Revisiting the structure of [PdAu₉(PPh₃)₈(CN)]²⁺ produced by atmospheric pressure plasma irradiation of [PdAu₈(PPh₃)₈]²⁺ in methanol

Some of the authors of the present research group have previously reported mass spectrometric detection of [PdAu₉(PPh₃)₈(CN)]²⁺ (PdAu₉CN) by atmospheric pressure plasma (APP) irradiation of [MAu₈(PPh₃)₈]²⁺ (PdAu₈) in methanol and proposed based on density functional theory (DFT) calculations that PdAu₉CN is constructed by inserting a CNAu or NCAu unit into the Au–PPh₃ bond of PdAu₈ [Emori et al., J. Chem. Phys. 155, 124312 (2021)]. In this follow-up study, we revisited the structure of PdAu₉CN by high-resolution ion mobility spectrometry on an isolated sample of PdAu₉CN with the help of dispersion-corrected DFT calculation. In contradiction to the previous proposal, we conclude that isomers in which an AuCN unit is directly bonded to the central Pd atom of PdAu₈ are better candidates. This assignment was supported by Fourier transform infrared and ultraviolet–visible spectroscopies of isolated PdAu₉CN. The simultaneous formation of [Au(PPh₃)₂]⁺ and PdAu₉CN suggests that the AuCN species are formed by APP irradiation at the expense of a portion of PdAu₈. These results indicate that APP may offer a unique method for transforming metal clusters into novel ones by generating in situ active species that were not originally added to the solution.