Counteranion-induced structural isomerization of phosphine-protected PdAu8 and PtAu8 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 [PdAu₈(PPh₃)₈]²⁺ (PdAu8-B, B means butterfly-motif) and [PtAu₈(PPh₃)₈]²⁺ (PtAu8-B) by the structural isomerization from crown-motif [PdAu₈(PPh₃)₈]²⁺ (PdAu8-C, C means crown-motif) and [PtAu₈(PPh₃)₈]²⁺ (PtAu8-C), induced by association with anionic polyoxometalate, [Mo₆O₁₉]^2– (Mo6) respectively, whereas their structural isomerization was suppressed by the use of [NO₃]^– and [PMo₁₂O₄₀]^3– as counter anions. DR-UV-vis-NIR and XAFS analyses and density functional theory calculations revealed that the synthesized [PdAu₈(PPh₃)₈][Mo₆O₁₉] (PdAu8-Mo6) and [PtAu₈(PPh₃)₈][Mo₆O₁₉] (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. Controlling the geometric structures of metal clusters through structural isomerization allows for tuning of their optical and catalytic properties. Here, structural isomerization of crown-motif clusters [PdAu₈(PPh₃)₈]²⁺ and [PtAu₈(PPh₃)₈]²⁺ to corresponding butterfly-motif clusters is induced using [Mo₆O₁₉]^2- anions. [ABSTRACT FROM AUTHOR]