Tuning intermolecular magnetic exchange interactions in the solids C xF2x(CNSSS)2(AsF6)2: Structural, EPR, and magnetic characterization of dimeric (x = 2, 4) diradicals

A series of diradical containing salts CxF2x(CNSSS) 2••2+(AsF6-)2 {x = 2, 1[AsF6]2; x = 3, 3[AsF6]2; x = 4, 2[AsF6]2} have been prepared. 1[AsF 6]2 and 2[AsF6]2 were fully characterized by X-ray, variable-temperature magnetic susceptibility, and solid-state EPR measurements, further allowing us to extend the number of examples of the family of rare 7π RCNSSS•+ radical cations. 1[AsF6]2: a = 6.5314(7) Å, b = 7.5658(9) Å, c = 9.6048(11) Å, α = 100.962(2)°, β = 96.885(2)̊, γ = 107.436(2)°, triclinic, space group P1, Z = 1, T = 173 K. 2[AsF6]2: a = 10.6398(16) Å, b = 7.9680(11) Å, c = 12.7468(19) Å, β = 99.758(2)deg;, monoclinic, space group P21/c, Z = 2, T = 173 K. In the solid-state, CxF 2x(CNSSS)2••2+ (x = 2, 4) formed one-dimensional polymeric chains of dications containing discrete centrosymmetric radical pairs in which radicals were linked by four centered two-electron π*- π* bonds [12+, d(S⋯S) = 3.455(1) Å; 22+, d(S⋯S) = 3.306(2) Å]. The exchange interactions in these bonds were determined to be -500 ± 30 and -900 ± 90 cm-1, by variable temperature magnetic susceptibility measurements, respectively, providing rare experimental data on the singlet-triplet gaps in the field of thiazyl radicals. For 2[AsF 6]2, the thermally excited triplet state was unambiguously characterized by EPR techniques [\D\ = 0.0254(8) cm-1, \E\ = 0.0013(8) cm-1]. These experimental data implied a weakly associated nature of the radical moieties contained in the solids 1[AsF6] 2 and 2[AsF6]2. Computational analysis of the dimerization process is presented, and we show that the 2c 4 electron π*-π* bonds in 1[AsF6]2 and 2[AsF 6]2 have ca. 50% and 40% diradical character, respectively. In contrast, 3[AsF6]2·SO2, containing diradical C3F6(CNSSS)2 ••2+ with an odd number of CF2 spacers, showed magnetic behavior that was consistent with the presence of monomeric radical centers in the solid state. © 2007 American Chemical Society.