Successive redox modulation in an iron(ii) spin-crossover framework

Abstract

Spin crossover (SCO) complexes capable of exhibiting distinct spin states under external stimuli have aroused intensive interest in materials science. Herein, we report an inverse-Hofmann-type metal–organic framework (MOF) [Fe^II(TPPE){Au^I(CN)₂}]I·2H₂O·7TCE (1, TPPE = 1,1,2,2-tetrakis(4-(pyridin-4-yl)phenyl)-ethene, TCE = 1,1,2,2-tetrachloroethane) with hysteretic SCO behavior. Most importantly, the redox-active unit [Au^I(CN)₂]⁻ in 1 can be sequentially oxidized by I₂ and Br₂ to form the corresponding [Au^III(CN)₂X₂]⁻ units via single-crystal to single-crystal transformation, and then reduced to [Au^I(CN)₂]⁻ by L-ascorbic acid (AA). Accordingly, the SCO behavior is first regulated by successive redox reactions in the SCO field, which provides a platform for developing multi-responsive materials.