Porous lanthanide metal-organic frameworks with metallic conductivity

Metallic charge transport and porosity appear almost mutually exclusive. Whereas metals demand large numbers of free carriers and must have minimal impurities and lattice vibrations to avoid charge scattering, the voids in porous materials limit the carrier concentration, provide ample space for impurities, and create more charge-scattering vibrations due to the size and flexibility of the lattice. No microporous material has been conclusively shown to behave as a metal. Here, we demonstrate that single crystals of the porous metal-organic framework Ln1.5HOTP (Ln = La, Nd; HOTP = 2,3,6,7,10,11-hexaoxytriphenylene) show the highest room-temperature conductivities of all porous materials, along with clear temperature-deactivated transport. A structural transition consistent with charge density wave ordering, present only in metals and rare in any materials, provides additional conclusive proof of the metallic nature of the materials.