Halogen-oxygen bridges

Annotinine, C gHjjOjN, (1). M.p. 232° perchlorate, m.p. 267°. In a later paper (1947) Manske and Marion record the results of the action of alkali and of halogen acids on annotinine, and of the oxidation of the base and discuss the reaction products. They conclude that two of the oxygen atoms are present as a lactone group and that the third oxygen may form an ether bridge in a 5- or 6-membered ring. 

In /r-bridged dimers, two phthalocyanine moieties are linked by one or more bridging atoms such as oxygen or halogens. Niobium(V) oxide tribromide (NbOBr,) when treated with phthalonitrile in 1-chloronaphthalene at 230CC for 3 hours produces /r-bromo-/t-dioxobis[nio-bium(V) phthalocyanine] tribromide in 52%.232... 

Table 5 lists parameters for a selection of halogen-bridged species with this type of asymmetry. The effect of multiply bonded oxygen is larger than the other ligands listed, and the comparison of oxide as part of the ligand, in the pentane-2,4-dionate complex,27 where the asymmetric Mo—Cl distances only differ by 0.091 A, with the oxide trichloride, where the difference is 0.44 A, is particularly striking. 

These redox reactions, in which oxygen transfer occurs, involve changes of two units in the oxidation numbers of reactant and product. One-electron redox reactions may occur with the transfer of a halogen. The reaction between Cr+2 and Fe 3, for example, is strongly catalyzed by added chloride ion and when chloride is added to the reaction mixture, the resultant Cr(III) is present as (BUO CrC 2. It might be suggested that Cl becomes attached to Cr+a after the redox has occurred, but this cannot be. In the first place, independent experiments show that under these conditions the reaction between Cr+3 and Cl is very slow second, chloride attachment after the redox has occurred would not explain the catalytic role of chloride. It is more likely that the reaction occurs via a chloride-bridge transition state, and that the redox is accomplished by a chlorine transfer ... 

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