Ligands basicity

Simple comparisons of stability constants in this way have been criticized because no allowance is made for the differences in ligand basicities. Increased basicity as a rule parallels increased metal binding. Also, in the majority of cases competition between hydrogen ion and metal ion occurs (equation 3). The equilibrium constant (K) for reaction (3) is then given by equation (4). 

Martin advocates the use of equation (5) in order not to overemphasize the role of ligand basicity 10 the more positive log K in equations (4) or (5) the greater the thermodynamic stability of the complex. Examination of the data in Table 2 in this way then reveals that Arg, Lys and Trp (with basic side chain) are bidentate in the normal way, Glu2- and Gin display weak tridentate behaviour towards Co" and Ni I in their 1 1 complexes, and His-, Cys2- and Pen2- are most obviously tridentate in behaviour, as can be judged from the unadjusted stability constants themselves. 

Table 6 Effect of Axial Ligand Basicity and Cis and Trans Effects on the Equilibrium Constants for FeIH(Por)... 

Mohapatra, P.K. Manchanda, V.K. Role of ligand basicity and stereochemistry in the extraction of plutonium(IV) isoxazolonates, Radiochim. Acta 91 (2003) 705-712. 

In Section ILEA, I shall discuss and correlate various factors that could be involved in promoting the Co—C bond homolysis in biological systems. First, I wish to focus on two structural features and their relationship to Co—C BDE. The first factor is the effect of ligand basicity and steric bulk on Co—C BDE. In a series of (pyridine)Co(Hdmg)2R compounds, Halpem et al. [90] found that the Co—C BDEs (kcal moC1) increased with the basicity of the pyridine ... 

J = 3/2 levels, (v) the correlation between oscillator strength of hypersensitive transitions and ligand basicity. 

The increased abundance of the C3 isomer with increasing ligand basicity presumably occurs because the semi-bridging carbonyl attached to the substituted metal can become more full-bridging and remove the excess electron density released by the basic phosphine. Consistent with this hypothesis is the... 

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