Synthesis and Structure of a Neutral Trimetallic Biicosahedral Cluster, (Ph3P)10Au11Ag12Pt2Cl7. A Comparative Study of Molecular and Crystal Structures of Vertex-Sharing Biicosahedral Mixed-Metal Nanoclusters

The synthesis and structure of a new, neutral Au–Ag–Pt vertex-sharing biicosahedral cluster, (Ph₃P)₁₀Au₁₁Ag₁₂Pt₂Cl₇] (3), is reported. The title cluster was synthesized via a new synthetic strategy based on preformed clusters. The title cluster crystallizes in a monoclinic unit cell of P2₁/m space-group symmetry with lattice parameters a=16.553(14) Å, b=25.130(7) Å, c=29.633(13) Å, =103.03(5); V=12009.3 ų and Z=2. The structure was refined to R₁=7.7% and R₂=9.2% for 3585 independent reflections (242°) with I>3. The metal core of the title structure can be described as two Pt-centered Au₆Ag₆ icosahedra sharing a common Au atom. The four metal pentagons adopt the staggered–eclipsed–staggered (ses) configuration, or, the R(0) rotamer. The ten triphenylphosphine ligands coordinate to the ten peripheral (surface) Au atoms in a radial fashion. There are five doubly-bridging chloride ligands connecting two Ag₅ pentagons and two more chloride ligands coordinating terminally to two apical Ag atoms. The title cluster completes the series of Au-shared biicosahedral clusters with 0, 1, and 2 Pt atom(s) occupying the two icosahedral centers, as exemplified by (p-Tol₃P)₁₀Au₁₃Ag₁₂Cl₇]²⁺ (1), (Ph₃P)₁₀Au₁₂Ag₁₂PtCl₇]⁺ (2), and the title cluster (Ph₃P)₁₀Au₁₁Ag₁₂Pt₂Cl₇] (3), respectively. The structure of the title cluster satisfies the site preference rules established for mixed-metal vertex-sharing polyicosahedral nanoclusters. The molecular structural invariance and the ubiquity of the P2₁/m space group for the crystal structures of the biicosahedral cluster series with Ph₃P as phosphine ligands and conforming to the R(0) rotameric metal configuration are discussed. Furthermore, endo- and exo-icosahedral chemistries, and rotamerism and roulettamerism of an extensive series of vertex-sharing biicosahedral nanoclusters, as well as their bonding implications, are described via a comparative study.