A New Geometry for Homoleptic Organochromium Compounds

[NBu 4 ] 2 [Cr(C 6 F 5 ) 5 ] ( 1 ) has been obtained by low-temperature treatment of [CrCl 3 (THF) 3 ] with LiC 6 F 5 . The five-coordinate anion [Cr(C 6 F 5 ) 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 (d 3 electron configuration) point to the existence of two types of Cr III centers with very similar coordination environments. A comparison with the titanium(III) isoleptic species [Ti(C 6 F 5 ) 5 ] 2 - allows us to conclude that the fact that [Cr(C 6 F 5 ) 5 ] 2 - in 1 adopts a SPY -5 structure must be due to electronic reasons associated with the electron configuration of the metal center.