Zeolitic Polyoxometalate-Based Metal–Organic Frameworks(Z-POMOFs): Computational Evaluation of HypotheticalPolymorphs and the Successful Targeted Synthesis of theRedox-Active Z-POMOF1

摘要

The targeted design and simulation of a new family of zeolitic metal-organic frameworks (MOFs)based on benzenedicarboxylate (BDC) as the ligand and ε-type Keggin polyoxometalates (POMs) as buildingunits, named here Z-POMOFs, have been performed. A key feature is the use of the analogy between theconnectivity of silicon in dense minerals and zeolites with that of the ε-type Keggin POMs capped withZn(II) ions. Handling the e-Keggin as a building block, a selection of 21 zeotype structures, together witha series of dense minerals were constructed and their relative stabilities computed. Among these Z-POMOFs,the cristobalite-like structure was predicted to be the most stable structure. This prediction has beenexperimentally validated by the targeted synthesis of the first experimental Z-POMOF structure, whichwas strikingly found to possess the cristobalite topology, with three interpenetrated networks. Crystals ofNBu_4_3PMo~v8M_o~VI_4O_36(OH)_4Zn_4(BDC)_2.2H_20 (Z-POMOF1) have been isolated under hydrothermalconditions from the reduction of ammonium heptamolybdate in the presence of phosphorous acid andZn(II) ions. Tetrabutylammonium cations play the role of counterions and space-filling agents in thistridimensional interpenetrated framework. Moreover, the electrochemistry of the e-Keggin POM is maintainedand can be exploited in the insoluble Z-POMOF1 framework, as demonstrated by the electrocatalyticreduction of bromate.