Physical characterization of uranium oxide pellets and powder applied in the Nuclear Forensics International Technical Working Group Collaborative Materials Exercise 4

Journal of Radioanalytical and Nuclear Chemistry - Physical characterization is one of the most broad and important categories of techniques to apply in a nuclear forensic examination. Physical...     

Addition of H2 Across a Cobalt–Phosphorus Bond

Addition of H₂ across the cobalt–phosphorus bond of (PPP)CoPMe₃ ( 3 ) is demonstrated, where PPP is a monoanionic diphosphine pincer ligand with a central N‐heterocyclic phosphido (NHP^?) donor. The chlorophosphine Co^II complex (PP^ClP)CoCl₂ ( 2 ) can be generated through coordination of the chlorophosphine ligand (PP^ClP, 1 ) to CoCl₂. Subsequent reduction of 2 with KC₈ in the presence of PMe₃ generates (PPP)CoPMe₃ ( 3 ), in which both the phosphorus and cobalt centers have been reduced. The addition of 1 atm of H₂ to complex 3 cleanly affords (PP^HP)Co(H)PMe₃ ( 4 ), in which H₂ has ultimately been added across the metal–phosphorus bond. Complex 4 was characterized spectroscopically and using computational methods to predict its geometry.     

Multimetallic assemblies using piperazine-based dithiocarbamate building blocks

Treatment of cis-[RuCl2(dppm)2] (dppm = bis(diphenylphosphino)methane) with dithiocarbamates, NaS2CNR2 (R = Me, Et) and [H2NC5H10][S2CNC5H10], yields cations [Ru(S2CNR2)2(dppm)2](+) and [Ru(S2CNC5H10)2(dppm)2](+), respectively. The zwitterions S2CNC4H8NHR (R = Me, Et) react with the same metal complex in the presence of base to yield [Ru(S2CNC4H8NR)(dppm)2](+). Piperazine or 2,6-dimethylpiperazine reacts with carbon disulfide to give the zwitterionic dithiocarbamate salts H2NC4H6(R2-3,5)NCS2 (R = H; R = Me), which form the complexes [Ru(S2CNC4H6(R2-3,5)NH2)(dppm)2](2+) on reaction with cis-[RuCl2(dppm)2]. Sequential treatment of [Ru(S2CNC4H8NH2)(dppm)2](2+) with triethylamine and carbon disulfide forms the versatile metalla-dithiocarbamate complex [Ru(S2CNC4H8NCS2)(dppm)2] which reacts readily with cis-[RuCl2(dppm)2] to yield [{Ru(dppm)2}2(S2CNC4H8NCS2)]. Reaction of [Ru(S2CNC4H8NCS2)(dppm)2] with [Os(CH=CHC6H4Me-4)Cl(CO)(BTD)(PPh3)2] (BTD = 2,1,3-benzothiadiazole), [Pd(C6H4CH2NMe2)Cl]2, [PtCl2(PEt3)2], and [NiCl2(dppp)] (dppp = 1,3-bis(diphenylphosphino)propane) results in the heterobimetallic complexes [(dppm)2Ru(S2CNC4H8NCS2)ML(n))](m+) (ML(n) = Os(CH=CHC6H4Me-4)(CO)(PPh3)2](+), m = 1; ML(n) = Pd(C,N-C6H4CH2NMe2), m = 1; ML(n) = Pt(PEt3)2, m = 2; ML(n) = Ni(dppp), m = 2). Reaction of [NiCl2(dppp)] with H2NC4H8NCS2 yields the structurally characterized compound, [Ni(S2CNC4H8NH2)(dppp)](2+), which reacts with base, CS2, and cis-[RuCl2(dppm)2] to provide an alternative route to [(dppm)2Ru(S2CNC4H8NCS2)Ni(dppp)](+). A further metalla-dithiocarbamate based on cobalt, [CpCo(S2CNC4H8NH2)(PPh3)](2+), is formed by treatment of CpCoI2(CO) with S2CNC4H8NH2 followed by PPh3. Further reaction with NEt3, CS2, and cis-[RuCl2(dppm)2] yields [(Ph3P)CpCo(S2CNC4H8NCS2)Ru(dppm)2](2+). Heterotrimetallic species of the form [{(dppm)2Ru(S2CNC4H8NCS2)}2M](2+) result from the reaction of [Ru(S2CNC4H8NCS2)(dppm)2] and M(OAc)2 (where M = Ni, Cu, Zn). Reaction of [Ru(S2CNC4H8NCS2)(dppm)2] with Co(acac)3 and LaCl3 results in the formation of the compounds [{(dppm)2Ru(S2CNC4H8NCS2)}3Co](3+) and [{(dppm)2Ru(S2CNC4H8NCS2)}3La](3+), respectively. The electrochemical behavior of selected examples is also reported.     

Energy transfer dynamics in Re(I)-based polynuclear assemblies: a quantitative application of Förster theory

The synthesis, structure, and photophysical properties of a new family of tetranuclear FeRe 3 chromophore-quencher complexes having the general form [Fe(pyacac) 3(Re(bpy')(CO) 3) 3](OTf) 3 (where pyacac = 3-(4-pyridyl)-acetylacetonate and bpy' is 4,4',5,5'-tetramethyl-2,2'-bipyridine (tmb, 1), 2,2'-bipyridine (bpy, 2), and 4,4'-diethylester-2,2'-bipyridine (deeb, 3)) are reported. Time-resolved emission data acquired in room-temperature CH 2Cl 2 solutions exhibited single exponential decay kinetics with observed lifetimes of 450 +/- 30 ps, 755 +/- 40 ps, and 2.5 +/- 0.1 ns for complexes 1, 2, and 3, respectively. The emission in each case is assigned to the decay of the Re (I)-based (3)MLCT excited state; the lifetimes are all significantly less than the corresponding AlRe 3 analogues (2250 +/- 100 ns, 560 +/- 30 ns, and 235 +/- 20 ns for 4, 5, and 6, respectively), which were also prepared and characterized. Electron transfer is found to be thermodynamically unfavorable for all three Re (I)-containing systems: this fact coupled with the absence of optical signatures for the expected charge-separated photoproducts in the time-resolved differential absorption spectra and favorable spectral overlap between the donor emission and the acceptor absorption profiles implicates dipolar energy transfer from the Re (I)-based excited state to the high-spin Fe (III) core as the dominant quenching pathway in these compounds. Details obtained from the X-ray structural data of complex 2 allowed for a quantitative application of Forster energy transfer theory by systematically calculating the separation and spatial orientation of the donor and acceptor transition moment dipoles. Deviations between the calculated and observed rate constants for energy transfer were less that a factor of 3 for all three complexes. This uncommonly high degree of precision testifies to both the appropriateness of the Forster model as applied to these systems, as well as the accuracy that can be achieved in quantifying energy transfer rates if relative dipole orientations can be accounted for explicitly.     

The Hertz contact problem,coupled Volterra integral equations and a linear complementarity problem

This paper is concerned with the indentation of an elastic half-space by an axisymmetric punch under a monotonically applied normal force and under the assumption of Coulomb friction with coefficient μ$\mu$ in the region of contact. Within an inner (unknown) circle the contact is adhesive, while in the surrounding annulus the surface moves inwards with increasing load. In this paper it is shown how this problem is equivalent to two coupled Abel's equations with an unknown free point, the inner circumference of the annulus. It is further shown that a product integration finite difference approximation of those integral equations leads to a mixed linear complementarity problem (mixed LCP). A method based on Newton's method for solving non-smooth nonlinear equations is demonstrated to converge under restrictive assumptions on the physical parameters defining the system; and numerical experimentation verifies that it has much wider applicability. The method is also validated against the approach of Spence. The advantage of the mixed LCP formulation is that it provides the radius of the inner adhesive circle directly using the physical parameters of the problem.     

Pectenotoxin-2 synthetic studies. 3. Assessment of the capacity for stereocontrolled cyclization to form the entire C1-C26 subunit based upon the double bond geometry across C15-C16

Second-generation synthetic routes to enantiopure sulfone 21 and aldehyde 24 are described. The union of these two intermediates by means of a Julia-Kocienski coupling gave rise to a series of E-configured building blocks that did not prove amenable to transannular cyclization. Alternatively, when the C15-C16 double bond was introduced with Z-geometry by Wittig olefination, spontaneous closure to generate a tetrahydrofuran culminated an ensuing direct dihydroxylation step. The structural assignment to 35, undergirded by detailed 1H and 13C NMR studies, is consistent with proper transannular bonding so as to deliver the entire C1-C26 fragment of PTX2.     

Synthesis of Ozone at Atmospheric Pressure by a Quenched Induction-Coupled Plasma Torch

The technical feasibility of using an induction-coupled plasma (ICP) torch to synthesize ozone at atmospheric pressure is explored. Ozone concentrations up to ~250 ppm were achieved using a thermal plasma reactor system based on an ICP torch operating at 2.5 MHz and ~11 kVA with an argon/oxygen mixture as the plasma-forming gas. The corresponding production rate and yield were ~20 g ozone/hr and ~2g ozone/kWh, respectively. A gaseous oxygen quench formed ozone by rapid mixing of molecular oxygen with atomic oxygen produced by the torch. The ozone concentration in the reaction chamber was measured by Fourier Transform infrared (FTIR) spectroscopy over a wide range of experimental conditions and configurations. The geometry of the quench gas flow, the quench flow velocity, and the quench flow rate played important roles in determining the ozone concentration. The ozone concentration was sensitive to the torch RF power, but was insensitive to the torch gas flow rates. These observations are interpreted within the framework of a simple model of ozone synthesis.     

An electronic spectroscope for classroom displays of visible spectra

This article is an electronic publication in Spectrochimica Acta Electronica (SAE), a section of Spectrochimica Acta Part B (SAB). The hardcopy text is accompanied by an electronic archive, stored on the SAE homepage at http://www.elsevier.nl/locate/sabe. The archive contains program, data and text files. The hardcopy text describes a program that has been developed to accept data from a compact electronic spectrograph and translate the data into a display on a computer screen. The computer display mimics the view seen through a direct vision spectroscope. Atomic spectra appear as vertical lines of the appropriate color dispersed on a black field. A conventional plot of intensity versus wavelength is simultaneously displayed. The update of the display is sufficiently rapid that the image on the screen is essentially a real-time representation of the light entering the spectrograph. The system was designed for use in conjunction with video projection equipment in demonstrations to large groups of students.