Cerocene Revisited: The Electronic Structure of and Interconversion Between Ce2(C8H8)3 and Ce(C8H8)2

New synthetic procedures for the preparation of Ce(cot)(2), cerocene, from [Li(thf)(4)][Ce(cot)(2)], and Ce-2(cot)(3) in high yield and purity are reported. Heating solid Ce(cot)(2) yields Ce-2(cot)(3) and COT while heating Ce-2(cot)(3) with an excess of COT in C6D6 to 65 degrees C over four months yields Ce(cot)(2). The solid state magnetic susceptibility data of these three organocerium compounds show that Ce(cot)(2) behaves as a TIP (temperature independent paramagnet) over the temperature range of 5-300 K, while that of Ce-2(cot)(3) shows that the spin carriers are antiferromagnetically coupled below 10 K; above 10 K, the individual spins are uncorrelated, and [Ce(cot)(2)](-) behaves as an isolated f(1) paramagnet. The EPR spectra recorded at 1.5 K confirm that Ce-2(cot)(3) and [Ce(cot)(2)](-) have a erround-state of M-j= +/- 1/2. The L-III edge XANES of Ce(cot)(2) (Booth, C.H.; Walter, M.D.; Daniel, M.; Lukens, W.W., Andersen, R.A., Phys. Rev. Lett. 2005, 95, 267202) and Ce-2(cot)(3) over 30-500 K are reported; the Ce(cot)(2) XANES spectra show Ce(III) and Ce(IV) signatures up to a temperature of approximately 500 K, whereupon the Ce(IV) signature disappears, consistent with the thermal behavior observed in the melting experiment. The EXAFS of Ce(cot)(2) and Ce-2(cot)(3) are reported at 30 K; the agreement between the molecular parameters for Ce(cot)(2) derived from EXAFS and single crystal X-ray diffraction data are excellent. In the case of Ce-2(cot)(3) no X-ray diffraction data are known to exist, but the EXAFS are consistent with a triple-decker sandwich structure. A molecular rationalization is presented for the electronic structure of cerocene having a multiconfiguration ground-state that is an admixture of the two configurations Ce(III, 4f(1))(cot(1.5-))2 and Ce(IV, 4f(0))(Cot(2-))(2); the multiconfigurational ground-state has profound effects on the magnetic properties and on the nature of the chemical bond in cerocene and, perhaps, other molecules.