A Monoclinic Polymorph of Uranyl Dinitrate Trihydrate, [UO₂(NO₃)₂(H₂O)₂] ×H₂O.

Abstract

For Abstract see ChemInform Abstract in Full Text.

Insights into the Structural Chemistry of Anhydrous and Hydrous Hexavalent Uranium and Neptunium Dinitrato, Trinitrato, and Tetranitrato Complexes

“…A trans coordination configuration for NO 3 – and H 2 O ligands can also be observed in orthorhombic [NpO 2 (NO 3 ) 2 (H 2 O) 2 ]·4H 2 O, identified in this investigation, and also in the isostructural [UO 2 (NO 3 ) 2 (H 2 O) 2 ]·4H 2 O . Notably the occurrence of this form of geometric isomerism leads to polymorphism and starkly different structure types for monoclinic and triclinic forms of [UO 2 (NO 3 ) 2 (H 2 O) 2 ]·H 2 O. This is in contrast to the A 2 [UO 2 - cis / trans -(NO 3 ) 4 ] ternary hexavalent uranium tetranitrate variants described previously, which maintain consistent space groups despite the different nitrate coordination geometry and as a result are thus related geometric isomers rather than polymorphs.…”

“…This can be readily observed when the hydrous ternary hexavalent uranium dinitrato complexes [UO 2 (NO 3 ) 2 (H 2 O) 2 ]· x H 2 O in Table are examined. For instance, the triclinic variant of [UO 2 (NO 3 ) 2 (H 2 O) 2 ]·H 2 O was described by Hughes and Burns to form under relatively neutral solution conditions, whereas Shuvalov and Burns described obtaining a monoclinic polymorph under more acidic conditions via addition of nitric acid. Interestingly, Lindqvist-Reis et al described obtaining [NpO 2 (NO 3 ) 2 (H 2 O) 2 ]·H 2 O in a triclinic structure (Table ), isostructural with [UO 2 (NO 3 ) 2 (H 2 O) 2 ]·H 2 O, while Gaunt et al obtained the isostructural plutonium variant [PuO 2 (NO 3 ) 2 (H 2 O) 2 ]·H 2 O; both of these syntheses were conducted under acidic conditions using nitric acid.…”

“…By systematically examining and comparing these structures with respect to the literature, we have identified the occurrence of geometric isomerism in uranyl nitrates. Interestingly it is shown that geometric isomerism in uranyl nitrates plays a key role in structural chemistry, where its occurrence can lead to either purely geometric isomeric relationships in the case of K 2 [UO 2 - cis -(NO 3 ) 4 ] and K 2 [UO 2 - trans -(NO 3 ) 4 ] , or polymorphic relationships in the case of monoclinic [UO 2 (NO 3 ) 2 (H 2 O) 2 ]·H 2 O and triclinic [UO 2 (NO 3 ) 2 (H 2 O) 2 ]·H 2 O . Although such geometric isomerism has not been specifically identified in neptunium nitrates, on comparison of the structural trends and isomorphic/isotypic relationships discussed in this investigation (Tables and ), it is to be expected that such phenomena will be identified as further transuranic synthesis investigations are made.…”

“…Central to this investigation has been the role of the solution conditions; in particular, the effect the level of acidity has in coercing a specific structure formation in uranium and neptunium nitrate complexes. This can be readily observed when the hydrous ternary hexavalent uranium dinitrato complexes 46 to form under relatively neutral solution conditions, whereas Shuvalov and Burns 47 described obtaining a monoclinic polymorph under more acidic conditions via addition of nitric acid. Interestingly, Lindqvist-Reis et al 42 described obtaining [NpO 2 (NO 3 ) 2 (H 2 O) 2 ]•H 2 O in a triclinic structure (Table 3), isostructural with [UO 2 (NO 3 ) 2 (H 2 O) 2 ]• H 2 O, while Gaunt et al 48 obtained the isostructural plutonium variant [PuO 2 (NO 3 ) 2 (H 2 O) 2 ]•H 2 O; both of these syntheses were conducted under acidic conditions using nitric acid.…”

Novel [(UO 2 )O 6 (NO 3 ) n ] ( n = 1, 2) based units in organically templated uranyl compounds

“…Four O eq atoms of U(2)O 8 uranyl hexagonal bipyramid belong to the nitrate groups, which results in the formation of UrO 2 (NO 3 ) 2 unit. Such uranyl nitrate units were previously observed in a number of inorganic compounds [21].…”