Can One σ*-Antibonding Orbital Interact with Six Electrons of Lewis Bases? Analysis of a Multiply Interacting σ* Orbital

One empty orbital normally interacts
with one lone pair of a Lewis
base to form one dative bond, and we do not know any example where
one antibonding orbital interacts with more than two lone pairs of
Lewis bases. We wish to report here the first example which is beyond
our aforementioned common knowledge of dative bonds. We synthesized
heptacoordinate tris­{(o-diphenylphosphino)­phenyl}­tin
fluoride and found that three lone pairs of phosphine donors equivalently
interact with the antibonding σ*­(Sn–F) orbital of the
Sn center. The nature of this “multiply interacting σ*
orbital” was theoretically elucidated by DFT calculations.