The ability to change the electronic energy levels of the valence and conduction bands in semiconductors is one of the foundational principles of modern electronics. In principle, the same applies to electrically conducting metal−organic frameworks (MOFs), a class of emerging crystalline porous conductors. Inspired by the band engineering of inorganic semiconductors using isostructural alloying strategy, we showed that one of the prototypical electrically conducting MOFs, Ni3(HITP)2 (HITP = 2,3,6,7,10,11-hexaiminotriphenylene), is amenable to similar compositional tuning. Binary alloys (MxM′3−x)(HITP)2 (MM′ = CuNi, CoNi, and CoCu) allow precise control over the M/M′ ratios by controlling the precursor ratios, and are isostructural with the parent compounds M3(HITP)2 (M = Co, Ni, Cu). Alloying enables continuous variation of electrical conductivity of over 4 orders of magnitude from 5.8 × 10−3 to 55.4 S/cm. We attribute the continuous tuning of both band gaps and electrical conductivity to changes in free carrier concentrations and to subtle differences in the interlayer displacement or spacing, both of which are defined by metal substitution. The activation energy of (CoxNi3−x)(HITP)2 alloys scales inversely with an increasing Ni percentage, confirming thermally activated bulk transport.

Continuous electrical conductivity variation in two-dimensional metal-organic framework alloys

ACS Spring Meeting 2021

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