Water Induced Structural Transformations in Flexible Two-Dimensional Layered Conductive Metal–Organic Frameworks

Abstract

The flexible and ever-changing layered structure of electrically conductive 2D metal–organic frameworks (MOFs) poses a formidable challenge for establishing any structure–application relationships. Here, we employ a combined quantum mechanics and classical molecular dynamics (MD) approach allowing large-scale/long-time simulations of the dynamics of both dry and hydrated systems to investigate the intrinsic flexibility and dynamical motions of layered 2D MOFs and its effect on their physical and chemical properties. The Co3(HHTP)2 and Cu3(HHTP)2 [HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene] MOFs as two representatives of the layered family of MOFs are studied in great details with a focus on their experimentally observed differential framework stabilities in aqueous solutions. Our MD simulations reproduce structural properties of both MOFs as well as a higher tendency of the Co3(HHTP)2 MOF towards water attack and hydrolysis than its Cu3(HHTP)2 counterpart, in agreement with available experimental reports. The results show the presence of two distinctive metastable metal centers with (pseudo)planar vs (pseudo)tetrahedral configurations where the latter are more positively charged than the former and hence more susceptible to water nucleophilic attacks. The accurate ωB97M-v quantum-mechanical calculations show the higher tendency of the open Co2+ sites for coordination to water molecules than the open Cu2+ sites. Our multifaceted strategy paves the way towards simulation of realistic MOF-based materials and their interface with confined water molecules which is especially relevant to designing more robust water stable materials with desired properties and applications.