A 2:1 Dicationic Complex of Tetraethyl Methylenebisphosphonate with Uranyl Ion in Acetonitrile and Ionic Liquids

A new 2:1 dicationic complex formed by TEMBP with uranyl ion in acetonitrile and two hydrophobic ILs, [BMIm]­[NTf₂] and [N₄₁₁₁]­[NTf₂], has been identified with combination of optical spectroscopic and mass spectrometric studies. With excess of TEMBP ligand (L/U > 2.0), the uranyl is completely coordinated by two ligands to form a dicationic complex [UO₂(TEMBP)₂]²⁺. The UV–vis spectra of [UO₂(TEMBP)₂]²⁺ in acetonitrile and in the two ILs are similar. The vibronic fine structures in UV–vis spectrum of [UO₂(TEMBP)₂]²⁺ show characters of tetragonal coordination in the uranyl equatorial plane. The symmetry of proposed structure of [UO₂(TEMBP)₂]²⁺ is <i>D</i>_2<i>h</i>, and its UV–vis spectrum is tentatively interpreted based on the structural similarity to the well studied [UO₂Cl₄]^2– complex. The luminescence emission spectrum of [UO₂(TEMBP)₂]²⁺ shows typical vibronic bands, having a mirror relationship with the 455–500 nm region of the corresponding absorption spectrum. The stoichiometry of [UO₂(TEMBP)₂]²⁺ is confirmed by electrospray ionization–ion trap mass spectrometry (ESI-ITMS) studies with acetonitrile as solvent. The “naked” dication (<i>m</i>/<i>z</i> 423) is characterized by the remarkable eight peaks with interval of 14 <i>m</i>/<i>z</i> units in its tandem mass spectra, representing the fragmentation of ligands by losing C₂H₄ units from their ethoxy groups. However, the dication tends to exist as a weak adduct with either an additional ligand or an anion in the ESI mass spectrum. The adducts {[UO₂(TEMBP)₂]²⁺ + TEMBP} (<i>m</i>/<i>z</i> 567) and {[UO₂(TEMBP)₂]²⁺ + [ClO₄]⁻} (<i>m</i>/<i>z</i> 945) are favorable in pure acetonitrile, while only one adduct {[UO₂(TEMBP)₂]²⁺ + [NTf₂]⁻} (<i>m</i>/<i>z</i> 1126) is predominant in [BMIm]­[NTf₂] (diluted with acetonitrile). The results of ESI-ITMS study are consistent with those of optical spectroscopic studies

Synthesis and crystal structures of two new uranyl coordination compounds obtained in aqueous solutions of 1-butyl-2,3-dimethylimidazolium chloride

<p>Two new uranyl coordination compounds, [C₉H₁₇N₂]₃[(UO₂)₂(CrO₄)₂Cl₂(H₂O)₂]Cl·5H₂O (<b>1</b>) and (C₉H₁₇N₂)[(UO₂)(C₂O₄)Cl] (<b>2</b>), have been synthesized by adding potassium dichromate (K₂Cr₂O₇) or oxalic acid dihydrate (H₂C₂O₄·2H₂O) solution into an aqueous solution of uranyl nitrate and 1-butyl-2,3-dimethylimidazolium chloride [Bmmim]Cl. [Bmmim]Cl provides the charge balance and Cl ions that coordinate with uranyl ions. The fundamental building units of <b>1</b> and <b>2</b> are UO₆Cl pentagonal bipyramidal structures. Compound <b>1</b> exhibits a graphene-like structure with a system molar ratio of 1:1 for U:Cr and crystallizes in the orthorhombic space group Pbca, with <i>a</i> = 25.644(3) Å, <i>b</i> = 12.996(14) Å and <i>c</i> = 29.198(4) Å. 16-Membered rings are formed by CrO₄²⁻ and UO₂²⁺ in the crystal structure of <b>1</b>. Compound <b>2</b> crystallizes in monoclinic space group P2₁/n, with <i>a</i> = 10.759(3) Å, <i>b</i> = 11.395(3) Å, <i>c</i> = 14.149(4) Å, <i>β</i> = 102.962(9)° and shows one-dimensional (1D) serrated chains. Within the crystal structures of <b>1</b> and <b>2</b>, C–H_[Bmmim]Cl⋯O hydrogen bonds are identified. O–H_water⋯Cl hydrogen bonds are also detected in the crystal structure for <b>1</b>.</p