New J. Chem. 45, 21844 (2021)

The reactivity of Nb_n⁺ clusters with acetylene and ethylene to produce a cubic aromatic metal carbide Nb₄C₄⁺

Wen Gan^ab, Benben Huang^ab, Mengzhou Yang^ab, Lijun Geng^a, Zhixun Luo^*ab and  Klavs Hansen^c

a Beijing National Laboratory for Molecular Science, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, Institute of Chemistry, Chinese Academy of Sciences, Beijing, China

b University of Chinese Academy of Sciences, Beijing 100049, China

c Center for Joint Quantum Studies and Department of Physics, School of Science, Tianjin University, 92 Weijin Road, Tianjin 300072, China

*  zxluo@iccas.ac.cn

Abstract

The study of clusters with strongly size-dependent properties has attracted extensive attention due to their potential applications in building new materials. Utilizing a home-made multiple-ion laminar flow tube reactor in tandem with a customized triple quadrupole mass spectrometer, we have studied the reactions of niobium cationic clusters with acetylene and ethylene. It is observed that dehydrogenation dominates the reaction process, and Nb₄C₄⁺ shows up prominently in the mass spectra. Quantum chemistry calculations reveal that the most stable structure of Nb₄C₄⁺ corresponds to a slightly distorted cubic structure with D_2d symmetry, with reasonable stability pertaining to its cubic aromaticity. We illustrate the dehydrogenation reaction paths of Nb₄⁺ + 2C₂H₂ to form the prominent Nb₄C₄⁺ product, along with the highly exothermic reactions to produce H₂.