Novel non-spherical deltahedra in tritungstaboranes related to the experimentally known Cp*3W3(H)B8H8

Abstract

The geometries and energetics of tritungstaboranes Cp₃W₃(H)B_n−3H_n−3 (Cp = η⁵-C₅H₅; n = 5 to 12), related to the experimentally known Cp*₃W₃(H)B₈H₈ (Cp* = η⁵-Me₅C₅), have been investigated using density functional theory and coupled cluster calculations. Such low-energy structures have central W₃B_n−3 deltahedra with superimposed bonded W₃ triangles. The “extra” hydrogen atom either bridges a deltahedral edge or caps a deltahedral face containing at least one tungsten atom. The tungsten atoms are located at degree 5 to 7 vertices in regions of a relatively low surface curvature whereas the boron atoms are located at degree 3 to 5 vertices in regions of a relatively high surface curvature. The five lowest-energy structures of the 11-vertex tritungstaborane Cp₃W₃(H)B₈H₈ all have the same central W₃B₈ deltahedron and differ only by the location of the “extra” hydrogen atom. The isosceles W₃ triangles in these structures have two long ∼3.0 Å W–W edges through the inside of the deltahedron with the third shorter W–W edge of ∼2.7 to ∼2.8 Å corresponding to a surface deltahedral edge. The five Cp₃W₃(H)B₈H₈ structures differ only by the location of the “extra” hydrogen atom. The lowest energy such structure has the “extra” hydrogen atom bridging the surface W–W bond and corresponds to the experimental Cp*₃W₃(H)B₈H₈ structure, as determined using X-ray crystallography.