A THERMOCHEMICAL AND SPECTROPHOTOMETRICAL STUDY OF COMPLEX FORMATION BETWEEN COPPER(II) ION AND α, π-THIADIAMINES

Abstract

The enthalpies of formation of the complexes [CuLH]³⁺ and [CuL]²⁺ (L = RR'N(CH₂)_nS(CH₂)_mNH₂ with R = CH₃ or H; R' = CH₃; n.m = 2,3) have been determined at 25° and in 0.5 mol dm⁻³ KNO₃ by means of direct calorimetric titrations. The corresponding entropy changes have been calculated using the enthalpy changes and previously reported ΔG values. The absorption maxima of the d-d transitions of the [CuL]²⁺ complexes have also been measured under the same conditions. For purposes of comparison the spectral investigation was extended to that of the 1:1 complexes between Cu(H) and 1,7-diaza-4-thiaheptane (2,2-NSN) and 1,8-diaza-4-thiaoctane (2,3-NSN). The exothermicity of the formation of the [CuLH]³⁺ complexes is proportional to the distance between the free ammonium group and the central Cu²⁺ ion. The change of the state properties of the normal 1:1 complexes on increasing N-methyl substitution of the ligands suggests a decreasing solvation of the complex ion.