Aperiodic core structures of Pd and Pt giant clusters chemically stabilized with diphenyl phosphide ligands

Atomic scale structures and compositions of “giant” clusters [Pd2(PPh2)Hx]n, (I) and [Pt(PPh2)]n (II) (PPh2 = diphenyl phosphide, n ≅ 6–10) and Pd∼561Phen∼60(OAc)∼180 (III) (Phen = 1,10-phenanthroline; OAc = CH3COO−) have been investigated by high-resolution electron microscopy, electron diffraction and integrated field-emission analytical electron microscopy combining high-angle annular dark-field scanning transmission electron imaging, electron energy-loss spectroscopy (EELS) and windowless energy-dispersive X-ray nanoanalyses of metal cores and ligand shells. Observations revealed a uniform cell structure of the cluster matter with the unimodal core size distributions. Compositional deviations from the ideal stoichiometry were determined by EELS line profile analyses starting at the interfaces between cluster (I) cores and ligand shells. For clusters (I) and (II), with core sizes centered around 1.6 ± 0.3 nm and 1.5 ± 0.3 nm, respectively, lattice fringes and Debye–Scherrer diffraction rings were not observed, thus indicating that the structure within particles is not periodic. This was in contrast with the sputtered reference 1–2 nm Pt particles, which show clear evidence of crystallinity. Polyhedral Pd cores of clusters (III) with the diameter of 2.4 ± 0.3 nm also revealed lattice fringes assigned to an expanded face-centered cubic (fcc) structure, sometimes with multiple twinning. The structural differences suggest a ligand induced metal-to-molecular (non-crystalline) state transformation in clusters (I) and (II).

Atomic scale structures of “giant” clusters [Pd2(PPh2)Hx]n, (I) and [Pt(PPh2)]n (II) (n ≅ 6–10) and Pd∼561Phen∼60(OAc)∼180 (III) have been investigated by HRTEM and integrated AEM. For (I) and (II), with 1.5–1.6 nm cores, the structure was found aperiodic. 2.4 nm Pd cores of (III) revealed fcc lattice fringes. The differences suggest a ligand induced metal-to-molecular (non-crystalline) state transformation in (I) and (II). Figure optionsDownload as PowerPoint slide