Magnetic Properties

Edelstein, Norman M.; Lander, G. H.

doi:10.1007/978-94-007-0211-0_20

Cited by 6 publications

(10 citation statements)

References 264 publications

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“…This contribution can be suppressed under stronger magnetic fields ( H dc ≥ 1 T), such that, for example, the 300-K χ M T value at 5 T is 1.56 cm 3 ·K·mol –1 for 5 . The smaller magnitude of the experimental room temperature χ M T value for each complex relative to the calculated free-ion value is typical of actinide complexes and can be ascribed to their large magnetic anisotropies, which cause an unequal thermal population of excited crystal field states …”

Section: Resultsmentioning

confidence: 99%

Structural, Electrochemical, and Magnetic Studies of Bulky Uranium(III) and Uranium(IV) Metallocenes

et al. 2019

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Addition of the potassium salt of the bulky tetra-(isopropyl)cyclopentadienyl (Cp iPr4 ) ligand to UI 3 (1,4-dioxane) 1.5 results in the formation of the bent metallocene uranium(III) complex (Cp iPr4 ) 2 UI (1), which is then used to obtain the uranium(IV) and uraniumas mononuclear, donor-free complexes, for X − = F − , Cl − , Br − , and I − . Interestingly, reaction of 1 with chloride and cyanide salts of alkali metal ions leads to isolation of the chloride-and cyanide-bridged coordination solids [(Cp iPr4 ) 2 U(μ-Cl) 2 Cs] n (4-Cl) and [(Cp iPr4 ) 2 U(μ-CN) 2 Na(OEt 2 ) 2 ] n (4-CN). Abstraction of the iodide ligand from 1 further enables isolation of the "base-free" metallocenium cation salt [(Cp iPr4 ) 2 U][B(C 6 F 5 ) 4 ] (5) and its DME adduct [(Cp iPr4 ) 2 U(DME)][B(C 6 F 5 ) 4 ] (5-DME). Solid-state structures of all of the compounds, determined by X-ray crystallography, facilitate a detailed analysis of the effect of changing oxidation state or halide ligand on the molecular structure. NMR spectroscopy, X-ray crystallography, cyclic voltammetry, and UV−visible spectroscopy studies of 2-X and 3-X further reveal that the difluoride species in both series exhibit properties that differ significantly from trends observed among the other dihalides, such as a substantial negative shift in the potential of the [(Cp iPr4 ) 2 UX 2 ] uranium(III/IV) redox couple. Magnetic characterization of 1 and 5 reveals that both compounds exhibit slow magnetic relaxation of molecular origin under applied magnetic fields; this process is dominated by a Raman relaxation mechanism.

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Section: Resultsmentioning

confidence: 99%

Structural, Electrochemical, and Magnetic Studies of Bulky Uranium(III) and Uranium(IV) Metallocenes

et al. 2019

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“… 71 − 73 The value of the trimethylsiloxide derivative 4 is similar to that of other R 3 SiO-ligated uranium complexes, U(OSiBu 3 t ) 4 (2.83 μ B ) and U(OSiMe 3 ) 2 I 2 (bipy) 2 (bipy = 2,2′-bipyridine) (2.7 μ B ). 65 , 74 To account for these increases, and the strongly paramagnetically shifted 31 P chemical shifts for 4 and 5 , we compared the composition of the two f-based NLMOs for the iodide ( 3–Ni ) and fluoride ( 5 ) to look for different U 5f contributions that would lead to larger paramagnetic shifts for the Ni-bound atoms. For the iodide, they are 99.18% U (99.56% 5f) and 94.81% U (97.24 5f, 2.05 s, 1.75% total contribution from P) (see also Table S4 of the SI for a comparison of the predominantly Ni d-σ and π NLMOs).…”

Section: Synthesismentioning

confidence: 99%

Metal–Metal Bonding in Uranium–Group 10 Complexes

et al. 2016

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Heterobimetallic complexes containing short uranium–group 10 metal bonds have been prepared from monometallic IUIV(OArP-κ2O,P)3 (2) {[ArPO]− = 2-tert-butyl-4-methyl-6-(diphenylphosphino)phenolate}. The U–M bond in IUIV(μ-OArP-1κ1O,2κ1P)3M0, M = Ni (3–Ni), Pd (3–Pd), and Pt (3–Pt), has been investigated by experimental and DFT computational methods. Comparisons of 3–Ni with two further U–Ni complexes XUIV(μ-OArP-1κ1O,2κ1P)3Ni0, X = Me3SiO (4) and F (5), was also possible via iodide substitution. All complexes were characterized by variable-temperature NMR spectroscopy, electrochemistry, and single crystal X-ray diffraction. The U–M bonds are significantly shorter than any other crystallographically characterized d–f-block bimetallic, even though the ligand flexes to allow a variable U–M separation. Excellent agreement is found between the experimental and computed structures for 3–Ni and 3–Pd. Natural population analysis and natural localized molecular orbital (NLMO) compositions indicate that U employs both 5f and 6d orbitals in covalent bonding to a significant extent. Quantum theory of atoms-in-molecules analysis reveals U–M bond critical point properties typical of metallic bonding and a larger delocalization index (bond order) for the less polar U–Ni bond than U–Pd. Electrochemical studies agree with the computational analyses and the X-ray structural data for the U–X adducts 3–Ni, 4, and 5. The data show a trend in uranium–metal bond strength that decreases from 3–Ni down to 3–Pt and suggest that exchanging the iodide for a fluoride strengthens the metal–metal bond. Despite short U–TM (transition metal) distances, four other computational approaches also suggest low U–TM bond orders, reflecting highly transition metal localized valence NLMOs. These are more so for 3–Pd than 3–Ni, consistent with slightly larger U–TM bond orders in the latter. Computational studies of the model systems (PH3)3MU(OH)3I (M = Ni, Pd) reveal longer and weaker unsupported U–TM bonds vs 3.

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“…Since uranium has several common paramagnetic oxidation states, i.e., 5f 1 U 5+ , 5f 2 U 4+ , and 5f 3 U 3+ , one of the analytical methods commonly used for characterizing uranium complexes is measurement of magnetic susceptibilities. − A variety of solid state and solution methods have been used to obtain magnetic data on uranium complexes under different conditions at both room and low temperature, and data are often cited to support the assignment of oxidation state. Statements like “the magnetic moment of compound X is consistent with U n + ” are common in uranium papers.…”

Section: Introductionmentioning

confidence: 99%

“…However, it has been pointed out repeatedly in the literature − ,,,− that evaluating the magnetic susceptibility of uranium complexes is not as straightforward as it is for transition metal and lanthanide complexes. For any metal complex, the magnetic moment arises from the sum of the contributions of the ground state and the low-lying thermally accessible excited states as well as any temperature-independent magnetism in the system.…”

Section: Introductionmentioning

confidence: 99%

“…The actinides are intermediate between lanthanides and transition metals in the sense that the greater radial extension of the 5f orbitals means that ligand field effects cannot be ignored, yet spin–orbit coupling is large. − ,,,− In a case where two effects can be comparable, finding a simple model is usually more difficult. Neither the spin-only μ S approximation used for transition metals nor the total angular momentum μ J approximation used for the lanthanides is adequate for uranium, although μ J is often used as an approximate starting point.…”

Section: Introductionmentioning

confidence: 99%

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