Rhenium(V) complexes with Schiff bases: Synthesis and reaction mechanisms

Summary Some isomers of the ReOX₂LPPh₃ complexes [X = Cl or Br and L =N-methylsalicylideneiminate,N-phenylsalicylideneiminate, halfN,N'-ethylenebis(salicylideneiminate) or 8-hydroxyquinolinate] have been synthesized and characterized. Two different mechanisms for reaction of thetrans-ReOX₃(PPh₃)₂ complexes (X = Cl or Br) with the Schiff bases are supported by qualitative studies on such parameters as the Schiff base ligand form, concentration of free triphenylphosphine ligand, reaction solvent and temperature.     

1,4-Benzodiazepines as ligands. Synthesis,characterization and crystal and molecular structure ofbis(8-chloro-6-(o-chlorophenyl)-1-methyl-4H-s-triazolo[4,3-a]1,4-benzodiazepine (triazolam)) cadmium (II) dichloride

The compound C₃₄H₂₄CdN₈Cl₆ was prepared and characterized by means of X-ray, IR, and Raman measurements. The crystals are monoclinic, space groupC2/c, (No. 14) witha=22.284(3),b=14.501(2),c=14.595(2) Å=129.77(1)° andZ=4. The structure was solved by the heavy-atom method, and least-squares refinement of structural parameters led to a conventionalR factor of 0.040 for 2379 independent reflections. The structure consists of discrete molecules, in which the Cd atom is coordinated in a distorted tetrahedral geometry by two chlorine atoms and by two nitrogens of two triazolic rings of triazolam molecules. Infrared and Raman bands are assigned on the basis of the known structure. An electronic charge calculation has been performed on the unbonded ligand.     

Liquid-crystalline structure of poly(L-lysine) containing azobenzene units in the side chain

The structure of poly(L -lysine) containing 44% azobenzene units in the side chain was studied by X-ray diffraction between room temperature and 150°C. The polymer exhibits a mesomorphic structure of the smectic A1 type. In this structure, stable at least until 150°C, each smectic layer of thickness d results from the superposition of two layers: one of thickness d_A contains the free lysine side chains, the other of thickness d_B contains the azobenzene modified lysine side chains and the polypeptide main chains, that in their planes are arranged as in the “antiparallel” β-structure classical for polypeptides.     

The IR spectra of Mg5C(CO) complexes on the (0 0 1) surfaces of polycrystalline and single crystal MgO

The FTIR spectroscopy of carbon monoxide adsorbed on polycrystalline MgO smoke has been investigated as a function of the CO equilibrium pressure at constant temperature (60 K) (optical isotherm) and of the temperature (in the 300–60 K range) at constant CO pressure (optical isobar). In both cases the spectra fully reproduce those of CO adsorbed on the (0 0 1) surface of UHV cleaved single crystals [Heidberg et al., Surf. Sci. 331–333 (1995) 1467]. This result, never attained in previous investigations on dispersed MgO, contribute to bridging the gap which is commonly supposed to exist between surface science and the study of “real” (defective) systems. Depending on the surface coverage θ the main spectral features due to the CO/MgO smoke interaction are a single band shifting from 2157.5 (at θ→0) to 2150.2 cm⁻¹ (at θ=1/4) or a triplet, at 2151.5, 2137.2 and 2132.4 cm⁻¹ (at θ>1/4). These manifestations are due to the ν(CO) modes of Mg_5C²⁺· · · CO adducts formed on the (0 0 1) terminations of the cubic MgO smoke microcrystals. The formation of the CO monolayer is occurring in two different phases: (i) a first phase with CO oscillators perpendicularly oriented to the surface (2157–2150 cm⁻¹) and (ii) a second phase constituted by an array of coexisting perpendicular and tilted species (triplet at 2151.5, 2137.2 and 2132.4 cm⁻¹). A much weaker feature at 2167.5–2164 cm⁻¹ is assigned to Mg_4C²⁺· · · CO adducts at the edges of the microcrystals. The heat of adsorption of the perpendicular Mg_5C²⁺· · · CO complex in the first phase has been estimated from the optical isobar and results to be 11 kJ mol⁻¹.     

Enhanced terahertz bistability in a nonlinear Fabry-Perot resonator with n-type quantum wells

The intrinsic bistable terahertz response of intersubband plasmons in wide n-type delta-doped quantum wells is predicted to be enhanced by a resonant Fabry-Perot cavity. With a simple low-Q resonator, the threshold for bistability is decreased by a factor of 2-3 compared with that for bare multiple quantum wells.