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

Abstract

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 C 6 D 6 to 65 °C over four months yields Ce(cot) 2 . The solid state magnetic susceptibility of these three organocerium compounds shows 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) 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

Decamethylytterbocene Complexes of Bipyridines and Diazabutadienes: Multiconfigurational Ground States and Open-Shell Singlet Formation

“…These data therefore point to the formation of a multiconfigurational, open-shell singlet ground-state with anomalously strong antiferromagnetic coupling between the moments on the metal and the aromatic ligand. Similar behavior was predicted for cerocene [17][18][19] (Ce(cot) 2 , cot = cyclooctatetraene = C 8 H 8 ) and supported by experiments on cerocene, 16,20 substituted cerocenes, 21,22 the isoelectronic compounds Pn* 2 Ce (Pn* = permethylpentalene = C 8 25 Cp* 2 Yb(terpy = 2,2′:6′,2′′-terpyridine), 7 and Cp* 2 Yb(bipy). 16 This interpretation is further supported by a Complete Active Space Self-Consistent Yb L III -edge XANES and magnetic susceptibility measurements are reported below on several bipy and dad adducts of Cp* 2 Yb of the type Cp* 2 Yb(L) (Scheme 1), where L is either bipy, a 4,4′-disubstituted bipyridine, or a 1,4-diazabutadiene derivative, including purely di-and trivalent Yb complexes.…”

Cerium oxidation state and covalent 4f-orbital contributions in the ground state of bis(η8-pentalene)cerium

“…Large-scale multi-configurational relativistic quantum chemical calculations supported this view [6,7], as did X-ray absorption nearedge structure (XANES) spectroscopy using the Ce K-edge [8] as well as low-temperature absorption and luminiscence spectra and magnetic circular dicroism (MCD) measurements [9]. Further evidence for a molecular Kondo-system cerocene was gained more recently by magnetic measurements and L III -edge XANES studies [10] as well as further extensive experimental studies [11].…”

Reversible Sigma C–C Bond Formation Between Phenanthroline Ligands Activated by (C5Me5)2Yb

“…While the MO model does not capture the stabilization of the triplet or singlet state due to configuration interaction, the stable spin state is indicated by the relative spins of the electrons as indicated by the arrows in Figure 14. Inspection of the b 1 -orbital in phen •-shows that the spin density is more likely to reside on N, C(2,9), C (3,8), and C(4,7) whereas in the a 2 -orbital the spin density is likely to be found on C(2,9), C(4,7) and C(5,6), chart 1. Thus, the unpaired spin density on N is greater in the b 1 -orbital than in the a 2 -orbital.…”