Insight into the Uranyl Oxyfluoride Topologies through the Synthesis, Crystal Structure, and Evidence of a New Oxyfluoride Layer in [(UO₂)₄F₁₃][Sr₃(H₂O)₈](NO₃)·H₂O

Abstract

A new strontium uranyl oxyfluoride, [(UO)F][Sr(HO)](NO)·HO, was synthesized under hydrothermal conditions. The single-crystal X-ray structure was determined. This compound crystallizes in the triclinic space group P1̅ (No. 2), with unit cell parameters a = 10.7925(16) Å, b = 10.9183(16) Å, c = 13.231(2) Å, α = 92.570(8)°, β = 109.147(8)°, γ = 92.778(8)°, V = 1468.1(4) Å, and Z = 2. The structure is built from uranyl-containing [Formula: see text] chains of tetrameric units of corner-sharing UOF pentagonal bipyramids. These chains are linked through trimeric strontium units to form strontium-uranyl oxyfluoride layers further assembled by nitrate groups. The interlayer space is occupied by free water molecules. This compound was characterized by spectroscopic methods, especially F NMR highlighting the many different fluoride sites. Structural relationships with other uranyl oxyfluorides were investigated through the different F/O ratios, the structural building unit, and the structural arrangement.

Spectral Analysis of the Uranyl Squarate and Croconate System: Evaluating Differences between the Solution and Solid-State Phases

“…Raman spectroscopy can be an important tool to explore aqueous uranyl chemistry because the presence of a strong symmetric stretching band (ν 1 ) associated with the uranyl cation that is located at 870 cm –1 for the pentaaquauranyl ([(UO 2 )­(H 2 O) 5 ] 2+ ) complex . This band typically red shifts up to 70 cm –1 upon hydrolysis or ligand complexation and has previously been used to identify specific uranyl species present aqueous solutions and throughout the crystallization process. − We have previously utilized Raman spectroscopy to understand the major species in solution within uranyl citrate, where there was a direct correlation between the bands in the solid-state material and the solution phase . However, analysis of the spectral features is not always straightforward as the exact band shifts are not always known or there can be changes during the crystallization process.…”

“…Our initial interest in the oxocarbon anions was piqued by the synthesis of the unusual porous uranyl squarate metal organic framework developed by Rowland and Cahill and their reported building units based upon hydrothermal reaction conditions . Herein, we build upon this previous study with the syntheses and structural characterization of the uranyl building units within the squarate (( USq1 ) [C 4 H 12 N 2 ]­[(UO 2 )­(C 4 O 4 ) 2 ­(H 2 O)]­·(H 2 O), ( USq2 ) [C 5 H 6 N]­[(UO 2 )­(C 4 O 4 )­(μ 2 -OH)]­·2H 2 O, and ( USq3 ) [C 2 H 10 N 2 ] 2 ­[(UO 2 ) 6 (C 4 O 4 ) 3 ­(μ 3 -O) 2 ­(μ 2 -OH) 6 ]) and croconate (( UCr1 ) [C 4 H 12 N 2 ] 2 ­[(UO 2 )­(C 5 O 5 ) 3 ­(H 2 O)]­·3H 2 O, ( UCr2 ) [C 5 H 6 N] 4 [(UO 2 ) 4 ­(C 5 O 5 ) 4 (μ 2 -OH) 4 ­(H 2 O) 4 ], and ( UCr3 ) [C 2 H 10 N 2 ] 5 ­[(UO 2 ) 6 (C 5 O 5 ) 6 ­(μ 3 -O) 2 (μ 2 -OH) 6 ­(H 2 O) 4 ]) system. The solid state and solution phases were further characterized by Raman spectroscopy to explore variations in the chemical signatures associated with the uranyl solution and solid state phases.…”