Extended Structures and Physicochemical Properties of Uranyl–Organic Compounds

Abstract

The ability of uranium to undergo nuclear fission has been exploited primarily to manufacture nuclear weapons and to generate nuclear power. Outside of its nuclear physics, uranium also exhibits rich chemistry, and it forms various compounds with other elements. Among the uranium-bearing compounds, those with a uranium oxidation state of +6 are most common and a particular structural unit, uranyl UO(2)(2+) is usually involved in these hexavalent uranium compounds. Apart from forming solids with inorganic ions, the uranyl unit also bonds to organic molecules to generate uranyl-organic coordination materials. If appropriate reaction conditions are employed, uranyl-organic extended structures (1-D chains, 2-D layers, and 3-D frameworks) can be obtained. Research on uranyl-organic compounds with extended structures allows for the exploration of their rich structural chemistry, and such studies also point to potential applications such as in materials that could facilitate nuclear waste disposal. In this Account, we describe the structural features of uranyl-organic compounds and efforts to synthesize uranyl-organic compounds with desired structures. We address strategies to construct 3-D uranyl-organic frameworks through rational selection of organic ligands and the incorporation of heteroatoms. The UO(2)(2+) species with inactive U═O double bonds usually form bipyramidal polyhedral structures with ligands coordinated at the equatorial positions, and these polyhedra act as primary building units (PBUs) for the construction of uranyl-organic compounds. The geometry of the uranyl ions and the steric arrangements and functionalities of organic ligands can be exploited in the the design of uranyl--organic extended structures, We also focus on the investigation of the promising physicochemical properties of uranyl-organic compounds. Uranyl-organic materials with an extended structure may exhibit attractive properties, such as photoluminescence, photocatalysis, photocurrent, and photovoltaic responses. In particular, the intriguing, visible-light photocatalytic activities of uranyl-organic compounds are potentially applicable in decomposition of organic pollutants and in water-splitting with the irradiation of solar light. We ascribe the photochemical properties of uranyl-organic compounds to the electronic transitions within the U═O bonds, which may be affected by the presence of organic ligands.

Solvothermal Synthesis of Tetravalent Uranium with Isophthalate or Pyromellitate Ligands

“…[1] Taking advantage of the interest in coordination polymers or metal-organic frameworks (MOFs), the crystallization of coordination complexes involving uranyl and carboxylic acid has seen a growing interest since a decade. [7][8][9] A part of this research is directly linked to environmental concern and could allow in identifying molecular organizations that could exist in soils or ground water. [4,[10][11][12] So far, the study dedicated to the crystallization of tetravalent uranium-based carboxylate complexes remains relatively rare.…”

Crown Ethers and Their Alkali Metal Ion Complexes as Assembler Groups in Uranyl–Organic Coordination Polymers with cis-1,3-, cis-1,2-, and trans-1,2-Cyclohexanedicarboxylates

“…[1][2][3][4][5] The cations exploited in this way have been drawn from most possible types and include non-metal species such as protonated polypyridines, (alkyl)ammonium ions and phosphonium ions, as well as metal ions in various forms depending upon coligands that they may carry. For alkali metal cations, prediction of the ways in which they might influence a uranyl ion/ligand array is rendered particularly difficult by their variable coordination numbers and flexible coordination geometry.…”

Nanomaterials and nanotechnologies in nuclear energy chemistry

“…However, in the strict sense, this material is just a uranium-inorganic framework material based on an organic template. To date, a series of uranyl-organic materials including 1-D chains, 2-D layers, and 3-D frameworks have been synthesized [23][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39][40][41][42] In China, the UOF (uranium organic-framework) materials have also been extensively studied [38][39][40][41][42]. Chen et al have prepared a series of UOF materials under hydrothermal conditions.…”