The poor electrical conductivity of metal-organic frameworks originates in the low electron mobility that exists within the material due to the ionic nature of the metal-organic interface. This ionic characteristic prohibits charge delocalization in 3D MOFs, where charge transfer relies heavily on the through-bond charge transfer pathway.1 On the other hand, 2D MOFs with their extended conjugated system and π-π orbitals overlap allows charge delocalization to happen via other charge transport pathways making them electrically conductive.2 The conductivity of 2D MOFs is relativity low3 compared to other conductive materials such as graphene,4 and their chemical properties are not well understood. In this study, using ab initio DFT calculations, we investigated the electronic properties of two well-known conductive 2D MOFs, Ni3(HITP)25 and Ni3(HIB)2,6 under various modifications directed toward the metal-organic interface to elucidate the role of the square-planar coordination sphere and the d-antibonding orbitals in maintaining charge mobility within and between the 2D layers. We revealed a reduction event within the nickel center under the elongation of the metal-organic interface and an induced metallic occurrence in the semi-conductive monolayer of Ni3(HITP)2.7 The electronic band structure also showed a decrease in band dispersion with increasing metal-ligand bond length corresponding to a higher electron density localized at the metal sites. The electronic properties of the modified retrofitted MOFs revealed the role of the dz2 orbitals in retaining the in-plane charge mobility, and how redox activity within this orbital can enhance or reduce charge mobility through out the frameworks. Our study elucidates the key chemical interactions that give raise to sufficient charge mobility in 2D MOFs to make them conductive and may be used as a design principle for enhancing MOF’s conductivity.

An investigation on the effect of the metal-organic interface in conductive 2-dimensional metal organic frameworks

ACS Spring Meeting 2021

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.