Zigzag chains linear polymers

Coordination polymers have also been investigated for third-order NLO properties. " Thus, [Co(NCS)2(bpms)2] (bpms = l,2-bis(4-pyridylmethyl)disulfenyl) affords a 1-D double zigzag chain coordination polymer (1-D double chain Scheme 5c) and shows significant third-order NLO properties.Mn-4,4 -bpy polymers also show third-order NLO properties. Recently, the 1-D quantum wire [ Ni(l,2-chxn)2Br 2Br] j (1-D linear chain Scheme 5a) demonstrated gigantic third-order NLO activity. ... 

In all cases, linear polymers were obtained with chains that consisted predominantly of l-methylene-3-cyclopentyl or l-methylene-3-cyclohexyl units, respectively, and were characterised by a chain planar zigzag conformation [446, 495, 496],... 

Examples of linear chain polymers shown as a zigzag chain to emphasize that the bond angles on the carbon atoms in the chain are 109°. 

The carbon atom is normally (exclusively, for our purposes) tetravalent. In compounds such as methane (CH4) and carbon tetrachloride (CCU) the four identical substituents surround it in a symmetrical tetrahedral geometry. If the substituent atoms are not identical, the symmetry is destroyed, but the general tetrahedral pattern is maintained. This is stiU true for each carbon atom in the interior of a linear polymer chain, where two of the substituents are chains. If a polyethylene chain were to be stretched out, for example, the carbon atoms in the chain backbone would lie in a zigzag fashion in a plane, with the hydrogen substituents on either side of the plane (Fig. 4.1). In the case of polyethylene, in which aU the substituents are the same, this is the only arrangement possible. With vinyl polymers, however, there are several possibilities. 

A [Cu Co Ni ] coordination polymer, [ LCu(CH30H)(H20)Mn Ni(CN)4 ] (H20)(CH3CN), which consists of linear zigzag chains constructed from LCuMn nodes connected by [Ni(CN)4] spacers (Fig. 18) has been obtained. The [Ni(CN)4] ions interact only with the manganese(II) ions from two nodes through two trans CN groups. 

From the viewpoint of synthetic polymer chemistry, although the formation of stereospecific polymers (isotactic and syndiotactic) is very popular, the present polymer is the first example having a double syndiotactic structure. In ad tion, the polymer consists of an alternating zigzag-linear main chain structure. 

Linear macromolecules having a constitutional repeating unit such as -CH2-CHX- (X H) show two further stereoisomerisms, i.e., optical isomerism and tacticity. The stereoisomerism named tacticity has its origin in the different spatial arrangements of the substituents X. When we arrange the carbon atoms of the polymer main chain in a planar zigzag conformation in the paper plane. 

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