Pressure-Induced Cooperative Bond Rearrangement in a Zinc Imidazolate Framework: A High-Pressure Single-Crystal X-Ray Diffraction Study

The pressure-dependent structural evolution of a neutral zinc-imidazolate framework [Zn2(C3H3N2)4]n (ZnIm) has been investigated. The as-synthesized three-dimensional ZnIm network (α-phase) crystallizes in the tetragonal space group I41cd (a = 23.5028(4) Å, c = 12.4607(3) Å). The ZnIm crystal undergoes a phase transition to a previously unknown β-phase within the 0.543(5)−0.847(5) GPa pressure range. The tetragonal crystal system is conserved during this transformation, and the β-phase space group is I41 (a = 22.7482(3) Å, c = 13.0168(3) Å). The physical mechanism by which the transition occurs involves a complex cooperative bond rearrangement process. The room-temperature bulk modulus for ZnIm is estimated to be ∼14 GPa. This study represents the first example of a high-pressure single-crystal X-ray diffraction analysis of a metal−organic framework.