Structural Isomerization in Cu(I) Clusters: Tracing the Cu Thermal Migration Paths and Unveiling the Structure-Dependent Photoluminescence

Revealing structural isomerization in metal clusters would bridge a huge structural gap between small molecular isomerization and solid-solid phase transformation. However, genuine structural isomerism in metal clusters is still rare. In this work, we report the first example of structural isomerismin Cu clusters. By utilizing the coordination flexibility of alkyne to enable the migration of partial Cu atoms in Cu metal cores, two Cu-15 cluster complexes (Cu-15-a and Cu-15-c) possessing identical composition but different metal core structures have been successfully isolated. Interestingly, although the structure of Cu-15-a can be retained in CH2Cl2 solution below 27 degrees C, it will gradually change to give an intermediate state, Cu-15-b, as the temperature rises (at about 31 degrees C) before it eventually transforms into Cu-15-c (at 40 similar to 65 degrees C). Significantly, atomically precise Cu-15-b clearly provides footprints for tracing the thermal migration process of Cu atoms during the thermal transformation from Cu-15-a to Cu-15-c. In addition, Cu-15-a and Cu-15-c exhibit diverse crystallization-induced emission enhancement phenomena. Crystalline Cu-15-c displays redshifted photoluminescence (820 nm) compared with Cu-15-a (726 nm) due to the shorter mean Cu center dot center dot center dot Cu distance in Cu-15-c. Notwithstanding, crystalline Cu-15-a exhibits much more intense photoluminescence at room temperature than that in Cu-15-c, which might be attributed to the stronger intermolecular C-H center dot center dot center dot pi interactions in Cu-15-a. These results indicate that cluster isomerism provides valuable opportunities for insight into the structure-property relationships and understanding the complex evolution of phase transformation in nanometallic solids. [GRAPHICS] .