A theoretical study of the magnetism of the α- p-cyano-tetrafluorophenyl-dithiadiazolyl radical using a first principles bottom-up procedure

• Published in: Polyhedron 2007-06, Vol.26 (9), p.1949-1958
• Main Authors: Deumal, M., LeRoux, S., Rawson, J.M., Robb, M.A., Novoa, J.J.
• Format: Article
• Language: English
• Subjects: DFT; First principles calculations; Magnetism; Theoretical studies; α- p-Cyano-tetrafluorophenyl-dithiadiazolyl crystals
• ISSN: 0277-5387
• DOI: 10.1016/j.poly.2006.09.090

A first-principles bottom-up theoretical study of this polymorph indicates that there are six non-negligible magnetic interactions, two of them (+10.91 and −10.25 cm −1) dominating. The magnetic topology (figure) presents a complex 3D topology that explains the experimental bulk antiferromagnetic properties. The computed magnetic susceptibility curve reproduces well the experimental one. The mechanism of the magnetic interaction in the α phase of the organic radical p-cyano-tetrafluorophenyl-dithiadiazolyl has been studied using a first-principles bottom-up theoretical procedure. Six J AB radical–radical magnetic interactions are computed to be larger than ∣0.05∣ cm −1 (two, with values +10.91 and −10.25 cm −1, dominate over the others, whose absolute values are always smaller than 1.5 cm −1). The connectivity of these non-negligible J AB interactions creates a complex 3D magnetic topology within the crystal. The computed magnetic susceptibility curve, χ, was also calculated by diagonalizing the matrix representation of the Heisenberg Hamiltonian, whose J AB parameters are set to their computed values. This fully reproduces the shape of the experimental curve and is consistent with the bulk antiferromagnetism reported experimentally (reflected in a sharp maximum observed in χ at 10 K). Attempts to model the magnetic susceptibility data using a simple model based only upon the two dominant interactions proved impossible.