Hydrophobic effects in the stabilisation of copper(I) by the macrocyclic ligands 16,17,19,20-tetramethyl-2,6,9,13-tetraaza[14]paracyclophane and 14,15,17,18-tetramethyl-2,5,8,11-tetraaza[12]paracyclophane

The interaction of Cu2+ With the para-azacyclophanes 16,17,19,20-tetramethyl-2,6,9,13-tetraaza[14]paracyclophane (L1) and 14,15,17,18-tetramethyl-2,5,8,11-tetraaza [12]paracyclophane (L2) has been studied by potentiometry, and direct microcalorimetry at 298.1+/-0.1 K in 0.15 mol dm(-3) NaClO4. The stability constants (log K-CuL1=13.35(3), log K-CuL2 = 9.32(4)) and the thermodynamic parameters (Delta H degrees(CuL1) = -47.3(8) kJ mol(-1), Delta H degrees(CuL2) = -20.9(8) kJ mol(-1)) evidence that not all four nitrogen atoms in the ligands are involved in the coordination to the metal centre. These results, particularly in the case of L1, are similar to those reported for the analogous cyclophanes containing benzene as spacer, 2,6,9,13-tetraaza[14]paracyclophane (L3) and tetraaza[12]paracyclophane (L4). In spite of their similar stability, cyclic voltammetric studies show that L1 and L2 stabilise Cu+ towards disproportion into Cu2+ and Cu-0 to a larger extent than L3 and L4.