STABILITY OF CU+ AND CU2+ COMPLEXES WITH CRYPTANDS IN APROTIC MEDIA

The effect of solvent on the stability constants of copper (I) and (II ) complexes with macrocyclic and macrobicyclic ligands: 23, 22, 21, 21 1, 221, 222, 222B and 222BB, were investigated by potentiometric titra tion in acetonitrile, propanenitrile, butanenitrile, benzonitrile, ace tone, propylene carbonate, N,N-dimethylacetamide, N,N-dimethylformamid e, dimethylsulfoxide and in tetramethylene sulfone (sulfolane). In all cases 1:1 complexes were detected. The stabilities depend upon the so lvent, ligand and oxidation state of the copper cation, The strong sol vation of the Cu+ cation in nitriles leads to CuL(+) complexes whose s tabilities are within the range of 1.5 < log K < 5.2. In dimethylsulfo xide, where both oxidation states are thermodynamically stable, the st ability constants of CuL(+) and CuL(2+) complexes lie within a similar range. In all cases the presence of the macrocycle increases the stab ility of the monovalent oxidation state even if the divalent cation fo rms a more stable complex. In the remaining solvents the monovalent co pper form is unstable, but the stabilities of the divalent copper comp lexes, CuL(2+), expressed as log K, range from 1.5 up to 25.