Syntheses, crystal structures, magnetochemistry and electrochemistry of macrocyclic dicopper(II) complexes: Monodentate behavior of a potentially chelating ligand

The syntheses, characterization, crystal and molecular structures, magnetochemistry and electrochemistry of four diphenoxo-bridged dicopper(II) compounds derived from four Robson type tetraiminodiphenolate macrocyclic ligands are presented here. Three of the complexes, [CuII2L1(ClO4)2] (1), [CuII2L2(ClO4)2] (2) and [CuII2L3(ClO4)2] (3), are derived from three macrocyclic ligands H2L1/H2L2/H2L3 having 4-ethyl-2,6-diformylphenol as the aldehyde component and ethylenediamine/1,1-dimethylethylenediamine/trans-1,2-diaminocyclohexane as the diamine component. The remaining system, [CuII2L4(MD-Phenolate)2]·2H2O (4; MD-Phenolate = 4-methyl-2,6-diformylphenolate), is derived from H2L4, which is the condensation product of 4-methyl-2,6-diformylphenol and 2,2-dimethyl-1,3-diaminopropane. Compounds 1–3 crystallize in monoclinic P21/c system, while the crystal system for 4 is triclinic P 1 ¯ . Variable-temperature magnetic susceptibility measurement reveals that the compounds 1–4 are coupled by strong/very strong antiferromagnetic interaction with J values −391, −318, −270 and −412 cm−1, respectively. Cyclic voltammetric and square wave voltammetric measurements of the systems have been carried out, revealing two-step redox couples CuIICuII/CuIICuI and CuIICuI/CuICuI. The E½ values (V) of the well resolved peaks are −0.413 for 1, −0.437 and −1.075 for 2, −0.432 for 3 and −0.363 and −0.865 for 4. Sole example of 4-substituted-2,6-diformylphenolate behaving as a monodentate ligand is presented and a new correlation of the E½ values on the displacement of copper(II) center from the basal plane is proposed.