Terunosuke Nomura

Structure of trans-chloronitrosyltetrakis(pyridine)ruthenium(II) bis(hexafluorophosphate) hemihydrate

Abstract The structure of trans-chloronitrosyltetrakis(pyridine)ruthenium(II) bis(hexafluorophosphate) hemihydrate, [RuClpy4NO] (PF6)2·1/2H2O, was determined by X-ray structure analysis. The compound crystallizes in monoclinic form, space group P21/c, with a = 16.0201(12), b = 1.5306(15), c = 27.0912(20) A, β = 91.78(1)°, Z = 8. Least-squares refinement of the structure yielded a final R factor of 0.051 for 4229 independent reflections with |Fo|⩾ 3σ(|Fo|) collected byu a counter method. There are two crystallographically independent formula units in the asymmetric unit. Both have essentially the same structure. The complex cation has a trans octahedral geometry with a nitrosyl and a chloride in the axial position and four pyridines in the equatorial position. The four pyridines form a propeller-like arrangement with an average pitch of about 46°. The RuNO group is approximately linear: the RuNO angle is 174.8(1.9)°, the RuN bond length is 1.760(9) and that of N is 1.132(13) A. The RuCl bond length is 2.314(1) A; this is shortened by the trans-shortening effect of the nitrosyl. The average separation distance of Ru(pyridine) is 2.111(6) A. NMR spectra, along with their temperature dependence, suggests that rapid cogwheel rotation of pyridine rings about RuN(py) axis is occuring in solution.

Theory of chromatographic separation of isotopes. II. Theory and practical parameters for displacement chromatographies.:Theory and Practical Parameters for Displacement Chromatographies

A mathematical model for chromatographic isotope separation systems is derived starting from a simple theoretical equation for concentration profiles in an ideal displacement chromatogram. The theoretical equation is combined with appropriate material balances to develop a set of equations which relate the size, production rate and start-up time of chromatographic separation equipment to the degree of isotope enrichment. These equations are easy to use, and require a minimum of empirical data. The model incorporates a series of simplifying assumptions which are valid for displacement chromatographies where the isotopic separation coefficient is small and the degree of enrichment accomplished in a single column is not very high. Thus the model is applicable to most isotope separation systems of practical interest (including uranium enrichment), although it may be inadequate for certain special cases.

Theory of Chromatographic Separation of Isotopes, (III): Analysis of Non-Displacement Chromatography

A fundamental equation applicable to any kind of chromatography is solved on the assumption that velocity and chromatographic diffusion coefficient of the species under consideration are constant and its concentration is finite. The results can be used to describe the chromatographic behavior of the species in breakthrough, reverse break. through and band operations, covering not only the chromatographic distribution of isotopes but also that of easily separable chemical species, especially in the case of elution chromatography. Some numerical calculations are performed to show how the shapes of the isotopic mole fraction and isotopic concentration profiles in band operation of a two-isotope chromatography are influenced by the velocity ratio and chromatographic diffusion coeffi-cient ratio of the two isotopes, and by the initial band width. These calculations yield some interesting results, including a clear indication of the possibility of reverse enrich-ment.KEYWORDS: non-displacement chromatography, radioisotopes, radioactivity, diffusion coefficients, velocity ratio, isotope separation, equations, numerical solutions, mole fraction