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 [Co-II(Fctp)(2)](2+)(Fctp = 4 '-(2-ferrocenyl)-2,2 ':6 ' 2 ''-terpyridine) cation in the solid state. The cocrystallization of [Co-II(Fctp)(2)](2+)with TCNQ & x2d9;(-)yielded the two pseudo-polymorphic products [Co-II(Fctp)(2)] (TCNQ)(2)(1) and [Co-II(Fctp)(2)] (TCNQ)(2)center dot MeCN (2) whereas the analogous reaction with TCNQF & x2d9;(-)(TCNQF = 2-fluoro-7,7,8,8-tetracyanoquinodimethane) exclusively yielded [Co-II(Fctp)(2)] (TCNQF)(2)center dot MeCN (3). Compound1exhibits slow relaxation of magnetization under an applied DC field withU(eff)= 19.1 K and tau(0)= 9.8 x 10(-6)s. Compounds2and3are isostructural but exhibit different spin-crossover behavior with transition temperatures ofT(1/2)= 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, [Co-II(Fctp)(2)](2+), are induced by supramolecular interactions between [Co-II(Fctp)(2)](2+)and tunable TCNQ & x2d9;(-)/TCNQF & x2d9;(-)anion-radical derivatives.