Bridging ligands hydroxides

The observation of a bonding arrangement of the type shown in Fig. 20a in (AlO)2-centred dimers is a recurrent feature of aluminium hydroxides and organooxides of simple, electron rich ligands [44, 99, 110, 125, 134, 204, 205, 214-231]. Those more complex dimers which have been noted take two main forms both polydentate terminal and bridging ligands allow multiple interactions with the Group 13 metal centres. 

Hydroxy-bridged complexes [Pt2(,u-OH)2(PEt3)4]2+ can also be prepared. The structure consists of two square planar platinum(II) centers bridged by hydroxide ligands with an angle of 36.4° between the mean plane normals.1569 A useful method to prepare these complexes involves the use of phase-transfer catalysis with crown ethers to facilitate the reaction of KOH with platinum(II) chloro complexes.1570... 

Polynuclear complexes with hydroxide (or oxide) as bridging ligands constitute an important class of complexes. They are formed by hydrolysis of mononuclear aqua complexes of most metal ions and they therefore constitute an important aspect of the hydrolytic chemistry of metal ions. They display a chemistry which is interesting in itself, but which is also relevant in relation to applied chemistry and to biochemistry, as mentioned in Section XIII. 

Decarboxylation of carbonate complexes is usually effected by acid hydrolysis with the formation of a C02 free oxide or hydroxide complex.128 All such reactions involve a protonated (bicarbonate) intermediate but there are some useful deferences which, in many instances, may be reconciled with the three main structural types of carbonate complexes. Both unidentate and chelate carbonates readily yield C02 on acidification, while there is a greater resistance to C02 loss when the carbonate is a bridging ligand. Unidentate carbonate complexes decarboxylate with the initial formation of a bicarbonate intermediate and subsequent loss of C02 without rupture of the M—O bond, viz. structure (3). By contrast, in chelate carbonate complexes, cleavage of the M—O bond occurs (with ring opening) with the formation of a bicarbonate aqua ion before the loss of C02, viz. equation (5).29... 

The hydroxide ion is a well-established bridging ligand, and hydroxo-bridged complexes of iridium(III) have been reviewed. Among the dinuclear iridium(I) complexes that have structures supported by 0H ligands is [Cp Ir(/u.-0H)3lrCp ]+, and closely related to this is (cod)Ir(/u.-OPh)2lr(cod). The presence of the three OH... 

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