Unveiling the multifaceted properties of a 3d covalent-organic framework: Pressure-induced phase transition, negative linear compressibility and auxeticity
Özet
High-pressure behavior and mechanical properties of a three-dimensional covalent-organic framework (NPN-1)
were investigated by using different types of first principles molecular simulations. An irreversible pressureinduced first-order isosymmetric phase transition was predicted at 0.14 GPa. The subunit of NPN-1 retains its
rigidity under pressure thanks to the strong covalent bonds. However, compression leads to significant tilting of
the nitrophenyl groups. The mechanical properties of frameworks are highly anisotropic. Remarkably, both
phases exhibit not only negative linear compressibility along the c-axis but also negative Poisson’s ratio in certain
directions. Detailed structural analysis revealed that the origin of the phase transition and anomalous mechanical
properties of both phases are the wine-rack motif and strut-hinge mechanism. To the best of our knowledge, this
study is the first report of such behavior in COFs, opening up new avenues for the exploration of COFs as materials for many promising applications.
