Polymorphism in Atomically Precise Cu Nanocluster Incorporating Tetrahedral [Cu] Kernel.

Because of the typical instability of copper nanoclusters, atom-precise structural elucidation of these nanoclusters has remained elusive. Herein, we report an air- and moisture-stable 23-copper nanocluster ( or ) isolated from the reaction of Cu(CFCOO), BuC≡CH, Cu powder, and PhSiH using a gradient reduction (Cu → Cu → Cu) strategy (GRS), which is competent for controlling the kinetics of the reduction reaction, thus avoiding formation of pure Cu complexes or large Cu nanoparticles. The solid-state structure of the Cu nanocluster shows a rare [Cu] tetrahedral kernel surrounded by an outer Cu shell, which is protected by BuC≡C and CFCOO ligands. The Cunanocluster is a rare four-electron superatom with a 1S1P electronic shell closure and can be crystallized in two polymorphs (3 and 3̅) depending on the solvent used. The crystallization of in the 3 space group is mainly governed by van der Waals forces and C-H···F interactions, whereas additional intermolecular C-H···Cl interactions are responsible for the 3̅ space group of . This work not only shows the ingenuity of a gradient reduction strategy for the synthesis of copper nanoclusters but also provides a better fundamental understanding of how to produce the polymorphic copper nanoclusters in a precisely tunable fashion.