Anion-Dependent Electron Transfer in the Cyanide-Bridged [FeCo] Capsules.

A family of molecular capsules, {[(Tp*)Fe(CN)Co(bpybpy)][X]}·sol (, X = ClO, sol = 6DMF; , X = PF, sol = 6DMF; , X = OTf, sol = 6DMF; , X = BPh, sol = 2DMF; Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate; bpy = 2,2'-bipyridine), were prepared via the Schiff-base condensation of the aldehyde-substituted bpy (bpy) and 1,7-diaminoheptane (HN(CH)NH). All the complexes contain the same cyanide-bridged cationic square cores ([FeCo]), which are encapsuled by the flexible alkyl chains. Variable-temperature single-crystal X-ray diffraction, FT-IR spectra, and magnetic studies reveal the abrupt and complete, thermo- and photo-induced electron-transfer-coupled spin transition for -, while the pure high-spin phase for . Such distinct behavior is attributed to the effective long-range cooperative interactions mediated by the intercluster π-π couplings in -, which, however, are significantly blocked in due to the steric effect of interstitial BPh anions. Furthermore, the shift in the thermally induced transition temperatures of 254 K for , 233 K for , and 187 K for , respectively, is likely correlated to the variable H···O and H···F interactions between the solvent molecules, anions, and the bipyridine ligands of the [FeCo] squares, suggesting the significant anion-dependent effect in such a system.