Phosphonate Metal-Organic Frameworks: A Novel Family of Semiconductors

Herein, the first semiconducting and magnetic phosphonate metal-organic framework (MOF), TUB75, is reported, which contains a 1D inorganic building unit composed of a zigzag chain of corner-sharing copper dimers. The solid-state UV-vis spectrum of TUB75 reveals the existence of a narrow bandgap of 1.4 eV, which agrees well with the density functional theory (DFT)-calculated bandgap of 1.77 eV. Single-crystal conductivity measurements for different orientations of the individual crystals yield a range of conductances from 10^-3 to 10³ S m^-1 at room temperature, pointing to the directional nature of the electrical conductivity in TUB75. Magnetization measurements show that TUB75 is composed of antiferromagnetically coupled copper dimer chains. Due to their rich structural chemistry and exceptionally high thermal/chemical stabilities, phosphonate MOFs like TUB75 may open new vistas in engineerable electrodes for supercapacitors.