Construction of the tetrahedral trifluorophosphine platinum cluster Pt4(PF3)8 from smaller building blocks.

Abstract

The experimentally known but structurally uncharacterized Pt4(PF3)8 is predicted to have an S4 structure with a central distorted Pt4 tetrahedron having four short Pt═Pt distances, two long Pt-Pt distances, and all terminal PF3 groups. The structures of the lower nuclearity species Pt(PF3)n (n = 4, 3, 2), Pt2(PF3)n (n = 7, 6, 5, 4), and Pt3(PF3)6 were investigated by density functional theory to assess their possible roles as intermediates in the formation of Pt4(PF3)8 by the pyrolysis of Pt(PF3)4. The expected tetrahedral, trigonal planar, and linear structures are found for Pt(PF3)4, Pt(PF3)3, and Pt(PF3)2, respectively. However, the dicoordinate Pt(PF3)2 structure is bent from the ideal 180° linear structure to approximately 160°. Most of the low-energy binuclear Pt2(PF3)n (n = 7, 6, 5) structures can be derived from the mononuclear Pt(PF3)n (n = 4, 3, 2) structures by replacing one of the PF3 groups by a Pt(PF3)4 or Pt(PF3)3 ligand. In some of these binuclear structures one of the PF3 groups on the Pt(PF3)n ligand becomes a bridging group. The low-energy binuclear structures also include symmetrical [Pt(PF3)n]2 dimers (n = 2, 3) of the coordinately unsaturated Pt(PF3)n (n = 3, 2). The four low-energy structures for the trinuclear Pt3(PF3)6 include two structures with central equilateral Pt3 triangles and two structures with isosceles Pt3 triangles and various arrangements of terminal and bridging PF3 groups. Among these four structures the lowest-energy Pt3(PF3)6 structure has an unprecedented four-electron donor η(2)-μ3-PF3 group bridging the central Pt3 triangle through three Pt-P bonds and one Pt-F bond. Thermochemical studies on the aggregation of these Pt-PF3 complexes suggest the tetramerization of Pt(PF3)2 to Pt4(PF3)8 to be highly exothermic regardless of the mechanistic details.