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Outstanding Nobility Observed in Cu5 Clusters Reveals the Key Role of Collective Quantum Effects

submitted on 28.01.2021, 23:22 and posted on 01.02.2021, 05:50 by David Buceta, Shahana Huseyinova, Miguel Cuerva, Héctor Lozano, Lisandro J. Giovanetti, José M. Ramallo-López, Patricia López-Caballero, Alexandre Zanchet, Alexander O. Mitrushchenkov, Andreas W. Hauser, Giampaolo Barone, Cristián Huck-Iriart, Carlos Escudero, Juan Carlos Hernández-Garrido, José Calvino, Miguel Lopez-Haro, Maria Pilar de Lara-Castells, Felix G. Requejo, M. Arturo López-Quintela
Subnanometer-sized metal clusters often feature a molecule-like electronic structure, which makes their physical and chemical properties significantly different from those of nanoparticles and bulk material. Considering potential applications, there is a major concern about their thermal stability and susceptibility towards oxidation. Cu clusters of only 5 atoms (Cu5 clusters) are first synthesized in high concentration using a new-generation wet chemical method. Next, it is shown that, contrary to what is currently assumed, Cu5 clusters display nobility, beyond resistance to irreversible oxidation, at a broad range of temperatures and oxygen pressures. The outstanding nobility arises from an unusual reversible oxidation which is observed by in situ X-ray Absorption Spectroscopy and X-ray Photoelectron Spectroscopy on Cu5 clusters deposited onto highly oriented pyrolitic graphite at different oxygen pressures and up to 773 K. This atypical property is explained by a theoretical approach combining different state-of-the-art first principles theories. It reveals the essential role of collective quantum effects in the physical mechanism responsible for the nobility of Cu5 clusters, encompassing a structural ‘breathing’ through concerted Cu–Cu elongations/contractions upon O2 uptake/release, and collective charge transfer as well. A predictive phase diagram of their reversible oxidation states is also delivered, agreeing with the experimental observations. The collective quantum effects responsible of the observed nobility are expected to be general in subnanometer-sized metal clusters, pushing this new generation of materials to an upper level.


This work has been partly supported by the European Union’s Horizon 2020 Research and Innovation Programme un-der Grant Agreement No. 825999; the Spanish Agencia Estatal de Investigación (AEI) and the Fondo Europeo de Desarrollo Regional (FEDER, UE) under Grant No. MAT2016-75354-P; the Austrian Science Fund (FWF) under Grant P29893-N36; the CMST COST Action CM1405 “Molecules in Motion” (MOLIM); the Xunta de Galicia, Spain (Grupos Ref. Comp.ED431C 2017/22 and AEMAT ED431E 2018/08); Obra Social Fundación La Caixa: Ref.LCF/PR/PR12/11070003; ANPCyT PICT (2017-1220 and 2017-3944) and UNLP (Project11/X790), Argentina.


Email Address of Submitting Author


Institute of Fundamental Physics, Spanish National Research Council



ORCID For Submitting Author


Declaration of Conflict of Interest

David Buceta and M.A. López-Quintela are stackholders of Nanogap, company dedicated to the exploitation of clusters, synthesized by wet chemical methods, in different fields (

Version Notes

Submitted on 28th of January, 2021