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

Eric Villa,Thomas Albrecht-Schmitt,Justin Cross

doi:10.3390/min8110497

Abstract

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.

Highlights

Nuclear waste associated with energy production poses potential long-term hazards due to the vast quantities of nuclear material used in the industry
The phosphite anion, HPO3 2−, has a tetrahedral geometry with the phosphorus atom bound by three oxygen atoms and one hydrogen atom
Several light-yellow prisms suitable for crystallographic studies of the formula stated above were isolated. (H2 PZ)[UO2 (HPO3 )2 ] was the only single-crystalline product observed in the reaction vessel, and approximate yields ranged between 60–80% based on the mass of uranium based on visual inspection

Summary

Introduction

Nuclear waste associated with energy production poses potential long-term hazards due to the vast quantities of nuclear material used in the industry. We expanded to study the in-situ redox chemistry that occurs within different uranium-phosphite systems by varying reaction times and pHs to isolate compounds with various oxidation states of U and P [16,17,18]. In these studies, uranyl phosphite compounds were formed at short reaction times (a few hours) with the addition of carbonate salts. The two new compounds described here illustrate the interesting networks that can be obtained when carefully controlling the oxidation state of the oxoanions present

Materials and Methods

Results and Discussion

UV-vis-NIR