The synthesis of the new heteroleptic heterotrimetallic cluster, [(C5H5)Sn(μ-OBut)2Ge(OBut)Mo(CO)5] (1) has been achieved by a thermally induced CO substitution of the transition metal derivative, Mo(CO)6, by the basic germanium atom of the cyclopentadienyl heterobimetallic alkoxide, [(C5H5)Sn(μ-OBut)2Ge(OBut)]. The microanalysis, molecular weight (monomer in benzene), IR and multinuclear NMR data and X-ray diffraction study is consistent with the formulation of 1. The Sn atom has a trigonal pyramidal coordination environment formed by a aysmmterically π-bonded terminal C5H5 ring and two symmetrically bridged tert-butoxy groups. The four-coordinate Ge atom lies at the centre of a distorted tetrahedron and is terminally attached to a tert-butoxy group and a Mo(CO)55? fragment. 相似文献
Abstract Large-scale multi-reference single and double-excitation configuration interaction (MRD-CI) calculations are employed for the study of the isovalent compounds H2CNH, HLSiNH, hLCPH and H2SiPH in their ground state equilibrium geometry. The dipole moments and charge distributions are given. The vertical excitation energies to the intravalence states 3,1 (n, π*) and 3,1(π,π*) and to the first members of the Rydberg series originating from n and - MO's respectively are predicted; the first two ionization potentials and the Rydberg term values are also calculated. In H2CNH, mixing of Rydberg and valence-shell states with CN stretching is analyzed. The trends in relative stability of electronic and ionized states can be directly related to increased orbital stability of n relative to π as soon as a first-row constituent is replaced by a second-row atom. The calculations explain the diffuse character of the uv spectrum of imines; they treat the molecules H2SiNH and H2SiPH for the first time and present a large number of data for all four molecules which can serve as a basis for future experimental investigations on these and related compounds. 相似文献
Abstract Nitro-substituted poly[2,2′-(m-phenylene)-5,5′-bibenzimidazole]s (PBIs) were synthesized by the reaction of PBI with nitric acid in sulfuric acid under various conditions. The number of nitro groups substituted on the aromatic ring of PBI per polymeric unit varied from 1.44 to 3.55 according to the reaction conditions. An increase in reaction temperature and concentration of the nitric acid increased the degree of substitution. The inherent viscosity of the substituted polymer increased as the reaction temperature decreased. When the reaction temperature was 30°C, the inherent viscosity of the polymer increased as the concentration of nitric acid increased. The nitro-substituted PBI exhibited polyelectrolyte behavior in formic acid. The nitro groups substituted on PBI were dissociated when the polymer was heated to 450°C, displaying exothermic behavior, and the decomposition of polymer was proportional to its nitro group content. All nitro-substituted PBIs showed better solubilities in polar aprotic and acidic solvents, such as dimethylacetamide, dimethylsulfoxide, dimethylformamide, N-methylpyrrolidone, formic acid, sulfuric acid, and trifluoromethanesulfonic acid. 相似文献
Polymers with electrically charged groups exhibit a zeta potential when in contact with electrolyte solutions in water. This can be measured with solid polymers as fibers, foils, or granulates. The method of streaming potential/streaming current allows the determination of the carboxyl content of cellulose grafted with poly-(acrylic acid). Since zeta-potential measurements concern the surface of the sample, the method yields information on the type of grafting; i.e., whether it takes place mainly on the surface or throughout the bulk. By measuring the pH dependence of the zeta potential it is possible to obtain the pK value of the charged groups. The significance of zeta potential as an analytical tool is emphasized. 相似文献
Blends of poly(vinylidene fluoride) (PVDF) and polyaniline (PAni) were prepared through melt blending in a batch mixer. The morphology, rheological behavior and electrical conductivity were investigated through transmission electron microscopy (TEM) and combined electro-rheological measurements. Through TEM analysis, it was possible to observe that all blends showed typical phase separation with the presence of conductive polymer aggregates. Deformations imposed during a strain sweep caused, not only disturbance of the linear viscoelastic behavior, but also changes in electrical conductivity. The oscillatory shear altered the morphology, breaking the PAni domains into smaller ones. This effect increases the distance between them and, consequently, resulted in a decrease of the electrical conductivity. The measurements under quiescent conditions and steady shear proved that the disturbance in morphology for PVDF/PAni system is non-recoverable. Through combined electrical and rheological measurements, it was possible to achieve good correlation between the electrical and flow behavior of PVDF/PAni blends. 相似文献
The developments in membranes based on tailored block copolymers are reported with an emphasis on isoporous membranes. These membranes can be prepared in different geometries, namely flat sheets and hollow fibers. They display narrow pore size distributions due to their formation by self‐assembly. The preparation of these membranes and possibilities to further functionalize such membranes will be discussed. Different ways to control the pore size will be addressed, and the potential of block copolymer blends to fabricate membranes with tailored pore sizes will be shown.