A New Geometry for Homoleptic Organochromium Compounds

[NBu4]2[Cr(C6F5)5] (1) has been obtained by low-temperature treatment of [CrCl3(THF)3]
with LiC6F5. The five-coordinate anion [Cr(C6F5)5]2- has been found to be square pyramidal
by X-ray diffraction methods. The SPY-5 geometry is unprecedented for homoleptic
organochromium compounds. EPR data for this paramagnetic S = 3/2 system (d3 electron
configuration) point to the existence of two types of CrIII centers with very similar coordination
environments. A comparison with the titanium(III) isoleptic species [Ti(C6F5)5]2- allows us
to conclude that the fact that [Cr(C6F5)5]2- in 1 adopts a SPY-5 structure must be due to
electronic reasons associated with the electron configuration of the metal center.