H.E. Rohwer

Interactions of uranium and thorium with arsenazo III in an aqueous medium

Complex formation of arsenazo III with U(IV), U(VI) and Th(IV) was examined using spectrophotometric techniques together with computational methods. U(VI) (added as UO22+) forms only a 1: 1 complex at pH 1.5, and in 6 M HCl and HClO4. Both U(IV) and Th(IV) form ML and ML2 complexes in 6 M HCl. The arsenazo III-U(IV) and Th(IV) system in 6 M HCl has isosbestic points, although there are more than two absorbing species in equilibrium.

Spectrophotometric study of arsenazo III and its interactions with lanthanides

Abstract Complex formation between arsenazo III and the lanthanides was examined. Spectrophotometric methods were used, in particular mole ratio and mole fraction (Jobs plot) methods, to show that only the 1:1 complex forms at low arsenazo III concentrations and in dilute acidic medium (pH 3.5).

pH dependence of the reactions of arsenazo III with the lanthanides

Abstract Spectrophotometric techniques, together with computer simulations, were used to show that the 1 : 1 arsenazo III (3,6-bis[(2-arsonophenyl)-azo]-4,5-dihydroxy-2,7-naphthalenedisulphonic acid)-lanthanide(III) complex has four protonation states which respectively dominate at pH 3.3, 6.0, 8.3 and >10. Formation and molar absorptivity constants were calculated for the various complexes. Acid dissociation constants for free arsenazo III were also calculated from Spectrophotometric data.

Interaction of anions with arsenazo III-lanthanide (III) complexes

Abstract Spectrophotometric techniques, together with computer simulations, were used to investigate the interaction of selected anions on the complex formation of arsenazo III with the lanthanides in solutions of pH 3.3. The anions influence complexation by reacting with both the free lanthanide ion and the arsenazo III complex.

SECONDARY EFFECTS ASSOCIATED WITH THE FUNCTIONING OF BULKY SUBSTITUTED AMMONIUM CATIONS — REVISED INTERPRETATIONS.

ABSTRACT The behaviour of mono and diquaternary ammonium cations during extraction and precipitation of CoCI4 2 ions is used to clarify some aspects of the secondary effects present during their operation. A quantitative treatment of the “HCI effect” is offered. It is illustrated that this effect must be ascribed to a lowering of the activity of the cation rather than formation of undissociated acid species like H2CoCI4

POLYNITROGEN REAGENTS, IN METAL SEPARATION. PART 5 THE EXTRACTION OF URANIUM(VI) FROM SULPHURIC, NITRIC AND HYDROCHLORIC ACID MEDIA WITH ALKYLDIAMHONIUM EXTRACTANTS.

ABSTRACT A variety of a1kyldiammonium extractants (tertiary and quaternary) were used to extract uranium(VI) from sulphuric, nitric and hydrochloric acid media. The performance of these extractants was compared with that of Aliquat-336 and Alamine-336. Extractions from dilute uranium(VI) solutions were carried out in order to simulate conditions employed in the local mining industry

The chemistry of uranium. Part X. Octahedral pentahalouranate(IV) complexes

Abstract Spectrophotometric and conductometric evidence for the existence of the octahedral (UX5·L)− species (X = Cl, Br and I and L = neutral monodentate ligand) has been obtained. The conditions for the formation of these and their UX62− analogues in different non-aqueous solvents and in the presence of a variety of neutral ligands are reported. The following donor strength order was established using the data obtained: chloride ≧ tmpo, hmpa > sulphoxides (dmso), CO amides (dma, cl, etc.) > Br− > acetone, acetonitrile > iodide (tmpo = trimethylphosphine oxide, hmpa = hexamethylphosphoramide, dmso = dimethyl sulphoxide, dma = N,N-dimethylacetamide, cl = e-caprolactam). The positions of nitrate and thiocyanate are also discussed. The implications of this order on the positions of the different equilibria obtained in the practical chemistry of uranium(IV) in non-aqueous solution are discussed. Conductometric evidence obtained for ThCl4 suggests that eight coordinated (ThCl5·3L)− and ThCl84− species exist in non-aqueous solution.

The chemistry of uranium. Part 41. Complexes of uranium tetrahalide, with emphasis on iodide, and triphenylphosphine oxide, tris(dimethylamino)phosphine oxide or tris(pyrrolidinyl)phosphine oxide. Crystal structure of tetrabromobis[tris(pyrrolidinyl)phosphine oxide]uranium(IV)

Abstract The complexes UI4(tppo)2 (tppo=triphenylphosphine oxide), UI4(tdpo)2 (tdpo=tris(dimethylamino)phosphine oxide) and UI4(tpyrpo)2(tpyrpo=tris(pyrrolidinyl)phosphine oxide) have been prepared and IR and electronic spectra of both the solid and solutions are reported for them. The crystal structure of UBr4(tpyrpo)2 has been determined by X-ray crystallography. The compound is monoclinic, space group C2/c, with a=17.226(5), b=11.883(5), c=18.372(5) A, β=109.30(3)°; Dc=2.005(5)g cm−3. There are four molecules in the unit cell and the uranium atoms, which are trans-octahedrally surrounded by meridional bromide ions and apical oxygen atoms of the tpyrpo ligands, are in special positions on inversion centres. Selected bond lengths are: UBr 2.775(2) A, UO 2.22(1) A, PO 1.52(1) A, PN 1.62(1) A. The relative donor strengths of the three phosphine oxide ligands towards the uranium tetrahalides, as obtained from crystallographic data, are discussed. The preparation and characterization of the less common [UX3L3] complexes, where X=Cl, Br, I; Y=I, Ph4B; L=tdpo, tpyrpo and [UI(tdpo)5]I3 is discussed. Six coordinate chromophores are assigned to these complexes.

The chemistry of uranium—XVII Ligand donor strength order towards uranium(IV): (Rationalization and application)

Abstract Some experimental methods of determining ligand donor strengths are compared. The advantages of a potentiometric method, in which halide ion replacement could be measured directly, are indicated. The ligand donor strength order for UCl 4 and CoCl 2 as Lewis acids thus obtained is rationalized in terms of a simplified electrostatic treatment and the relative significance of the various factors important in determining donor strength for the UCl 4 system, was obtained. The donor strength order, solution equilibria and approximate lattice energy ratios of the species in solution are used to interpret the chemical behaviour of these systems.

The coordination chemistry of divalent cobalt, nickel and copper. Part II. The characterisation of a mixed ligand nickel(II) species and its thermal decomposition products. The crystal structure of (pyridine-2,6-dicarboxylato)(N,N,N′,N′-tetramethyl-1,2-diaminoethane)nickel(II) dihydrate

Abstract The magnetic and spectral properties of the complex Ni(pydca)(tmen)·2H 2 O (1) and those of the thermally-derived species Ni(pydca)(tmen)·H 2 O (2) and Ni(pydca)(tmen) (3) have been studied (pydca = pyridine-2,6-dicarboxylate, tmen = N,N,N,′,N′-tetramethyl-1,2-diaminoethane). Conflicting features in the electronic spectra prevented unambiguous stereo-chemical assignments. The presence of split ν 8 (COO) and ν as (COO) infrared absorption bands in the regions 1350–1400 cm −1 and 1610–1680 cm −1 respectively suggested dissimilar co-ordination of the carboxylate groups. The structure of (1) has been determined by the heavy-atom technique and refined by least-squares. Crystals are triclinic, space group P 1 , with a = 10.806(5), b = 8.626(4), c = 9.825(5) A, α = 114.32(2), β = 91.52(2), γ = 96.67(2)°, d obs = 1.50 (by flotation), d calc = 1.51 g cm −3 and Z = 2. With N obs = 2218, the final R factor was 0.047. Complex (1) is properly formulated as [Ni(pydca)(tmen)(H 2 O)]·H 2 O with Ni in a distorted octahedral environment, being bonded to two O atoms and the N atom of pydca, the two N atoms of tmen and one water molecule. The NiN(amine) distances differ significantly but structural parameters for the two carboxylate groups agree within experimental error. The anomalous spectral splitting appears to be common to analogous species containing fully-substituted diamines. Distorted octahedral and distorted square pyramidal symmetries are assigned to (2) and (3) respectively.