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 [Zn-2(C3H3N2)(4)](n) (Znlm) has been investigated. The as-synthesized three-dimensional Znlm network (a-phase) crystallizes in the tetragonal space group I4(1)cd(a = 23.5028(4) angstrom, c = 12.4607(3) angstrom). The Znlm crystal undergoes a phase transition to a previously unknown beta-phase within the 0.543(5)-0.847(5) GPa pressure range. The tetragonal crystal system is conserved during this transformation, and the beta-phase space group is I41 (a = 22.7482(3) angstrom, c = 13.0168(3) angstrom). The physical mechanism by which the transition occurs involves a complex cooperative bond rearrangement process. The room-temperature bulk modulus for Znlm is estimated to be similar to 14 GPa. This study represents the first example of a high-pressure single-crystal X-ray diffraction analysis of a metal-organic framework.