Treatment of cerous Cp R 3 Ce(thf) (Cp R = C 5 H 4 R; R = H, Me) with the halogenating reagents C 2 Cl 6 , TeBr 4 , and I 2 afforded the ceric halides Cp R 3 CeX (X = Cl, Br, I) in high yield. Subsequent salt metathesis with sodium alkoxides and siloxides led to a series of alkoxy and siloxy derivatives. Compounds Cp R 3 CeOR′ with R′ = Me, Et, CH 2 tBu, iPr, tBu, SiMe 3 , SiEt 3 , Si(iPr) 3 SiPh 3 (and Si(OtBu) 3 ) have been isolated and characterized by 1 H, 13 C, and 29 Si NMR and DRIFT spectroscopy, magnetic measurements, X-ray structure analyses, cyclic voltammetry, and elemental analyses. The ceric complexes Cp R 3 CeX and Cp R 3 CeOR′ are isostructural, featuring terminal ligands X and OR′. The magnetic measurements revealed temperature-independent paramagnetism (TIP), with positive magnetic susceptibilities in the range χ 0 (1.53−3.9) × 10 −4 emu/mol. Cyclic voltammetry indicated two types of redox processes: (a) chemical and electrochemical reversibility for halide and siloxide complexes and (b) EC-or ECE-type mechanisms for the alkoxides (chemical reversibility at high scan rates). In all cases formal potentials could be determined ranging from −0.583 V vs Fc/Fc + for Cp 3 CeI to −1.259 V vs Fc/Fc + for Cp Me 3 Ce(OEt). The electrochemical data revealed an increase in stabilization with respect to reduction of the cerium(IV) center in the series I < Br < Cl < siloxy < alkoxy ligand and a better stabilization with Cp Me in comparison to Cp ligands by approximately 0.05−0.1 V. As a result, an improved stabilization of Ce(IV) was observed for more strongly electron donating ligands.

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We investigate pressure-induced structural changes to the Peierls-type distorted low-temperature phase of the low-dimensional Sc 3 CoC 4 as a possible origin of its pressure-enhanced superconductivity. By means of cryogenic high-pressure x-ray diffraction experiments we could reveal subtle, but significant structural differences between the low-temperature phase at ambient and elevated pressures. We could thus establish the structure of the superconducting phase of the title compound, which interestingly still shows the main features of the Peierls-type distorted low-temperature phase. This indicates that in contrast to other low-dimensional materials a suppression of periodic structural distortions is no prerequisite for superconductivity in the transition-metal carbide.

Single-crystal cryogenic X-ray diffraction at 6 K, electron paramagnetic resonance spectroscopy, and correlated electronic structure calculations are combined to shed light on the nature of the metal−tris(aryloxide) and η 2 −H, C metal−alkane interactions in the [(( t•Bu ArO) 3 tacn)U III ( Me cy-C6)]•( Me cy-C6) adduct. An analysis of the ligand field experienced by the uranium center using ab initio ligand field theory in combination with the angular overlap model yields rather unusual U−O ArO and U−N tacn bonding parameters for the metal−tris(aryloxide) interaction. These parameters are incompatible with the concept of σ and π metal−ligand overlap. For that reason, it is deduced that metal− ligand bonding in the [(( t•Bu ArO) 3 tacn)U III ] moiety is predominantly ionic. The bonding interaction within the [(( t•Bu ArO) 3 tacn)-U III ] moiety is shown to be dispersive in nature and essentially supported by the upper-rim t Bu groups of the ( t•Bu ArO) 3 tacn 3− ligand.Our findings indicate that the axial alkane molecule is held in place by the guest−host effect rather than direct metal−alkane ionic or covalent interactions.