Size of chelate ring

Quadridentate Ligands. The effect of extent of chelation on aquation rates has been studied for the compounds raK5-[Co(N02)2(LLLL)]+, where LLLL = (NH3)4, (en>2, (pnja, or cyclam (5), and ci5-[Co(N02)2(LLLL)]+, where LLLL = (NHg)4, (en)a, or trien (6). Rates of aquation increase as the number and size of chelate rings decrease, which is consistent with a dissociative mechanism. Rates of aquation are also sensitive to steric crowding around the leaving group. This is well illustrated by the 10 -fold difference in aquation rates of [Co(C03)(LLLL)]+ when LLLL = (en)a or tet-b (7), and by rate variations in the series... 

Metal coordination preference Ligating atom type Ligand denticity Size of chelate ring Ligand-ligand interactions Spacer geometry... 

Effect of Chelate Ring Size on Complex Stability Comparison of Stabilities of Complexes of EDTA (Chelate Ring Size Five Involving the Two Nitrogens) and TMDTA (Analogous Chelate Ring Size Six ) ... 

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

Romeo et al. (1978) clearly indicate that complexes of divalent metal ions with 1,2-diaminoethane are more stable than those with 1,3-diaminopro-pane. Moreover, in a thorough discussion of the relations between the chelate effect and the ring size, Anderegg (1980) has listed thermodynamic data of complex formation between divalent metal ions and ligand [45], showing that almost invariably the stability of chelate rings decreases with increasing n in the order 5 > 6 > 7. 

Table 4.16 Consultants for Extraction of Actinide Amides from Nitrate Solutions into an Organic Solvent Showing the Effect of Chelate Ring Size...

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. "... 

Tesic, Z.L., Janfic, T.J., Malimar, M.J. and Celap, M.B. (1989) Effect of chelate ring size of diamine cobalt(II) complexes on RF values obtained by paper chromatography. J. Chromatogr., 481, 471-476. 

This result corresponds to the conformational analysis which predicts 24 as the most stable one. As already mentioned, it is possible to fix the absolute configuration of a given isomer by a suitable choice of substituents. A selection between different geometrical isomers — e.g. on the base of chelate ring size — seems to be less easy. It... 

Another aspect to be considered is the stability of chelate rings as a function of the ring size. Carboxylic acids of the formula (CH2) COOH, where n = 0 to 4 form complexes with lanthanides with different sizes of the chelate ring [23]. A plot of logySioi for Sm3+ versus ]CpKa of the ligands is shown in Fig. 3.20. 

Theoretical and experimental studies on penta-coordinate silicon derivatives demonstrate that their existence is determined by a combination of factors electronegativity of the substituents and steric interactions between substituents. One should also emphasize the role and significance of polydentate ligand (chelate effect), the size and number of chelate rings involving the silicon atom, and strain reduction for five-membered ring system, wich can stabilize unusual structures, as well as to the role of medium effect. This is consistent with the results of NMR spectroscopic studies. 

A) is somewhat higher than those in the corresponding macrobicyclic tris-dioximates, which is indicative of a larger ligand cavity size. All chelate rings have skew conformations with the... 

Casey WH, Phillips BL (2000) The kinetics of oxygen exchange between sites in the Ga04Ali2(0H)24(H20)i2 (aq) molecule and aqueous solution. Geochim Cosmochim Acta 65 705-714 Casey WH, Phillips BL, Nordin JP, Sullivan DJ (1998) The rates of exchange of water molecules from Al(III)-methylmalonate complexes The effect of chelate ring size. Geochim Cosmochim Acta 62 2789-2797... 

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