page_title: Pentavalent uranyl complexes
section_title: Coordination Chemistry
hierarchical_section_title: Pentavalent uranyl complexes / Coordination Chemistry
caption_attribution_description: Some examples of [UO2]1+
context_page_description: Uⱽ is the +5 oxidation state of uranium which is found in the form of [UO₂]¹⁺. This species is known as pentavalent uranyl cation and has a low stability due to the disproportionation into tetravalent and hexavalent uranium species.
  2Uⱽ → Uᴵⱽ + Uⱽᴵ
  The oxidation states of uranium compounds vary from +2 to +6. Out of all these oxidation states +6 is the most common one and it is found in the form of [UO₂]²⁺. This hexavalent form of uranium species is known to be the most thermodynamically stable species and it is soluble in water. Even though the uranium chemistry is well explored pentavalent uranyl chemistry is under developed due to the low stability of these compounds. There are two naturally occurring pentavalent uranium-containing minerals reported.
  Wyartite – Ca[Uⱽ(UⱽᴵO₂)₂O₄](H₂O)₇
  Dehydrated Wyartite – Ca[Uⱽ(UⱽᴵO₂)₂O₄](H₂O)₃
context_section_description: Given below are some of the pentavalent uranyl compounds reported recently.
  The electrochemical reduction of [UO₂]²⁺ in an anaerobic solution is used to obtain pentavalent uranyl complexes (Figure 2. Compound 1-3). The coordination numbers of complexes 1-4 are 7, 7, 8 and 6. The rate of disproportionation of Uⱽ which results Uᴵⱽ and Uⱽᴵ is reported to be slow in an aqueous medium with pH 2-4 hence Uⱽ is obtained via electrochemical reduction. In these compounds tetradentate Schiff-base phenoxide (salophen) and β-diketonate ligands are bound along the equatorial plane, which stabilizes the Uⱽ species obtained by the single electron reduction of Uⱽᴵ species. Anhydrous uranyl triflate compounds (Figure 2, compound 4) contains discrete cation-anion pairs and it is synthesized by the crystallization of [UO₂(OPPh₃)₄][OTf]₂. Uⱽ containing cation in this uranyl triflate compound shows an octahedral geometry.
caption: Figure 2. Some examples of [UO2]1+
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