Double-metal chains

Both single- and double-stranded chains are found. The most important members of single chains are the pyroxenes including diopside. The most important double-chained minerals are the amphiboles. Some of these contain hydroxyl and fluoride ions, bonded directly to the metal cation and not to the silicon atom. 

Many highly reduced halides of scandium, yttrium, and zirconium have been found to have infinite metal-metal bonded chains.169 Zirconium chloride, for example, contains double metal layers alternating with double chlorine layers (Fig. 16.68). It was dis-... 

Both the linkages to form planes and their stacking are different depending on the kinds of A and M metals. The trigonal planar [MN3]6- unit was also observed in Ca6FeN5.18 The existence of double metal nitrides has not yet been reported for cobalt. Cobalt is between iron and nickel in the periodic table. It is an open question whether the double metal nitride with cobalt has a linear chain or a trigonal planar coordination. 

The end member of side-by-side chain condensation is the double-metal-between-double-halogen layers first found in the metallic ZrCI and ZrBr, Figure 15. 

The reaction of hydroxyl dehydration, which eliminates the chain terminal hydroxyl is a drawback in the case of production of polyols for polyurethane industry, therefore several catalysts apart from potassium and sodium hydroxide have been proposed. These catalysts, including hydroxide of rubidium, cesium, barium and strontium, or double metal cyanide, are much more expensive and toxic than classical catalysts [11], Recently, a new class of catalyst has been... 

Impact A continuous process for making long-chain polyether polyols as precursors for polyurethanes. Uses a double metal cyanide catalyst. 

Sun, X.-K. Zhang, X.-H. Wei, R.-J. Du, B.-Y Wang, Q. Fan, Z.-Q. Qi, G.-R. Mechanistic Insight into Initiation and Chain Transfer Reaction of COj/Cyclohexene Oxide Copolymerization Catalyzed by Zinc-Cobalt Double Metal Cyanide Complex Catalysts. J. Polymer Sci. Part A Polymer Chem. 2012, 50,2924-2934. 

Okuda also presented a series of rare earth compounds formed by adduct formation with the NHC moiety and simultaneous C-H activation of a side chain of the ligand (Scheme 6.6). By conducting the reaction of rare earth alkyls [MR3(THF)2] (R = CH2SiMe3) with 1 equivalent of IMes in THF at room temperature, an ortfto-metallation of one methyl group of the mesityl group in NHC ligand occurred (44). Reaction of [MR3(THF)2] (R = CH2SiMc3) with an excess of IMes in toluene yielded double metallated NHC product 45. ... 

Critical micelle concentration (Section 19 5) Concentration above which substances such as salts of fatty acids aggre gate to form micelles in aqueous solution Crown ether (Section 16 4) A cyclic polyether that via lon-dipole attractive forces forms stable complexes with metal 10ns Such complexes along with their accompany mg anion are soluble in nonpolar solvents C terminus (Section 27 7) The amino acid at the end of a pep tide or protein chain that has its carboxyl group intact—that IS in which the carboxyl group is not part of a peptide bond Cumulated diene (Section 10 5) Diene of the type C=C=C in which a single carbon atom participates in double bonds with two others... 

A common example of the Peieds distortion is the linear polyene, polyacetylene. A simple molecular orbital approach would predict S hybddization at each carbon and metallic behavior as a result of a half-filled delocalized TT-orbital along the chain. Uniform bond lengths would be expected (as in benzene) as a result of the delocalization. However, a Peieds distortion leads to alternating single and double bonds (Fig. 3) and the opening up of a band gap. As a result, undoped polyacetylene is a semiconductor. 

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