Pressure-induced metallicity and piezoreductive transition of metal-centres in conductive 2-dimensional metal-organic frameworks.

ABSTRACT

Due to their generally poor conductivity, metal-organic frameworks (MOFs) have been limited in electrical applications. The highest performing materials are two-dimensionally connected Ni3(hexaiminotriphenylene)2 and Ni3(hexaiminobenzene)2; both feature experimental conductivities exceeding 500 S m-1. From theory, both are predicted to be bulk metals but the former is known to be a semiconductor within a single monolayer. In this work we explore structural deformation as a route to augmenting the electronic properties of these two high performing materials. We show that, under hydrostatic negative pressure, metallicity can be installed in the Ni3(hexaiminotriphenylene)2 monolayer. Further, we predict a unique piezoreduction of metal ions and induced-magnetization in Ni3(hexaiminobenzene)2 due to the shift in energy of metal-ligand bonding and antibonding orbitals. These observations aid in our understanding of how MOFs conduct electricity and may also be used as a design principle in future MOF technologies.