Structure and Solution Behavior of Rare-Earth-Metal Complexes with Tripodal N-Donor Ligands

Rare-earth-metal complexes (Ln=Y, La, Ce, Sm and Lu) of tripodal N-donor ligands respecting the CHON principle have been synthetized and characterized. The selectivity of the ligands through the lanthanide cations was investigated and related to their donor strength.

Synthesis, Crystal Structures, and Ion Pairing of κ6 N Complexes with Rare-Earth Elements in the Solid State and in Solution

The rare earth element complexes (Ln=Y, La, Sm, Lu, Ce) of several podant κ6 N-coordinating ligands have been synthetized and thoroughly characterized. The structural properties of the complexes have been investigated by X-ray diffraction in the solid state and by advanced NMR methods in solution. To estimate the donor capabilities of the presented ligands, an experimental comparison study has been conducted by cyclic voltammetry as well as absorption experiments using the cerium complexes and by analyzing 89 Y NMR chemical shifts of the different yttrium complexes. In order to obtain a complete and detailed picture, all experiments were corroborated by state-of-the-art quantum chemical calculations. Finally, coordination competition studies have been carried out by means of 1 H and 31 P NMR spectroscopy to investigate the correlation with donor properties and selectivity.

NMR and luminescence experiments reveal the structure and symmetry adaptation of a europium ionic liquid to solvent polarity

By combining NMR data (nuclear Overhauser effect and pseudocontact shifts) with luminescence measurements, we uncover how the structure of an anionic europium complex adapts to different solvent polarities as a result of the different relative proximities of the ion pairs. In nonpolar solvents, the detected contact ion pairs, CIPs, indicate that the ions remain in proximity, with the molecular cation, and then perturbing and distorting the coordination polyhedron of the anion complex to a low symmetry configuration, which promotes luminescence. Differently, solvent separated ion pairs occur in polar solvents, indicating that the molecular ions have been disconnected. Thus, in polar solvents, the europium complex anion becomes free from the close influence of the molecular cation, allowing the coordination polyhedron to increase its symmetry, which in turn reduces the luminescence of the anionic europium complex. This reduction of coordination polyhedron symmetry by the close proximity of the molecular cation in nonpolar solvents was confirmed by additional photophysical measurements combined with quantum chemical RM1 calculations, suggesting that, in nonpolar solvents, the symmetry point group of the coordination polyhedron is C1, whereas in polar solvents it is either D2d or S4. The nonpolar solvents used were benzene, chloroform and dichloromethane; and the polar ones were acetone and acetonitrile. The synthesized ionic liquids were tetrakis [C5mim][La(BTFA)4] and [C5mim][Eu(BTFA)4], where BTFA stands for 4,4,4-trifluoro-1-phenyl-1,3-butanedione, lanthanoids (La3+ and Eu3+) and C5mim stands for 1-methyl-3-isopentylimidazolium. They were synthesized by a microwave methodology that is both fast and green (the synthetic reaction takes about 15 min) and also leads to more easily purifiable crystals.

Series of Tetravalent Actinide Amidinates: Structure Determination and Bonding Analysis

Two series of isostructural tetravalent actinide amidinates [AnX((S)-PEBA)₃] (An = Th, U, Np; X = Cl, N₃) bearing the chiral (S,S)-N,N'-bis(1-phenylethyl)benzamidinate ((S)-PEBA) ligand have been synthesized and thoroughly characterized in solid and in solution. This study expands the already reported tetravalent neptunium complexes to the lighter actinides thorium and uranium. Furthermore, a rare Ce(IV) amidinate [CeCl((S)-PEBA)₃] was synthesized to compare its properties to those of the analogous tetravalent actinide complexes. All compounds were characterized in the solid state using single-crystal XRD and infrared spectroscopy and in solution using NMR spectroscopy. Quantum chemical bonding analysis including also the isostructural Pa and Pu complexes was used to characterize the covalent contributions to any bond involving the metal cation. Th shows the least covalent character throughout the series, even substantially smaller than for the Ce complex. For U, Np, and Pu, similar covalent bonding contributions are found, but a natural population analysis reveals different origins. The 6d participation is the highest for U and decreases afterward, whereas the 5f participation increases continuously from Pa to Pu.

A Redox-Switchable Germylene and its Ligating Properties in Selected Transition Metal Complexes

The synthesis, structure, and full characterization of a redox-switchable germylene based on a [3]ferrocenophane ligand arrangement, [Fc(NMes)₂ Ge] (4), is presented. The mesityl (Mes)-substituted title compound is readily available from Fc(NHMes)₂ (2) and Ge{N(SiMe₃ )₂ }₂ , or from the dilithiated, highly air- and moisture-sensitive compound Fc(NLiMes)₂ ⋅3 Et₂ O (3) and GeCl₂ . Cyclic voltammetry studies are provided for 4, confirming the above-mentioned view of a redox-switchable germylene metalloligand. Although several 1:1 Rh^I and Ir^I complexes of 4 (5-7) are cleanly formed in solution, all attempts to isolate them in pure form failed due to stability problems. However, crystalline solids of [Mo(κ¹ Ge-4)₂ (CO)₄ ] (8) and [W(κ¹ Ge-4)₂ (CO)₄ ] (9) were isolated and fully characterized by common spectroscopic techniques (8 by X-ray diffraction). DFT calculations were performed on a series of model compounds to elucidate a conceivable interplay between the metal atoms in neutral and cationic bimetallic complexes of the type [Rh(κ¹ E-qE)(CO)₂ Cl]^0/+ (qE=[Fc(NPh)₂ E] with E=C, Si, Ge). The bonding characteristics of the coordinated Fc-based metalloligands (qE/qE⁺ ) are strongly affected upon in silico oxidation of the calculated complexes. The calculated Tolman electronic parameter (TEP) significantly increases by approximately 20 cm^-1 (E=C) to 25 cm^-1 (E=Si, Ge) upon oxidation. The change in the ligand-donating abilities upon oxidation can mainly be attributed to Coulombic effects, whereas an orbital-based interaction appears to have only a minor influence.

A new Pu(iii) coordination geometry in (C5H5NBr)2[PuCl3(H2O)5]·2Cl·2H2O as obtained via supramolecular assembly in aqueous, high chloride media

A novel hydrated Pu(iii) chloride, (C₅H₅NBr)₂[PuCl₃(H₂O)₅]·Cl·2H₂O, is prepared from aqueous media and the non-covalent interaction pairings are rationalized using electrostatic potentials.

Molecular Spin Crossover in Slow Motion: Light-Induced Spin-State Transitions in Trigonal Prismatic Iron(II) Complexes

A straightforward access is provided to iron(II) complexes showing exceedingly slow spin-state interconversion by utilizing trigonal-prismatic directing ligands (L(n)) of the extended-tripod type. A detailed analysis of the interrelations between complex structure (X-ray diffraction, density functional theory) and electronic character (SQUID magnetometry, Mössbauer spectroscopy, UV/vis spectroscopy) of the iron(II) center in mononuclear complexes [FeL(n)] reveals spin crossover to occur along a coupled breathing/torsion reaction coordinate, shuttling the complex between the octahedral low-spin state and the trigonal-prismatic high-spin state along Bailar's trigonal twist pathway. We associate both the long spin-state lifetimes in the millisecond domain close to room temperature and the substantial barriers against thermal scrambling (Ea ≈ 33 kJ mol(-1), from Arrhenius analysis) with stereochemical constraints. In particular, the topology of the κ(6)N ligands controls the temporary and structural dynamics during spin crossover.