Probe electrode study of cathodically polarized PtIr-YSZ interfaces

Journal of Solid State Electrochemistry - Local cathodic polarizations of yttria-stabilized zirconia were carried out with a PtIr probe as the working electrode in a controlled atmosphere high...     

On the Relation between the Scalar Moment Problem and the Matrix Moment Problem on *-Semigroups

There is a countable cancellative commutative *-semigroup S withzero (in fact, a *-subsemigroup of G × N₀ for some abelian group G carrying the inverse involution) such that the answer to the question “if f is a function on S , with values in M_d(C) (the square matrices of order d) and such that $\sum^{n}_{j,k=1} \lbrak f(s^*_k s_j)\xi_j, \xi_k \rbrak \ge 0$ for all n in N, s₁, . . . , s_n in S , and $\xi_1$, . . . , $\xi_n$ in C^d, does it follow that $f(s) = \int_{S^*}\sigma (s) d\mu(\sigma) (s \memb S)$ for some measure $\mu$ (with values in M_d(C)₊ , the positive semidenite matrices) on the space S of hermitian multiplicative functions on S?” is “yes” if d = 1 but “no” if d = 2 (hence also for d > 2).     

New structural motifs in the aggregation of neutral gold(I) complexes: structures and luminescence from (alkyl isocyanide)AuCN

The preparation and X-ray crystal structures of (CyNC)Au(I)CN, (n-BuNC)Au(I)CN, and (i-PrNC)Au(I)CN.0.5CH(2)Cl(2) are reported and compared with those of (MeNC)Au(I)CN and (t-BuNC)Au(I)CN, which were previously described. These linear molecules are all organized through aurophilic interactions into three structural classes: simple chains ((CyNC)Au(I)CN and (t-BuNC)Au(I)CN), side-by-side chains in which two strands make Au...Au contact with each other ((n-BuNC)Au(I)CN), and nets in which multiple aurophilic interactions produce layers of gold(I) centers ((i-PrNC)Au(I)CN and (MeNC)Au(I)CN). All of these five solids dissolve to produce colorless, nonluminescent solutions with similar UV/vis spectra. However, each of the solids displays a unique luminescence with emission maxima occurring in the range 371-430 nm.     

Synthesis and Characterization of Ge(II), Sn(II), and Pb(II) Monoamides with -NH2 Ligands

The synthesis and characterization of the first divalent germanium, tin, and lead monoamide derivatives of the parent amide group -NH(2) are presented. They have the general formula (ArMNH(2))(2) (M = Ge, Ar = Ar'(C(6)H(3)-2,6-Pr(i)(2)) or Ar* (C(6)H(3)-2,6(C(6)H(2)-2,4,6-Pr(i)(3))); M = Sn, Ar = Ar*; M = Pb, Ar = Ar*). For germanium and tin, they were obtained by reacting the corresponding terphenyl halides of the group 14 elements with liquid ammonia in diethyl ether. The lead amide derivative (Ar*PbNH(2))(2) was synthesized by reaction of LiNH(2) with Ar*PbBr in diethyl ether. The compounds were characterized by IR and multinuclear NMR spectroscopies and by X-ray crystallography in the case of the (Ar'GeNH(2))(2) or (Ar*SnNH(2))(2) derivatives. They possess dimeric structures with two -NH(2) groups bridging the germanium and tin centers. For lead, the reaction with ammonia led to isolation of a stable ammine complex of formula Ar*PbBr(NH(3)) which was characterized by IR and NMR spectroscopies and by X-ray crystallography. It is the first structural characterization of a divalent lead ammine complex.     

On the mechanism of the copper-catalyzed cyclopropanation reaction

The selectivity-determining step in enantioselective copper-catalyzed cyclopropanation with diazo compounds has been studied by experimental and computational methods. The addition of the very reactive metallacarbene intermediate in an early transition state to the substrate alkene is concerted but strongly asynchronous, with substantial cationic character on one alkene carbon in the neighborhood of the transition state. Evidence from isotope effects and Hammett studies supports the nature of the transition state. Formation of a metallacyclobutane intermediate by a [2+2] addition is kinetically disfavored. Ligand-substrate interactions influencing the enantio- and diastereoselectivity have been identified, and the preferred orientation of the alkene substrate during the addition is suggested.     

Direct determination of rate constants for coupling between aromatic radical anions and alkyl and benzyl radicals by laser-flash photolysis

Coupling rates between the radicals methyl, n-, sec-, tert-butyl and benzyl (R.) and the aromatic radical anions of 1,4-dicyanonaphthalene, 9,10-dicyanoanthracene and fluorenone (A-.) have been obtained using a new laser-flash photolysis method. The radicals R. and the radical anions A-. were generated by a photoinduced electron transfer reaction between the aromatic compound A and the alkyl or benzyl triphenylborate anion RB(Ph)3-. For the first time the rate constants of the coupling reaction between methyl and benzyl radicals with aromatic radical anions have been obtained. For all the measured coupling rate constants an average value of k1 = 1.9 x 10(9) M-1 s-1 was found with a relatively small variation in the coupling rates (0.8-2.9 x 10(9) M-1 s-1). The results demonstrate that the coupling rate k1 is insensitive to changes in the steric and electronic properties of the radicals and the structure and standard potentials of the aromatic radical anions.     

On vibrations in non-linear,forced, friction-excited systems

To accelerate the development of non-linear, friction-excited systems, i.e. automotive friction brakes, novel test procedures are being developed. These include the study of the system's forced vibrations. However, there is a lack of knowledge concerning feasible test procedures, the assessment of the gathered data, and the possible vibration phenomena. In this context, the contribution at hand discusses vibrations in non-linear, forced, friction-excited systems. In the pre-flutter regime proposed criteria for identification of parameter regions in which limit cycle oscillations can occur are challenged. In the post-flutter regime frequency spectra for different excitation conditions are studied. (© 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)