STRUCTURES AND PROPERTIES OF COBALT(III) COMPLEXES OF LIGANDS HAVING THE 1,4,8,11-TETRAAZACYCLOTETRADECANE-5,7-DIONE MOIETY

Chloride salts of cobalt(III) complexes of 1,4,8,11-tetraazacyclotetra decane-5,7-dione (L1) and ethyl)-1,4,8,11-tetraazacyclotetradecane-5,7 -dione (L2), acting as a water-soluble anion carrier capable of a sele ctive recognition of nitrite and thiocyanate, were isolated, and their solid state structures and properties in water were studied. IR spect roscopic and X-ray crystallographic approaches have clarified that the isolated complexes have iminol tautomeric structures, in which the am ide oxygen atoms are protonated, but the amide nitrogen atoms bound to cobalt(III) are deprotonated. Conductivity and pH titration studies o n aqueous solutions of the complexes have revealed that the iminol gro ups act as a strong acid in water; the acid-dissociation constants of the water molecule axially coordinated to the cobalt(III) are 10(-6.65 ) and 10(-7.01) for the L1 and L2 complexes, respectively.