Other Hexadentate Ligands

Reaction of 24S6 with [Ni(EtOH)g] yields the turquoise complex [Ni(24S6)] (Table 1) [23, 159], Traces of moisture or donor solvents quickly decompose the complex, which reflects the weakness of the long Ni-S bonds. Adoption of meridional stereochemistry here contrasts with the facial coordination in [M(18S6)] (M = Co, Ni, Cu). 

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Ammonia is an example of a monodentate ligand. See Table 5.3 for other examples. EDTA is a hexadentate ligand. A monodentate ligand is one that has just one bonding site for bonding to a metal ion. 

For the hexadentate ligands, such as tppn and bbpmax, tetranuclear complexes containing two [Mn2(/i-0)(/i-0Ac)2] " units are obtained. In the cation of the complex [(Mn20(OAc)2)2(bbp-max)2](C104)4 (99) the two dinuclear units are related to each other by a mirror plane. 

A typical example of the more complex reactions that may occur when aromatic compounds react with dioxygen in the presence of copper salts is seen in Fig. 9-30. When solutions of the hexadentate ligand 9.14 react with copper salts and dioxygen, a complex of a new ligand is obtained. The new phenolic compound that is formed acts as a dinucleating ligand and its dinuclear copper(n) complexes turn out to be effective oxygenation catalysts for other substrates. 

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