Set Of Ionic Radii Research Articles

Estimating the Gibbs Hydration Energies of Actinium and Trans-Plutonium Actinides.

The use of actinides for medical, scientific and technological purposes has gained momentum in the recent years. This creates a need to understand their interactions with biomolecules, both at the interface and as they become complexed. Calculation of the Gibbs binding energies of the ions to biomolecules, i. e., the Gibbs energy change associated with a transfer of an ion from the water phase to its binding site, could help to understand the actinides' toxicities and to design agents that bind them with high affinities. To this end, there is a need to obtain accurate reference values for actinide hydration, that for most actinides are not available from experiment. In this study, a set of ionic radii is developed that enables future calculations of binding energies for Pu3+ and five actinides with renewed scientific and technological interest: Ac3+ , Am3+ , Cm3+ , Bk3+ and Cf3+ . Reference hydration energies were calculated using quantum chemistry and ion solvation theory and agree well for all ions except Ac3+ , where ion solvation theory seems to underestimate the magnitude of the Gibbs hydration energy. The set of radii and reference energies that are presented here provide means to calculate binding energies for actinides and biomolecules.

Persona of Transition Metal Ions in Solids: A Statistical Learning on Local Structures of Transition Metal Oxides.

The local structure of a transition metal (TM) ion is a function of cation elements and valence states. More than that, in this work, by employing a trove of first‐principles data of TM oxides, the local structures of TM cations are statistically analyzed to extract detailed information about cation site preference, bond length, site structural distortion, and cation magnetization. It is found that cation radius alone poorly describes the local structure of a transition metal oxide, while the statistics of coordination number as well as the TM—O bond length distribution, especially that of the 3d TMs, can provide comprehensive knowledge for understanding the behavior of TM elements. Based on these statistics, the interplay of site distortion due to the Jahn–Teller effect, cation site similarity, and a new set of ionic radii are all obtained to chart the “persona” of transition metal ions in solids.

Revised Ionic Radii of Lanthanoid(III) Ions in Aqueous Solution

A new set of ionic radii in aqueous solution has been derived for lanthanoid(III) cations starting from a very accurate experimental determination of the ion-water distances obtained from extended X-ray absorption fine structure (EXAFS) data. At variance with previous results, a very regular trend has been obtained, as expected for this series of elements. A general procedure to compute ionic radii in solution by combining the EXAFS technique and molecular dynamics (MD) structural data has been developed. This method can be applied to other ions allowing one to determine ionic radii in solution with an accuracy comparable to that of the Shannon crystal ionic radii.

Application of the mean spherical approximation to the estimation of single ion thermodynamic quantities of salvation for monoatomic monovalent ions in aqueous solutions

Abstract : The expression for the Gibbs energy of solvation for simple 1-1 electrolytes within the mean spherical approximation has been fitted to data for 20 alkali metal halides in water. In performing this fit, one needs to assume a radius for each ion, the Pauling values often having been chosen in the past. The MSA parameters appear as corrections to these radii and are different for cations and anions. Two sets of ionic radii were considered, the Pauling values from crystallographic data and values based on X-ray diffraction results obtained in aqueous solutions. Excellent fits between theory and experiment were obtained, the results with the latter set of radii being preferred. This analysis provides an extrathermodynamic route to single ion solvation free energies and yields results which are very close to the real free energy of solvation measured by Randles.

ChemInform Abstract: ASPECTS OF PLUTONIUM SOLUTION CHEMISTRY

The effect of pH and complexation on the relative stabilities of the oxidation states of Pu is discussed. A set of ionic radii are presented for Pu in different oxidation states and different coordination numbers. A model for Pu hydration is presented and the relation between hydrolysis and oxidation state evaluated, including the problem of hydrous polymerization. Complexation of Pu is discussed in terms of the relative stabilities of different oxidation states and the effective ionic charge of PuO/sub 2//sup +/ and PuO/sub 2//sup +2/. An equation is proposed for calculating stability constants of Pu complexes and its correlation with experimental values demonstrated. The competition between inner vs outer sphere complexation as affected by the oxidation state of Pu and the pKa of the ligand is reviewed. Two examples of uses of specific complexing agents for Pu indicate a useful direction for future studies. 29 references, 8 figures, 3 tables.

Sizes and electronic polarizabilities of divalent ions in crystals

The Pauling’s form for the overlap repulsive energy is used to calculate the sizes of isoelectronic divalent ions in MgO, CaS, SrSe and BaTe crystals by minimising the next nearest neighbour repulsive interaction. The radii calculated by this method differ significantly from the conventional sets of ionic radii in a consistent way, being larger for cations and smaller for anions. The polarizability-radius cube relation is also utilized to calculate the electronic polarizabilities of ions. The electronic polarizabilities, thus obtained agree with the values determined from the refractivity measurements.

Pyrochlores. III. X-Ray, neutron, infrared, and dielectric studies of A2Sn2O7 stannates

A number of compositions [Formula: see text] and of related mixed phases were prepared and investigated. For the trivalent lanthanons from La to Lu, and for Y, the homogeneous A2Sn2O7 phases were of the cubic pyrochlore type (space group Fd3m, No. 227). Their lattice parameters gave a very good linear relationship when plotted against the Templeton–Dauben radii of A3+. The applicability of other sets of ionic radii was also tested. The lower limit of the r(A3+):r(Sn4+) ratio for cubic pyrochlore stannates is about 1.19 (Ahrens radii), while the upper limit is at least 1.60. Attempts to extend the lower limit by preparing mixed Yb + Sc stannates were only partially successful. Bi2Sn2O7 is not a cubic pyrochlore.The structures of Y2Sn2O7 and Sm2Sn2O7 were refined from X-ray powder data, and that of La2Sn2O7, from neutron powder data. The positional parameter of the majority oxygen atom, x(O2), has been found to increase with the size of A3+. The distortion of the SnO6 octahedra in the pyrochlore structure thus decreases with increasing r(A3+).From a systematic study of the infrared spectra of the stannates it appears that it is the size of the Y3+ ion rather than its chemistry (as distinct from the Ln3+ ions) that determines its place among the 3–4 pyrochlores. No evidence of ferroelectricity was found in Pr, Er, and Lu stannates between room temperature and 4.2 °K.