Spectra and structure of hexavalent uranium nanoclusters with mixed acido ligands in the coordination sphere

Abstract

543.42:546.791.6 We have obtained and spectroscopically studied mixed acido ligand (Cl, I) uranyl complexes. We used IR absorption spectra to analyze the nature of incorporation of neutral molecules (in particular, dimethylsulfoxide) into the inner coordination sphere of uranium that that do not completely exhaust the coordination capacity of the central uranium atom. We have observed a good correlation between the frequencies of the totally symmetric stretching vibration of the UO 2 2+ ion in the IR absorption and luminescence.Introduction. Nanosized structures based on uranium complexes have recently attracted steady attention from many researchers in connection with design and development of new technologies ("nanotechnologies"). This includes, for example, cluster catalysts for chemical reactions [1], photoprotectors [2], complexation of uranium with macrocyclic ligands [3]. Development of such technologies in turn depends on knowing the basic rules for cluster formation. Establishing these rules, knowing how to control and make targeted changes in the conditions for joining of individual atoms and molecules into nanosized clusters will make it possible to form new nanostructures with prespecified properties.Synthesis of compounds (complexes) of specified chemical composition and structure is associated with the need to ensure targeted addition to the original molecule (or replacement within its structure) of individual atomic groups. This process is relatively easily carried out when obtaining low molecular weight compounds; but when obtaining more complex materials, we encounter certain difficulties due to the characteristic features of their structure and chemical conversions. Such a situation develops most often when reactions are run in the liquid phase, since in this case the reaction system is characterized by the dynamics of the chemical processes occurring in it. For reactions in the solid phase, the limiting step is approach of the reagents to each other within some distance, after which their reaction begins.The aim of this work was to study the mechanism of formation and the spectroscopic properties of nanosized complexes (clusters) of uranium with a first (inner) coordination sphere containing mixed acido ligands. The problem was posed in this way because to date, only complex systems with the uranium in an environment including just one type of acido ligand have been studied. Introducing another acido ligand (or replacing one with another acido ligand) within the first coordination sphere is associated with significantly greater difficulties, which may explain the lack of such research in the literature.The Experiment. We attempted to obtain and spectroscopically study the systems UO 2 Cl 2 ⋅3S-UO 2 I 2 ⋅3S, UO 2 (NO 3 ) 2 2S-UO 2 I 2 ⋅3S, where S = H 2 O, dimethylsulfoxide (DMSO), or hexamethylphosphoramide (HMPA). Since the attempt to obtain uranyl iodide in the solid state by direct substitution of chlorine by iodine did not lead to the desired result, first we prepared a solution of th...