Unraveling the Semiconducting/Metallic Discrepancy in Ni-3(HITP)(2)

Ni-3(2,3,6,7,10,11-hexaiminotriphenylene)(2) is a pi-stacked layered metal-organic framework material with extended pi-conjugation that is analogous to graphene. Published experimental results indicate that the material is semiconducting, but all theoretical studies to date predict the bulk material to be metallic. Given that previous experimental work was carried out on specimens containing complex nanocrystalline microstructures and the tendency for internal interfaces to introduce transport barriers, we apply DFT to investigate the influence of internal interface defects on the electronic structure of Ni-3(HITP)(2). The results show that interface defects can introduce a transport barrier by breaking the pi-conjugation and/or decreasing the dispersion of the electronic bands near the Fermi level. We demonstrate that the presence of defects can open a small gap, in the range of 15-200 meV, which is consistent with the experimentally inferred hopping barrier.