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.