Observation of Non-FCC Copper in Alkynyl-Protected Cu₅₃ Nanoclusters

The only feasible access to non-face-centered cubic (FCC) copper was by physical vapor deposition under high vacuum. Now, non-FCC copper is observed in a series of alkynyl-protected Cu₅₃ nanoclusters (NCs) obtained from solution-phase synthesis. Determined by single-crystal X-ray crystallography, the structures of Cu₅₃ (C≡CPhPh)₉ (dppp)₆ Cl₃ (NO₃ )₉ and its two derivatives reveal an ABABC stacking sequence involving 41 Cu atoms. It can be regarded as a mixed FCC and HCP structure, which gives strong evidence that Cu can be arranged in non-FCC lattice at ambient conditions when proper ligands are provided. Characterization methods including X-ray absorption fine structure, XPS, ESI-MS, UV/Vis, Auger spectroscopy, and DFT calculations were carried out. Cu^II was shown to successively coordinate with introduced ligands and changed to Cu^I after bonding with phosphine. The following addition of NaBH₄ and the aging step further reduced it to the Cu₅₃ NC.