Potentiometric finish in the Schöniger Halogen Method

Summary Modifications for a potentiometric finish to the oxygen flask halogen method are given. Results show its reliability for routine determinations.

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Zusammenfassung Die potentiometrische Endbestimmung der Halogene nach der Flaschen-methode vonSchöniger wird beschrieben. Die Ergebnisse zeigen die Anwendbarkeit für Routineanalysen.

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Résumé On apporte des modifications à la méthode de dosage des halogènes par la fiole à oxygène, pour terminer potentiométriquement. Les résultats montrent que l'on peut l'appliquer aux dosages en série.

     

Apparate

Ohne Zusammenfassung     

Tetrakis(triphenylphosphine oxide) complexes of the lanthanide nitrates; synthesis, characterisation and crystal structures of [La(Ph3PO)4(NO3)3]·Me2CO and [Lu(Ph3PO)4(NO3)2]NO3

The reaction of Ln(NO₃)₃·6H₂O (Ln=La, Ce, Pr or Nd) with a sixfold excess of Ph₃PO in acetone formed [Ln(Ph₃PO)₄(NO₃)₃]·Me₂CO. The crystal structure of the La complex shows a nine-coordinate metal centre with four phosphine oxides, two bidentate and one monodentate nitrate groups, and PXRD studies show the same structure is present in the other three complexes. In CH₂Cl₂ or Me₂CO solutions, ³¹P NMR studies show that the complexes are essentially completely decomposed into [Ln(Ph₃PO)₃(NO₃)₃] and Ph₃PO. Similar reactions in ethanol gave [Ln(Ph₃PO)₃(NO₃)₃] only. In contrast for Ln=Sm, Eu or Gd, only the [Ln(Ph₃PO)₃(NO₃)₃] are formed from either acetone or ethanol solutions. For the later lanthanides Ln=Tb–Lu, acetone solutions of Ln(NO₃)₃·6H₂O and Ph₃PO gave [Ln(Ph₃PO)₃(NO₃)₃] only, even with a large excess of Ph₃PO, but from cold ethanol [Ln(Ph₃PO)₄(NO₃)₂]NO₃ (Ln=Tb, Ho–Lu) were obtained. The structure of [Lu(Ph₃PO)₄(NO₃)₂]NO₃ shows an eight-coordinate metal centre with four phosphine oxides and two bidentate nitrate groups. In solution in CH₂Cl₂ or Me₂CO the tetrakis-complexes show varying amounts of decomposition into mixtures of [Ln(Ph₃PO)₃(NO₃)₃], [Ln(Ph₃PO)₄(NO₃)₂]NO₃ and Ph₃PO as judged by ³¹P{¹H} NMR spectroscopy. The [Ln(Ph₃PO)₃(NO₃)₃] also partially decompose in solution for Ln=Dy–Lu, forming some tetrakis(phosphine oxide) species.     

Template synthesis of 1,4,7-triphosphacyclononanes

Iron(II) templates based on a [(eta(5)-Cp(R))Fe]+ core have been employed for the successful synthesis of 1,4,7-triphosphacyclononane derivatives (9-aneP3R'3) from a range of appropriately functionalized coordinated diphosphines and monophosphines. 1,2-Diphosphinoethane (1,2-dpe) or (2-phosphinoethyl)phenylphosphine (Phdpe) undergo a base-catalyzed Michael-type addition to trivinylphosphine, divinyl(benzyl)phosphine, or divinyl(phenyl)phosphine in [(eta(5)-Cp(R))Fe(diphosphine)(monophosphine)]+ complexes (2a-j) to give [(eta(5)-Cp(R))Fe(9aneP3R'3)]+ derivatives (4a-j) containing coordinated triphosphacyclononanes bearing one (with Phdpe) or two (with 1,2-dpe) secondary phosphine donors. The rates of macrocyclization show a dependence on the nature of the substituent(s) R on the cyclopentadienyl ligand with increased rates being observed along the series R = H5 < (Me3Si)H4 < 1,3-(Me3Si)2H3 approximately = Me5. For coupling reactions with trivinylphosphine, a pendant vinyl function remains in the macrocyclic product (4a-g) which is readily hydrogenated to the corresponding ethyl derivatives (5a-g). Further functionalization of coordinated secondary phosphines in the initially formed macrocycles (5a-g) is achieved by proton abstraction followed by addition of the appropriate alkyl halide electrophile and gives rise to tritertiary-triphospha-cyclononanes (7a-g, 7l, 7m). All new complexes have been fully characterized by spectroscopic and analytical methods in addition to the structural determination by single-crystal X-ray techniques of [{eta(5)-(Me3Si)2C5H3)Fe(9-aneP3H2C2H3)]PF6, 4c, and [(eta(5)-Me3SiC5H4)Fe(9-aneP3Et3)]BF4, 7b. 1,4,7-Triethyl-1,4,7-triphosphacyclononane is released from its metal template (7a, 7b) by treatment with either H2O2 or Br2/H2O to give the trioxide 9-aneP3(O)3Et3 (8). Attempts to recover the trivalent phosphorus species, 1,4,7-triethyl-1,4,7-triphosphacyclononane, from the trioxide by reduction proved unsuccessful.     

Critical points and transitions in an electric power transmission model for cascading failure blackouts

Cascading failures in large-scale electric power transmission systems are an important cause of blackouts. Analysis of North American blackout data has revealed power law (algebraic) tails in the blackout size probability distribution which suggests a dynamical origin. With this observation as motivation, we examine cascading failure in a simplified transmission system model as load power demand is increased. The model represents generators, loads, the transmission line network, and the operating limits on these components. Two types of critical points are identified and are characterized by transmission line flow limits and generator capability limits, respectively. Results are obtained for tree networks of a regular form and a more realistic 118-node network. It is found that operation near critical points can produce power law tails in the blackout size probability distribution similar to those observed. The complex nature of the solution space due to the interaction of the two critical points is examined.(c) 2002 American Institute of Physics.     

Optimal design,robustness, and risk aversion

Highly optimized tolerance is a model of optimization in engineered systems, which gives rise to power-law distributions of failure events in such systems. The archetypal example is the highly optimized forest fire model. Here we give an analytic solution for this model which explains the origin of the power laws. We also generalize the model to incorporate risk aversion, which results in truncation of the tails of the power law so that the probability of catastrophically large events is dramatically lowered, giving the system more robustness.     

Isoscalar quadrupole strength in Ca from the (p,p′α0) reaction at Ep = 100 MeV

The ⁴⁰Ca(p,p′ α) reaction has been studied at an incident proton energy E_p = 99.5 MeV for proton laboratory scattering angles Θ_p^lab = 17°, 23° and 27°. Emission of α particles coincident with the scattered proton has been measured for an angular range Θ_α 0° − 180° relative to the recoil axis. A multipole decomposition for the α₀-decay channel to the ³⁶Ar ground state has been performed from the angular-correlation functions. The energy distribution of the dominating E2 strength deduced in the excitation energy range E_x = 11–21 MeV agrees reasonably well with the results from electron and α-induced α₀-decay investigations. The exhaustion of the E2 energy-weighted sum rule in this channel up to an energy of 17 MeV is 16.1(4.0)%, in accord with the study of the (α, α′ α₀) reaction. However, this value is twice what is found in the (e,e′ α₀) experiment in the same energy region. Thus, the puzzling discrepancy in the E2 strengths derived from electromagnetic and hadronic probes remains unsolved.     

Geršgorin revisited

A proof of the Ger?gorin disk theorem is given, in which the only analytic tool used is a contour integral.