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)(C(3)H(3)N(2))(4)](n) (ZnIm) has been investigated. The as-synthesized three-dimensional ZnIm network (alpha-phase) crystallizes in the tetragonal space group I4(1)cd (a = 23.5028(4) A, c = 12.4607(3) A). The ZnIm 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 I4(1) (a = 22.7482(3) A, c = 13.0168(3) A). 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 approximately 14 GPa. This study represents the first example of a high-pressure single-crystal X-ray diffraction analysis of a metal-organic framework.