Iaroslav Doroshenko

Sonochemical precipitation of amorphous uranium phosphates from trialkyl phosphate solutions and their thermal conversion to UP2O7

Insoluble amorphous precipitates containing uranyl and phosphate ions are obtained by sonication of solutions of three uranyl precursors, UO2(X)2, X=NO3, CH3COO, CH3C(O)CHC(O)CH3 (acetylacetonate, acac), in triesters of phosphoric acid, OP(OR)3, R=Me (trimethyl phosphate, TMP), Et (triethyl phosphate, TEP). TMP and TEP are used as high-boiling solvents and they serve also as a source of phosphate anions. Sonolysis experiments were carried out under flow of Ar at 40°C on a Sonics and Materials VXC 500W system (f=20 kHz, Pac=0.49 W cm(-3)). Powder X-ray diffraction (PXRD) reveals amorphous character of all obtained precipitates. The presence of uranyl and phosphate is evidenced by IR spectroscopy and ICP-OES analysis reveals the content of both U (38.6-43.4 wt%) and P (11.0-13.6 wt%). The thermal behavior of the substances was studied by TG/DSC analysis, which shows weight losses in the range of 19.21-24.08%. On heating the amorphous precipitates to 1000°C, crystalline uranium diphosphate UP2O7 is obtained in all cases as the only crystalline phase. Uranyl(VI) is reduced during thermolysis to U(IV) as there is no characteristic vibration of UO2(2+) in the IR spectra of solid UP2O7 products. The ICP-OES analysis of U and P content in precipitates allowed us to calculate the efficiency of precipitation of uranium from mother liquor and to compare it with the efficiency calculated from the data received by the PXRD and TG/DSC analyses. The efficiency of the uranium removal attained by our sonoprecipitation procedure was typically 30-35%. These sonochemical precipitation reactions providing insoluble uranium phosphates may be potentially interesting models for the description of behavior of uranium-containing waste or reprocessing streams.

Hexanuclear iron(III) α-aminophosphonate: synthesis, structure, and magnetic properties of a molecular wheel

A new hexanuclear molecular iron phosphonate complex, [Fe6(HAIPA)12(OH)6]·nH2O (1·nH2O) (H2AIPA = NH2(CH3)2CP(O)(OH)2, (2-aminopropan-2-yl)phosphonic acid), was synthesized from Fe2+ and Fe3+ salts in water by interaction with the ligand salts. Addition of corresponding amounts of sodium or tetramethylammonium salts of H2AIPA to the solution of iron precursors led to the formation of large bright-green crystals of complex 1. Isolated products were studied by spectroscopic and analytical methods – IR, Mossbauer spectroscopy, TG/DSC, ICP-OES, and CHN analysis. A novel {Fe6} hexanuclear molecular structure of 1 was confirmed by single crystal X-ray diffraction analysis. An octahedral coordination environment of iron cations is formed by phosphonate and hydroxo oxygens. Twelve phosphonate groups and six –OH groups act as bridging ligands and bind six Fe octahedra. Because of protonation of the amino group, the phosphonate anions coordinate in the zwitterionic form as HAIPA− (NH3+(CH3)2CPO32−). The iron cations are present in the form of high-spin Fe3+, which was confirmed by the bond valence sum (BVS) calculations and the 57Fe Mossbauer spectra. The magnetic measurements show antiferromagnetic coupling between the iron centers with decreasing temperature.

New molecular heptanuclear cobalt phosphonates: synthesis, structures and magnetic properties

The synthesis, structures and magnetic properties of two novel heptanuclear homoleptic molecular cobalt phosphonates are described. Reactions between CoCl2·6H2O and (2-{[(E)-(2-hydroxyphenyl)methylidene]amino}propan-2-yl)phosphonate ligand (HSAA2−) in methanol lead to the crystalline products [Co7(SAA)2(HSAA)4] (1) and [Co7(SAA)2(NaSAA)4] (2), which crystallize in the space groups P21/n (1) and P (2). Complexes show a similar structure motif – a centered trigonal antiprism composed of seven Co2+ ions with different coordination environments for the central and peripheral atoms. These heptanuclear molecular cages {Co7} are held together by six phosphonate ligands. The main difference in their molecular cores is the presence of four sodium cations in 2 instead of four phenolic protons in 1. Magnetic measurements reveal a strong magnetic anisotropy for both structures 1 and 2. Above 50 K, both complexes follow the Curie–Weiss law. The low temperature susceptibility data indicate differences in the intramolecular exchange coupling, as ferromagnetic and antiferromagnetic interactions are observed for 1 and 2, respectively. This can be related to structural differences leading to variations in the Co–O–Co bridging angles between the central octahedral and the six peripheral trigonal-bipyramidal Co2+ ions.