Redox Activities of Metal-Organic Frameworks Incorporating Rare Earth Metal Chains and Tetrathiafulvalene Linkers

Metal-organic frameworks (MOFs) incorporating lanthanide nodes and tetrathiafulvalene (TTF) linkers offer a viable approach for combining redox activity and magnetism in one material. Four rare-earth lanthanide ions (RE = Tb, Dy, Ho, and Er) were found to form isostructural MOFs consisting of metal chains bridged by redox-active tetrathiafulvalenetetrabenzoate (TTFTB4-) whereby the carboxylate moieties act in both anti anti and syn-syn coordination modes. These materials display tunable redoxactive properties and slow magnetic relaxation phenomenon (Er and Dy). While the as-synthesized crystals contain the neutral diamagnetic TTF moiety, using either a solid-solution electrochemical method or iodine oxidation transforms part of the latter to the paramagnetic TTF"- radical in a single-crystal-to-single crystal manner without altering the internal structure of the building chains and the frameworks. This is accompanied by inclusion of 13- replacing some of the solvents, as well as changes in the central C-C bond length of TTFTB, a strong EPR response at g- 2, and an enhancement of the reflectance at low energies originating from absorption by the radical.