Isolation of copper complex through inclusion in β-cyclodextrin

Herein, a free Cu complex, K2[Cu(maleonitriledithiolate)2], and an inclusion Cu complex, K2{[Cu(maleonitriledithiolate)2]@(β-cyclodextrin)2}, were synthesised and characterised. Single-crystal X-ray diffraction revealed that the inclusion complex consisted of [Cu(maleonitriledithiolate)2]2– as a guest and two β-cyclodextrins as a host. The structure of the guest fragment, [Cu(maleonitriledithiolate)2]2–, was essentially the same in the two complexes. The shortest Cu – Cu distance in the free complex and the inclusion complex was 6.91 and 15.5 Å, respectively. Hyperfine splitting was observed in the electron paramagnetic resonance spectrum of the inclusion complex (g// = 2.090, g⊥ = 2.025, A// = 448 MHz, A⊥ = 108 MHz), whereas the free complex showed no hyperfine splitting (g// = 2.083, g⊥ = 2.025). The difference was attributed to the isolation of the Cu(II) ion included in the β-cyclodextrins from other Cu ions. The association of host–guest in the solution-state and electrochemical behaviour were also investigated.