Rb₂[Ca(NpO₂)₂(PO₄)₂], the First Mixed Alkali–Alkaline Earth Metals Neptunyl(V) Phosphate: Crystal Chemistry and Sheet Stereoisomerism

Abstract

A novel anhydrous neptunyl(V) compound, Rb 2 [Ca(NpO 2 ) 2 (PO 4 ) 2 ], was obtained by hydrothermal synthesis. It crystallizes in the orthorhombic space group Pbca with the unit-cell parameters a = 12.972(2), b = 13.213(3), c = 7.090(3) Å, V = 1215.3(6) Å 3 , Z = 4. The crystal structure is based on sheets of neptunyl and phosphate polyhedra representing a new geometrical isomer related to the uranophane-anion topology. The intercalation of calcium in octahedral coordination between adjacent sheets results in a heteropolyhedral framework. This phase is the first inorganic neptunyl compound containing both alkali and alkaline earth metals. The straightforward route used to obtain this compound offers interesting possibilities for the development of a new family of heteropolyhedral framework-type neptunyl oxysalts.

Polytypism of Ln(SeO3)(HSeO3)·2H2O compounds: synthesis and crystal structure of the first monoclinic modification of Nd(SeO3)(HSeO3)·2H2O, DFT calculations and order/disorder description

“…The crystal structure of the first monoclinic modification of Nd(SeO 3 )(HSeO 3 )Á2H 2 O is overall similar to that of orthorhombic analogues with the general formula Ln 3+ (SeO 3 )-(HSeO 3 )Á2H 2 O, where Ln = Sm 3+ (Koskenlinna et al, 1994), Tb 3+ (Burns & Ibers, 2009), Nd 3+ (de Pedro et al, 1994) and Lu 3+ (Wu et al, 2020), and is based on the electroneutral {Nd(SeO 3 )(HSeO 3 )(H 2 O)} 11 -heteropolyhedral layers parallel to (001), which are characterized by the uranophanetype anion topology (Burns et al, 1996;Dal Bo et al, 2018) [Fig. 3(a)].…”

Framework Polymorphism and Modular Crystal Structures of Uranyl Vanadates of Divalent Cations: Synthesis and Characterization of M(UO2)(V2O7) (M = Ca, Sr) and Sr3(UO2)(V2O7)2

“…In module I of the structure of Sr 3 (UO 2 )(V 2 O 7 ) 2 , the sequences of both PT and ST chains are UUUU (Figure d). The ST and PT sequences of Ca(UO 2 )V 2 O 7 are the same as in uranophane‐α, boltwoodite, cuprosklodowskite, sklodowskite, and kasolite, whereas the ST and PT sequences of Sr(UO 2 )V 2 O 7 are the same as the neptunyl phosphate Rb 2 [Ca(Np 5+ O 2 ) 2 (PO 4 ) 2 ] . Module I of Sr 3 (UO 2 )(V 2 O 7 ) 2 and La(UO 2 ) 2 (VO 4 )(V 2 O 7 ) shows ST and PT sequences that have not been reported for any inorganic compound, and therefore corresponds to a new stereoisomer for the uranophane‐anion topology.…”

Periodic trends in trivalent actinide halides, phosphates, and arsenates

“…91 Studies on poly-phosphates, hydrated and/or double-salt-like phosphates and arsenates are present in the literature, 2,7,8,61 but they are of the actinyl type ions, i.e., uranyl, neptunyl, plutonyl, not of trivalent ions. 35,92,93 This is mainly due to the fact that, except for that of actinium, the most stable oxidation state for the early actinides (Th, Pa, U, Np, and Pu) is not +3. 7,12,15 While the trivalent actinide trihalides are common for four of the first six actinides (Th and Pa being the exceptions), 16 the tetravalent state is generally observed in their respective phosphates (excluding for Ac).…”