Mixed O,N donors

Mixed O, N donor molecules are truly extensive and structurally diverse, and only a few selected examples will be presented. In line with other 2-substituted pyridine analogs reported in this chapter, it is worthwhile noting the chemistry of 2-pyridone (or 2-hydroxypyridine, Hopy), which can form O-bonded monodentate complexes such as Co(Hopy)4(N03)2, but as the monoanion is an effective chelate ligand, forming Co(opy)2 and Co(bpy)(opy)2 compounds.454 An unusual solid state melt reaction with Co(OAc)2 yields the dodecanuclear cluster Co12 (OH)6(OAc)6(opy )12.455... 

Section 5.1.4). However such is the affinity of transition metals for nitrogen donors that even if these compounds are derivatised to give macrotricyclic cryptands (3.76), Cu(II) and Ni(II) still only form 1 1 complexes rather than a 2 1 complex taking advantage of the mixed O/N donor array.31 In contrast the analogous all-nitrogen macrocycles (3.77) form 2 1 complexes. 

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