Chain structure extension

Halide bridged nickel(II)/platinum(IV) and palladium(II)/platinum(IV) complexes with onedimensional linear-chain structures have been studied extensively.556-559 These are analogous to the linear-chain platinum(II)/platinum(IV) systems described in Section 6.5.13 and have similar broad and intense intervalence bands.556-559 However, they have weaker metal-metal interactions resulting in more localized valences than the all platinum analogues.556-559... 

Thus for all //, u fn) increases at least proportionally to n, this fact being a consequence of the chain structure. The estimate (10.1) a priori is correct only for the number of simultaneous contacts among // noninteracting and uncorrelated chains, occupying the same volume of extension Rq. ... 

In polysilane polymers, the polymer backbone is made up entirely of silicon atoms. Therefore these materials differ from other important inorganic polymers, the siloxanes and phosphazenes, in which the polymer chain is heteroatomic. Structurally, they are more closely related to homoatomic organic polymers such as the polyolefins. However, because the units in the main chain are all silicon atoms, the polysilanes exhibit quite unusual properties. The cumulated silicon-silicon bonds in the polymer chain allow extensive electron delocalization to take place, and this delocalization of the sigma electrons in the Si-Si bonds gives the polysilanes unique optical and electronic properties. Many of the potential technical uses, as well as the remarkable properties, of polysilanes result from this unusual mobility of the sigma electrons. 

Be and Mg form an extensive range of organometallic compounds, those of Ca, Sr, and Ba being much more reactive and difficult to characterise. Beryllium alkyls such as Be(CH3)2 have chain structures with... 

Thus obtained results show that the polyamorphic transitions occur not only at compression (Si02, H20, etc.) but at extension as well (C) in the systems having stable or metastable crystal analogs with a different density and a different coordination number z. At the minimal z=2 (chain structures) the transitions may occurs only at compression, at the maximal z=12 (close-packed structures) - only at extension, at the intermediate z (2structure-sensitive properties change and new metastable phases can appear. Amorphization under radiation (crystal lattice extension) can be associated with a softening of phonon frequencies. The transitions in the molecular glasses consisted from the molecules with unsaturated bonds are accompanied by creation of atomic or polymeric amorphous systems. 

The single-chain structure factors calculated in the previous sections correspond to the infinite dilution limit. This limit also corresponds to zero scattering intensity and is not useful so that concentration effects have to be included in the modeling of polymer solutions. First, Zimm s single-contact approximation [5] is reviewed for dilute polymer solutions then, a slight extension of that formula which applies to semidilute solutions, is discussed. 

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