Engineering High Electrical Conductivity in Stable Zirconium-based PCN-222 MOFs with Permanent Mesoporosity

Pratik, S. M.; Gagliardi, L.; Cramer, C. J.
Chem. Mater. 2020, 32, 6137 (doi:10.1021/acs.chemmater.0c01847).

Electrically conductive metal-organic frameworks (MOFs) featuring zirconium-based nodes are of great interest for electrochemical and optoelectronic applications due to their exceptional thermal and chemical stability, although the number of such MOFs remains limited. Herein, we demonstrate that electron deficient molecules such as transition metal(IV) bis(dicarbollide) (TM^IV(C₂B₉H₁₁)₂; TM^IVCB for short, where TM=Ni, Pd and Pt) or C₆₀, spatially infiltrated in the microporous channels of the zirconium-based porphyrinic MOFs PCN-222 and PCN-222-Zn, generate highly stable and electrically conductive frameworks in which the mesopores remain accessible to other guests. Solid-state density functional theory (DFT) and ab initio molecular dynamics (AIMD) simulations indicate incorporation of Ni^IVCB and C₆₀ in the MOF micropores is energetically and structurally feasible. Interestingly, in contrast to the free species, strong donor-acceptor interactions between the MOF and Ni^IVCB restrain it to a single conformation. Calculated electronic structures and charge-hopping conduction probabilities illustrate that efficient charge-transfer (CT) from photoexcited linkers to the guest molecules facilitates charge hopping in the framework, making the MOFs electrically conductive. The donor-acceptor conjugates also enhance exciton dissociation at their heterojunctions, fostering the formation of long-lived electron-trapped states with potential utility for photo- and electrochemical devices.