Coordination Chemistry of Perhalogenated Cyclopentadienes and Alkynes. 17. Reaction of Dichloroethyne With Platinum(0) Phosphine Complexes: Formation of a .pi.-Complex, Isomerization to .beta.-Chloroethynyl Complexes, and Syntheses of Diplatinioethyne Derivatives. Molecular Structures of (Ph3P)2Pt(.eta.2-ClC.tplbond.CCl) and Cl(Ph3P)2PtC.tplbond.CPt(PPh3)2Cl

Dichloroethyne ClCECCl reacts with Pt(PPh3)2(C2H4) or Pt(PPh& to give the a-complex Pt(PPh3)2(+21C=CC1) (l),w hich can be isomerized by prolonged refluxing in toluene to trans- (Ph3P)zC1Pt-C==CC1 (2). 2 easily undergoes exchange reactions with alkylphosphines and with halide anions to yield trans-(R3P)2ClPt-C=CCl (R = Et (3)) Bu (4)) and trans-(Ph3P)z- (X)Pt-C=CCl (X = F (5a), Br (5b), I (5c)), respectively. The alkylphosphine complexes 3 and 4 can also be obtained by reaction of Pt(PR3)4 (R = Et, “Bu) with ClCECCl or from 1 and the corresponding phosphine. When Pt(PPh&(CzH4) is added to a solution of 3, a dinuclear complex 6 is formed, in which the C=C-Cl group acts as a a,a-bridging ligand. Upon standing, oxidative addition of the remaining C-C1 bond occurs and the p-ethynediyl complex trans- C1(R3P)2Pt-C=C-Pt(PPh3)2C1-Cis (R = Et (7a)) can be obtained. The corresponding p-ethynediyl complex 7b (R = Ph) is formed directly from 2 and Pt(PPh&(CzH4). 7b isomerizes upon heating in toluene to the symmetrical all-trans isomer 8. The molecular structures of 1 and 8 were determined by X-ray diffraction (1: C ~ ~ H ~ ~ C ~ Z P ~ Pa ~=C 10H.3Z11C(3~) AZ,, b = 10.392(4) A, c = 33.675(16) A, P = 90.17(3)’, monoclinic, P21/n, 2 = 4. 8: C74H&1zP4Ptz9 a = 12.938(2) A, b = 19.964(3) A, c = 24.844(3) A, P = 96.14(1)’, monoclinic, C2/c, 2 = 4)

Post legal positivism: new paradigm of legal science (jurisprudence) and practice in Brazil

The relation between law, moral, society and science is shifting in Brazil as it is changing in democratic contemporary societies. This paper proposes to reflect about this change in the Brazilian legal and social context. Jurisprudence and legal practice have been transformed intensively after the Brazilian redemocratization that began in 1985 and Federal Constitution of 1988. In the field of Jurisprudence (Legal Theory), a new legal theory called post-positivism progressively has been overcoming legal critical studies and legal positivism. In recent years, ideas as any moral values can be improved by law (positivism) or law is one of many oppressive institutions in capitalist society (legal critical studies – Marxism) have been losing place in legal theory. Nowadays, when Brazilian Constitution implements just society and legal system, different from the authoritarian military regime (1964 – 1985), it is difficult to work with a complete relativistic idea of law (positivism) or difficult to accept that law is necessarily oppressive in capitalistic societies. Otherwise the idea of science in law at post-positivistic point of view try to overcome in a dialectic way a pure science methodology (normativistic positivism) and the complete political and economic studies of law (critical legal studies – Marxism). After that, the text will show that Brazilian legal practice have changed intensively after post positivistic methodology of law and will reflect about same dilemmas of post-positivism in Brazil in the legal theory and practice

The Magnetized Electron Gas in terms of Hurwitz Zeta Functions

We obtain explicit expressions for thermodynamic quantities of a relativistic degenerate free electron gas in a magnetic field in terms of Hurwitz Zeta functions. The formulation allows for systematic expansion in all regimes. Three energy scales appear naturally in the degenerate relativistic gas: the Fermi energy Ef, the temperature T and an energy related to the magnetic field or Landau level spacing, eB/Ef. We study the cold and warm scenarios, T << eB/Ef and eB/Ef << T, respectively. We reproduce the oscillations of the magnetization as a function of the field in the cold regime and the dilution of them in the warm regime.Comment: 33 pages, 6 figures, LaTeX 2e, uses epsf. v2: References added, minor additions to content

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e+e−e^+e^- Pair Production from 10 GeV to 10 ZeV

At very high energies, pair production ($\gamma\to e^+e^-$) exhibits many interesting features. The momentum transfer from the target is very small, so the reaction probes the macroscopic properties of the target, rather than individual nuclei. Interference between interactions with different atoms reduces the pair production cross section considerably below the Bethe-Heitler values. At very high energies, photonuclear interactions may outnumber pair production. In contrast, in crystals, the interaction amplitudes may add coherently, greatly increasing the cross sections. Pair production in matter-free magnetic fields is also possible. The highest energy pair production occurs at high energy particle colliders. This article will compare pair production in these very different regimes.Comment: 37 pages with 9 figures. Invited Review for "Radiation Physics and Chemistry" Version for publication, incorporating comments by the referee, and by Gerhard Baur and Roman Le