High‐Pressure Synthesis and Characterization of the Actinide Borate Phosphate U₂[BO₄][PO₄]

Abstract

A new actinide borate phosphate, U2[BO4][PO4], was synthesized in a Walker-type multianvil apparatus at 12.5 GPa and 1000 °C. The crystal structure was determined from single-crystal X-ray diffraction data collected at room temperature. U2[BO4][PO4] crystallizes in the monoclinic space group P21/c with four formula units per unit cell and the lattice parameters a = 854.6(2), b = 775.3(2), c = 816.3(2) pm, and β = 102.52(3)°. The structure consists of double layers of linked uranium–oxygen polyhedra parallel to [100]. The borate tetrahedra are located between the uranium–oxygen layers inside the double layer. The phosphate groups link the double layers.

Advances and perspectives of actinide chemistry fromex situhigh pressure and high temperature chemical studies

“…Indeed, this seems to extend further with the coerced oligomerisation of building units with the application of pressure and temperature. Another interesting observations seems to be the unexpected flexibility of actinide valence states under pressure, emphasised in uranium studies 12,37,38 where despite beginning with oxidised uranium either reduced forms are found after HP/HT conditions are applied or structure formation seems to diverge from what is expected in ambient pressure studies regarding uranium valence. 63 Generally, it can be observed that HP/HT conditions provide an open playground in which actinide compounds are able to exhibit flexible and exotic structure formation, through the adoption of multiple polymorphs at elevated pressures, exhibit distinctive bonding and polyhedra distortions and sometimes unexpected valence behaviour.…”

“…The complex assemblies for both modules, which are designed for the generation of hydrothermal pressure conditions, are internally heated (graphite or LaCrO 3 heater) and temperature control is conducted using an in situ thermocouple. A comparable setup was used by Huppertz, Hinteregger and coworkers [37][38][39][40] for their high-pressure research on 3d and 4f elements. Hydrothermal conditions ( p < 0.25 GPa, t < 850 °C) with sample quantities of up to 1 gram can be achieved using a cold seal vessel 41 (here water is used as pressure media in an externally heated pressure vessel, often made out of inconel®).…”

“…Pertinent to the structure is the occurrence of multi-oxo components of uranyl in addition to AlO 6 and AlO 5 groups that gives rise to its unique structure which deviates sharply from ambient pressure studies. Hinteregger et al 38 examined the formation uranyl borophosphates under HP/HT conditions of 7.0 GPa and 700 °C. Similar to their previous study 37 on uranium borates, they were able to synthesis a tetravalent uranium borophosphate despite starting with hexavalent uranium nitrate.…”

Influence of extreme conditions on the formation and structures of caesium uranium(vi) arsenates

“…Such studies were performed mainly at relatively low pressures and temperatures. [27][28][29][30][31][32] In this report we present the results of the U-As-Cs oxo-system investigations, aiming to explore the synthetic and coordination chemistry of uranium under extreme (HT/HP) conditions. Herein, we obtained four new uranium(VI) arsenates, Cs 4), respectively.…”

The Effect of the Ratio of [M/(B+P)] on the Configuration of Anionic Groups: Synthesis of the Borate–Phosphate LiPb4(BO3)(PO4)2

“…Compounds containing both B–O and P–O groups have been classified into two types in terms of reviews by Kniep et al:5 (1) borophosphates in which a common oxygen atom between the B–O and P–O groups exists and (2) borate–phosphates in which all of the B–O and P–O anionic units are isolated. Whereas hundreds of borophosphate compounds have been reported over recent decades, M 3 (BO 3 )(PO 4 ) (M = Be, Mg, Ba, Zn, and Co),7 SrCo 2 (BO 3 )(PO 4 ),8 Ln 7 O 6 (BO 3 )(PO 4 ) 2 (Ln = La, Pr, Nd, Sm, Gd, and Dy),9 K 3 Ln[OB(OH) 2 ] 2 [HOPO 3 ] 2 (Ln = Yb, Lu),10 Th 2 (BO 4 )(PO 4 ),11U 2 (BO 4 )(PO 4 ),12 Ba 5 [(UO 2 )(PO 4 ) 3 (B 5 O 9 )] · n H 2 O,13 and Mn 3 (OH) 2 [B(OH) 4 ][PO 4 ]14 are the only reported borate–phosphates that we could retrieve. Compared with the hundreds of borophosphates, borate–phosphates are extremely rare.…”