ACID DISSOCIATION BEHAVIOR OF 2, 3- AND 2, 3, 9,lO-METHYL- OR CYCLOHEXYL-SUBSTITUTED CYCLAMS, THEIR COMPLEXATION BEHAVIOR WITH COPPER@) AND THE AXIAL SOLVENT SPECTRUM OF THEIR COMPLEXESINTERACTION EFFECT ON THE LIGAND-FIELD

Abstract

Stability constants of Cu(Il)-complexes for 1, 4, 8, 11-tetra-azacyclotetradecane (cyclam) analogs with periphery substituted [14]aneN4-ring, 2, 3-tetramethyl-, 2, 3, 9, 10-octamethyl-, 2, 3-cyclohexyl, and 2, 3, 9, 10-dicyclohexyl-cyclams have been determined at 25°C in aqueous solution. The UV-Vis absorption spectra of their complexes, ([Cu(L)] (C1O4)2), were measured in water and some typical organic solvents (methanol, acetone, propylene carbonate, formamide, N, N-dimethylformamide, and dimethylsulfoxide). A good linear relationship was found between the stability constant logKCuL) and the difference between the wavenumber of maximum absorption in water and in the organic solvents (δλmax −1 (W-S)). The value of logKCuL at δλmax −1(W-S) = 0 not only shows a linear relation to solvent parameters, donor number and dielectric constant, but also to the enthalpy of transfer of ClO4 − from water to the organic solvents. The value is proposed as a new solvent parameter ‘Kλlue’ to be used as an index for solvent-effects on Cu(II)-complexes of cyclam analogs. The increasing order of the new parameter (log scale) is as follows; DMF(27.24)>DMSO(27.14)>FA(26.82)>MeOH(26.27)>PC(25.75)>AC(24.71). Another meaning of the new parameter is assumed from connection of the potentiometric data with spectrometric data. The solvent effects on stability and the UV-Vis spectra are assumed to be caused by perturbation of the D4 h or axially-elongated ligand field through axial approach of solvent to the Cu(II)-complexes and by formation of a solvent-separated ion pair between a solvated Cu(lI)-complex cation and counter anion (ClO4)