Intermolecular ferromagnetic interaction in the crystal of a diphenyl nitroxide derivative. The role of spin-polarized hydrogen atoms located near a neighboring N–O site

The crystal of 9,9-dipropyl-9,10-dihydroacridin-10-yloxyl exhibited a positive Weiss constant (+0.77 K) ascribable to a three-dimensional network of ferromagnetic interactions. The orbital orthogonality between the antibonding N–O π∗ and H 1s orbitals was found in a nearly isosceles triangle geometry of neighboring H atoms and the N–O site. The following spin polarization scheme is proposed: N(↑)–C(↓)Co(↑)–Cm(↓)–Hm(↑)⋯⋅O(↑)–N, where o- and m-positions are defined with respect to the N–O group.