Gallium complexes hydroxides

Porphyrin, octaethyl-, gallium hydroxide complex cyclic voltammetry, 4, 399 <73JA5140)... 

Gallium hydroxide is amphoteric, and is a much stronger acid than aluminum hydroxide. For Ga(OH)3 the first acid dissociation constant is 1.4 x 10-7 [for Al(OH)3 the value is 2 x 10-11].1 Polymerization occurs in aqueous Ga3+ solutions to which OH- is added,533 but this tendency is less than in the case of aluminum solutions (Section 25.1.5.1). The formation constants of mononuclear hydroxo complexes of Ga, including Ga(OH)4, and the hydrolysis constants of gallium ions have been measured by a competing ligand technique.534... 

Several other examples of porphycene complexes with trivalent metals have also appeared in the literature.3.4.12,29,29-32 These include the aluminum(III) complexes 3.75a-d and 3.76, as well at the manganese(III), cobalt(III) iron(III), indium(III), and gallium(III) complexes 3.77-3.81 (Figure 3.1.16). Interestingly, a p-oxo-dialuminum(III)porphycenate 3.85 analogous to the p-oxo-diiron(III)porphycenates 3.72 and 3.73 has also been prepared. This was accomplished by heating the aluminum(III)porphycenato hydroxide complex 3.76 to 350 °C under reduced pressure (Scheme 3.1.12). 

Gallium (Ga, at. mass 69.72) forms colourless Ga " ions. It occurs in solution exclusively in the III oxidation state. Gallium resembles aluminium and zinc in its properties. The hydroxide, Ga(OH)3, precipitates at pH 3, but dissolves in weakly alkaline media (pH 8-9). Gallium forms halide, oxalate, tartrate, acetate, and EDTA complexes. 

Gallium is not readily absorbed from the gastrointestinal tract. Chemical examination of the tissues of animals fed 1000 ppm gallium lactate exhibited only trace amounts in the liver, spleen, and kidney, and 1-3 ppm in bone [39]. This suggests that the alkalinity of the intestinal tract is sufficient to convert gallium chloride to the hydroxide or other insoluble complexes. By subcutaneous or intravenous injection, gallium is rapidly deposited in the tissues, particularly in the bone once deposited there it is relatively immobile [40]. Gallium is excreted rapidly in animals, with about 50% excreted by the kidneys within 24 hr [42]. 

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