ELECTRONIC PROPERTIES OF "BIS(ETA-5-CYCLOPENTADIENYL)TITANIUM 2,2'-BIPYRIDYL - SINGLET MOLECULE WITH A LOW-LYING TRIPLET EXCITED-STATE

Magnetic susceptibility and EPR studies show that (η5-C5H5)2Ti(bpy) has a triplet excited state which is thermally accessible from the ground-state singlet. The temperature dependence of the magnetic susceptibility and the EPR spectra was measured and confirms that the singlet and triplet states are separated by approximately 600 cm-1 in toluene solution and 750 cm-1 in the solid state. In both solution and solid state (η5-C5H5)2Ti(bpy) is monomeric so that the presence of extended Ti-Ti interactions is unlikely. The low-lying triplet most likely corresponds to a state in which one unpaired electron formally occupies a molecular orbital which is localized on (η5-C5H5)2Ti while a second unpaired electron resides in the lowest energy π* orbital of the bipyridyl group. This conclusion is supported by Fenske-Hall molecular orbital calculations. The calculations and single crystal X-ray data also suggest that the preferred molecular geometries of the singlet and triplet states are not the same. The cationic complex formed by the one-electron oxidation of (η5-C5H5)2Ti(bpy) has been isolated as a hexafluorophosphate salt. The magnetic susceptibility and EPR spectrum of this material are characteristic of a d1 complex. Copyright © 1979, American Chemical Society. All rights reserved.