A Porous, Electrically Conductive Hexa-Zirconium(IV) Metal-Organic Framework

Goswami, S.; Ray, D.; Otake, K.-i.; Kung, C.-W.; Garibay, S. J.; Islamoglu, T.; Cui, Y.; Cramer, C. J.; Farha, O. K.; Hupp, J. T.
Chem. Sci. 2018, 9, 4477 (doi:10.1039/c8sc00961a).

Engendering electrical conductivity in high-porosity metal-organic frameworks (MOFs) promises to unlock the full potential of MOFs for electrical energy storage, electrocatalysis, or integration of MOFs with conventional electronic materials. Here we report that a porous zirconium-node-containing MOF, NU-901, can be rendered electronically conductive by physically encapsulating C₆₀, an excellent electron acceptor, within a fraction (ca. 60%) of the diamond-shaped cavities of the MOF. The cavities are defined by node-connected tetra-phenyl-carboxylated pyrene linkers, i.e., species that are excellent electron donors. The bulk electrical conductivity of the MOF is shown to increase from immeasurably low to 10^–3 S cm^–1, following fullerene incorporation. The observed conductivity originates from electron donor-acceptor interactions, i.e., charge-transfer interactions — a conclusion that is supported by density functional theory calculations and by the observation of a charge-transfer-derived band in the electronic absorption spectrum of the hybrid material. Notably, the conductive version of the MOF retains substantial nanoscale porosity and continues to display a sizable internal surface area, suggesting potential future applications that capitalize on the ability of the material to sorb molecular species.