Mechanistic Insights into Solvent-Mediated Halide-Specific Irreversible Transformation of Cu-MOF with Iodide Detection Capability

Abstract The fascinating feature of metal−organic frameworks is that they can respond toexternal stimuli, unlikeother inorganicmaterials.This featurecorresponds to the framework’s flexibility,whichoriginateswiththelong-rangecrystallineorderof the framework accompanied by cooperative structural transformability.We have synthesized a novelmetal−organic frameworkcomprisedofCu(I)nodeswithpyrazinelinkersandbenzene1,3,5-tricarboxylateactingas templateanions, namedCUCAM-1 [Cu(Py)2(BTC)]n. In the presence of polar solvent systems, CUCAM-1undergoesanirreversiblestructural transformationto yield a mixed phase that consists of HKUST-1 [Cu3(BTC)2(H2O)3]n andanotherCUCAM-2[Cu(Py)(BTC)]n MOFs,whosenovelstructureissuccessfullyrevealedbycontinuousrotationelectrondiffractionfromthemixture. Inthisstructural transformation, anewligandexchangeoccurswhere templateanionsbecome ligands, confirmedbysinglecrystalX-rayanalysis. Further, structural transformation and themechanismare explained by ab initiomolecular dynamics (AIMD) simulations. Interestingly, differenthalides(F−,Cl−, andBr−)canbeaccompaniedtoaffect/control thecompositionof thesecondphaseby favoring the formationof theHKUST-1phase overCUCAM-2, whichwas evident by the powderX-raydiffraction studies. Furthermore, thestructural transformationinducedbyI−resultedinacolorimetricresponseduetotheformationofanewMOF CUCAM-3,pavingthewayforuseasaniodidedetector.