Ligand strain energy

In another study, Co(m) has been shown to be favoured over Co(n) as the ligand strain energy decreases in the complexes of the N4-donor aliphatic macrocycles (278 X = NH). Thus, for the 13- to 16-membered ring complexes of type /ra s-[CoCl2L]2+, it is the complex of cyclam (14-membered) which most promotes the Co(n)/Co(m) transformation (Hung et al., 1977). 

Strain-energy calculations on [Cu(nS4)(OH2)2] complexes (n = 12-16) [175] parallel the experimental results an increase in ligand strain energy decreases both the stability constant and the dissociation rate constant (in a linear manner, the origin of which is unclear). Comparison of the various complexes indicates that the strain-free free energy of formation of a Cu(II)-tetrathioether complex is — 8.65(0.66) kcal mol and that the strain energy is surprisingly small 2.9-5.5 kcalmol . 

Minimize the remaining structures in the presence and absence of the active site to estimate the ligand strain energy and delete any duplicates created by minimization. After this step, 4449 structures remained. 

Remove any structures with a ligand strain energy in excess of 35 kj/mol. After this step, 3937 structures remained. 

Table 25. Selected nickel-ligand bond enthalpy contributions, D (Ni-L), kJ mol-1 in NiL as a function of ligand cone angle, 6, (Ref.113 ) and strain energy, Q, kJ mol-1...

All these methods have found applications in theoretical considerations of numerous problems more or less directly related to solvent extraction. The MM calculated structures and strain energies of cobalt(III) amino acid complexes have been related to the experimental distribution of isomers, their thermodynamic stability, and some kinetic data connected with transition state energies [15]. The influence of steric strain upon chelate stability, the preference of metal ions for ligands forming five- and six-membered chelate rings, the conformational isomerism of macrocyclic ligands, and the size-match selectivity were analyzed [16] as well as the relation between ligand structures, coordination stereochemistry, and the thermodynamic properties of TM complexes [17]. 

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