New Uranyl Open Framework and Sheet Compounds Formed via In-Situ Protonation of Piperazine by Phosphorous Acid

• Main Authors: Eric M. Villa, Justin N. Cross, Thomas E. Albrecht-Schmitt
• Format: Article
• Language: English
• Published: MDPI AG 2018-11-01
• Series: Minerals
• Subjects: uranium(VI); phosphite; piperazinium; hydrothermal redox; crystal structures
• Online Access: https://www.mdpi.com/2075-163X/8/11/497

Two new uranyl compounds were hydrothermally synthesized employing piperazine as an organic templating agent. The piperazine was protonated in-situ by phosphorous acid, forming the piperazinium dication featured in these compounds. The two new structures presented here are a uranyl phosphite 2D sheet and a 3D uranyl mixed phosphite⁻phosphate network with cation occupied channels. Both included strong hydrogen bonding from the piperazinium cation to the uranyl phosphite or mixed phosphite⁻phosphate network. These two structures can be reliably formed through careful control of pH of the starting solution and the reaction duration. The piperazinium uranyl phosphite compound was the latest in a family of uranyl phosphites, and demonstrates the structural versatility of this combination. The mixed phosphite⁻phosphate compound builds on hydrothermal redox chemistry, illustrating the variety of compounds that can be isolated by exploiting in-situ redox processes to elucidate new uranium structure types.