Octahedral complexes of uranium(IV). II. Magnetic and spectral effects of tetragonal distortion

Lane, Bruce; Venanzi, L. M.

doi:10.1016/s0020-1693(00)92487-3

Cited by 28 publications

(5 citation statements)

References 13 publications

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“…37 Applying the Boltzmann distribution, a state energy gap of ~125 cm -1 can be expected. [37][38] As with the other complexes, χT of 6 is strongly temperature dependent at 300 K, which is consistent with the large crystal field splitting observed in its NIR spectrum. On the other hand, the structure of 7 is quite similar to that of 3 and could be a useful diamagnetic substitute if one can account for the susceptibility of the U IV center.…”

supporting

confidence: 81%

“…To estimate the energy gap between the ground and excited states, it is assumed that an excited-state population of less than 5% leads to no change in magnetic susceptibility . When the Boltzmann distribution is applied, a state energy gap of ∼125 cm –1 can be expected. , …”

Section: Results and Discussionmentioning

confidence: 99%

“…37 When the Boltzmann distribution is applied, a state energy gap of ∼125 cm −1 can be expected. 37,38 The free-ion ground state for U IV is 3 H 4 , which is split by the ligand field into three non-Kramers doublet states and one singlet state. The singlet state has a g value of zero and displays only TIP, which is consistent with the ground-state magnetic susceptibility observed for 3.…”

Section: ■ Introductionmentioning

confidence: 99%

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Molecular and Electronic Structure of Dinuclear Uranium Bis-μ-Oxo Complexes with Diamond Core Structural Motifs

et al. 2014

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In a multiple-bond metathesis reaction, the triazacyclononane (tacn)-anchored methyl- and neopentyl (nP)-substituted tris(aryloxide) U(III) complex [(((nP,Me)ArO)3tacn)U(III)] (1) reacts with mesityl azide and CO2 to form mesityl isocyanate and the dinuclear bis(μ-oxo)-bridged U(V)/U(V) complex [{(((nP,Me)ArO)3tacn)U(V)}2(μ-O)2] (3). This reaction proceeds via the mononuclear U(V) imido intermediate [(((nP,Me)ArO)3tacn)U(V)(NMes)] (2), which has been synthesized and fully characterized independently. The dimeric U(V) oxo species shows rich redox behavior: complex 3 can be reduced by one and two electrons, respectively, yielding the mixed-valent U(IV)/U(V) bis(μ-oxo) complex [K(crypt)][{(((nP,Me)ArO)3tacn)U(IV/V)}2(μ-O)2] (7) and the U(IV)/U(IV) bis(μ-oxo) complex K2[{(((nP,Me)ArO)3tacn)U(IV)}2(μ-O)2] (6). In addition, complex 3 can be oxidized to provide the mononuclear uranium(VI) oxo complexes [(((nP,Me)ArO)3tacn)U(VI)(O)eq(OTf)ax] (8) and [(((nP,Me)ArO)3tacn)U(VI)(O)eq]SbF6 (9). The unique series of bis(μ-oxo) complexes also shows notable magnetic behavior, which was investigated in detail by UV/vis/NIR and EPR spectroscopy as well as SQUID magnetization studies. In order to understand possible magnetic exchange phenomena, the mononuclear terminal oxo complexes [(((nP,Me)ArO)3tacn)U(V)(O)(O-pyridine)] (4) and [(((nP,Me)ArO)3tacn)U(V)(O)(O-NMe3)] (5) were synthesized and fully characterized. The magnetic study revealed an unusually strong antiferromagnetic exchange coupling between the two U(V) ions in 3. Examination of the (18)O-labeled bis(μ-oxo)-bridged dinuclear complexes 3, 6, and 7 allowed for the first time the unambiguous assignment of the vibrational signature of the [U(μ-O)2U] diamond core structural motif.

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confidence: 81%

Section: Results and Discussionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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Molecular and Electronic Structure of Dinuclear Uranium Bis-μ-Oxo Complexes with Diamond Core Structural Motifs

et al. 2014

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“…103 A similar rationale has been invoked to explain the magnetic behavior of UBr 4 (Et 3 AsO) 2 , which exhibits a large tetragonal distortion and possibly an e ground state. 101,104 Comparable low-temperature behavior with 2 and 3 has also been observed in another U(IV) complex, namely (( tBu ArO) 3 tacn)-U(OC tBu Ph 2 ); 100 however this complex possesses a ligandcentered radical, in addition to the paramagnetic U(IV) center. It should be noted, however, that this qualitative model is probably one of many that could describe the magnetic behavior of these alkyl complexes, and as such further experimental and theoretical studies will be required to fully understand the origins of their magnetic properties.…”

Section: Resultsmentioning

confidence: 89%

Homoleptic Uranium(IV) Alkyl Complexes: Synthesis and Characterization

et al. 2009

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The addition of 4.5 equiv of LiCH(2)SiMe(3) to [Li(THF)](2)[U(O(t)Bu)(6)], in the presence of LiCl, results in the formation of the homoleptic uranium(IV) alkyl complex [Li(14)(O(t)Bu)(12)Cl][U(CH(2)SiMe(3))(5)] (1) in low yield. Complex 1 has been characterized by X-ray crystallography. As a solid, 1 is thermally stable for several days at room temperature. However, 1 rapidly decomposes in C(6)D(6), as indicated by (1)H and (7)Li{(1)H} NMR spectroscopy, owing to the lability of the [Li(14)(O(t)Bu)(12)Cl](+) cation. To avoid the formation of the [Li(14)(O(t)Bu)(12)Cl](+) counterion, alkylation of UCl(4) was investigated. Treatment of UCl(4) with 5 equiv of LiCH(2)SiMe(3) or LiCH(2)(t)Bu at -25 degrees C in THF/Et(2)O affords [Li(DME)(3)][U(CH(2)SiMe(3))(5)] (2) and [Li(THF)(4)][U(CH(2)(t)Bu)(5)] (3), respectively, in good yields. Similarly, treatment of UCl(4) with 6 equiv of MeLi or KCH(2)C(6)H(5) generates the U(IV) hexa(alkyl) complexes [Li(TMEDA)](2)[UMe(6)] (4) and {[K(THF)](3)[K(THF)(2)][U(CH(2)C(6)H(5))(6)](2)}(x) (5) in 38% and 70% yields, respectively. The structures of 3-5 have been confirmed by X-ray crystallography. Complexes 2, 3, and 5 are thermally stable solids which can be stored at room temperature for several days, whereas 4 decomposes upon warming above -25 degrees C. The electronic and magnetic properties of 2, 3, and 5 were also investigated by NIR spectroscopy and SQUID magnetometry.

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“…The TIP (χ TIP = 7.7 × 10 –4 emu K mol –1 at 300 K) dictates the susceptibility and ultimately leads to the lower than anticipated room temperature magnetic moment . Temperature-independent susceptibility over such a wide range has been observed previously for U 4+ in octahedral tetrahalide systems incorporating strongly donating amide, phosphine oxide, and arsine oxide ligands. , In the absence of thermally accessible excited states, the observed paramagnetic susceptibility arises from field-induced mixing of the ground state with a higher-spin excited state. For 2 , the persistence of linearity in χ M T versus T as high as 340 K (Figure S4, Supporting Information) reveals that, even at this temperature, excited states remain thermally inaccessible, and the observed susceptibility can be ascribed to field-induced mixing of the singlet ground state with a paramagnetic excited state.…”

Section: Resultsmentioning

confidence: 99%

Synthesis, Structure, and Magnetism of an f Element Nitrosyl Complex, (C₅Me₄H)₃UNO

et al. 2011

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(C(5)Me(4)H)(3)U, 1, reacts with 1 equiv of NO to form the first f element nitrosyl complex (C(5)Me(4)H)(3)UNO, 2. X-ray crystallography revealed a 180° U-N-O bond angle, typical for (NO)(1+) complexes. However, 2 has a 1.231(5) Å N═O distance in the range for (NO)(1-) complexes and a short 2.013(4) Å U-N bond like the U═N bond of uranium imido complexes. Structural, spectroscopic, and magnetic data as well as DFT calculations suggest that reduction of NO by U(3+) has occurred to form a U(4+) complex of (NO)(1-) that has π interactions between uranium 5f orbitals and NO π* orbitals. These bonding interactions account for the linear geometry and short U-N bond. The complex displays temperature-independent paramagnetism with a magnetic moment of 1.36 μ(B) at room temperature. Complex 2 reacts with Al(2)Me(6) to form the adduct (C(5)Me(4)H)(3)UNO(AlMe(3)), 3.

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Octahedral complexes of uranium(IV). II. Magnetic and spectral effects of tetragonal distortion

Cited by 28 publications

References 13 publications

Molecular and Electronic Structure of Dinuclear Uranium Bis-μ-Oxo Complexes with Diamond Core Structural Motifs

Molecular and Electronic Structure of Dinuclear Uranium Bis-μ-Oxo Complexes with Diamond Core Structural Motifs

Homoleptic Uranium(IV) Alkyl Complexes: Synthesis and Characterization

Synthesis, Structure, and Magnetism of an f Element Nitrosyl Complex, (C₅Me₄H)₃UNO

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Octahedral complexes of uranium(IV). II. Magnetic and spectral effects of tetragonal distortion

Cited by 28 publications

References 13 publications

Molecular and Electronic Structure of Dinuclear Uranium Bis-μ-Oxo Complexes with Diamond Core Structural Motifs

Molecular and Electronic Structure of Dinuclear Uranium Bis-μ-Oxo Complexes with Diamond Core Structural Motifs

Homoleptic Uranium(IV) Alkyl Complexes: Synthesis and Characterization

Synthesis, Structure, and Magnetism of an f Element Nitrosyl Complex, (C5Me4H)3UNO

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Synthesis, Structure, and Magnetism of an f Element Nitrosyl Complex, (C₅Me₄H)₃UNO