A Host–Guest Electron Transfer Mechanism for Magnetic and Electronic Modifications in a Redox-Active Metal–Organic Framework

Host–guest electron transfer (HGET) in molecular framework systems is a critical trigger for drastic functional changes in both host framework and guest. A reversible magnetic phase transition was achieved via HGET in a layered framework, [{Ru₂(2,6-F₂PhCO₂)₄}₂(BTDA-TCNQ)] (1), where 2,6-F₂PhCO₂⁻ and BTDA-TCNQ represent 2,6-difluorobenzoate and bis[1,2,5]dithiazolotetracyanoquinodimethane, respectively. The guest-free 1 with an antiferromagnetic ground state transformed into a paramagnet, [{Ru₂(2,6-F₂PhCO₂)₄}₂(BTDA-TCNQ)]I₃ (1-I₃), by adsorbing iodine (I₂). The local charge distribution of [{Ru₂^II,III}⁺-(BTDA-TCNQ)^.−-{Ru₂^II,II}] in 1 was reversibly modified to [{Ru₂^II,III}⁺-(BTDA-TCNQ)⁰-{Ru₂^II,II}](I₃⁻) in 1-I₃ through HGET. Theoretical calculations of 1-I₃ indicated a partial charge delocalization as [{Ru₂}^(1−δ)+-(BTDA-TCNQ)⁰-{Ru₂}^δ+](I₃⁻) with δ≈0.2, aided by weak ferromagnetic coupling. 1-I₃ exhibited a hundred-fold enhancement in electrical conductivity compared to that of 1.