Gadolinium complexes constants

The gadolinium complex with Cxi displays a reasonable relaxivity and it has been assessed as a potential contrast agent for magnetic resonance imaging. Its stability constant is however too low to make this complex a good candidate for in vivo applications. Until now, no calixarene derivative has proved efficient in this field, contrary to the pendant-arm substituted coronands. 

The second group of ligands have complex formation constants for the elements past gadolinium which are very nearly the same. 

The enthalpy variation is endothermic and is suggestive of the formation of weakly bonded complexes. The values of log K and AH show a break at gadolinium which may be due to electronic effects and change in coordination. The formation constants and the enthalpy value for bromo complexes of La and Nd showed that bromo complexes are less stable than chloro complexes (Cl > Br ) for La and the order is Br- > Cl- for Nd3+ ion. The data have been interpreted in terms of inner-sphere complexes in the case of both chloride and bromide [125]. Studies in DMSO medium showed that no Pr-Cl could be detected while Er3+ formed inner-sphere [ErCl]2+ complex [98]. 

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