Magnetic exchange interactions in perfluorophenyl dithiadiazolyl radicals.

EPR, electrochemical studies and neutron diffraction studies on a large range of 1,2,3,5-dithiadiazolyl radicals have shown that the spin density distribution is essentially unaffected by substituent effects. The variation of magnetic properties previously reported for a series of perfluorophenyl-dithiadiazolyl radicals p-XC6F4CNSSN (X = CN, Br, NO2 and NCC6F4) is therefore due to differences in molecular packing. The nearest-neighbour magnetic exchange interactions in these radicals are probed through DFT studies (B3LYP/6-311G**) and are shown to exhibit a variety of both ferromagnetic and antiferromagnetic interactions. All exchange interactions with vertical bar J vertical bar > 1 cm(-1) coincide with close heterocyclic contacts between dithiadiazolyl rings (3.18-4.00 angstrom) and produce vertical bar J vertical bar values up to 40 K. An analysis of these interactions indicates that the dominant exchange pathway would appear to be a direct exchange mechanism between radical centres, with orthogonality of the singly-occupied molecular orbitals (SOMOs) favouring ferromagnetic interactions. (c) 2005 Elsevier B.V. All rights reserved.