Porous Uranyl Borophosphates with Unique Three-Dimensional Open-Framework Structures

Abstract

Two novel alkali-metal uranyl borophosphates have been prepared and characterized for the first time, namely, K(UO)[BPO(OH)](OH)(HO) and K(UO)[B(HPO)](PO)(OH)(HO) denoted as KUPB1 and KUPB2, respectively. KUPB1 was obtained hydrothermally at 220 °C and crystallizes in a monoclinic structure in the chiral space group P2. The unit cell parameters of KUPB1 are a = 6.7623(2) Å, b = 19.5584(7) Å, c = 11.0110(4) Å, α = γ = 90°, β = 95.579(3)°, and V = 1449.42(8) Å. It features a unique three-dimensional (3D) open-framework structure, composed of two corner-sharing linked one-dimensional (1D) anionic borophosphates (BP), [BPO], along the a axis and uranyl phosphate (UP), [(UO)(PO)], chains along the c axis, further bridged by PO tetrahedra. Multi-intersectional channels can be observed within the structure, in which the largest 11-ring (11-R) tunnel size is ∼7.0 Å × 8.8 Å. Its simplified framework can be described as a new 4-nodal net topological type with a point symbol of {4.8.10}{4.6}{4.6.8.10}{8.10}. By modification of the synthetic conditions of KUPB1 through an increase in the amount of HBO as flux 4-fold and a reduction of water as the reaction medium, the novel compound KUPB2 is generated. The unit cell parameters of KUPB2 are a = b = 21.8747(3) Å, c = 7.0652(2) Å, α = β = γ = 90°, and V = 3380.72(12) Å. KUPB2 crystallizes in a tetragonal structure in the polar space group I4̅2m, and its structure is based on a highly complex 3D framework, {(UO)[B(PO)](PO)}, in which 1D 8-R UP [(UO)(PO)] tubes can be observed along the c axis. The [(UO)(PO)] tubes consist of three uranyl chains along the c axis, which are linked alternately by [PO] tetrahedra. Those isolated 1D [(UO)(PO)] tubes are further bridged through [(UO)B(PO)] clusters, forming an exceptional 3D open-framework structure. Its simplified cation network is a new 5-nodal net topological type such as {3.4.5.6.7.8}{3.4.5.6}{4.6.8}{4.6}{4.6}. Their facile hydrothermal synthetic routes, porous structure topology, thermal stability, and Raman spectroscopy properties are reported and discussed.

The Role of Acidity in the Synthesis of Novel Uranyl Selenate and Selenite Compounds and Their Structures

“…Many of these studies were performed on what can be described as an explorative basis which left little understanding regarding chemical conditions which dictate synthesis control and outcome. However, more contemporary investigations have utilized systematic approaches, which better enable improved synthesis control and increased understanding and prediction of potential reaction outcomes [17,[26][27][28][29][30][31][32][33]. Saliently, many of these more recent studies have highlighted the unique ability and promising application of uranium derived compounds in societally important materials such as radiation detectors, scintillators to proton conductors [34][35][36].…”

“…We have recently embarked on a systematic investigation into the structure-property relations and effect of synthesis on novel SNF related actinide phase formation under variable conditions [14,17,[29][30][31]37,38]. In light of the identification of the effect of acid on controlling the polymerization of iodate units in uranyl iodates [14] (60 wt.%) was added to the reaction mixtures to reduce the pH to below 1 confirmed using pH paper.…”

Hydrothermal Synthesis and Structural Investigation of a Crystalline Uranyl Borosilicate

“…It is therefore unsurprising that incorporation of mixed-oxoanions into the structures of uranyl compounds often facilitates further structural diversity. For example, a few uranyl borophosphate [25,26], borogermanate [27], aluminoborate [28], and aluminophosphate [29] compounds are known, most of which exhibit complex open-framework structures. No such uranyl compounds containing borosilicate units have been reported, although there are several existing non-uranyl compounds exhibiting a variety of different borosilicate units.…”

Crystal Growth of Alkali Uranyl Borates from Molten Salt Fluxes: Characterization and Ion Exchange Behavior of A2(UO2)B2O5 (A = Cs, Rb, K)

“…A considerable number of uranium borates have been synthesized by the Albrecht-Schmitt and Alekseev groups; however, the majority of these reported phases were prepared via mild hydrothermal routes − and high-temperature, high-pressure hydrothermal synthesis methods, − while only a handful have been prepared via high-temperature flux synthesis. The latter consist of the simple ternary and quaternary uranium borates UO 2 B 2 O 4 , Mg­(UO 2 )­B 2 O 5 , Ca­(UO 2 ) 2 B 2 O 6 , and A­(UO 2 )­(BO 3 ) (A = Li, Na, K, Rb, Cs), − along with the transition-metal-containing quaternary phase Ni 7 (UO 2 )­(B 4 O 14 ) .…”