Metal chelate ring size

The chelate ring size principle can have structural effects as well as effects on thermodynamic stability in aqueous solution. An example is coordination of metal ions by sugars (44). The cyclic polyol cts-inositol can coordinate metal ions in two distinct ways (Fig. 14) (45). In ax-ax-ax bonding (Fig. 14), the metal ion is part of three fused six-membered chelate rings. Alternatively, in ax-eq-ax coordination, the metal ion is part of two fused five-membered and one six-membered chelate rings. Angyal has noted that metal ions of radius more than 0.8 A adopt the ax-eq-ax structure (44), whereas with an ionic radius... 

Effect of Chelate Ring Size on Complex Stability with Metal Ions of Different Sizes Oxalate (Ring Size Five) and Malonate (Ring Size Six)°... 

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. "... 

Lewis acid-base interactions, 42 89-143 change of HSAB behavior, 42 104 chelate ring size and metal ion selectivity, 42 109-118... 

Elimination of metals by chelators benefits from a recognition that the ability of the chelator depends on several factors, the size of the metal-chelate ring, the donor atoms involved, and... 

Kx for copper (II)-diamine complex is 10.36 and 9.45 for 1,2-ethanediamine and 1,3-propanediamine, respectively (-2)]. The large difference in the stabilities of the two copper (II)-diamine complexes is attributed to an unfavorable entropy effect associated with an increase in the size of the metal-chelate ring (2). Extrapolating to the / -ketoimine derivatives, it seems reasonable to expect that the stability of bisacetylacetonetrimethylenediiminocopper(II) would be less than that of the ethylenediamine analog and to suspect that the former compound is less stable than bis-(4-iminopentane-2-ono) copper (II). That this is reasonable is... 

Binding of urea to metal ions may be reinforced and coordination through the N atom may be favored even for 3d metal ions by incorporating the urea moiety in a chelate arrangement. A -(2-Pyridylmethyl)urea was found to bind either as an N,0-chelate (45) or as an N,N-chelate (46), depending on the metal ion, which is most likely due to the different bond angles and the preferred chelate ring sizes in tetrahedral zinc(ll) or square-planar copper(ll) (107). 

Cyclometalation is one of the most reliable and versatile methods for the synthesis of stable Pd-C a-bonds. In this reaction, a palladium (or other metal) complex is reacted with a ligand possessing a donor atom. The metal is directed by the donor atom to insert into a C-H bond, forming a chelate ring. This donor is usually the nitrogen of a tertiary amine, heterocyclic amine, or imine, or a phosphorus in a tertiary phosphine or phosphite. Other donor atoms, such as O and S, are occasionally encountered. The chelate ring size is normally five. ... 

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