Chelating ligands mixed ligand structures

In principle, as a preliminary conclusion, the following three formal electron distributions may be envisaged for [la]0 [ FeNO 7(L )2], [ FeNO 6(L )(L)], and [ FeNO 5(L)2]. The latter option was discarded, since species with this distribution have not been characterized to date. The X-ray data suggest an electronic structure with n = 6, [Fen(NO + )(L )(L)]° <-> [Fen(NO + )(L)(L )]°, with a class III (delocalized) chelating ligand mixed valency. The EPR spectrum confirms this assignment,... 

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... 

Thioether ligand complexes are not very common, however, studies since the mid 1990s have dramatically increased the number of structurally characterized examples. Almost all of these compounds are with chelate or macrocyclic ligands that will stabilize thioether coordination. Mixed donor multidentate ligands containing thioether donors will be discussed in Section 6.8.11. 

On treatment of (91 R = R = H) with a strong chelating agent, such as phen, the dimer is broken, with the formation of a mononuclear mixed-ligand complex [VO(SB)(phen)].765 The dimeric structure is also broken on treatment of complex (91 R = H, R = 5-C1) with pyridine a monopyridine adduct forms which obeys the Curie-Weiss law with 6 - 2 K and = 1.75 BM.763... 

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