Helical chain structures

Fig. 17 Section of the helical chain structure found in (C70)(o-carborane)(CTV)(l,2-dichloro-benzene) 34 with C70 guest molecules in each CTV molecular cavity [79]... 

All three heavy chalcogens form polymers with an infinite helical chain structure however, the conditions under which they are produced differ... 

The 8-N rule states that the number of bonds (or local coordination, x) equals 8 minus the number of the periodic group. This rule is illustrated in Fig. 1.2 where we see that for N — 7 the halogens take dimeric structure types with x = 1, for N = 6 the chalcogenides selenium and tellurium take helical chain structures with x = 2, for N = 5 the pnictides arsenic, antimony, and bismuth take a puckered layer structure with x = 3, and for N = 4 the semiconductors... 

Use of the optically resolved complex leads to the optically active polymer, but this property, which arises from the helical chain structure, is found only in the swollen polymer and is easily lost in toluene or dichloroacetic acid solution 144). The polymerization occurs with a high degree of enantioface selection, and the model for the product backbone is indeed chiral. However, because of the presence of a mirror, plane in the polymer chain (effects of chain termini neglected), the product does not have chiral properties in solution. 

Such normal vibration analyses have been applied to the spectra of macromolecules to only a limited extent. In the first place, the only structure which has been analyzed in detail is that of the planar zig-zag chain of CHg groups, i.e., polyethylene. Neither substituted planar zig-zag chains nor the helical chain structures characteristic of many polymers [Bunn and Holmes (28)] have been submitted to such a theoretical analysis. In the second place, even for the case of polyethylene the answers are not in all instances unambiguous. Different assumptions as to the nature of the force field, and lack of knowledge of some of the force constants, has led to varying predictions of band positions in the observed spectrum. For the identification of certain modes, viz., those which retain the characteristics of separable group frequencies, such an analysis is not of primary importance, but for knowledge of skeletal frequencies and of interactions... 

An infinite ID complex [Ag( 14)( 15) with a single-stranded helical chain structure was obtained through the reaction of 6-amino-1-naphthalenesulfonic acid (H-14) and 2-methylpyrazine (15) with Ag2CC>3.58 Furthermore, when tetra- and hexaethyleneglycol-spaced ligands, 1,1 l-(3,6,9-trioxaundecane)diyl-bis(nicotinate) (16) and l,17-(3,6,9,12,15-pentaoxaheptadecane)diyl-bis(nicotinate) (17), were reacted with silver salts, double-stranded helical complexes (as exhibited in Fig. 11.24) were formed.59... 

In the gas phase, monomeric SO3 has a >3h planar structure with bond length S-0 142 pm, as shown in Fig. 16.6.2(a). The cyclic trimer (803)3 occurs in colorless orthorhombic y-S03 (mp 16.9°C), and its structure is shown in Fig. 16.6.2(b). The helical chain structure of P-SO3 is shown in Fig. 16.6.2(c). A third and still more stable form, a-S03 (mp 62°C), involves cross-linkage between the chains to give a complex layer structure. The standard enthalpies of formation of the four forms of SO3 at 298 K are listed below ... 

The Pb—Br bond (2.696 A) has been shortened relative to the terminal bond (2.852 A) and the bridging (3.106 A) Pb—Br bonds in the parent Lewis acid, which adopts a helical chain structure . The molecule Ph2PbCl2 forms chains in which an octahedral Pb atom is linked by Cl bridges. 

A number of studies have been carried out on the helical chain structure. Two crystals i.e. polyoxymethylene (POM) and poly(4-methylpentene 1) (P4MP1) have been extensively studied by Choy and Nakafuku [64] and White et al [42], respectively. Choy and Nakafuku... 

A unique, helical chain structure, 34, was described for a-( phenyl phosphonato)-trimethyltin, obtained from trimethyltin acetate and phenylphosphonic acid, formulated as [Me3Sn]+[Ph(0H)P(0)SnMe30P(0)(0H)Ph] [82]. It contains chains incorporating five-coordinate Mc3Sn units. The chains are linear at tin, but bent at... 

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