Counteranion-induced structural isomerization of phosphine-protected PdAu and PtAu clusters.

Controlling the geometric structures of metal clusters through structural isomerization allows for tuning of their electronic state. In this study, we successfully synthesized butterfly-motif [PdAu(PPh)] (PdAu8-B, B means butterfly-motif) and [PtAu(PPh)] (PtAu8-B) by the structural isomerization from crown-motif [PdAu(PPh)] (PdAu8-C, C means crown-motif) and [PtAu(PPh)] (PtAu8-C), induced by association with anionic polyoxometalate, [MoO] (Mo6) respectively, whereas their structural isomerization was suppressed by the use of [NO] and [PMoO] as counter anions. DR-UV-vis-NIR and XAFS analyses and density functional theory calculations revealed that the synthesized [PdAu(PPh)][MoO] (PdAu8-Mo6) and [PtAu(PPh)][MoO] (PtAu8-Mo6) had PdAu8-B and PtAu8-B respectively because PdAu8-Mo6 and PtAu8-Mo6 had bands in optical absorption at the longer wavelength region and different structural parameters characteristic of the butterfly-motif structure obtained by XAFS analysis. Single-crystal and powder X-ray diffraction analyses revealed that PdAu8-B and PtAu8-B were surrounded by six Mo6 with rock salt-type packing, which stabilizes the semi-stable butterfly-motif structure to overcome high activation energy for structural isomerization.