CRYSTAL-STRUCTURES OF TITANOCENE 2,2'-BIPYRIDYL COMPLEXES - SINGLET VERSUS TRIPLET-STATE DEPENDENCE ON METHYL SUBSTITUENTS AT THE CYCLOPENTADIENYL LIGANDS

The X-ray diffraction analysis of titanocene-2,2'-bipyridyl complexes (C5H5)(2)Ti(bpy) (1), (C5HMe4)(2)Ti(bpy) (2) and (C5Me5)(2)Ti(bpy) (3) revealed that the bpy ligand is inclined to one of the cyclopentadien yl ligands in 1 and 2 whereas in 3 it lies in the plane bisecting the CE-Ti-CE angle of the titanocene skeleton. The triplet state ESR signa l of solid 3 grows in intensity while those of 1 and 2 decrease in int ensity with lowering of temperature down to 77 K. This behaviour shows that the symmetrical position of bpy ligand in 3 is associated with a ground triplet state and the asymmetrical position in 1 and 2 with a ground singlet state. The relation of the spin state of titanocene-bpy complexes to their structure as deduced by McPherson et al. [A.M. McP herson, B.F. Fieselmann, D.L. Lichtenberger, G.L. McPherson and G.D. S tucky, J. Am. Chem. Sec., 101 (1979) 3425] from properties of 1 has th us been confirmed. (C) 1998 Elsevier Science S.A.