Despite the great effort, the only feasible access to non face-centered cubic ( FCC ) copper is by physical vapor deposition under high vacuum. We report the first observation of non- FCC copper in a series of alkynyl protected Cu 53 nanoclusters (NCs) obtained from solution phase synthesis. Determined by single-crystal X-ray crystallography, the total structures of Cu 53 (C≡CPhPh) 9 (dppp) 6 Cl 3 (NO 3 ) 9 and its two derivatives reveal their most prominent feature: 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 condition when proper ligands are provided. To gain a deeper understanding of the formation mechanism of Cu NCs, characterization methods including X-ray absorption fine structure, XPS, ESI-MS, UV-vis, Auger spectroscopies and DFT calculations are carried out. It is revealed that Cu II successively coordinated with introduced ligands and changed to Cu I after bonding with phosphine. The following addition of NaBH 4 and the aging step further reduced it to the title NC. Their applications in homocoupling of phenylacetylene are also studied.