Actinyl ion

In aqueous solutions hydrolysis of the actinyl ions is important and such solutions are distinctly acidic. The reactions are complicated but, at least in the case of U02 +, it appears that loss of H+ from coordinated H2O is followed by polymerization involving -OH- bridges and yielding species such as [(U02)(0H)]+, [(U02)2(OH)2] + and [(U02)3(0H)5]+. 

Dechnicke K, Shihada A-F (1976) Structural and Bonding Aspects in Phosphorus Chemistry-Inorganic Derivates of Oxohalogeno Phosphoric Acids. 28 51-82 Denning RG (1992) Electronic Structure and Bonding in Actinyl Ions. 79 215-276 Dhubhghaill OMN, Sadler PJ (1991) The Structure and Reactivity of Arsenic Compounds. 

As mentioned in the Introduction, the actinyl ions are not stable under all chemical conditions. Plutonium can coexist in solution in several oxidation states, the stability of which often depends strongly on acidity (26). As a result, great care must be taken to obtain pure solutions of PuOl(27). On the other hand, the neptunyl ion NpO is the most stable form of neptunium in aqueous solution. It is noteworthy that the exchange between the oxygen atoms of PuO and H20 is very slow (ti/2 > 10 h) (25), whereas it is quite fast (h/2 2.2 s) in the case of NpO. ... 

Two other actinyl ions, UO (5/°) and NpO (5/ ), are worth mentioning here. Although the uranyl ion contains no unpaired/electrons, its complexes may display a weak temperature-independent paramagnetism because of... 

The aqueous chemistry of the +3 and +4 actinide ions is complicated by their tendency to hydrolyze and polymerize. Higher oxidation states are represented by stable actinyl ions (e.g., MO, MO2, and MO ). 

The actinide ions in 5+ and 6+ oxidation states are prone to severe hydrolysis as compared to lower oxidation states in view of their high ionic potentials. Consequently, these oxidation states exist as the actinyl ions MOt and MO + even under acidic conditions, which can further hydrolyze under high pH conditions. The oxygen atoms of these ions do not possess any basic property and thus do not interact with protons. The tetravalent ions do not exist as the oxy-cations and can be readily hydrolyzed at low to moderate pH solutions. The degree of hydrolysis for actinide ions decreases in the order M4 > MOT > M3 > MOt, which is similar to their complex formation properties (4). In general, the hydrolysis of the actinides ions can be represented as follows ... 

Eine der hervorstechendsten Eigenschaften der Chemie der Actiniden ist die Stabilitat des Actinyl -Ions MeO (w = 1 fiir Me(V) und n — 2 fiir Me(VI)). Eine Ausnahme davon bildet nur Protactinium, von dem kein. .yT -Ion Pa02 bekannt ist. Bei Kristallstrukturuntersuchungen... 

All neutral base adducts of hexavalent actinides are those of the dioxo, or actinyl ions (An02 ). Although at least one report has appeared which indicates the stability of base adducts of UFg. However, subsequent researchers have demonstrated that reduction occurs in these systems." ... 

Sulfates and sulfites. Mono- and bis-sulfate complexes of actinyl ions, An02S04 and An02(S04)2 , are generally prepared from acidic solutions. The geometry about the actinide metal center is pentagonal biypyramidal from actinyl, sulfato, and aquo oxygen atoms. A tris(sulfato) complex has been reported, but it is very weak if it does exist. Ternary hydroxo, sulfato complexes have been reported for uranyl, but they have not been structurally characterized. 

The dominant species in the +6 oxidation state is the actinyl ion, An02 where the most stable member of the series is the uranyl ion, The majority of well-characterized coordination... 

Amine N-oxides, phosphine oxides, arsine oxides, and related ligands. The prototypical system for extraction of the uranyl ion from aqueous solution into organic solvent is tributylphosphate in hydrocarbons such as kerosene. This has stimulated interest in understanding the coordination chemistry of actinyl ions with P=0 (and related) functional groups in order to optimize extraction efficiency or discrimination among actinides to be separated. Of all classes of neutral group 16-atom donor ligands, phosphine oxide adducts are the most common examples of complexes of transuranic elements (Np, Pu). 

Sulfoxides. Table 44 presents some of the reported derivatives of actinyl ions coordinated by sulfoxide and related ligands. These ligands coordinate through the oxide oxygen atom in the equatorial plane of the actinyl ion. Coordination numbers about the metal can range from six to eight, as is typical for actinyl species. One of the most common geometries of complexes is... 

The stractural chemistry of actinides is very diverse due to the possibility of different oxidation states and the richness of actinide coordination geometries. Whereas actiiudes in lower oxidation states sometimes mimic rare earth elements, actinides in higher oxidation states possess unique coordination chemistry, due to the tendency to form linear actinyl ions. The reviews in this book are written by specialists in their fields and the subjects range from low-valence actinide compoimds to actinide-based metal-orgaiuc frameworks. The active participation of Russian authors provides overviews of some activities undertaken by scientists in the former Soviet Uiuon. Their results are sometimes not well known to western readers because of the relatively closed nature of works in this field during the Cold War years. 

D. Actinyl ions require higher oxygen coordination (7-8) while d-block elements in the same valence state often have (4 or 6) oxygen coordination. 

---