Thermodynamic, electronic, and electron paramagnetic resonance investigation of the co-ordinating properties of 3-azaheptane-1,7-diamine in aqueous solution

Abstract

The heats of protonation and of complex formation with Cu^II of the ligand 3-azaheptane-1.7 diamine (L) have been measured calorimetrically at 25 °C in 0.5 mol dm^–3 K[NO₃] solution, and the corresponding entropy values have been calculated. The results are compared with those from previously investigated systems with homologous triamines. The present system has also been examined by electronic absorption and e.p.r. spectroscopy. For the simple complex [CuL]²⁺, evidence is presented for a structure with two fused chelate rings, one five-membered and the other seven-membered. The complexes [Cu(HL)₂]⁴⁺, [CuL(HL)]³⁺, and [CuL₂]²⁺ contain only two five-membered chelate rings, both the molecules of the iigand acting as bidentates. The difference between the enthalpies of formation of the complexes is attributed to different desolvation processes.