Strain energy minimization
calculations have been performed for several octahedral chloropenta-amine
cobalt(III) complexes with polyamine ligands. Similar calculations on the
five-coordinate residue obtained by removal of the chloro
ligand allow an estimation of the geometry and energy of a potential
intermediate in a chloride release reaction proceeding via a dissociative
mechanism. In all cases the five-coordinate residue is less strained than the
six-coordinate octahedron and the non-replaced ligands play an essential role
in determining the resulting distortion. Thus for the series mer-CoCl(NN)(dien)2+ (NN = en, (NH3)2,tn),
the total strain energy difference between the minimized ground state and the
minimized five-coordinate residue is 12.2, 18.3 and 25.8 kJ mol-1,
respectively. This order is identical (where data are available) to that of the
rate constants (and activation energies) for thermal aquation,
Hg2+ assisted aquation and mer → fac-dien isomerization in this series.
Similar calculations have been performed for a series of trans-CoCl2(N4)+
systems and again the energy differences are in the approximate order of the
rates of thermal aquation. In the case of N4
= (NH3)2, the energy difference between trans-and cis-CoCl(NH3)4(OH2)2+
products is about 1 kJ mol-1, the trans-isomer being the more stable.
Three-dimensional Elastic Image Registration Based on Strain Energy Minimization: Application to Prostate Magnetic Resonance Imaging
