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

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.