Synthesis, crystal structures and density functional theory study of dimeric copper(II) complexes of a tridentate Schiff-base ligand

The X-ray crystal structures of two related trans-N2S2 copper macrocycles are reported. One was isolated with the copper in the divalent form and the other with copper in its univalent form affording a valuable insight into the changes of geometry and metrical parameters that occur during redox processes in macrocyclic copper complexes. A variable temperature NMR study of the copper(I) complex is reported, indicative of a chair-boat conformational change within the alkyl chain backbone of the macrocycle. It was possible to extract the relevant kinetic and thermodynamic parameters (ΔG‡, 57.8 kJ mol−1; ΔH‡, 52.1 kJ mol−1; ΔS‡, −19.2 J K−1 mol−1) for this process at 298 K. DFT molecular orbital calculations were used to confirm these observations and to calculate the energy difference (26.2 kJmol−1) between the copper(I) macrocycle in a planar and a distorted tetrahedral disposition.