Missing Building Blocks Defects in a Porous Hydrogen-bonded Amide-Imidazolate Network Proven by Positron Annihilation Lifetime Spectroscopy

In situ imidazolate-4,5-diamide-2-olate (L2) linker generation under conventional electrical (CE) heating and microwave (MW)-assisted conditions leads to the formation of the porous three-dimensional hydrogen-bonded molecular building block (MBB) [Cd-14(L2)(12)(O)(OH)(2)(H2O)(4)(DMF)(4)] based network, named as HIF-3. In the MBB a Cd-6 octahedron is inscribed in a Cd-8 cube. The evacuated materials show good N-2, CO2, and H-2 gas sorption, in comparison with other H-bonded networks. The desorption branches exhibit a broad hysteresis, suggesting that the materials show flexible behavior during gas uptake. Positron annihilation lifetime spectroscopy (PALS) shows inherent crystal defects of the materials. PALS indicates that the contribution of mesopores (10 and 14% for HIF-3-CE and -MW, respectively) due to missing building blocks, makes the frameworks structurally flexible.