Ferromagnetic ordering in bisthiaselenazolyl radicals: variations on a tetragonal theme.

TLDR: Variable-temperature magnetic susceptibility measurements indicate that antiferromagnetic exchange between radicals along the pi-stacks increases with pi-stack slippage, and the origin of the dramatically different magnetic behavior across the series has been explored in terms of a direct through-space mechanism by means of DFT calculations on individual pairwise exchange energies.

Abstract: A series of five isostructural bisthiaselenazolyl radicals 2 have been prepared and characterized by X-ray crystallography. The crystal structures, all belonging to the tetragonal space group P421m, consist of slipped π-stack arrays of undimerized radicals packed about 4 centers running along the z-direction, an arrangement which gives rise to a complex lattice-wide network of close intermolecular Se---Se′ contacts. Variations in R1 (Et, Pr, CH2CF3) with R2 = Cl lead to significant changes in the degree of slippage of the π-stacks and hence the proximity of the Se---Se′ interactions. By contrast, variations in R2 (Cl, Br, Me) with R1 = Et induce very little change in either the degree of slippage or the intermolecular contacts. Variable-temperature conductivity (σ) measurements show relatively constant values for the conductivity σ(300 K) (10−5−10−4 S cm−1) and thermal activation energy Eact (0.27−0.31 eV). Variable-temperature magnetic susceptibility measurements indicate that radicals 2b and 2c (R1 = ...