Interaction of the Post-transition Metal Ions and New Macrocycles in Solution

摘要

Complexation of Cd2+, Pb2+ and Hg2+ ions with four cryptands were studied by potentiometry and solution calorimetry in various weight percent methanol-aqueous solvent at 25∩ under CO2 free nitrogen atmosphere. The stabilities of the complexes were dependent on the cavity size of macrocycles. The Hg2+ ion stability constants are higher than those of Cd2+ and Pb2+ ion. All the cryptands formed complexes having 1 : 1 (metal to ligand) mole-ratio except for Hg2+-L1 (cryptand 1,2b: 3,5-benzo-9,14,17-trioxa-1,7-diazabicyclo-(8,5,5) heptadecane) and Cd2+-L2 (cryptand 2,2b: 3,5-benzo-10,13,18,21-tetraoxa-1,7-diazabicyclo (8,5,5) eicosane) complexes. Hg2+-L1 complex was a sandwitch type, and the Cd2+-L2 complex showed two stepwise reactions. Thermodynamic parameters of the Cd2+-L2 complex were 6.08(log K1), -7.28 Kcal/mol (♀H1), and 4.78 (log K2), -4.62 Kcal/mol (♀H2), respectively, for 1 : 1 and 2: 1 mole-ratio. The sequences of the selectivity were increased in the order of Hg2+ > Pb2+ > Cd2+ ion for L3 and L4 macrocycles, and the L2-macrocycle has a selectivity for Cd2+ ion relative to Zn2+, Ni2+, Pb2+ and Hg2+ ions. Thus, it is expected that the L2 can be used as carrier for seperation of the post transition metals by macrocycles-mediated liquid membrane because L2 is not soluble in water, and the difference of stability constants of the metal complexes with L2 are large as compared with the other transition metal complexes. The 1H and 13C-NMR studies indicated that the nitrogen atoms of cryptands have greater affinity to the post transition metal ions than the oxygen atoms, and that the planarities of the macrocycles were lost by complexation with the metal ions because of the perturbation of ring current of benzene molecule attached to macrocycles and counter-anions.