From Spin-Crossover to Single Molecule Magnetism: Tuning Magnetic Properties of Co(II) bis-ferrocenylterpy Cations via Supramolecular Interactions with Organocyanide Radical Anions

TCNQ (7,7,8,8-Tetracyanoquinodimethane) anion-radical derivatives were used to fine tune the magnetic properties of the [CoII(Fctp)2]2+ (Fctp = 4'-(2-ferrocenyl)-2,2':6'2''-terpyridine) cation in the solid state. The cocrystallization of [CoII(Fctp)2]2+ with TCNQ⋅- yielded the two pseudo-polymorphic products [CoII(Fctp)2] (TCNQ)2 (1) and [CoII(Fctp)2] (TCNQ)2·MeCN (2) whereas the analogous reaction with TCNQF⋅- (TCNQF = 2-fluoro-7,7,8,8-Tetracyanoquinodimethane) exclusively yielded [CoII(Fctp)2] (TCNQF)2·MeCN (3). Compound 1 exhibits slow relaxation of magnetization under an applied DC field with Ueff = 19.1 K and τ0 = 9.8 × 10-6 s. Compounds 2 and 3 are isostructural but exhibit different spin cross-over behavior with transition temperatures of T1/2 = 336 K and 226 K, respectively. Investigations of the solid state structures by DFT calculations indicate that the differences in magnetic properties of the cationic moiety, [CoII(Fctp)2]2+, are induced by supramolecular interactions between [CoII(Fctp)2]2+ and tunable TCNQ⋅-/TCNQF⋅- anion-radical derivatives.