Ionothermal and Hydrothermal Flux Syntheses of Five New Uranyl Phosphonates

Four new uranyl phosphonate compounds have been synthesized via ionothermal flux in the ionic liquids 1-butyl-3-methylimidazolium chloride ([Bmim]­[Cl]) and 1-ethyl-3-methylimidazolium bromide ([Emim]­[Br]). [C₈H₁₅N₂]­[UO₂(C₆H₅PO₃H)­(C₆H₅PO₃)] (<b>[Bmim]­[UPhPO]</b>), [C₈H₁₅N₂]₂[(UO₂)₄(C₆H₅PO₃)₃Cl₄] (<b>[Bmim]­[UPhPOCl]</b>), [C₈H₁₅N₂]­[UO₂(HO₃P­(CH₂)₃PO₃)] (<b>α-[Bmim]­[UC</b>_<b>3</b><b>DPO]</b>), and [C₆H₁₁N₂]₂[(UO₂)₂(<i>p</i>-C₆H₄(PO₃H)₂)₃]·2H₂O (<b>[Emim]­[UPhDPO]</b>) form one-dimensional chains, two-dimensional sheets, or three-dimensional frameworks. For comparison, analogous reactions were carried out hydrothermally, which lead to one new framework structure, [C₈H₁₅N₂]₂[(UO₂)₅(HO₃P­(CH₂)₃PO₃)₄] (<b>β-[Bmim]­[UC</b>_<b>3</b><b>DPO]</b>), and one previously characterized tubular uranyl phosphonate. It was found that the structure is equally dictated by the choice of flux method, the choice of ligand, and the choice of ionic liquid

Ionothermal and Hydrothermal Flux Syntheses of Five New Uranyl Phosphonates

Four new uranyl phosphonate compounds have been synthesized via ionothermal flux in the ionic liquids 1-butyl-3-methylimidazolium chloride ([Bmim]­[Cl]) and 1-ethyl-3-methylimidazolium bromide ([Emim]­[Br]). [C₈H₁₅N₂]­[UO₂(C₆H₅PO₃H)­(C₆H₅PO₃)] (<b>[Bmim]­[UPhPO]</b>), [C₈H₁₅N₂]₂[(UO₂)₄(C₆H₅PO₃)₃Cl₄] (<b>[Bmim]­[UPhPOCl]</b>), [C₈H₁₅N₂]­[UO₂(HO₃P­(CH₂)₃PO₃)] (<b>α-[Bmim]­[UC</b>_<b>3</b><b>DPO]</b>), and [C₆H₁₁N₂]₂[(UO₂)₂(<i>p</i>-C₆H₄(PO₃H)₂)₃]·2H₂O (<b>[Emim]­[UPhDPO]</b>) form one-dimensional chains, two-dimensional sheets, or three-dimensional frameworks. For comparison, analogous reactions were carried out hydrothermally, which lead to one new framework structure, [C₈H₁₅N₂]₂[(UO₂)₅(HO₃P­(CH₂)₃PO₃)₄] (<b>β-[Bmim]­[UC</b>_<b>3</b><b>DPO]</b>), and one previously characterized tubular uranyl phosphonate. It was found that the structure is equally dictated by the choice of flux method, the choice of ligand, and the choice of ionic liquid

Covalency-Driven Dimerization of Plutonium(IV) in a Hydroxamate Complex

The reaction of formohydroxamic acid [NH­(OH)­CHO, FHA] with Pu^III should result in stabilization of the trivalent oxidation state. However, slow oxidation to Pu^IV occurs, which leads to formation of the dimeric plutonium­(IV) formohydroxamate complex Pu₂(FHA)₈. In addition to being reductants, hydroxamates are also strong π-donor ligands. Here we show that formation of the Pu₂(FHA)₈ dimer occurs via covalency between the 5f orbitals on plutonium and the π* orbitals of FHA^– anions, which gives rise to a broad and intense ligand-to-metal charge-transfer feature. Time-dependent density functional theory calculations corroborate this assignment

Covalency-Driven Dimerization of Plutonium(IV) in a Hydroxamate Complex

The reaction of formohydroxamic acid [NH­(OH)­CHO, FHA] with Pu^III should result in stabilization of the trivalent oxidation state. However, slow oxidation to Pu^IV occurs, which leads to formation of the dimeric plutonium­(IV) formohydroxamate complex Pu₂(FHA)₈. In addition to being reductants, hydroxamates are also strong π-donor ligands. Here we show that formation of the Pu₂(FHA)₈ dimer occurs via covalency between the 5f orbitals on plutonium and the π* orbitals of FHA^– anions, which gives rise to a broad and intense ligand-to-metal charge-transfer feature. Time-dependent density functional theory calculations corroborate this assignment

Ionothermal Synthesis of Tetranuclear Borate Clusters Containing <i>f</i>- and <i>p</i>‑Block Metals

The reactions of simple oxides or halides of trivalent lanthanides and actinides or bismuth with boric acid in the ionic liquid 1-butyl-3-methyl­imid­azolium chloride at 150 °C result in the formation and crystallization of a series of isomorphous tetranuclear borate clusters with the general formula M₄B₂₂O₃₆(OH)₆(H₂O)₁₃ (M = La, Ce, Pr, Nd, Sm, Eu, Gd, Pu, and Bi). These clusters do not assemble with trivalent cations smaller than Gd³⁺, suggesting that the formation of the clusters is dictated by the size of the metal ion. The cations are found in cavities along the periphery of a cage assembled from the corner- and edge-sharing interactions of BO₃ triangles and BO₄ tetrahedra, yielding a complex chiral cluster. Both enantiomers cocrystallize. The metal ions are nonacoordinate, and their geometries are best described as distorted tridiminished icosahedra. This coordination environment is new for both Pu³⁺ and Bi³⁺. In addition to detailed structural information, UV/vis–NIR absorption and photoluminescence spectra are also provided

Ionothermal Synthesis of Tetranuclear Borate Clusters Containing <i>f</i>- and <i>p</i>‑Block Metals

The reactions of simple oxides or halides of trivalent lanthanides and actinides or bismuth with boric acid in the ionic liquid 1-butyl-3-methyl­imid­azolium chloride at 150 °C result in the formation and crystallization of a series of isomorphous tetranuclear borate clusters with the general formula M₄B₂₂O₃₆(OH)₆(H₂O)₁₃ (M = La, Ce, Pr, Nd, Sm, Eu, Gd, Pu, and Bi). These clusters do not assemble with trivalent cations smaller than Gd³⁺, suggesting that the formation of the clusters is dictated by the size of the metal ion. The cations are found in cavities along the periphery of a cage assembled from the corner- and edge-sharing interactions of BO₃ triangles and BO₄ tetrahedra, yielding a complex chiral cluster. Both enantiomers cocrystallize. The metal ions are nonacoordinate, and their geometries are best described as distorted tridiminished icosahedra. This coordination environment is new for both Pu³⁺ and Bi³⁺. In addition to detailed structural information, UV/vis–NIR absorption and photoluminescence spectra are also provided

Elucidation of Tetraboric Acid with a New Borate Fundamental Building Block in a Chiral Uranyl Fluoroborate

A new neutral borate species, H₂B₄O₇ (also known as tetraboric acid), with a one-dimensional chain structure, is found in the interlayer spacing in Rb₂[(UO₂)₂B₈O₁₂F₆]·H₂B₄O₇ (<b>RbUBOF-2</b>) derived from boric acid flux reaction of uranyl­(VI) nitrate with RbBF₄. This new form of tetraboric acid possesses a novel borate fundamental building block with the symbol 4Δ:⟨3Δ⟩Δ

Elucidation of Tetraboric Acid with a New Borate Fundamental Building Block in a Chiral Uranyl Fluoroborate

A new neutral borate species, H₂B₄O₇ (also known as tetraboric acid), with a one-dimensional chain structure, is found in the interlayer spacing in Rb₂[(UO₂)₂B₈O₁₂F₆]·H₂B₄O₇ (<b>RbUBOF-2</b>) derived from boric acid flux reaction of uranyl­(VI) nitrate with RbBF₄. This new form of tetraboric acid possesses a novel borate fundamental building block with the symbol 4Δ:⟨3Δ⟩Δ

Synthesis and Crystal Structures of Volatile Neptunium(IV) β‑Diketonates

Production of certified reference materials in support of domestic nuclear forensics programs require volatile precursors for introduction into electromagnetic isotopic separation instruments. β-Diketone chelates of tetravalent actinides are known for their high volatility, but previously developed synthetic approaches require starting material (NpCl₄) that is prohibitively difficult and hazardous to prepare. An alternative strategy was developed here that uses controlled potential electrolysis to reduce neptunium to the tetravalent state in submolar concentrations of hydrochloric acid. Four different β-diketone ligands of varying degrees of fluorination were reacted with an aqueous solution of Np⁴⁺. Products of this reaction were characterized via X-ray diffraction and infrared spectroscopy, and were found to be neutral 8-coordinate complexes that adopt square antiprismatic crystal geometry. Synthesis of Np β-diketonates by this approach circumvents the necessity of using NpCl₄ in tetravalent Np coordination compound synthesis. The volatility of the complexes was assessed using thermogravimetric analysis, where the temperature of sublimation was determined to be in the range of 180° to 205 °C. The extent of fluorination did not appreciably alter the sublimation temperature of the complex. Thermal decomposition of these compounds was not observed during sublimation. High volatility and thermal stability of Np β-diketonates make them ideal candidates for gaseous introduction into isotopic separation instruments