V. I. Makarenkov

Synthesis and study of Np(V) and Pu(V) benzoate complexes with bipyridine

Heteroligand compounds AnO2(bipy)OOCC6H5 (An = Np, Pu; bipy = α,α-bipyridine, C10H8N2) were synthesized and studied. It follows from powder X-ray patterns that these compounds are isostructural. Their unit cell parameters, determined by indexing of the powder X-ray patterns, are as follows: a = 9.2162 (7), b = 10.2339(8), c = 17.4083(17) Å, and β = 96.48(1)° for Np and a = 9.1983(18), b = 10.2052(18), c = 17.370(3) Å and β = 96.51(1)° for Pu. The compounds crystallize in the monoclinic system space group P21/n, Z = 4. The electronic absorption spectra of crystalline compounds suggest pentagonal-bipyramidal surrounding of the central atom and the prescence of cation-cation bonds with AnO2+ ions acting as monodentate ligands with respect to each other. The IR spectra of the compounds were recorded, and their thermal behavior in air was studied.

Synthesis and Study of Complexes of Some Trivalent Lanthanides and Americium with N,N-Dimethylacetamide and PW12O403–Anions

The synthesis of crystalline complexes of trivalent lanthanides and americium with N,N-dimethylacetamide (DMAA) and PW12O403–anions was described. Their IR and electronic absorption spectra were studied. The structure of the neodymium complex [Nd(DMAA)6PW12O40] was determined using X-ray diffraction analysis. The thermal behavior of the lanthanide complexes was studied. In the 300–400°C temperature interval, even in air, intramolecular partial reduction of the anion occurs to form products which can be characterized as tungsten bronzes.

Crystallization of salts M3[NpO4(OH)2]·nH2O (M = Na, K, Rb, Cs) from concentrated alkali solutions at low temperatures. Synthesis and structure of a new Np(VII) compound, Na3[NpO4(OH)2]·6H2O

Precipitation of salts M3[NpO4(OH)2]·nH2O (M = Na, K, Rb, Cs) from concentrated alkali solutions at low temperatures (about −10°C) was studied. From solutions with [OH−] > 9.5 M, these compounds are isolated as coarse black crystals in high yield without impurity of other phases. The K, Rb, and Cs salts crystallize in the form of the previously studied compounds K3[NpO4(OH)2]·2H2O and M3[NpO4(OH)2]·3H2O (M = Rb, Cs). In the case of Na, a new hydrate Na3[NpO4(OH)2]·6H2O was obtained, and its crystal structure was determined. Crystals of the hexahydrate consist of centrosymmetrical tetragonal-bipyramidal anions [NpO4(OH)2]3−, crystallographically independent Na(1) and Na(2) cations, and water molecules. The coordination surrounding of the Np atom is characterized by noticeable difference (Δ = 0.0203 Å) in the Np-O bond lengths in the equatorial plane of the bipyramid. The [NpO4(OH)2]3− anions are combined with the Na(2) cations to form infinite chains [Na(2)NpO4(OH)2(H2O)2]2− in such a manner that the lateral edges of the anion are simultaneously the lateral edges of the Na(2) coordination polyhedron. Incorporation of one of the two crystallographically independent O atoms of the NpO4 group into the Na(2) coordination surrounding is responsible for a noticeable difference in the Np-O bond lengths in the equator of the [NpO4(OH)2]3− anion. The types of hydrogen bonding in the structures of Na3[NpO4(OH)2]·nH2O (n = 0, 2, 4, 6) are compared.

Model of the (PuO2)2SiO4·2H2O Crystal Structure, Based on Powder X-ray Diffraction Data

Plutonyl orthosilicate dihydrate (PuO2)2SiO4·2H2O was prepared by a hydrothermal procedure at 180°C. Its powder diffraction pattern (Guinier camera, CuKα1 radiation) was indexed in the tetragonal crystal system: a 6.912(3), c 18.563(3) Å, space group I41/amd. The structure of (PuO2)2SiO4·2H2O is similar to the known structures of (UO2)2SiO4·2H2O and (UO2)2GeO4·2H2O, but differs in the mutual orientation of the chains of coordination polyhedra of actinide atoms (pentagonal bipyramids) sharing common equatorial edges.

Synthesis and study of Np(V) sesquioxalates

Neptunium(V) at its relatively high concentrations in oxalate solutions forms, along with the mono-and bioxalate complexes, the intermediate binuclear anion (NpO2)2(C2O4)34−. This anion gradually crystallizes from cold aqueous-ethanol solutions in the form of the compound Na4(NpO2)2(C2O4)3 · 6H2O, and from hot aqueous-ethanol solutions, in the form of a lower hydrate, Na4(NpO2)2(C2O4)3 · 2H2O. Both compounds were characterized by powder X-ray diffraction and by electronic absorption and IR spectra. The thermal behavior of the hexahydrate in air was studied. Attempts to prepare the related crystalline compounds M4(NpO2)2(C2O4)3 · nH2O with M = Li or NH4 failed.

New data on Np(VII) compounds with Co(NH 3 ) 6 3+ . Crystal structure of [Co(NH 3 ) 6 ] 3 [NpO 4 (OH) 2 ] 3 ·4H 2 O and refinement of the structure of [Co(NH 3 ) 6 ][NpO 4 (OH) 2 ]·2H 2 O

The structure and properties of the needle-like phase of crystalline compounds of the general composition Co(NH3)6NpO5·nH2O, precipitated from alkaline Np(VII) solutions with [Co(NH3)6]3+ ions, were studied. The needle-like phase under the layer of the mother liquor is unstable and transforms into a platelike phase identified as [Co(NH3)6][NpO4(OH)2]·2H2O (1). In the structure of 1, all the Np atoms are equivalent, but the Mössbauer spectrum recorded at a liquid helium temperature revealed the presence of two nonequivalent Np atoms. The isolated needle-like phase, according to single crystal X-ray diffraction data, at 100 K has the composition [Co(NH3)6]3[NpO4(OH)2]3·4H2O (2). In the structure of 2, there are two crystallographically independent Np(VII) atoms. The Np(1) atom is in the inversion center, and the Np(2) atom occupies a general position. The structure of 1 was additionally refined, and the structures of 1 and 2 were compared. Both compounds have a similar structure, but the structure of 2 is less ordered, and the formation of both structures is influenced by hydrogen bonds involving water molecules and [NpO4(OH)2]3– ions. In the structure of 1, hydrogen bonds of type O–H···O form a three-dimensional network. In the structure of 2, the O–H···O hydrogen bonds are weaker and form a two-dimensional network. In the structure of 1, there are two water molecules per [NpO4(OH)2]3– anion, and in the structure of 2, 4/3 water molecules. Needle-like phase 2 in contact with solutions transforms into stable platelike phase 1 with dense packing and a three-dimensional system of hydrogen bonds. The size of needle-like crystals increases, and the rate of their transformation into platelike crystals decreases with increasing alkali concentration and decreasing temperature. The influence of the experiment conditions on the interaction of Np(VII) with [Co(NH3)6]3+ ions in weakly alkaline (0.05–0.15 M) solutions was also studied. The precipitates formed are characterized by the ratio [NpO4(OH)2]3–: [Co(NH3)6]3+ = 2: 1 and are identified as the known compound LiCo(NH3)6Np2O8(OH)2·2H2O.

Synthesis and crystal structure of Th(IV), U(IV), and Np(IV) tribromoacetates

Actinide(IV) tribromoacetates of the composition [An(CBr3COO)4(H2O)2]2 (An = Th, U, Np) were synthesized and studied. Their structural feature is the formation of electrically neutral dimeric complexes. The surrounding of the An(IV) atoms in the dimers is formed by the oxygen atoms of six CBr3COO− anions and two water molecules; the coordination number of An(IV) is 9, and the coordination polyhedron can be described as distorted base-monocapped tetragonal antiprism. Four independent CBr3COO− anions in the structure are coordinated to the An(IV) atoms in different fashions: monodentate, bidentate chelate, and bidentate bridging. Hydrogen bonding links the dimers in infinite chains along [010] direction. The hydrogen bonding noticeably influences the geometric characteristics of the coordination surrounding of the An(IV) atoms.

Synthesis and properties of complexes of Np(V) and Pu(V) benzoates with phenanthroline

Complexes of 1,10-phenanthroline (phen) with Np(V) and Pu(V) benzoates of the compositions NpO2(phen)(OOCC6H5) and PuO2(phen)(OOCC6H5) were synthesized. A powder X-ray diffraction study showed that these compounds, depending on the preparation conditions, exist in the form of two phases having essentially the same composition but different powder patterns. The phases isolated from hot (70–100°C) solutions are isostructural with the previously described complexes AnO2(bipy)(OOCC6H5) (An = Np and Pu, bipy = 2,2′-bipyridine), i.e., in their structure there are dimeric (AnO2)22+ cations formed by mutual coordination of two AnO2+ ions via “yl” oxygen atoms. The compounds AnO2(phen)(OOCC6H5) prepared by slow crystallization in the cold or at weak (up to 45°C) heating are isostructural with each other but appreciably differ in the structure from the high-temperature phases. The electronic absorption spectra of the compounds and their thermal behavior were examined.

Synthesis of Pu(V) sulfates

Synthesis of Pu(V) sulfates from aqueous solutions was studied, and previously unknown Co(NH3)6PuO2(SO4)2·2H2O was prepared and characterized by X-ray diffraction analysis. It was found that it is isostructural to neptunyl(V) analog. Thermal behavior of this compound in air was studied, and its IR spectrum was recorded and analyzed. The factors preventing formation of Cs3PuO2(SO4)2·2H2O and simple sulfates of the composition (PuO2)2SO4·xH2O were examined.

Synthesis and study of new complex Pu(V) and Np(V) acetates

Double Pu(V) and Np(V) acetates of the compositions BaPuO2Ac3·2H2O and SrAnO2Ac3·3H2O with An = Pu and Np were synthesized in a well-crystallized form. In the dry state the compounds are stable in prolonged storage and are not hygroscopic. The plutonyl(V) and neptunyl(V) salts of the similar composition are isostructural. The IR spectra of the compounds were measured, and their behavior in heating was studied.