Ligands chelate ring size

Experimental studies show that chelating spectator ligands impart a degree of stability to complexes of type 23 (Scheme 13.10) [42]. If monodentate phosphine ligands are used decomposition is rapid at 20°C, however, using dppp no decomposition is detected after 24 h [19]. It was found that the rate of decomposition could be linked to the chelate ring size at 65°C, with dppp decomposition was complete after 6 h, with dppe only a small amount of decomposition occurred after this time [42]. 

Formation of metal-organic chelate complexes results in stronger complexation (i.e., larger values) compared to interaction with monodentate ligands (Chapter 3). The common types of bidentate ligands are presented in Table 4.9 the chemistry of these complexes has been extensively discussed in the literature [14,47], Chapter 3 presents the most important factors in the formation of such complexes (1) the type of binding atom (2) the chelate ring size (or bite ) ... 

Similar, but more extensive, studies of the co-ordination behaviour of the bifunctional ligands (70a) and (70b) with a range of metals have revealed both P,N and P,P bonding. For the Pd" complexes [PdXjL] (X = Cl, Br, or I), i.r. data indicate that both ligands employ P,P co-ordination. The choice of donor atom is discussed in terms of chelate ring size and stereochemical preferences of the various metals. "... 

Chelate ring size can also be changed by substitution of acetic by propionic residues.2,3 The ligands (12) and (13) of Scheme 4 form weaker complexes in comparison with edta (see Table 7). In the case of the tetrapropionic acid, the lowest decrease of Kx is observed for Cu2+. For the other cations the dipropionate derivative shows values of log K which are not more than two units lower than those for edta. The data for the two propionic acids have to be further controlled by new measurements, because the method used is not always the most appropriate to obtain reliable values of Kx. 

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