A smart post-synthetic route towards [Fe2Co2] molecular capsules with electron transfer and bidirectional switching behaviors.

Aldehyde groups were intentionally equipped on the cyanide-bridged [Fe₂Co₂] square molecules: {[(Tp*)Fe(CN)₃Co(bpy^CHO)₂]₂-[PF₆]₂}·4MeOH (1, Tp* = hydrotris(3,5-dimethylpyrazol-1-yl)borate; bpy^CHO = 4-formyl-4′-methyl-2,2′-bipyridine), thus providing chemical-active windows for post-modification towards desired functions. In this contribution, by taking advantage of efficient Schiff-base condensation between the aldehyde-substituted bipyridine derivative (bpy^CHO) and alkyl diamines (H₂N-(CH₂)_nNH₂), two discrete [Fe₂Co₂] compounds { [ (Tp ∗) Fe (CN) 3 Co (bpy C = N (CH 2) n N = C bpy) ] 2 [ PF 6 ] 2 } ⋅ 6 DMF (2 , n = 5 ; 3 , n = 7) were prepared, where the cyanide-bridged [Fe₂Co₂] square cores were encapsulated by the flexible alkyl chains. Variable-temperature single-crystal X-ray diffraction and magnetic studies revealed complete thermo (T_1/2 = 233 K (2) and 237 K (3)) and photo-induced electron transfer event accompanying spin transition between the diamagnetic [Fe^II_LS2Co^III_LS2] state and the paramagnetic [Fe^III_LS2Co^II_HS2] state (LS, low spin; HS, high spin). In addition, the bidirectional switching between the two states was achieved with alternating laser irradiation at 808 and 532 nm at 10 K. [ABSTRACT FROM AUTHOR]