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-crossover 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.