High-Pressure Studies of Abnormal Guest-Dependent Expansion in {[Cu(CO₃)₂](CH₆N₃)₂}_n

High-pressure guest-dependent behaviors of porous coordination polymer {[Cu­(CO₃)₂]­(CH₆N₃)₂}_n (GCC) are investigated using synchrotron X-ray diffraction (XRD) and Raman techniques. In GCC, the host framework of 3D [Cu­(CO₃)₂]^2– coordination network presents a diamond-like topology, with guest guanidinium cations locating at the window of the pores through N–H···O hydrogen bonds. Above a critical pressure, the external force can squeeze the guanidinium ions into the pores, leading to the abnormal expansion of the structure. Meanwhile, the critical pressure for expansion can be effectively lowered when no pressure transmitting medium is employed. Moreover, nonhydrostatic effects can promote the insertion of guanidinium ions, along with the amorphization of the structure, and thus affect the reversibility of the structure after releasing the pressure. Our results show that pressure is an effective tool to tune the host–guest relationship and to prepare high-pressure phase host–guest materials. Meanwhile, this study broadens the understanding of host–guest chemistry and offers a new strategy for fabricating novel materials with applications of pressure switches and zero contraction material in porous coordination polymers.