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

Abstract

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-F₂ PhCO₂ )₄ }₂ (BTDA-TCNQ)] (1), where 2,6-F₂ PhCO₂ ^- 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-F₂ PhCO₂ )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.

Keywords: Electron Transfer; Host-Guest Interaction; Iodine; Metal-Organic Frameworks; Molecular Magnets.