Thermal stability of crown-motif [Au9(PPh3)8]3+ and [MAu8(PPh3)8]2+ (M = Pd, Pt) clusters: Effects of gas composition, single-atom doping, and counter anions

Abstract

The thermal behaviors of ligand-protected metal clusters, [Au9(PPh3)8]3+ and [MAu8(PPh3)8]2+ (M = Pd, Pt) with a crown-motif structure, were investigated to determine the effects of the gas composition, single-atom doping, and counter anions on the thermal stability of these clusters. We successfully synthesized crown-motif [PdAu8(PPh3)8][HPMo12O40] (PdAu8–PMo12) and [PtAu8(PPh3)8][HPMo12O40] (PtAu8–PMo12) salts with a cesium-chloride-type structure, which is the same as the [Au9(PPh3)8][PMo12O40] (Au9–PMo12) structure. Thermogravimetry-differential thermal analysis/mass spectrometry analysis revealed that the crown-motif structure of Au9–PMo12 was decomposed at ∼475 K without weight loss to form Au nanoparticles. After structural decomposition, the ligands were desorbed from the sample. The ligand desorption temperature of Au9–PMo12 increased under 20% O2 conditions because of the formation of Au nanoparticles and stronger interaction of the formed O=PPh3 than PPh3. The Pd and Pt single-atom doping improved the thermal stability of the clusters. This improvement was due to the formation of a large bonding index of M–Au and a change in Au–PPh3 bonding energy by heteroatom doping. Moreover, we found that the ligand desorption temperatures were also affected by the type of counter anions, whose charge and size influence the localized Coulomb interaction and cluster packing between the cationic ligand-protected metal clusters and counter anions.

Counteranion-induced structural isomerization of phosphine-protected PdAu8 and PtAu8 clusters

“…1 and Supplementary Fig. S 1 showed the characteristic optical properties of crown-motif Au9-C, PdAu8-C and PtAu8-C , respectively 34 . ESI-MS and NMR spectra in Fig.…”

“…In the case of non-doped [Au 9 (PPh 3 ) 8 ] 3+ , butterfly-motif Au9-B was formed in Au9-NO3 composite, which was formed from Au9-C ethanol solution by isomerization 32 . DR-UV-Vis-NIR spectrum of Au9-NO3 with a butterfly-motif structure showed a characteristic absorption peak at 687 nm, which differed from those of Au9-C solution ( Au9-NO3 in ethanol) and crown-motif [Au 9 (PPh 3 ) 8 ][PMo 12 O 40 ] ( Au9-PMo12 ) 34 . Since the optical property of [Au 9 (PPh 3 ) 8 ][Mo 6 O 19 ] composite ( Au9-Mo6 ) was in accordance with that of Au9-NO3 composite as shown in Supplementary Fig.…”

“…Figure 1C shows UV-Vis-NIR spectra of composites of [PdAu 8 (PPh 3 ) 8 ] 2+ and cations. The DR-UV-Vis-NIR spectra of PdAu8-NO3 and [PdAu 8 (PPh 3 ) 8 ][HPMo 12 O 40 ] ( PdAu8-PMo12 ) powders resembled that of PdAu8-NO3 in ethanol solution because both PdAu8-NO3 and PdAu8-PMo12 have been reported to have a crown-motif PdAu8-C structure 32 , 34 , 35 . Optical properties of [PdAu 8 (PPh 3 ) 8 ][Mo 6 O 19 ] ( PdAu8-Mo6 ) differed from those of PdAu8-NO3 and PdAu8-PMo12 , and an absorption peak appeared at a longer-wavelength region (703 nm).…”

Collision-Induced Fission of Oblate Gold Superatom in [Au9(PPh3)8]3+: Deformation-Mediated Mechanism

“…13−15 This isomerization was suppressed in [PdAu 8 (PPh 3 ) 8 ] 2+ (PdAu8, Scheme 1); previous EXAFS studies have shown that the radial Pd−Au and lateral Au−Au bonds in PdAu8 are both stiffer than the corresponding Au− Au bonds in [Au 9 (PPh 3 ) 8 ] 3+ . 13 Rigidification of the Au−Au bonds in Au9 by Pd atom doping (PdAu8) leads to the enhanced thermal stability 16 and catalytic activity after ligand removal. 17 In this study, we investigate how the fluxionality of superatomic cores affects the collision-induced dissociation (CID) pathway.…”

“…The desorption of L′ from Au9′ was more endothermic (1.22 eV, Figure 3) than that from PdAu8′ (0.75 eV, Figure 2). 16 These energetic considerations explain the occurrence of reaction 3 under low V i conditions without dissociation of the ligand (Figure 1f). The difference of preferable dissociation routes between PdAu8′ and Au9′, in particular at small collision energy (CE exp = 0.18 eV), could be partly rationalized by net atomic charge analyses (Figures 2 and 3).…”