Structure sandwich-like

Alkyl derivatives such as 1,4-S6(NR)2 and S4(NR)4 can be synthesized by reacting S2CI2 with primary amines RNH2 in an inert solvent. Compounds such as 1,4-S2(NR)4 (R = —C02Et) are now also well characterized.The bis-adduct [Ag(S4N4H4)2]" " has been isolated as its perchlorate this has a sandwich-like structure and is unique in being S-bonded rather than N-bonded to the metal ion. ... 

Figure 5. Sandwich-like structural element proposed for the morphological organization of Nafion. (Reprinted with permission from ref 71. Copyright 2001 Elsevier.)...

Fig. 34 DFT calculation PHB formation in a cage of the dimeric Cr (salphen) sandwich-like structure [94] (reproduced with permission of Macomolecules94)...

These systems are based on immersion of two photoactive electrodes in an electrolyte solution with connection via an external circuit. An overall solar-spectrum hydrogen conversion efficiency of 0.25% was found at zero bias for the n-Ti02/p-GaP cell. Nozik further designed a new type of cell, so-called photochemical diodes that do not require external wires and functions without electrical bias [26]. This device [26], consisting of a small sandwich-like structure, Fig.7.2, such as Pt/n-GaP, and n-Ti02/p-GaP connected through ohmic contacts, when suspended in an appropriate electrolyte causes decomposition of water upon exposure to light. 

The bis-macrocyclic ring is positively charged because of the presence of Ni(II) and Cu(II). The crown ether and the bis-azamacrocyclic ring form a sandwich-like structure in such a way that one of the crown ether aromatic rings is located between the two metal-coordinated macrocyclic rings. The second aromatic ring is located almost parallel to the previous one outside the two linked macrocycles. 

The aromatic character of ferrocene originates in the anionic cydopen-tadienide system (18), which has six 7t-electrons delocalised over a symmetrical cyclic five-carbon system. Coordination of two such ring systems with a metal ion (iron in the case of ferrocene) in a sandwich-like structure (20) gives rise to a remarkably stable compound. 

Each of the silicon atoms is coordinated almost tetrahedrally by three sulfur atoms and a Cp (CO)2Fe group. The 81383 ring adopts a chair conformation. Whereas the sterically demanding Cp (CO)2Fe groups occupy equatorial positions, the terminal sulfur atoms are arranged axially. As expected, the exocyclic Si-8 bonds (207.3(3)-207.6(3) pm) are significantly shorter than the endocyclic Si-8 distances (217.1(3)-219.6(3) pm). In the solid state two [ Cp (CO)2Fe 38i6] anions form a sandwich-like structure (Fig. 8)... 

There are two major subdivisions of layer lattice silicates a single layer type based on a condensation of a hydroxide layer structure with one silica plane and a double layer unit in which a further inverted silica plane completes a sandwich-like structure above the hydroxide unit. Each layer lattice is theoretically complete within itself and although similar layers can stack above each other there can be no formal inter-layer ionic or covalent bond formation. 

A compound formulated as Nai8[(U 0)3(H20)6(P2Wi5056)2] 27 H2O has been reported [55] but has not been structurally characterized. A sandwich-like structure does not seem plausible given the structure of the P2W15 unit, and further study is certainly warranted. 

This results in a sandwich-like structure of PDDA/AChE/PDDA on the MWCNTs surface, which provides a favorable microenvironment to the immobilized AChE. Transmission electron microscopy (TEM) results confirm the formation of layer-by-layer nanostructures on carboxyl-functionalized MWCNTs (Fig. 3). 

An active sample of the catalyst, having undergone the whole activation procedure, exhibits a sandwich-like structure built of four layers the original foil, the dispersed CoO layer, the dispersed Co layer, and finally, on top, the residual oxygen layer including O, OH" and H2O molecules. The dimension of the Co layer, in which Co active centers are localized, increases with the temperature of activation proper [2,3]. 

A chitosan-based tubular scaffold with a sandwich-like structure for blood vessel tissue engineering... 

Other P-sheet proteins. Influenza neuraminidase contains an unusual P-sheet propeUer-like structure (Figure 5.10E). Ascorbate oxidase and galactose oxidase are laige P-sheet proteins that contain parallel P-sheet domains in a jeUyroU- or sandwich-like structure. 

The complex [Cp 2U(CN)3][N-Bu4-n] was characterized crystallograph-ically and found to posses a bent sandwich-like structure. The average U-Cp and U-(CN) distances 2.727(15) and 2.520(16) A, respectively, is 0.1 A smaller than its U(lll) analog is in good agreement with the variation in the radii of to ions. 

Figure 4.28 shows that the card comprises a symmetrical, sandwich-like structure. At the center of the card is a core sheet (16) made from a relatively rigid plastic material, such as polyvinyl chloride. In practice, the core can be constructed of two PVC layers (16a, 16b). Each layer can have a thickness of about... 

The corneal epithelium (epithelium cornea anterior layer) is made up of epithelial tissue and covers the front of the cornea (Figure 51.4). It acts as a barrier to protect the cornea, resisting the free flow of fluids from the tears, and prevents bacteria and also therapeutic drugs from entering the epithelium and corneal stroma. The epithelium of the cornea consists of five to six layers of cells packed closely and connected by tight junctions. The cornea is composed of five layers epithelium, Bowman s membrane, stroma, Descemet s membrane, and endothelium, each of alternating polarity. This sandwich-like structure makes the cornea a crucial barrier to most lipophilic and hydrophilic drugs. To penetrate these layers, optimal lipophilicity for the permeant corresponds to log D values of 2-3. °... 

The mechanical properties of fire protecting interfacial film are essential for the final stability level of the W/0 emulsions. Concentrated polymeric interfacial films may display either elastic or viscous properties that make the destabilization process difficult and time consuming. The aromatic asphaltene molecules will normally undergo a stacking into sandwich-like structures as a consequence of tire molecular association. The presence of other nanosized-particles like organic wax particles and inorganic clay particles will further enhance the stability level. However, fliese compounds are not further dealt wifli in the present chapter. 

The macrostructure of the ceramic hollow fiber membranes can be controlled by modulating the suspension compositions as well as the spinning conditions, as shown in Figure 18.4." " When water is used as both internal and external coagulants, a sandwich-like structure, i.e. a central dense layer integrated with fingers on both sides is formed (Figure 18.4(a)). 

Other phthalocyaninatometal complexes can adopt a square pyramidal geometry having the metal positioned above the plane of the ring. Phthalocyanines can adopt a sandwich like structure when the central metals are lanthanoids and actinoids. In these complexes the coordination number of the metal atoms is 8 [4],... 

In particular, a sandwich-like structure of a piezoelectric layer from the copol5mer between two silver electrodes is inlqet-printed onto a PET substrate. 

CTcloDentadlenvl-alkali Metal Compounds. SCF calculations on CpLl(NHj),j (n l-3) indicated the complexes to be largely ionic. Crystal structures have been determined for (1) [CpLi(12-crown-4)], a sandwich-like structure with Li co-ordinated on one side by 4 0 and on the other by Cp, (li) [1,2.4-(Me)Si)jC,Hi][Li(12-crown-4)j], [Cp ][LlDi] an ion-pair structure with a free [Cp ] anion, (iii) [Me CsK.3py] a 3-legged stool type structure and (iv) [MesCjK.2py] a linear zig-zag chain polymer. The nmr spectra of MesCjM in pyridine have also been reported. A shown by nau , (14) (R Li) exists in THF solution as an equilibrium mixture of an exo-lithio-monomer, an... 

Transition metals substituted polyoxometalates are obtained starting from vacant or lacunary POMs. The latter are derived from the saturated parent POM, through formal loss of one or more MOe octahedral units. Such complexes present several coordinatively unsaturated oxygen atoms, which surround the defect and form a polydentate site, able to coordinate a multitude of transition metals, M . Fundamental modes of coordination of the transition metals are in pocket and out of pocket , the latter including sandwich-like structures and metal oxide cluster stabilization, depending both on the dimensions of M and on the stoichiometic ratio between M and the vacant units. " ... 

The x-ray crystal structure analysis of the fine colorless crystals obtained by the slow evaporation of a 1 1 mixture of (31) and CA in aqueous solution at pH 7.4 provided evidence for the formation of a 2 2 complex, 41 [(Zn2L )2-(CA The complex has a sandwich-like structure stabilized by four N(CA)-Zn + coordination bonds and 7t-n stacking interactions between two bpy units (Figure 3.10) in which two pyridine rings have a trans-configuration in the solid state. 

---