Selective Thermal Elongation of Metal–Metal Distances in the Two-Dimensional Assembly of Ag(I) Ions Templated by Assembled Peptide Ligands

To develop a tunable assembly of metal ions, we demonstrated a two-dimensional Ag(I) array in the crystalline state by using an assembly of dipeptide ligands as a template. The two-dimensional assembly of Ag(I) ions was obtained through the assembly of a Ag(I)-peptide polymer complex, which was held together by hydrogen bonding interactions. At –180 °C, one-dimensional zigzag chains of Ag(I) ions were formed in each layer, which further assembled to form two-dimensional layers. The arrangement of the Ag(I) ions included several Ag–Ag distances that are supported differently by the peptide assembly. Because of this difference, when heated from –180 to 50 °C, the Ag(I) layer displays anisotropic thermal expansion in the arrangements, in which one of the Ag–Ag distances selectively elongated. This expansion is reversible, allowing switching between the zigzag chain assembly and the Ag(I) dimer assembly. Moreover, the resulting crystalline Ag(I) complexes show luminescence at both room temperature and at –196 °C, suggesting the existence of Ag–Ag interactions.