RESUMEN
Traditional models of lanthanide electronic structure suggest that bonding is predominantly ionic, and that covalent orbital mixing is not an important factor in determining magnetic properties. Here, 4f orbital mixing and its impact on the magnetic susceptibility of Cp'3Eu (Cp' = C5H4SiMe3) was analyzed experimentally using magnetometry and X-ray absorption spectroscopy (XAS) methods at the C K-, Eu M5,4-, and L3-edges. Pre-edge features in the experimental and TDDFT-calculated C K-edge XAS spectra provided unequivocal evidence of C 2p and Eu 4f orbital mixing in the π-antibonding orbital of a' symmetry. The charge-transfer configurations resulting from 4f orbital mixing were identified spectroscopically by using Eu M5,4-edge and L3-edge XAS. Modeling of variable-temperature magnetic susceptibility data showed excellent agreement with the XAS results and indicated that increased magnetic susceptibility of Cp'3Eu is due to removal of the degeneracy of the 7F1 excited state due to mixing between the ligand and Eu 4f orbitals.
RESUMEN
Ni-catalyzed C-H functionalization reactions are becoming efficient routes to access a variety of functionalized arenes, yet the mechanisms of these catalytic C-C coupling reactions are not well understood. Here, we report the catalytic and stoichiometric arylation reactions of a nickel(II) metallacycle. Treatment of this species with silver(I)-aryl complexes results in facile arylation, consistent with a redox transmetalation step. Additionally, treatment with electrophilic coupling partners generates C-C and C-S bonds. We anticipate that this redox transmetalation step may be relevant to other coupling reactions that employ silver salts as additives.
RESUMEN
New coordination environments are reported for Np(III) and Pu(III) based on pilot studies of U(III) in 2.2.2-cryptand (crypt). The U(III)-in-crypt complex, [U(crypt)I2][I], obtained from the reaction between UI3 and crypt, is treated with Me3SiOTf (OTf = O3SCF3) in benzene to form the [U(crypt)(OTf)2][OTf] complex. Similarly, the isomorphous Np(III) and Pu(III) complexes were obtained similarly starting from [AnI3(THF)4]. All three complexes (1-An; An = U, Np, Pu) contain an encapsulated actinide in a THF-soluble complex. Absorption spectroscopy and DFT calculations are consistent with 5f3 U(III), 5f4 Np(III), and 5f5 Pu(III) electron configurations.
RESUMEN
The capacity of X-ray photoelectron spectroscopy (XPS) to provide information on the electronic structure of molecular organometallic complexes of Ln(II) ions (Ln = lanthanide) has been examined for the first time. XPS spectra were obtained on the air-sensitive molecular trivalent 4fn Cp'3LnIII complexes (Ln = Sm, Eu, Gd, Tb; Cp' = C5H4SiMe3) and compared to those of the highly reactive divalent complexes, [K(crypt)][Cp'3LnII] (crypt = 2.2.2-cryptand), which have either 4fn+1 (Sm, Eu) or 4fn5d1 electron configurations (Gd, Tb). The Ln 4d, Si 2p, and C 1s regions of the Ln(III) and Ln(II) complexes were identified and compared. The metal 4d peaks of these molecular lanthanide complexes were used diagnostically to compare oxidation states. The valence region of the Gd(III) and Gd(II) complexes was also examined with XPS and density function theory/random phase approximation (DFT/RPA) calculations, and this led to the tentative assignment of a signal from the 5d1 electron consistent with a 4f75d1 electron configuration for Gd(II).
RESUMEN
The electrochemical properties of U(III)-in-crypt (crypt = 2.2.2-cryptand) were examined in dimethylformamide (DMF) and acetonitrile (MeCN) to determine the oxidative stability offered by crypt as a ligand. Cyclic voltammetry revealed a U(III)/U(IV) irreversible oxidation at EPA= -0.49 V (vs Fe(C5H5)2+/0) in DMF and at EPA= -0.31 V (vs Fe(C5H5)2+/0) in MeCN. The electrochemistry of U(III)-in-crypt complexes in the presence of water was also examined. These studies are supported by crystallographically characterized examples of U(III)-in-crypt complexes as DMF, MeCN, and water adducts.
RESUMEN
Lanthanide triflates have been used to incorporate NdIII and SmIII ions into the 2.2.2-cryptand ligand (crypt) to explore their reductive chemistry. The Ln(OTf)3 complexes (Ln=Nd, Sm; OTf=SO3 CF3 ) react with crypt in THF to form the THF-soluble complexes [LnIII (crypt)(OTf)2 ][OTf] with two triflates bound to the metal encapsulated in the crypt. Reduction of these LnIII -in-crypt complexes using KC8 in THF forms the neutral LnII -in-crypt triflate complexes [LnII (crypt)(OTf)2 ]. DFT calculations on [NdII (crypt)]2+ ], the first NdII cryptand complex, assign a 4f4 electron configuration to this ion.