Forms of Rh(III) in Nitric Acid Solutions

The forms of Rh(III) in nitric acid solutions are studied by ¹⁴N, ¹⁵N, ¹⁷O, and ¹⁰³Rh NMR and electronic absorption spectra. At HNO₃concentrations below 5 mol/l, rhodium mainly exists as low-nuclear oligomers with a bridging fragment Rh(-OH)(-ONO₂)Rh; terminal positions of the central atoms are occupied by water molecules. It was found that the isotopic equilibrium ¹⁴NO^– ₃/¹⁵NO^– ₃of the bridging ligand sets in at an abnormally high rate, at which the isotopic exchange H₂ ¹⁷O/H₂ ¹⁶O of the terminal ligands also occurs in the dimers and trimers. The formation of low-nuclear oligomers is a common feature of Rh(III) complexes in aqueous solutions with ligand deficiency in the system. The possibility of isolating rhodium from nitric acid solutions using different methods is predicted.     

State of Rh(III) in Hydrofluoric Acid Solutions

A simple method is developed for synthesizing [Rh(H₂O)₆]F₃. 3H₂O with a yield of 80–90%. ¹⁹F, ¹⁰³Rh, and ¹⁷О NMR spectroscopic studies show that the following three processes simultaneously run in the Rh(III)–HF/K–H₂O system via parallel routes: the formation of mononuclear aquafluoro complexes [Rh(H₂O)₆]³⁺ + F–→ [Rh(H₂O)₅F]²⁺ + H₂O; the formation of aquahydrofluoro complexes [Rh(H₂O)₆]³⁺ + HF₂^-→ [Rh(H₂O)₅HF₂]²⁺ + H₂O; and hydrolysis of the aqua ion followed by coordination of fluoride ion and condensation of the hydroxo species [Rh(H₂O)₆]³⁺ + 2F^– → [Rh(H₂O)₄(OH)F]⁺ + HF → condensation. [Rh(H₂O)₆]³⁺ and [Rh(H2O)5F]²⁺ are the two species making a major contribution to the material balance at high acidity under equilibrium conditions. Parameters of the ¹⁹F NMR spectra of individual complex species are presented.     

Electrodeposition of Rhodium on Cathodes of Carbon-Fiber Material from Rh(III) Complexes in Nitric Acid Solutions

Rhodium electrodeposition on cathodes of a carbon-fiber material from nitric acid solutions containing various complex forms of Rh(III) is studied. Depending on the Rh(III) form, the deposition degree varies by several times, all other factors being the same. The charge of a complex species prevailing in solution is presumably a factor determining the electrochemical behavior of Rh(III).     

14N NMR of amminecobalt(III) compounds

Directly detected ammine ¹⁴N NMR chemical shifts of 20 amminecobalt(III) compounds are reported. The coordination shifts, δ_CS = δ_coord ? δ_free, are in all cases negative and range from ?4.4 ppm for the trans ammine ligand in [Co(NH₃)₅(CH₃)]²⁺ to ?73.6 ppm for the trans ammine ligand in [Co(NH₃)₅(F)]²⁺. Among the ligands studied, the NO₂^? ligand is unique in that it exerts a significant cis influence. The regularity in trans or cis influences upon the ammine nitrogen chemical shifts provides a basis for assignments in cases where this cannot be deduced from intensity ratios. Copyright © 2003 John Wiley & Sons, Ltd.     

Cerium(III) Electrooxidation in Nitric Acid Solutions of Rare-earth Elements

The electrochemical behavior of cerium(III) in nitric acid solutions of rare-earth elements was studied. The activation energy and reaction order of cerium(III) oxidation were determined for various levels of anodic polarization.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 6, 2005, pp. 928–932.Original Russian Text Copyright © 2005 by Sedneva.     

13C, 14N, 15N and 17O NMR spectra of nitropyrroles and nitroimidazoles

Carbon, nitrogen and oxygen NMR spectra of some nitro derivatives of pyrrole and imidazole have been investigated. The ¹³C chemical shifts of para-carbons and the ¹⁷O chemical shifts of the nitro group correlate qualitatively with the electron densities on these carbon and oxygen atoms, which in turn depend upon the degree of conjugation of the nitro groups with the heterocyclic ring. Conjugation of several nitro groups with the benzene ring is in most cases not impaired by mutual interactions and the ¹³C shifts show good additivity. Such additivity is much worse in pyrrole and imidazole derivatives. Taken together with the diamagnetic nature of these deviations from additivity, this leads to a possible conclusion about the less pronounced conjugation of the nitro groups with the heterocyclic ring in heterocyclic dinitro derivatives.     

Solubility of Lead Nitrate in Aqueous Solutions of Nitric Acid and Iron(III) Nitrate

Solubility of lead(II) nitrate in the system H₂O-Fe(NO₃)₃-HNO₃ was studied using the simplex-lattice method of experiment design.     

Platinum(IV) complexation with the nitrate ion in aqueous solutions according to 195Pt, 15N, 14N, and 17O NMR data

Solutions of platinum(IV) nitrate were studied by ¹⁹⁵Pt, ¹⁵N, ¹⁴N, and ¹⁷O NMR and IR and Raman spectroscopy. It was found that in nitric acid, two interrelated systems of nitrate complexes, mono- and polynuclear ones, coexist. The complexes predominating in concentrated solutions are [Pt₂(μ-OH)(μ-NO₃)(NO₃)₂(H₂O)_{6 ? x} (OH) _x ]^{(4 ? x)+}, [Pt₄(μ-OH)₃(μ-NO₃)₃(NO₃)₃(H₂O)_{9 ? x} (OH) _x ]^{(7 ? x)+}, [Pt4(μ-OH)₄(μ-NO₃)₂(NO₃)₄(H₂O)_{8 ? x} (OH) _x ]^{(6 ? x)+}, and [Pt₄(μ-OH)₆(NO₃)₃(H₂O)_{16 ? x} (OH) _x ]^{(7 ? x)+}.     

<Superscript>103</Superscript>Rh and <Superscript>17</Superscript>O NMR study of oligomer rhodium(III) sulfates in aqueous solutions

By virtue of ¹⁰³Rh-, ¹⁷O-NMR, electrophoresis in agarose gel, and pH-metry, we report on the formation of rhodium(III) sulfate complexes in aqueous solutions. At higher concentrations of sulfuric acid (above 3 M), more than 90% of metal was found to stay in the state of symmetric polynuclear complexes containing magnetically equivalent rhodium atoms. We also labeled the ¹⁰³Rh-NMR chemical shifts for the complexes with 3, 4 and 6 metal atoms in the spectra.     

Formation of mononuclear rhodium(III) sulfates: <Superscript>103</Superscript>Rh and <Superscript>17</Superscript>O NMR study

It was shown that the monomeric rhodium sulfate complexes [Rh(H₂O)₄(SO₄)]⁺, trans-[Rh(H₂O)₂(SO₄)₂]^?, cis-[Rh(H₂O)₂(SO₄)₂]^?, and [Rh(SO₄)₃]^3? were not predominant forms in aqueous solutions. The ¹⁰³Rh NMR chemical shifts of the complexes were assigned, and the conditions for their formation in solutions, concentration parameters, and acidity at which the fraction of the monomers was maximal were determined. The constants of formation of the complexes and ion pair (IP) were estimated: K _IP = 8 ± 3.5, K ₁ ≈ 8, K _2trans ≈ 1, K _2cis ≈ 1, and K ₃ ≈ 2.     

13C, 14N, 15N and 17O NMR spectra of the charged species of nitropyrroles and nitroimidazoles

Changes in ¹³C and ¹⁴N chemical shifts of the nitro derivatives of nitrogen heterocycles upon ionization (anion or cation formation) are twofold—first a uniform paramagnetic or in the case of protonation, a uniform diamagnetic shift of all the ring resonances that parallels the changes in the respective ultraviolet spectra and must be caused by changes in the molecular excited states, and second—the influence of the conjugated nitro group. About one third of the total negative anion charge may be localized on the nitro group, which causes unusually large shifts of the ring ¹³C resonances in this case.     

DMA水溶液的1H NMR研究

测量了N，N-二甲基乙酰胺(DMA)水溶液体系不同温度下全浓度范围的^1H NMR数据，对体系中的缔合情况进行了讨论。应用化学缔合模型求得了各缔合平衡常数K和缔合平衡的△H，结合N，N-二甲基甲酰胺(DMF)和N-甲基乙酰胺(NMA)水溶液的研究结果，发现酰胺自身结构和酰胺浓度是影响酰胺水溶液性质的主要因素。     

Magnetic relaxation characteristics of Gd(III) in N,N-dimethylformamide according to 1H and 14N NMR data

The solvation of Gd³⁺ is studied in N,N-dimethylformamide by ¹H and ¹⁴N NMR in the temperature range of 298–373 K.     

N2 emission in NO and N2O reduction on Rh(100) and Rh(110)

The angular distribution of desorbing N(2) was studied in both the thermal decomposition of N(2)O(a) on Rh(100) at 60-140 K and the steady-state NO (or N(2)O) + D(2) reaction on Rh(100) and Rh(110) at 280-900 K. In the former, N(2) desorption shows two peaks at around 85 and 110 K. At low N(2)O coverage, the desorption at 85 K collimates at about 66 degrees off normal towards the [001] direction, whereas at high coverage, it sharply collimates along the surface normal. In the NO reduction on Rh(100), the N(2) desorption preferentially collimates at around 71 degrees off normal towards the [001] direction below about 700 K, whereas it collimates predominantly along the surface normal at higher temperatures. At lower temperatures, the surface nitrogen removal in the NO reduction is due to the process of NO(a) + N(a) --> N(2)O(a) --> N(2)(g) + O(a). On the other hand, in the steady-state N(2)O + D(2) reaction on Rh(110), the N(2) desorption collimates closely along the [001] direction (close to the surface parallel) below 340 K and shifts to ca. 65 degrees off normal at higher temperatures. In the reduction with CO, the N(2) desorption collimates along around 65 degrees off normal towards the [001] direction above 520 K, and shifts to 45 degrees at 445 K with decreasing surface temperature. It is proposed that N(2)O is oriented along the [001] direction on both surfaces before dissociation and the emitted N(2) is not scattered by adsorbed hydrogen.     

N,N,N‘,N’—四己基丙二酰胺从硝酸介质中萃取铀（Ⅵ）

以甲苯为稀释剂研究了N，N，N'，N'－四己基两二酰胺从硝酸介质中萃取硝酸和铀（Ⅵ）的性能．考察了水相硝酸浓度、李取剂浓度、硝酸钠浓度以及温度对萃取分配比的影响，确定了萃合物的组成．借助红外光谱分析了萃合物的结构．求得了萃取硝酸和硝酸铀酰的平衡常数及反应的热力学焓变．与N，N，N'，N'－四丁基丙二酰胺萃取铀的性能比较，发现烷基链长的增加减少了三相生成的倾向，但酰胺的萃取能力却下降．     

CO LMR spectrum of ~(14)N~(16)O and its analysis with spectra of ~(14)N~(17)O and ~(14)N~(18)O

LMR spectra for v=1←0 transitions of 14N16O in X2Π1/2,3/2 states were observed at 5.6 μm and 5.4 μm of CO laser. Introducing the advanced isotopic molecular constant scaling function to Hund's case (a) diatomic structure model, these spectra were analyzed and fitted together with all reliable previous spectral data of 14N16O as well as 14N17O and 14N18O. A full set of precise molecular parameters and their vibrational dependencies have been determined with much higher precision (1 -2 orders for most parameters). Many of them have been obtained for the first time. Using isotopic scaling function, the molecular constants of 14N17O and 14N18O were deduced.     

CO LMR spectrum of14N16O and its analysis with spectra of14N17O and14N18O

LMR spectra for v=1←0 transitions of¹⁴N¹⁶O in X²II_{1/2, 3/2} states were observed at 5.6 μm and 5.4 μm of CO laser. Introducing the advanced isotopic molecular constant scaling function to Hund’s case (a) diatomic structure model, these spectra were analyzed and fitted together with all reliable previous spectral data of¹⁴N¹⁶O as well as¹⁴N¹⁷O and¹⁴N¹⁸O. A full set of precise molecular parameters and their vibrational dependencies have been determined with much higher precision (1–2 orders for most parameters). Many of them have been obtained for the first time. Using isotopic scaling function, the molecular constants of¹⁴N¹⁷O and¹⁴N¹⁸O were deduced.     

<Superscript>103</Superscript>Rh, <Superscript>17</Superscript>O,and <Superscript>31</Superscript>P NMR study of Rh(III) complex formation in acidic sulfate-phosphate media

Rhodium(III) complex formation with phosphoric acid in strong acidic solutions has been studied by ¹⁰³Rh, ¹⁷O, and ³¹P NMR. Phosphoric acid is mainly coordinated to rhodium as a monodentate terminal HPO₄²⁻ ion, while the coordinated phosphate ion accounts for no more than 7%.     

Reduction of Np(VI) in Irradiated Solutions of Nitric Acid

The reliable separation of neptunium from dissolved nuclear fuel assumes the ability to maintain a preferred oxidation state. However, regardless of its initial redox speciation, a series of reactions occurs in nitric acid to create a mixture of oxidation states including Np(V), Np(VI) and sometimes Np(IV). To further complicate the situation, irradiated solutions such as fuel dissolution contain both transient and long-lived radiolysis products which may be strongly oxidizing or reducing. Thus, irradiation may be expected to impact the equilibrium distributions of the various neptunium valences.We have irradiated nitric acid solutions of neptunium with ⁶⁰Co gamma-rays, and measured radiolytically-induced changes in neptunium valences, as well as the nitrous acid concentration, by UV/Vis spectroscopy. It was found that in 4 M HNO3 at low absorbed doses, the oxidizing radicals oxidized Np(V) to Np(VI). However, as the irradiation proceeded the concentration of nitrous acid became sufficient to reduce Np(VI) to Np(V), and then continued irradiation favored this reduction until an equilibrium was achieved in balance with the oxidation of Np(V) by nitric acid itself. The starting abundances of the two neptunium valences did not affect the final equilibrium concentrations of Np(V) and Np(VI), and no Np(IV) was detected.