With network structures

Some compounds with network structures are synthesized by high-temperature reactions of metals with elemental sulfur [2, 8]. Rauchfuss et al. exploited the low-temperature synthesis of metal polysulfides by the reaction of metals with elemental sulfur in strong donor solvents. The reaction of copper powder with Ss in pyridine gives a copper polysulfide cluster Cu4(S5)2(-py)4 as orange crystals (Scheme 10) [45]. Furthermore, zinc powder reacts... 

Part of this symposium was directed to the synthesis, properties and applications of inorganic and organometallic macromolecules with network structures. The section on organo-oxo macromolecules relevant to sol-gel processing addresses the interesting synthesis and challenging characterization efforts in this area. Brinker (p. 314) outlines the complex chemical and physical factors which affect network formation and structure resulting from the hydrolysis of a tetraalkoxysilane. 

Several compounds with network structures have been prepared, by high-temperature reaction of metals or metal halides with Sg and/or S2CI2, as for example in the reaction of a metal halide with sulfur and S2CI2 (92) (see also Section V). 

Several compounds with network structures which contain S2 units can be prepared by high-temperature reactions (250-700 °C). An example of a reaction of a metal halide with sulfur and S2C12 is shown in equation (7). The conditions under which these S2 -containing cluster compounds are formed illustrate their high stability. 

It has just been argued that the conductivities of simple ionic liquids, on the one hand, and liquid sihca and water, on the other, are vastly different because a fused salt is an unassociated liquid (it consists of individual particles) whereas both molten silica and water are associated liquids with network structures. What is the situation with regard to the viscosities of fused salts, water, and fused silica Experiments indicate that whereas water and fused NaCl have similar viscosities not far above the melting points of ice and solid salt, respectively, fused silica is a highly viscous liquid (Table 5.46). Here then is an interesting problem. 

Result to 1 Reaction of methylpheophorbide-a (S b) with poly(ethylenimine) leads under splitting of a 5-membered ring to the water soluble polymer chlorin derivative 14) (Eq. 7) containing one porphyrin per 10 - 10 units of the polymer. Reaction with epichlorhydrin produces unsoluble materials with network structure. The reaction is controlled by electronic spectra (typical red shift frmn 632 to 644 nm while turning 8 b to 14). 

The rationale for this approach further involved the hypothesis that swelling in water occurs by virtue of water uptake in the amorphous regions of the polymers with network structure provided by relatively water-insensitive crystallites in the polymers. In this approach, vinyl trifluoroacetate was polymerized or copolymerized to provide highly syndiotactic thermoplastic polymeric intermediates that were converted to the corresponding syndiotactic PVA homopolymers or copolymers by solvolysis with mild nucleophilic reagents in media that were not solvents for both starting and end-product polymers. 

Another type of micelle formation has also attracted the attention of researchers, a brief mention of which will be made below. Gravsholt [93], in an early work, reported viscoelasticity in highly diluted aqueous solutions of some cationic surfactants, namely, certain derivatives of the base structure of cetyltrimethylammonium bromide (CTAB), CTA-X (where X=salicylate, m-chlorobenzoate, p-chlorobenzoate). He came to the conclusion that the viscoelastic behavior indicates a micellar shape other than spheres and rods. Later it has been shown [e.g. 94] by fluorescence anisotropy using fluorescent probe molecules that CTAB and sodium p-toluenesulfonate, NapTS (with suitably weak fluorescence) in aqueous solution could produce long, threadlike micelles with network structure in which the cross-points had finite lifetime. Sodium salicylate was another useful additive for synthesis, but the intensity of its fluorescence was found unsuitable for examining the behavior of the probes. 

Reduction of organotrichlorosilanes RSiCL can be utilized to prepare polymers with network structures known as polysilynes [4]. The presenee... 

Using a combination of laser vaporization and molecular beam methods with TOF-MS analysis, plus photoionization, photoelectron spectroscopy, and reactions with small molecules for characterization, Kaya and coworkers were able to produce and characterize several intriguing rare earth organome-tallic clusters with network structures (Nakajima and Kaya, 2000). These studies employed Ceo as a ligand the M-Ceo clusters formed for M = Sc had chain or ring stmctures in which metal atoms and C o were alternately... 

---