Hexols types

In a similar way the pinene-phenylpyridine H[46] was prepared. Thus upon treatment of 4,5-(/f,/f)-pinene-2-phenylpyridine H[46] with IrCls.SHaO, the HEXOL-type tetranuclear iridium complexes [Ir IrCl2(46)2 3] were obtained as two isomers (5.67ab) in a ratio of 5 3 (Scheme 5.25). Each complex can be described as an inner core of HEXOL-type [Ir(IrCl2)3] units and a surface of six chiral bidentate cyclometallated ligands (46). 

Since each metal centre can have either a A- or a A-configuration, in theory there should be eight possible stereoisomers of the tetranuclear HEXOL-type complex (Figure 5. 27). An NMR analysis and X-ray structure determination were carried out on both isomers which showed that complexes 5.67ab acquire C2-symmetric configuration. Furthermore, in the two isomers 5.67a and 5.67b the central iridium atom has a A-configuration while the peripheral iridium atoms Ir2, Ir3 and Ir4 have A-, A-, A for 5.67a and A-, A-, A-configurations for 5.67b. 

The authors suggest that the stereoselectivity is complete for the central iridium atom since it acquires a A-configuration in both isomers of the tetranuclear Ir-HEXOL type complex. However, mixed configurations were obtained for the... 

Eight possible stereoisomers of the tetranuclear Ir-HEXOL-type complexes (reference ). 

It is evident that syntheses of the Lespieau type can lead to a great number of polyhydroxy compounds. Wiemann has prepared compounds such as CHsCH2(CHOH)6CH2CH3, which he calls diethyl mannitol. It would seem better to designate this substance a tetra-desoxy decitol or decane hexol since its configuration is not known with certainty. Apparently this type of synthesis leads to symmetrical arrangements of hydroxyl groups, since allitol, dulcitol and D,L-mannitol are the only hexitols that were identified as products. 

Polymerisation isomerism may be compared with polymerisation in organic compounds, and just as benzene may be regarded as a polymer of acetylene, so in the polynuclear cobalt-ammines the same type of isomerism may occur. For example, dodecammino-hexol-tetracobaltic salts are polymers of hexammino-triol-dicobaltic salts thus ... 

Coordination isomerism is another relatively rare, though well-known, phenomenon, exemplified in the compounds [Cr(NH3)6][Co(CN)6]/[Cr(CN)6][Co(NH3)6] and [Cr(en)20x]-[Cr(ox)2en]/[Cr(en)3][Cr(ox)3] (ox = 204 ). It is related to the structural isomerism that might be expected to be encountered in polynuclear systems (Figure 3). Although examples of such isomer types are known, e.g. the chiral cobalt(III) hexol , [Co Co(OH)2(NH3) 4]3] , and the chromium(III) rhodoso ion with the alternative achiral structure shown in Figure 3, no isomeric pairs have been thoroughly characterized. 

The colloids with very low reciprocal hexol numbers show flocculation or coacervation with 6—1, 5—1, 4—1, 3—1 and in some instance even with 2—1. Thus it seems that the equivalent weight (which multiplied by approximately 0.85 is the reciprocal hexol number) is an important factor in determining flocculability with salts of the types considered here. 

Finally we may mention that composite coacervate drops are also known in which the complex coacervates belong to the type colloid anion -f micro cation (p. 384, Ch. X, 3). They are produced for example with hexol nitrate in a mixture of sols of ... 

Reversal of charge by polyvalent complex ions such as for instance, the hexol ion is, judged by the influence of the pH, of the strychnine type and not of the type of the simple inorganic ions. But then the adsorbability of such a large ion (ion-weight 698) may be expected to be very high like that of organic ions. 

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