Ultra-Stable Metal–Organic Framework with Concurrent High Proton Conductivity and Fluorescence Sensing for Nitrobenzene

Luminescent
metal–organic frameworks (MOFs) coupled with
proton conduction offer wide applications in clean energy and luminescence
sensors. High stability and remarkable proton conductivity and sensing
are requisites for practical applications. Specifically, high thermal
and chemical stabilities under harsh conditions are important but
challenging to achieve. Herein, an ultra-stable Cu­(I)-tetrazolate
MOF, NaCu3(mtz)4 (1, mtz = 5-methyltetrazolate),
was prepared. It possesses a 3D framework with 1D channels and exhibits
outstanding thermal and chemical stabilities under various conditions,
including water, organic solvents, and acidic and basic solutions
of wide pH range. The compound exhibits strong green emissions, which
can be ascribed to metal-to-ligand charge transfer, and selective
fluorescence sensing for pollutant nitrobenzene. Moreover, compound 1 presents a high proton conductivity of over 10–2 S cm–1 at 70 °C and 100% relative humidity.
In 1, abundant uncoordinated nitrogen atoms on the pore
walls act as H-bonding acceptors to achieve its high proton conductivity
under water-assisted conditions. The compound is an unprecedented
water-dependent proton conductor of the tetrazole-based MOF, providing
a new avenue to design robust and high-performance proton-conductive
MOFs.