A new tetraiminodiphenol macrocyclic ligand and its two dicopper(II) complexes: Syntheses, crystal structures, electrochemistry and magnetochemistry

This paper deals with the diprotonated salt, [H4L](ClO4)2 (1), of the tetraiminodiphenolate macrocyclic ligand, H2L which is the [2 + 2] condensation product of 4-ethyl-2,6-diformylphenol and 2,2′-dimethyl-1,3-diaminopropane, and two diphenoxo-bridged dicopper(II) complexes [Cu2L(ClO4)2] (2) and [Cu2L(ClO4)](ClO4) (3). The syntheses, characterization and crystal structures of 1–3 and the magnetic and electrochemical properties of the metal complexes 2 and 3 are presented. The cationic macrocycle [H4L]2+ is stabilized by four intramolecular and symmetric NH…O…HN hydrogen bonds involving phenoxo oxygen and imino nitrogen atoms. One metal center in 3 is tetracoordinated and in a square planar geometry. The second metal ion of 3 and both the metal ions in 2 are pentacoordinated and in a square pyramidal geometry; one perchlorate oxygen atom occupies the apical position in each case. Both 2 and 3 exhibit quasireversible two-step one-electron couples in the reduction window. The E½ (ΔEp) values (in mV) for the CuIICuII/CuIICuI couple is −0.466 V (0.067 V) for 2 and −0.490 V (0.076 V) for 3, while the E½ (ΔEp) values (in mV) for the CuIICuI/CuICuI couple is −0.953 V (0.060 V) for 2 and −0.985 V (0.069 V) for 3. Variable-temperature (2–300 K) magnetic susceptibility measurements of the two compounds reveal that the metal centers in both of the complexes are coupled by strong antiferromagnetic interactions with 2J values (H = −JS1·S2) of −780 and −820 cm−1 for 2 and 3, respectively.