs (POMO) and the spin densities of high-spin systems.