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“Nanosecond” electrochemistry is used to study acoustically emulsified mixtures of aqueous electrolyte and smaller quantities of heptane. Significant current spikes of microsecond duration are observed under potentiostatic conditions and attributed to the impacting of heptane droplets onto the electrode surface. The polarity of the transients is found to change as the electrode potential varies through the accepted potential of zero charge of the electrode/electrolyte system for both gold and platinum electrodes. A possible explanation is suggested and the implications for a generic approach to the experimental measurements of potentials of zero charge (pzc) of solid electrodes noted.

A family of new organometallic and coordination compounds supported by the diamine−bis(phenolate) ligands O2NN‘^Me and O2NN‘^tBu are reported [H2O2NN‘^R = (2-C5H4N)CH2N(CH2-2-HO-3,5-C6H2R2)2, where R = Me (1a) or ^tBu (1b)]. Reaction of H2O2NN‘^R with sodium hydride in THF gives the corresponding sodium salts Na2O2NN‘^R (R = Me (2a) or ^tBu (2b)). Reaction of H2O2NN‘^R with Zr(CH2SiMe3)2Cl2(Et2O)2 gives the cis-dichloride derivatives ZrCl2(O2NN‘^R) (R = Me (3a) or ^tBu (3b)), which exist as two isomers (possessing either C1 (major) or Cs symmetry) in dynamic equilibrium with each other in solution. The compound 3b can also be prepared from Na2O2NN‘^tBu and ZrCl4(THF)2, but reaction of Na2O2NN‘^Me with either ZrCl4 in benzene or ZrCl4(THF)2 in THF gives mixtures of 3a and the eight-coordinate bis(diamine−bis(phenolate)) complex Zr(O2NN‘^Me)2 (4a). The latter can also be prepared from 2 equiv of H2O2NN‘^Me and Zr(CH2SiMe3)4. Treatment of Zr(NMe2)4 with H2O2NN‘^tBu leads to the bis(dimethylamide) derivative Zr(NMe2)2(O2NN‘^tBu) (5b). Similar protonolysis reactions between ZrR‘4 (R‘ = CH2SiMe3, CH2CMe3, or CH2Ph) give the corresponding organometallic alkyl or benzyl compounds ZrR‘2(O2NN‘^R) [R‘ = CH2SiMe3 (8a, 8b), CH2CMe3 (9a, 9b), or CH2Ph (10a, 10b); R = Me (suffix a) or ^tBu (suffix b)]. The dichloride complexes ZrCl2(O2NN‘^R) (3a, 3b) are also precursors to new organometallic derivatives, and treatment with LiR‘ (R‘ = Me or CH2SiMe3) or R‘MgCl (R‘ = CH2Ph or C3H5) yields ZrR‘2(O2NN‘^R) [R‘ = Me (6a, 6b), η³-C3H5 (7b), CH2SiMe3 (8a, 8b), CH2Ph (10a, 10b)]. The thermally unstable bis(η³-allyl) complex 7b is highly fluxional in solution. Reaction of the dibenzyl compound 10a or 10b with B(C6F5)3 in the presence of THF gives the cationic complexes [Zr(CH2Ph)(THF)(O2NN‘^R)]⁺ as the [PhCH2B(C6F5)3]^- salts (11a, 11b). The X-ray crystal structures of the compounds 3a, 3b, 4a, 5b, 6a, 6b, and 10a are described.

The molecular packing in Langmuir−Blodgett (LB) films of the title compound, 2,4-bis[4-(N-methyl-N-alkylamino)phenyl]squaraine, is influenced by chromophore-dominated interactions when the alkyl chains are short and by van der Waals interactions when they are sufficiently hydrophobic. The butyl to dodecyl analogues pack parallel to the substrate with interlayer spacings of 8.2−8.9 Å from grazing incidence X-ray synchrotron diffraction (GIXD). In contrast, the tetradecyl to docosyl analogues adopt a “U-shaped” configuration, with the chromophore parallel to the substrate, and the d spacing increases from 19.8 to 24.1 Å. The transition is manifested by an abrupt change in the molecular area in contact with the substrate and by subtle differences in the linear and second-order nonlinear optical properties. Freshly deposited monolayers have a broad absorption maximum at 660−695 nm and exhibit second-harmonic generation, but with time, films of the higher alkyl analogues, tetradecyl to docosyl, alter to an H-aggregate phase (λmax = 530 nm) with loss of SHG. Long-term stability has been observed for films of 2,4-bis[4-(N-methyl-N-hexylamino)phenyl]squaraine:  the LB monolayer has an optimum susceptibility of χ⁽²⁾zzz ≈ 710 pm V^-1 at 1.064 μm, a thickness from atomic force microscopy (AFM) and surface plasmon resonance (SPR) of 5.0 ± 0.5 Å (cf. 8.5 ± 1.5 Å layer^-1 in the bulk film), and real and imaginary components of the dielectric permittivity of εr = 3.0 ± 0.1 and εi = 0.7 ± 0.1 respectively at 532 nm.

The linear and nonlinear optical properties of 2,4-bis[4-(N-methyl-N-alkylamino)-2,6-dihydroxyphenyl]squaraine (I), 2,4-bis[4-(N,N-dialkylamino)-2-hydroxyphenyl]squaraine (II), and 2,4-bis(8-hydroxy-9-julolidinyl)squaraine (III) are reported. Electrospray ionization mass spectrometry (ESI-MS) has provided evidence of association in dilute solution (ca. 2 × 10^-5 mol dm^-3) with m/z values which may be assigned to dimeric aggregates for dye II. Solid solutions of this dye in poly(vinyl acetate) show second-harmonic generation (SHG), albeit very weak, and therefore indicate that the dimeric aggregate is noncentrosymmetric. In contrast, dyes I and III form heptameric aggregates with their solid solutions being SHG-inactive. There is some correlation between the type of aggregate from ESI-MS and the Langmuir film spectra, but van der Waals interactions between the hydrophobic groups play a more significant role in determining the structure at the air−water interface. The absorption maxima of the Langmuir and deposited Langmuir−Blodgett films vary from 530 nm to the near-infrared, but only those films with a maximum at 650−700 nm, or a significant shoulder in this range, are SHG-active. The second-order behavior is not an inherent property of the molecule itself but, instead, is a result of intermolecular effects and is dependent upon the noncentrosymmetry of the aggregate and the film.

Abstract: Host specificity ofUrophora quadrifasciata (Meig.) [Dipt.: Tephritidae], an introduced biological control agent of diffuse and spotted knapweed, was investigated by exposing flies to safflower,Carthamus tinctorius L., and 2 native knapweeds,Centaurea americana Nutt. andC. rothrockii Greenman. Results of the tests, and literature records indicate thatU. quadrifasciata is host specific to a few closely related plants of introduced knapweed species, and thus poses no threat to economically and ecologically important plant species in the United States.

The electrochemically induced substitution of thin films of polypyrrole, polythiophene, poly(3-methylthiophene), and poly(2,2‘-bithiophene) with the nucleophiles Cl^-, Br^-, methanol, and 3-bromopropanol has been investigated by cyclic voltammetry, electron microprobe analysis, IR spectroscopy, and NMR spectroscopy. The degree of substitution obtained is potential dependent and varies between nucleophile/polymer combinations. Thus, reaction of polythiophene, poly(3-methylthiophene), or polypyrrole with Cl^- at 1.4 V vs SSCE results in chlorination of approximately 80% of the rings, while for poly(2,2‘-bithiophene) only 20% substitution is obtained. Reaction with 3-bromopropanol, results in 25−35% substitution for both poly(3-methylthiophene) and polypyrrole. The substituted polymers are electroactive and conductive. However, for substitution of the polythiophenes by Cl^-, electrochemically deactivated intermediates with low conductivity can be isolated. Reaction of poly(3-methylthiophene) with methanol results in solubilization of the polymer in acetonitrile.

This paper presents a solution of the H∞ control problem for a class of continuous-time nonlinear systems. The method is based on a fuzzy dynamical model of the nonlinear system. A suitable piecewise differentiate quadratic (PDQ) Lyapunov function is used to establish asymptotic stability of the closed-loop system. Furthermore, a constructive algorithm is developed to obtain the stabilizing feedback control law. The controller design algorithm involves solving a set of suitable algebraic Riccati equations. An example is given to illustrate the application of the method

Nucleophilic addition of primary amines RNH2 to Cβ of the diiron allenyl complex [Fe2(CO)6(μ-PPh2){μ−η¹:η²-(H)C&dbd;C&dbd;CH2}] (1) affords the zwitterionic dimetallacyclopentane derivatives [Fe2(CO)6(μ-PPh2){μ−η¹:η¹-H2C−C(NHR)−CH2}] (R = Prⁱ (2a), CH2Ph (2b), C6H11 (2c), Prⁿ (2d)). In refluxing toluene, 2a−d rearrange to give the nitrogen-coordinated organodiiron α,β-unsaturated amines [Fe2(CO)5(μ-PPh2){μ−η¹(C):η²(C):η¹(N)-(H)C&dbd;CCH3(NHR)}] (R = Prⁱ (3a), CH2Ph (3b), C6H11 (3c), Prⁿ (3d)) via loss of carbon monoxide, a 1,3-hydrogen migration, and coordination of the β-amino group. The bridging hydrocarbon in 3a−d adopts a highly unusual exo conformation with respect to the phosphido ligand. Compounds 3a−d are the first diiron β-substituted enamine complexes to be isolated and structurally characterized. Such compounds have previously been proposed as short-lived intermediates which readily isomerize to their alkylidene-bridged counterparts. Complexes 3a and 3c react with trimethyl phosphite to afford the stable alkylidene valence isomers [Fe2(CO)5{P(OMe)3}(μ-PPh2){μ-CHC(CH3)(NHR)}] (R = Prⁱ (4a), C6H11 (4c)). In contrast, in refluxing toluene, 2a−b react with trimethyl phosphite to give the α,β-unsaturated bridging acyl complexes [Fe2(CO)5{P(OMe)3}(μ-PPh2){μ-O&dbd;C−CH&dbd;CMe(NHR)}] (R = Prⁱ (5a), CH2Ph (5b)), which probably result from the formal insertion of carbon monoxide into an alkylidene intermediate. Single-crystal X-ray analyses of 5a and 5b showed the position of substitution to be the iron atom σ-bonded to the acyl oxygen, trans to the phosphido bridge in 5a and trans to the iron−iron bond in 5b. Variable-temperature ³¹P{¹H} and ³¹P-³¹P 2D exchange NMR studies have been used to examine an exchange process that equilibrates two isomers of 4a and 5b, which differ in the position of the trimethyl phosphite. At low temperature, 4a exists as a 4:1 mixture of these two substitutional isomers, while at room temperature they are in fast exchange, on the NMR time scale. The free energy of activation associated with this exchange (ΔG^&thermod;273 = 9.5 kcal mol^-1, 4a; ΔG^&thermod;273 = 10.4 kcal mol^-1, 5b) is fully consistent with a restricted trigonal twist at the phosphite-substituted iron center. This exchange process also appears to be common to the alkylidene derivative 5b, which has similar ³¹P{¹H} line broadening characteristics and free energy of activation. Full structural details of compounds 2a, 3a, 4c, 5a, and 5b are reported.