Structure and Bonding of the Hexameric Platinum(II) Dichloride, Pt₆Cl₁₂ (<i>β</i>‐PtCl₂)

Abstract

Abstract The crystal structure of Pt 6 Cl 12 ( β ‐PtCl 2 ) was redetermined ( $R \bar 3 m$ a h = 13.126Å, c h = 8.666Å, Z = 3; a rh = 8.110Å, α = 108.04°; 367 hkl, R = 0.032). As has been shown earlier, the structure is in principle a hierarchical variant of the cubic structure type of tungsten (bcc), which atoms are replaced by the hexameric Pt 6 Cl 12 molecules. Due to the 60° rotation of the cuboctahedral clusters about one of the trigonal axes, the symmetry is reduced from $Im \bar 3 m$ to $R \bar 3 m$ ( $I \bar 3 m$ ). The molecule Pt 6 Cl 12 shows the (trigonally elongated) structure of the classic M 6 X 12 cluster compounds with (distorted) square‐planar PtCl 4 fragments, however without metal‐metal bonds. The Pt atoms are shifted outside the Cl 12 cuboctahedron by Δ = +0.046Å ( $\bar {\rm d}$ (Pt—Cl) = 2.315Å; $\bar {\rm d}$ (Pt—Pt) = 3.339Å). The scalar relativistic DFT calculations results in the full $m \bar 3 m$ symmetry for the optimized structure of the isolated molecule with d(Pt—Cl) = 2.381Å, d(Pt—Pt) = 3.468Å and Δ = +0.072Å. The electron distribution of the Pt‐Pt antibonding HOMO exhibits an outwards‐directed asymmetry perpendicular to the PtCl 4 fragments, that plays the decisive role for the cluster packing in the crystal. A comparative study of the Electron Localization Function with the hypothetical trans ‐(Nb 2 Zr 4 )Cl 12 molecule shows the distinct differences between Pt 6 Cl 12 and clusters with metal‐metal bonding. Due to the characteristic electronic structure, the crystal structure of Pt 6 Cl 12 in space group $R \bar 3 m$ is an optimal one, which results from comparison with rhombohedral Zr 6 I 12 and a cubic bcc arrangement.