A 3D-To-2D Phase Transition Mediated by Argentophilic Bond Rearrangements in a Coordination Polymer

When subjected to pressure, most materials typically either maintain their three-dimensional (3D) structure or undergo a transformation into high-dimensional configurations due to compacted spaces and shortened bond distances. Specifically, the formation of metallophilic interactions enhances the potential for increased structural dimensionality. In this study, we present a heterobimetallic coordination polymer, [Cu₂(pa)₂][Ag(CN)₂]₂·2H₂O (pa = deprotonated propanolamine). The ambient pressure phase exhibits a 3D structure consisting of binuclear alkoxo-bridged nodes [Cu₂(pa)₂]²⁺ and linear [Ag(CN)₂]^- spacers, and Ag···Ag interactions exist as ligand-supported one-dimensional (1D) zigzag chains. Increasing the hydrostatic pressure to ∼3.55 GPa induces a first-order phase transformation to phase II, which features a two-dimensional (2D) pillared-like structure. In phase II, the argentophilic interactions undergo substantial reconstructions, resulting in the establishment of discrete silver-silver dimers and rendering the structure ligand-unsupported. Furthermore, the unprecedented structural transformation from 3D to 2D in this compound is accompanied by a color change, which coincides with the collapse of the energy band gap. This study proposes a new strategy for reducing structural dimensionality by utilizing pressure as a means to modify the connectivity modes of argentophilic interactions in coordination supramolecular systems.