Uranocenium: Synthesis,Structure, and Chemical Bonding

Abstraction of iodide from [(η⁵‐C₅ⁱPr₅)₂UI] ( 1 ) produced the cationic uranium(III) metallocene [(η⁵‐C₅ⁱPr₅)₂U]⁺ ( 2 ) as a salt of [B(C₆F₅)₄]^?. The structure of 2 consists of unsymmetrically bonded cyclopentadienyl ligands and a bending angle of 167.82° at uranium. Analysis of the bonding in 2 showed that the uranium 5f orbitals are strongly split and mixed with the ligand orbitals, thus leading to non‐negligible covalent contributions to the bonding. Investigation of the dynamic magnetic properties of 2 revealed that the 5f covalency leads to partially quenched anisotropy and fast magnetic relaxation in zero applied magnetic field. Application of a magnetic field leads to dominant relaxation by a Raman process.     

Synthesis and Characterization of a Uranium(II) Monoarene Complex Supported by δ Backbonding

The low‐temperature (Ad,MeArO)₃mes}U] ( 1 ), with potassium spheres in the presence of a slight excess of 2.2.2‐cryptand, affords the quantitative conversion of 1 into the uranium(II) monoarene complex [K(2.2.2‐crypt)][((^Ad,MeArO)₃mes)U] ( 1‐K ). The molecular and electronic structure of 1‐K was established experimentally by single‐crystal X‐ray diffraction, variable‐temperature ¹H NMR and X‐band EPR spectroscopy, solution‐state and solid‐state magnetism studies, and optical absorption spectroscopy. The electronic structure of the complex was further investigated by DFT calculations. The complete body of evidence confirms that 1‐K is a uranium(II) monoarene complex with a 5f ⁴ electronic configuration supported by δ backbonding and that the nearly reversible, room‐temperature reduction observed for 1 at ?2.495 V vs. Fc/Fc⁺ is principally metal‐centered.     

Experimental and Computational Studies on a Base-Free Terminal Uranium Phosphinidene Metallocene

The first stable base-free terminal uranium phosphinidene metallocene is presented; and its structure and reactivity have been studied in detail and compared to that of the corresponding thorium derivative. Salt metathesis reaction of the methyl iodide uranium metallocene Cp’’’₂U(I)Me ( 2 , Cp’’’=η⁵-1,2,4-(Me₃C)₃C₅H₂) with Mes*PHK (Mes*=2,4,6-(Me₃C)₃C₆H₂) in THF yields the base-free terminal uranium phosphinidene metallocene, Cp’’’₂U=PMes* ( 3 ). In addition, density functional theory (DFT) studies suggest substantial 5f orbital contributions to the bonding within the uranium phosphinidene [U]=PAr moiety, which results in a more covalent bonding between the [Cp’’’₂U]²⁺ and [Mes*P]²⁻ fragments than that for the related thorium derivative. This difference in bonding besides steric reasons causes different reactivity patterns for both molecules. Therefore, the uranium derivative 3 may act as a Cp’’’₂U(II) synthon releasing the phosphinidene moiety (Mes*P:) when treated with alkynes or a variety of hetero-unsaturated molecules such as imines, thiazoles, ketazines, bipy, organic azides, diazene derivatives, ketones, and carbodiimides.     

Isolation of a Uranium(III)-Carbon Multiple Bond Complex

Low-valent uranium-element multiple bond complexes remain scarce, though there is burgeoning interest regarding to their bonding and reactivity. Herein, isolation of a uranium(III)-carbon double bond complex [(Cp*)₂U(CDP)](BPh₄) ( 1 ) comprising a tridentate carbodiphosphorane (CDP) was reported for the first time. Oxidation of 1 afforded the corresponding U(IV) complex [(Cp*)₂U(CDP)](BPh₄)₂ ( 2 ). The distance between U and C in 2 is 2.481 Å, indicating the existence of a typical U=C double bond, which is further confirmed by quantum chemical calculations. Bonding analysis suggested that the CDP also serves as both σ- and π-donor in complex 1 , though a longer U−C bond (2.666(3) Å) is observed. It implies that 1 is the first isolable mononuclear uranium(III) carbene complex. Moreover, these results suggest that CDPs are promising ligands to establish other low-valent f-block metal-carbon multiple bond complexes.     

Challenging the Metallocene Dominance in Actinide Chemistry with a Soft PNP Pincer Ligand: New Uranium Structures and Reactivity Patterns

A soft embrace for U : Replacement of C₅Me₅ by the soft PNP pincer ligand is a successful strategy to promote new reactivities and support new structures for the actinide series (see picture, py–O=pyridine‐N‐oxide). The specific electronic and steric properties of the PNP ligand enable access to previously unreported structures not available for the C₅Me₅ ligand set and support not only low‐valent uranium but also the high‐valent uranium(VI) ion.

     

Spectroscopic Determination of the Electronic Structure of a Uranium Single-Ion Magnet

Early actinide ions have large spin-orbit couplings and crystal field interactions, leading to large anisotropies. The success in using actinides as single-molecule magnets has so far been modest, underlining the need for rational strategies. Indeed, the electronic structure of actinide single-molecule magnets and its relation to their magnetic properties remains largely unexplored. A uranium(III) single-molecule magnet, [U^III{SiMe₂NPh}₃-tacn)(OPPh₃)] (tacn=1,4,7-triazacyclononane), has been investigated by means of a combination of magnetic, spectroscopic and theoretical methods to elucidate the origin of its static and dynamic magnetic properties.     

Synthesis and Insertion Chemistry of Mixed Tether Uranium Metallocene Complexes

The synthesis of mixed tethered alkyl uranium metallocenes has been investigated by examining the reactivity of the bis(tethered alkyl) metallocene [(η⁵‐C₅Me₄SiMe₂CH₂‐κC)₂U] ( 1 ) with substrates that react with only one of the U? C linkages. The effect of these mixed tether coordination environments on the reactivity of the remaining U? C bond has been studied by using CO insertion chemistry. One equivalent of azidoadamantane (AdN₃) reacts with 1 to yield the mixed tethered alkyl triazenido complex [(η⁵‐C₅Me₄SiMe₂CH₂‐κC)U(η⁵‐C₅Me₄SiMe₂‐CH₂NNN‐Ad‐κ²N^1,3)]. Similarly, a single equivalent of CS₂ reacts with 1 to form the mixed tethered alkyl dithiocarboxylate complex [(η⁵‐C₅Me₄SiMe₂CH₂‐κC)U(η⁵‐C₅Me₄SiMe₂‐ CH₂C(S)₂‐κ²S,S′)], a reaction that constitutes the first example of CS₂ insertion into a U⁴⁺? C bond. Complex 1 reacts with one equivalent of pyridine N‐oxide by C? H bond activation of the pyridine ring to form a mixed tethered alkyl cyclometalated pyridine N‐oxide complex [(η⁵‐C₅Me₄SiMe₂CH₂‐κC)(η⁵‐C₅Me₄SiMe₃)U(C₆H₄NO‐κ²C,O)]. The remaining (η⁵‐C₅Me₄SiMe₂CH₂‐κC)^2? ligand in each of these mixed tethered species show reactivity towards CO and tethered enolate ligands form by insertion. Subsequent rearrangement have been identified in [(η⁵‐C₅Me₄SiMe₃)U(C₅H₄NO‐κ²C,O)(η⁵‐C₅Me₄SiMe₂C(?CH₂)O‐κO)] and [(η⁵‐C₅Me₄SiMe₂CH₂NNN‐Ad‐κ²N^1,3)U(η⁵‐C₅Me₄SiMe₂C(?CH₂)O‐κO)].     

Inside Cover: Challenging the Metallocene Dominance in Actinide Chemistry with a Soft PNP Pincer Ligand: New Uranium Structures and Reactivity Patterns (Angew. Chem. Int. Ed. 20/2009)

A standing iceberg illustrates how the soft PNP pincer ligand challenges the metallocene dominance (ship) in actinide chemistry, as described by J. L. Kiplinger and co‐workers in their Communication on page 3681 ff. Replacement of C₅Me₅ by the PNP ligand is a successful strategy for the promotion of new reactivities and to support new actinide structures. The specific electronic and steric properties of the PNP ligand enable access to structures not available for the C₅Me₅ ligand set and as yet unreported for uranium. (We thank Mr. Anthony Mancinco for the design of the graphic.)

     

Investigation of Uranium Tris(imido) Complexes: Synthesis,Characterization, and Reduction Chemistry of [U(NDIPP)3(thf)3]

Addition of KC₈ to trivalent [UI₃(thf)₄] in the presence of three equivalents of 2,6‐diisopropylphenylazide (N₃DIPP) results in the formation of the hexavalent uranium tris(imido) complex [U(NDIPP)₃(thf)₃] ( 1 ) through a facile, single‐step synthesis. The X‐ray crystal structure shows an octahedral complex that adopts a facial orientation of the imido substituents. This structural trend is maintained during the single‐electron reduction of 1 to form dimeric [U(NDIPP)₃{K(Et₂O)}]₂ ( 2 ). Variable‐temperature/field magnetization studies of 2 show two independent U^V 5f ¹ centers, with no antiferromagnetic coupling present. Characterization of these complexes was accomplished using single‐crystal X‐ray diffraction, variable‐temperature ¹H NMR spectroscopy, as well as IR and UV/Vis absorption spectroscopic studies.     

铀的复合吸附材料

铀是重要核燃料资源,也是放射性废液中主要的污染元素之一。铀的吸附涉及到溶液中铀的提取、含铀废水的处理和铀元素化学分析的预富集等。本文从有机官能团化学键合修饰基体的复合材料出发,从基体和有机官能团两方面对溶液中的铀的吸附行为进行了综述,分析了各种官能团所适用的水相pH值、对铀的吸附量和选择性。含有机磷类官能团的复合材料具有pH适用范围广、吸附量和选择性较好的优点,是一种具有良好发展前景的铀复合吸附剂。     

铼(Ⅲ)三核氯化物[Re3(μ2-Cl)3Cl6+n]n-的电子结构与化学键

本文用EHMO法计算铼(Ⅲ)三核氯化物[Re₃(μ₂—Cl)₃Cl_6+n)^n-(n=0,1,2,3,)的分子轨道系数,能级相关图和占据轨道成分。结果表明,Re-Re之间的成键数都是2,铼原子的成键价轨道数有8和9两种情况。应用(nxcπ)结构规则分析这一系列分子的结构与成键能力,得到的结论与理论结果以及实验事实一致。讨论了Re₃Cl₉与平面配位氯原子的结合形式。     

A Mononuclear Uranium(IV) Single‐Molecule Magnet with an Azobenzene Radical Ligand

A tetravalent uranium compound with a radical azobenzene ligand, namely, [{(SiMe₂NPh)₃‐tacn}U^IV(η²‐N₂Ph₂^.)] ( 2 ), was obtained by one‐electron reduction of azobenzene by the trivalent uranium compound [U^III{(SiMe₂NPh)₃‐tacn}] ( 1 ). Compound 2 was characterized by single‐crystal X‐ray diffraction and ¹H NMR, IR, and UV/Vis/NIR spectroscopy. The magnetic properties of 2 and precursor 1 were studied by static magnetization and ac susceptibility measurements, which for the former revealed single‐molecule magnet behaviour for the first time in a mononuclear U^IV compound, whereas trivalent uranium compound 1 does not exhibit slow relaxation of the magnetization at low temperatures. A first approximation to the magnetic behaviour of these compounds was attempted by combining an effective electrostatic model with a phenomenological approach using the full single‐ion Hamiltonian.     

两个包含联苯三羧酸配体的铜(II)和锰(II)配合物的合成、晶体结构及磁性质

采用水热方法,用联苯三羧酸配体(H3dppa)和4,4′-联吡啶(4,4′-bipy)分别与CuCl_2·2H_2O和MnCl_2·4H_2O反应,合成了一个具有零维双核铜结构的配合物[Cu_2(Hdppa)_2(4,4′-bipy)(H_2O)_4]·4,4′-bipy·6H_2O(1)和一个基于双螺旋链单元的三维配位聚合物{[Mn_3(μ_5-dppa)_2(4,4′-bipy)(H_2O)_2]·4H_2O}_n(2),并对其结构和磁性质进行了研究。结构分析结果表明2个配合物分别属于三斜和单斜晶系,P1和C2/c空间群。配合物1具有零维双核铜结构,而且这些双核铜单元通过O-H…O/N氢键作用进一步形成了三维超分子框架。而配合物2中存在一个双螺旋锰链单元,这些锰链单元又通过配体进一步连接成了三维结构。研究表明,配合物2中相邻锰离子间存在反铁磁相互作用。     

Magnetization Slow Dynamics in Ferrocenium Complexes

The single-molecule magnet (SMM) properties of a series of ferrocenium complexes, [Fe(η⁵-C₅R₅)₂]⁺ (R=Me, Bn), are reported. In the presence of an applied dc field, the slow dynamics of the magnetization in [Fe(η⁵-C₅Me₅)₂]BAr_F are revealed. Multireference quantum mechanical calculations show a large energy difference between the ground and first excited states, excluding the commonly invoked, thermally activated (Orbach-like) mechanism of relaxation. In contrast, a detailed analysis of the relaxation time highlights that both direct and Raman processes are responsible for the SMM properties. Similarly, the bulky ferrocenium complexes, [Fe(η⁵-C₅Bn₅)₂]BF₄ and [Fe(η⁵-C₅Bn₅)₂]PF₆, also exhibit magnetization slow dynamics, however an additional relaxation process is clearly detected for these analogous systems.     

Synthesis,Characterization, and Reactivity of a Uranium(VI) Carbene Imido Oxo Complex

We report the uranium(VI) carbene imido oxo complex [U(BIPM^TMS)(NMes)(O)(DMAP)₂] ( 5 , BIPM^TMS=C(PPh₂NSiMe₃)₂; Mes=2,4,6‐Me₃C₆H₂; DMAP=4‐(dimethylamino)pyridine) which exhibits the unprecedented arrangement of three formal multiply bonded ligands to one metal center where the coordinated heteroatoms derive from different element groups. This complex was prepared by incorporation of carbene, imido, and then oxo groups at the uranium center by salt elimination, protonolysis, and two‐electron oxidation, respectively. The oxo and imido groups adopt axial positions in a T‐shaped motif with respect to the carbene, which is consistent with an inverse trans‐influence. Complex 5 reacts with tert‐butylisocyanate at the imido rather than carbene group to afford the uranyl(VI) carbene complex [U(BIPM^TMS)(O)₂(DMAP)₂] ( 6 ).     

解密铀元素

简介了铀元素的发现历史、基本核性质、独特的电子结构以及相关的配位化学性质;同时,还介绍了铀元素在核燃料、分子催化、单分子磁体、超导等方面的应用。     

铀氮化物晶体结构及电子结构

铀氮化物因其独特的物理化学性质及优良的性能而成为核燃料循环系统中重要的燃料材料,是核领域的研究热点材料之一。此外,铀氮化物也被用作抗腐蚀涂层材料,在金属铀的表面腐蚀防护领域具有重要的应用价值。在铀-氮体系中,五种结构铀氮化物,包括NaCl型UN、HgIn型UN、Mn₂O₃型α-U₂N₃、La₂O₃型β-U₂N₃和CaF₂型UN₂,已经被确认并进行了广泛研究。但是到目前为止,由于铀氮化物复杂的非化学计量比问题,导致对上述物相之间的转化关系的认识仍不清楚;而不同化学计量比的铀氮化物由于其电子结构的差异,使得其基本物理化学性质发生了根本的变化。有关铀氮化物晶体结构和电子结构方面的研究是探讨其优异性能起因的第一步,因此引起研究者的广泛关注。本文在归纳和分析大量文献的基础上,结合本课题组在铀氮化物相关方面的研究成果,着重介绍铀氮化物晶体结构和电子结构方面的主要进展,并对铀氮化物相结构的转化规律以及电子结构的演化规律进行总结,以期为铀氮化物的实验研究和功能应用提供参考。     

Isolation of Elusive HAsAsH in a Crystalline Diuranium(IV) Complex

The HAsAsH molecule has hitherto only been proposed tentatively as a short‐lived species generated in electrochemical or microwave‐plasma experiments. After two centuries of inconclusive or disproven claims of HAsAsH formation in the condensed phase, we report the isolation and structural authentication of HAsAsH in the diuranium(IV) complex [{U(Tren^TIPS)}₂(μ‐η²:η²‐As₂H₂)] ( 3 , Tren^TIPS=N(CH₂CH₂NSiPrⁱ₃)₃; Prⁱ=CH(CH₃)₂). Complex 3 was prepared by deprotonation and oxidative homocoupling of an arsenide precursor. Characterization and computational data are consistent with back‐bonding‐type interactions from uranium to the HAsAsH π*‐orbital. This experimentally confirms the theoretically predicted excellent π‐acceptor character of HAsAsH, and is tantamount to full reduction to the diarsane‐1,2‐diide form.