Semiconducting Mixed-Valence Metal–Organic Framework with Cu ^I /Cu ^III Based on Diethyldithiocarbamate Ligands

High Resolution Image Download MS PowerPoint Slide The unprecedented mixed-valent metal–organic framework (MOF) [Cu I 4 Cu III Br 5 (Et-dtc) 2 ]·CH 2 Cl 2 ( CuBrEt-3D; Et-dtc – = diethyldithiocarbamate), which facilitates solvent desorption, was characterized using single-crystal X-ray diffraction. CuBrEt-3D forms a three-dimensional framework featuring a planar Cu III center coordinated by diethyldithiocarbamate ligands, bridged by Cu I Br units. This mixed-valent characteristic was confirmed through solid-state adsorption spectra, revealing a broad absorption extending to 2500 nm, attributed to intervalence charge transfer from Cu I to Cu III . Remarkably, this compound exhibits significant air stability despite its mixed-valent nature. SQUID measurements verified its diamagnetic properties. CuBrEt-3D incorporates dichloromethane as a crystallization solvent within its pores, yet the solvent can be removed under mild conditions while maintaining porosity. Impedance spectroscopy demonstrated semiconducting behavior, and band-structure calculations clarified the carrier-transport pathways. CuBrEt-3D was employed as a cathode material for lithium-ion batteries, delivering capacities comparable to those of commonly used LiCoO 2 .