Chemical origin of C–O blue shift and nature of Cu^+…C bonding in non-classical copper carbonyl Cu⁺(CO)_n (n = 1–8) complexes

Abstract

Natural bond orbital (NBO) method and atoms-in-molecules (AIM) theory are used to study the chemical origin in the direction and ordering of C–O frequency shift, as well as Cu^+…C bond nature in copper carbonyl cations Cu⁺(CO)_n (n = 1–8). This study emphasises the role of π-back donation in explaining the ordering of C–O blue shift. NBO analyses show that the interplay of two competing factors, including π-back donation and rehybridization, is responsible for both the direction and the ordering of C–O stretching frequency shift in Cu⁺(CO)_n (n = 1–8) complexes. In addition, the Cu^+…C interaction is interesting because Cu⁺(CO)_n (n = 1–4) structure has one-sphere CO ligands but Cu⁺(CO)_n (n = 5–8) has two-sphere CO ligands. Topological analyses of electron density are applied to characterise the Cu^+…C interactions of first- and second-sphere CO with Cu⁺ and to explore the Cu^+…C interactions in the nature.

Keywords:

• non-classical carbonyl complexes
• blue shift
• π-back donation
• rehybridization
• vibrational frequency

Acknowledgements

This work was supported by the National Nature Science Foundation of China (No. 20975064) and the National Nature Science Foundation of Shandong Province (No. ZR2011BM016). We acknowledge generous support for this work from Prof. M.A. Duncan and his co-workers in the Department of Chemistry, University of Georgia, Athens, USA. The author also wishes to thank reviewers for their comments and suggestions; owing to them this article was improved significantly.