Synthesis and Spectral Studies on Copper(II) Complexes of Two Twelve-Membered and Tetradentate Macrocyclic Ligands

The synthesis and analysis of two series of copper(II) complexes derived from the ligands Dibenzo[e, K] 2, 3, 8, 9 tetrahydro-1, 4, 7, 10 tetraaza cyclo dodeca 1, 3, 7, 9−tetraene(II) (C₁₆H₁₂N₄) and dibenzo[e, K] 2, 9−tetra hydro-1, 4, 7, 10−Tetraaza cyclododeca diphenyl 3, 8−Dihydro-1, 4, 7, 10−tetra aza cyclododeca 1, 3, 7, 9−tetraene (L₂) (C₂₂H₂0N₄) have shown the molar conductance measurements in nitrobenzene that the complexes are non-electrolytes, thus indicating that the anions are coordinated to the metal ion in these complexes. So the general formula [CuLX₂] was suggested for these complexes. The magnetic moments of all the complexes at room temperature lie in the range 1.92 to 2.15 B.M. All the complexes were considered to have tetragonal geometries with planar coordination of the ligand around Cu²⁺ ion and the anions occupying the axial positions. Absence of strong band ∼1670−1750 cm⁻¹ confirmed the elimination of water molecules. Phenyl groups have shown absorptions in the range 700−780 and 1400−1600 cm⁻¹. IR spectra of all the complexes around 1370−1450 cm⁻¹ assigned to νC=N vibrations and these bands indicated the presence of coordinated azomethine group. The spectra of nitrato-complexes exhibited bands at 1230, 1030 and 800cm⁻¹. All the complexes shown anisotropic ESR spectra characteristic of tetragonal Cu²⁺. In an axial symmetry, the g-values were related by the expression G=(g|| −2)/(g⊥−2), which measure the exchange interaction between the copper centres in a poly-crystalline solid. The calculated G values were larger than 4, suggesting that there was no interaction between the copper centres. The IR spectrum of the complex showed bands corresponding to monodentate sulphate. The IR bands showed absorptions at frequencies ∼940, 1040−1060, 1180−1290 and 640 cm⁻¹ suggested five coordinate sturucture for this complex. The structures, square pyramidal and trigonal bipyramidal, had the ground state configuration ²B₁ (unpaired electron being in the dx² −y² orbital), and ²A1 (unpaired electron in the dz² orbital), respectively. The complex under study showed the value 25 of R to be less than 1, thus indicating ²B1 as the ground state. Thus for Cu(L²)SO4, a five coordinate square pyramidal structure was suggested.