Secondary bonds transition

Robeson et al. studied the secondary loss transitions of a series of poly(arylene ether)s using a torsion pendulum.15 They found that the secondary loss transitions are closely related to the segmental motion of the aryl ether bonds. The secondary... 

Monodentate (monometallic monoconnective) phosphor-1,1-dithiolato ligands are rare. Bidentate (monometallic biconnective) form chelate rings and three sub-types can be distinguished according to the degree of asymmetry (Scheme 2). The most asymmetric type (anisobidentate) occurs when a covalent bond is associated with a secondary bond this takes place mostly in main-group metal complexes. The second type is rare and is the result of the association between a covalent and a dative coordinate bond. The symmetric bidentate bonding (isobidentate) is found mainly in transition metal complexes. 

The structural chemistry of some metal dithiocarbamates, i.e. systematics, coordination modes, crystal packing, and supramolecular self-assembly patterns of nickel, zinc, cadmium, mercury,363 organotin,364 and tellurium,365 366 complexes has been thoroughly analyzed and discussed in detail. Supramolecular self-assembly frequently occurs in non-transition heavier soft metal dithiocarbamates. Thus, lead(II),367 bismuth(III)368 zinc,369 cadmium,370 and (organo)mercury371 dithiocarbamates are associated through M- S secondary bonds, to form either dimeric supermolecules or chain-like supramolecular arrays. The arsenic(III)372 and antimony(III)373 dithiocarbamates are... 

A rather new field emerging in organogold research is the study of luminescence and phosphorescence phenomena, associated in most cases with An An secondary bonding. The optical properties and the mechanism of the excitation and emission are stiU poorly understood, but may provide a new basis for applications (see Photochemistry of Transition Metal Complexes). 

The transition from crystalline to melt state, which is normal for crystalline polymers, is not observed with cellulose under normal conditions. It appears that the secondary bonds giving rise to the crystalline state are too strong and too numerous to be broken by a rise in temperature. Thermal degradation (beginning at ca. 180 °C) precedes melting under atmospheric pressure conditions. Nevertheless, a plastic deformation interpreted as melting has recently been reported for cellulose fibers exposed to laser radiation in a highly confined (pressurized) space [43]. The fracture surface of a thermoplastically deformed cellulose disc is shown in e Fig. 10. 

ACp could be made arbitrarily steep so as to very closely simulate the experimental glass transition. In the above expression, AHi refers to the maximum value of this enthalpy (at 0 K) Tr and D are adjustable temperatures. The idea of cooperativity used here is unconventional. It is understandable, however, that as temperature increases, a few secondary bonds get broken (such as hydrogen bonds in glassy water), the strains in... 

The occurrence of short intermolecular approach distances in crystals has been interpreted as corresponding to weak secondary bonding between the molecules and hence to incipient stages of chemical reactions [58]. The directional preferences shown in such interactions are thus guides to the preferred (low-energy) directions of approach leading to transition states. More quantitative expressions of the directional dependence of atom-atom interactions are obviously required. 

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