Iodine complex state

Interestingly, there is a tendency to obtain only certain stoichiometries of crownether iodine complexes in the solid state, i.e. product formation is governed by packing behaviour and solubility of the particular complexes. In solution, 1 1 adducts are often the predominant species.24,31 34... 

Solid-state cellulose can also be noncrystalline, sometimes called amorphous. Intermediate situations are also likely to be important but not well characterized. One example, nematic ordered cellulose has been described [230]. In most treatments that produce amorphous cellulose, the whole fiber is severely degraded. For example, decrystallization can be effected by ball milling, which leaves the cellulose as a fine dust. In this case, some crystalline structure can be recreated by placing the sample in a humid environment. Another approach uses phosphoric acid, which can dissolve the cellulose. Precipitation by dilution with water results in a material with very little crystallinity. There is some chance that the chain may adopt a different shape (a collapsed, sixfold helix) after phosphoric acid treatment. This was concluded because the cellulose stains blue with iodine (see Figure 5.12), similar to the sixfold amylose helix in the starch-iodine complex. 

The closed-shell configuration of noble gas atoms Ng does not prevent formation of compounds, either as even, positive oxidation states of xenon, isosteric with iodine complexes (and to a smaller extent by krypton and radon) or functioning as Lewis bases. In condensed matter, Ar, Kr, and Xe form distinct NgCr(CO)j and ArCi(NN)5 complexes. Gaseous noble gas molecular ions, especially HeX and ArX, numerous organo-helium cations, and some neon-containing cations are calculated to be quite stable, and several of them are indeed detected in mass-spectra. The history of Ng chemistry and its relations with the Periodic Table, atomic spectra, and ionization energies, are discussed. 

When starch is fractionated into its two components, usually by precipitating the amylose from solution by means of an organic solvent (such as an alcohol), a third type of structure is found this survives drying, and ultimately reverts to the B structure upon rehydration. This structure has been termed the V form, and it yields an x-ray pattern that is distinctly different from the other two types. Essentially the same pattern was observed for the amylose-iodine complex. Bundle and coworkers studied the various V amyloses obtained by complexing with alcohols or iodine, and, on the basis of powder diagrams, suggested unit-cell parameters for both the wet and dry (hydrated and anhydrous) states, as shown in Table I (seep. 422). From these data, Bear had suggested earlier that the "V structure of amylose is helical. (Historically, it is of... 

Cross-linked polymers produced in this way cannot be worked easily. In this respect, charge transfer complexes from polymeric donors and acceptors are more advantageous. The poly(2-vinyl pyridine) and iodine complex, for example, has a specific conductivity of 10 H" cm . It is used as a cathode in Li/h batteries for implantable heart pacemakers. This solid state battery has a higher energy density than the best lead accumulators and a lifetime of about ten years. 

FIGURE 7. (a) Spectra of chlorpro-mazine and of its iodine complex in the frequency range F = 3500-1200 cm Curve marked A refers to crystalline chlor-promazine at 20°C. Curve marked B refers to the iodine complex of chlorpromazine base at 20 °C. Curve marked C refers to chlorpromazine in the liquid state at 60°C. (b) Same as for Figure 7a but in the range 1300-400 cm T is transmittance in arbitrary units. 

Modern versions of the Winkler method improve the sensitivity and accuracy of the method by computer control of the titration procedure and the endpoint detection. Instead of visual observation of the decolouration of the blue starch-iodine complex, either the starch-iodine complex colour or the iodine colour itself is measured photometrically in the visible to ultraviolet (UV) spectral range. The spectral absorbance of an I3- solution (oxygen sample before titration) is depicted in Fig. 4-1. Grasshoff (1981) described a dead-stop titration of iodine with thiosulphate using amperometric endpoint detection. Bradburg and Hambly (1952) have compared various endpoint detections for iodine-thiosulphate titrations in low concentration ranges and stated relative sensitivities for visual-starch, colouri-metric-starch, amperometric, UV absorption as 1 0.2 0.002 0.0015. 

The predissociation lifetime of l2Hen is found to be dependent on the iodine vibrational level initially excited and for n = 1 ranges from 38 ps (v = 26) to 221 ps (v = 12) with a variation that is a nonlinear function of the iodine vibrational quantum"number v . The predissociation lifetimes for the neon hydrogen and deuterium van der Waals complexes with iodine are found to be somewhat shorter. As for the product iodine vibrational state distribution for l2Hen the A v = -n channel is dominant with a branching ratio of greater than 0.95 for v =... 

The I2 solid state complexes of Xll the phenothiazines are reddish brown, those of the metal porphyrins and the Fe phthalocyanine are deep blue, or blue green and brittle. The MgMTBP PVP complex is dark green. The iodine complexes of all the compounds, except PVP, are very stable, i.e., readily retain I2. The order of decreasing stability is phenothiazines, metalloporphyrins, metallophthalocyanine, ionenes, polyvinyIpyr id ine. 

Although the transition to difhision control is satisfactorily described in such an approach, even for these apparently simple elementary reactions the situation in reality appears to be more complex due to the participation of weakly bonding or repulsive electronic states which may become increasingly coupled as the bath gas density increases. These processes manifest tliemselves in iodine atom and bromine atom recombination in some bath gases at high densities where marked deviations from TronnaF behaviour are observed [3, 4]. In particular, it is found that the transition from Lto is significantly broader than... 

Reactions in Aqueous Media. The chemistry of aqueous iodine has been extensively studied because of the role of iodine as a disinfectant (see Disinfectants AND antiseptics). The system is very complex, owing to the number of oxidation states available to iodine under ambient conditions (48). 

Rhenium Halides and Halide Complexes. Rhenium reacts with chlorine at ca 600°C to produce rheniumpentachloride [39368-69-9], Re2Cl2Q, a volatile species that is dimeric via bridging hahde groups. Rhenium reacts with elemental bromine in a similar fashion, but the metal is unreactive toward iodine. The compounds ReCl, ReBr [36753-03-4], and Rel [59301-47-2] can be prepared by careful evaporation of a solution of HReO and HX. Substantiation in a modem laboratory would be desirable. Lower oxidation state hahdes (Re X ) are also prepared from the pentavalent or tetravalent compounds by thermal decomposition or chemical reduction. 

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