A structural and magnetochemical study of some copper(II) complexes containing the ligands 1,4,7-triazacyclononane-N-acetate (L¹) and N-(2-hydroxybenzyl)-1,4,7-triazacyclononane (HL²)

The tetradentate macrocyclic ligands 1,4,7-triazacyclononane-N-acetate (L¹) and N-(2-hydroxybenzyl)-1,4,7-triazacyclononane (HL²) react in methanol with CuCl₂ or Cu(ClO₄)₂·6H₂O in the absence or presence of LiOH·H₂O with formation of the following complexes containing square based pyramidal Cu(II)ions: [L¹CuCl] (1), [L¹CuCl]LiCl·2H₂O (2), [L¹Cu](ClO₄) (3) and [L²₂Cu₂](ClO₄)₂ (4). Complexes 2 and 4 have been characterized by single crystal X-ray crystallography; the structure of 3 has been reported previously [3]. Crystal data: 2, space group P2₁/c, a = 11.674(4), b = 7.543(2), c = 17.560(5) Å, β = 106.59(8)°, V = 1481.9(7) ų, Z = 4, D_calc = 1.63 g cm^-3, R = 0.044 based on 2499 reflections; 4, space group Pbca, a = 17.742(4), b = 10.335(2), c = 17.742(4) Å, V = 3253(1) ų, D_calc = 1.62, Z = 4, R = 0.048 based on 2147 reflections. From temperature dependent magnetic susceptibility measurements (2-293 K) weak intermolecular antiferromagnetic exchange coupling has been established for 1 and 2, whereas for the helical chain structure 3 weak ferromagnetic exchange coupling has been observed. In dinuclear 4 strong antiferromagnetic intramolecular coupling leads to an S = 0 ground state.