Semiconducting Mixed-Valence Metal-Organic Framework with CuI/CuIII Based on Diethyldithiocarbamate Ligands.

The unprecedented mixed-valent metal-organic framework (MOF) [CuI4CuIIIBr5(Et-dtc)2]·CH2Cl2 (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 CuIII center coordinated by diethyldithiocarbamate ligands, bridged by CuIBr 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 CuI to CuIII. 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 LiCoO2.