Search

A single-source-precursor approach was developed to synthesize uranium-based materials outside of the typically-studied oxides. This approach allows for shorter reaction times, milder reaction conditions, and control over the chemicals present in synthesis. To this end, the first homoleptic uranium thioamidate complex was synthesized as a precursor for US 2 materials. Pyrolysis of the thioamidate results in decomposition via an alkene elimination pathway and formation of γ-US 2 , which has historically been hard to access without the need for a secondary sulfur source. Despite the oxophilicity of uranium, the method successfully forms US 2 without the inclusion of oxygen in the bulk final product. These findings are supported by simultaneous thermal analysis, elemental analysis, powder X-ray diffraction, and uranium L 3 -edge X-ray absorption fine-structure spectroscopy. This work represents the first example of a single-source precursor approach to target and synthesize actinide materials other than the oxides., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Reaction of the potassium pentamethylcyclopentadienyl iridate tris-hydride K[IrCp*H 3 ] with UCl 4 and ThCl 4 (DME) 2 led to the complete replacement of the halide ligands to generate multimetallic complexes U{(μ-H) 3 IrCp*} 4 (1) and Th{[(μ-H 2 )(H)IrCp*] 2 [(μ-H) 3 IrCp*] 2 } (2), respectively. These analogues feature a significant discrepancy in hydride bonding modes; 1 contains twelve bridging hydrides while 2 contains ten bridging hydrides and two terminal, Ir-bound hydrides. Use of a U(iii) starting material, UI 3 (1,4-dioxane) 1.5 , resulted in the octanuclear complex {U[(μ 2 -H 3 )IrCp*] 2 [(μ 3 -H 2 )IrCp*]} 2 (3). Computational studies indicate significant bonding character between U/Th and Ir in 1 and 2, with f-orbital involvement in the singly-occupied molecular orbitals of the uranium species 1. In addition, these studies attribute the variation in hydride bonding between 1 and 2 to differences in dispersion effects., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

We report the synthesis of four homoleptic thorium(iv) amidate complexes as single-source molecular precursors for thorium dioxide. Each can be sublimed at atmospheric pressure, with the substituents on the amidate ligands significantly impacting their volatility and thermal stability. These complexes decompose via alkene elimination to give ThO2 without need for a secondary oxygen source. ThO2 samples formed from pyrolysis of C-alkyl amidates were found to have higher purity and crystallinity than ThO2 samples formed from C-aryl amidates.

This Perspective provides a detailed overview of the chemistry of low-valent (di- and trivalent) uranium. The reactivity of uranium(ii) and uranium(iii) complexes is discussed both to illustrate the general types of reactions that might be expected and to highlight the many unusual modes of reactivity observed with this element. A particular emphasis is given to redox reactions with uranium(iii) species, including reduction of small molecules, multi-electron reductions involving redox-active ligands, and formation of uranium-ligand multiple bonds. In addition, redox-neutral adduct formation with uranium(iii) complexes as well as the current state of the young field of uranium(ii) redox chemistry are also covered. Synthetic protocols to prepare a wide range of low-valent compounds are presented.

Reaction of the uranium(iii) metallocenium salt [(CpiPr4)2U][B(C6F5)4] with tert-butyl isocyanide (tBuNC) yielded the dicationic uranium(iv) complex [(CpiPr4)2U(CNtBu)4][B(C6F5)4]2 (1), which displays a linear metallocene geometry. Use of crude mixtures of [(CpiPr4)2U][B(C6F5)4], which contain a soluble source of iodide, led instead to isolation of the monocationic uranium(iv) iodide complex [(CpiPr4)2U(I)(CNtBu)2][B(C6F5)4] (2). Adduct formation with no change in oxidation state was observed upon addition of tBuNC to the neutral uranium(iii) species (CpiPr4)2UI, resulting in isolation of (CpiPr4)2U(I)(CNtBu) (3). X-ray crystallographic and IR spectroscopic studies both showed effects ascribed to the presence of multiple strongly donating isocyanide ligands in 1.

We describe the functionalisation of the previously reported uranium(iii) β-diketiminate complex (BDI)UI 2 (THF) 2 (1) with one and two equivalents of a sterically demanding 2,6-diisopropylphenolate ligand (ODipp) leading to the formation of two heteroleptic complexes: [(BDI)UI(ODipp)] 2 (2) and (BDI)U(ODipp) 2 (3). The latter is a rare example of a tetrahedral uranium(iii) complex, and it shows single-molecule magnet behaviour.

A new, air-stable, permanently porous uranium(iv) metal-organic framework U(bdc) 2 ( 1 , bdc 2- = 1,4-benzenedicarboxylate) was synthesized and its H 2 and CH 4 adsorption properties were investigated. Low temperature adsorption isotherms confirm strong adsorption of both gases in the framework at low pressures. In situ gas-dosed neutron diffraction experiments with different D 2 loadings revealed a rare example of cooperative framework contraction (Δ V = -7.8%), triggered by D 2 adsorption at low pressures. This deformation creates two optimized binding pockets for hydrogen ( Q st = -8.6 kJ mol -1 ) per pore, in agreement with H 2 adsorption data. Analogous experiments with CD 4 ( Q st = -24.8 kJ mol -1 ) and N , N -dimethylformamide as guests revealed that the binding pockets in 1 adjust by selective framework contractions that are unique for each adsorbent, augmenting individual host-guest interactions. Our results suggest that the strategic combination of binding pockets and structural flexibility in metal-organic frameworks holds great potential for the development of new adsorbents with an enhanced substrate affinity., (This journal is © The Royal Society of Chemistry 2020.)

Reaction of (CpiPr4)2UI with NaN3 resulted in formation of tetrameric uranium(iii) azide-bridged 'molecular square' [(CpiPr4)2U(μ-η1:η1-N3)]4 (1). Addition of B(C6F5)3 to 1 induced loss of N2 at room temperature, yielding the uranium(v) borane-capped nitrido (CpiPr4)2U(μ-N)B(C6F5)3 (2).

Straightforward syntheses are provided for the m-terphenyl dithiocarboxylic acid 2,6-(C 6 H 4 -4- t Bu) 2 C 6 H 3 CS 2 H (TerphCS 2 H, 2) and its lithium and potassium salts, TerphCS 2 Li(Et 2 O) 2 and TerphCS 2 K (1·Et 2 O and 4, respectively). These compounds can be isolated in good yields on multi-gram scales starting from Terph-I without isolating intermediates. Salt metathesis and protonolysis reactions provided access to the homoleptic actinide(iv) complexes (TerphCS 2 ) 4 An (An = Th (5) and U (6)). Electrochemical and reactivity studies revealed that the dithiocarboxylate ligand is incompatible with U(iii). The homoleptic lanthanum(iii) complex (TerphCS 2 ) 3 La and its η 6 -toluene adduct (7 and 7·tol, respectively) were also structurally characterized. Binding of toluene to 7 was shown to displace intramolecular La-C arene close contacts that are facilitated by a distortion from the usual geometry of bound dithiocarboxylate ligands.