Macrocycle-Based Metal-Organic Frameworks with NO₂-Driven On/Off Switch of Conductivity

Conductive metal-organic frameworks (MOFs) have a wide range of applications in supercapacitors, electrocatalysts, and fuel cells, while gas-driven conductive MOFs have not yet been synthesized so far. Herein, we report a gas-driven conductive MOF (A) constructed from calix[4]resorcinarene macrocycle and Co(II) cations, which shows the conductivity enhancement by about eight orders of magnitude through NO₂ adsorption. The conductivities of MOF A before and after the adsorption of NO₂ were calculated to be about 1.3 × 10^-11 and 8.4 × 10^-4 S/cm, respectively. MOF A realizes the conversion from an insulator to a conductor by adsorbing NO₂. When NO₂ is evacuated, MOF A quickly changes from a conductor back to an insulator in 42 s. In the crystal structure of NO₂-adsorbed MOF (termed as A-NO), NO₂ molecule connects Co(II) and uncoordinated carboxylate groups through hydrogen-bonding interactions to form a conductive pathway, greatly reducing the electron transmission distance between each two metal clusters. In addition, NO₂ molecule and H₃O⁺ may also form a conductive pathway by hydrogen-bonding interactions. This work presents an interesting macrocycle-based MOF with a NO₂-driven on/off conductivity switch, proving the possibility for designing advanced gas-driven conductive systems.