Polyacetylene, crystal structure

Fig. 14a-c. Crystal structures of a /ranr-polyacetylene, b cis-polyacetylene and c polyphenylene. Reproduced with permission a from Ref.6) p. 103, b and c from Ref. 2861... 

Fig. 16a-c. Proposed crystal structures for a metal-ion doped polyacetylenes and fa metal-ion doped polyphenylene. Reproduced with permission from Ref. 4651... 

R. C. Haddon (AT T Bell Laboratories, U.SA.). I was wondering, are there any other crystal structures, besides the one you showed, of the long polyacetylene molecules for structures known ... 

To a large extent, current interest in solid-state polymerization of monoacetylenes derives from the observation of interesting electrical, magnetic, and optical phenomena in polyacetylene, (CH)j (45), a pEutially crystalline material unstable to ambient conditions typically synthesized by Ziegler-Natta techniques. The fundamental study of (CH), and its electron-transferred ( doped ) forms has been retarded by the lack of fully ordered materials. Ftilly ordered polyacetylenes are also of interest because it is conceivable that their crystal structures could allow significant interchain interactions, a situation precluded in most PDA by side chains. 

The preparation of a fully ordered polymer containing both PDA and polyacetylene moieties from the oxidatively coupled dimer of 1,11-dodecadiyne (3) has been reported (46). While the polymerization of the acetylene to an ordered polymer is revealed by the reported crystal structure ( ), the intrinsic properties of this novel polymer are imcertain at present. 

Table 1.2. Crystal structure data for trons-polyacetylene...

In their evaluation of the high-pressure, solid-state polymerization at room temperature, Aoki et al. [17] have found that both ci.r- and frans-polyacetylene are formed, as is the case for the catalytic systems. The crystal structure of solid acetylene as determined by Koski and Sandor [162] by neutron diffraction on C2D2 at liquid helium temperature, is the starting point for their discussion of the mechanism. 

Doping may impose further structural effects that depend on the size and nature of the dopant species. Although there may still not be complete accord on the crystal structure of lithium-doped polyacetylene, it appears that at low doping levels entropic factors are important in inserting a small nonaggregating ion, such as Li", into polyacetylene (PAc), with the dopant occupying sites with minimal strain or disruption of the host lattice. Iodine, on the other hand, in the form of IJ and IJ (and possibly higher polyiodides), produces structures in which anions cluster in columns or sheets to form intercalated layers between polymer chains. ... 

Zhu, Q., J.E. Fischer, R. Zuzok, and S. Roth. 1992. Crystal-structure of polyacetylene revisited— an x-ray study. Solid State Commun 83 179. 

Chien, J.W., F.E. Karasz, and K. Shimamura. 1988. Crystal-structure of pristine and iodine-doped cis-polyacetylene. Macromolecules 15 1012. 

Figure 5 shows typical x-ray diffraction curves of two types of polyacetylene films. The usual Shirakawa-type film [1,23] gave a very sharp diffraction curve. The halfwidth of the x-ray diffraction peak at 2 of 23.2 (110 and 2(X) reflections) was small (A20 = 1.2 ). However, it increased to 1.8 after the heat treatment for thermal isomerization from cis to trans form, implying that the ordered crystal structure in the as-grown cis-rich film suffered some destruction in the trans film. On the other hand, the highly stretchable film synthesized by the SE method gave a little diffused diffraction curve, as shown in Fig. 5. As the mechanical stretching proceeds, the half-width of the x-ray diffraction peak (A20 = 2.0°) decreased drastically to 1.5...

The crystal structures of the conductive polymers have been studied extensively. Polyacetylene [101], polythiophene [102], and poly(p-phenylene) [103] are typical illustrations. Compared to the low molecular-weight materials, however, the crystal structure of the... 

Another view has recently been proposed by Wegner.Naphthalene and other simple aromarics can be oxidize electrochemi-cally to form monomelic radial cat n salts (Ar. X ) which have conductivities of 10 to 10 s/cm. The crystal structures of these reveal that the aromatic moieties form stacks, along which the charges and the electrons are presumably delocalized. The structure is formally analogous to that deduced for oxidized (doped) polyacetylene in which the polyene chains are arranged in stacks. This leads to the idea that intermolecular delocalization is the important feature which leads to high conductivity. Other data are consistent with this rationale. Biphenyl and terphenyl radical cation salts have crystal structures very similar to that of oxidized (doped) poly(p-phenylene lO). In the older literature oligoanilines (26) are reported upon iodine treatment to yield conductivities up to 1 s/cm the aniline moieties are stacked in these materials as well. Poly(N-vinyl-carbazole) (27) forms radical cation structures by oxidation with... 

If polyacetylene is oxidized by either of the methods described in the proceeding section, the reaction product has a crystal structure different from the pristine polymer. This was first observed for the oxidation by treatment with iodine, AsFc-etc. by R. H. Baughman et al. The diffraction patterns of electrochemically oxidized poly(acetylene) containing AsFg, CIO, and SbF as the counterions were investigated by Monkenbusch et al. Further work on the diffraction pattern of iodinated polyacetylene is available from a number of other sources, especially from Shimamura et al. on the diffraction from oriented samples. 

Investigation of thinner c/.v-polyacetylene films revealed large numbers of even smaller fibrils, microfibrils, with a diameter of 2-3 nm. On the basis of the crystal structure of the unit cell of m-polyacetylene. the number of polyacetylene chains contained in and therefore making up the microfibrils was deduced. This ranged from about 13 chains (for 2 nm microfibrils) to 60 (for 3 nm microfibrils). Since then, these microfibrils have been regarded as the basic morphological unit of the fibril hypothesis. On this basis the fibrils discovered earlier are made up of straight microfibrils. 

Calculations of the hybridization in macrocyclic polyacetylenes have been carried out based on planar and non-planar geometries. The crystal structure of (153) shows acetylenic bonds crossed at 47.6° to each other and a cisoid deviation of 8.7° from a linear structure at each end of the acetylenes. ... 

The SCF method for molecules has been extended into the Crystal Orbital (CO) method for systems with ID- or 3D- translational periodicityiMi). The CO method is in fact the band theory method of solid state theory applied in the spirit of molecular orbital methods. It is used to obtain the band structure as a means to explain the conductivity in these materials, and we have done so in our study of polyacetylene. There are however some difficulties associated with the use of the CO method to describe impurities or defects in polymers. The periodicity assumed in the CO formalism implies that impurities have the same periodicity. Thus the unit cell on which the translational periodicity is applied must be chosen carefully in such a way that the repeating impurities do not interact. In general this requirement implies that the unit cell be very large, a feature which results in extremely demanding computations and thus hinders the use of the CO method for the study of impurities. 

Five aspects of the preparation of solids can be distinguished (i) preparation of a series of compounds in order to investigate a specific property, as exemplified by a series of perovskite oxides to examine their electrical properties or by a series of spinel ferrites to screen their magnetic properties (ii) preparation of unknown members of a structurally related class of solids to extend (or extrapolate) structure-property relations, as exemplified by the synthesis of layered chalcogenides and their intercalates or derivatives of TTF-TCNQ to study their superconductivity (iii) synthesis of a new class of compounds (e.g. sialons, (Si, Al)3(0, N)4, or doped polyacetylenes), with novel structural properties (iv) preparation of known solids of prescribed specifications (crystallinity, shape, purity, etc.) as in the case of crystals of Si, III-V compounds and... 

The process results in a cis-transoid structure. The formation of trans-polyacetylene is suggested to take place through isomerization of the new segment formed by cis insertion before it can crystallize.412... 

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