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.