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 N-H center dot center dot center dot O center dot center dot center dot H-N 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 E-1/2 (Delta E-p) values (in mV) for the (CuCuII)-Cu-II/(CuCuI)-Cu-II couple is -0.466 V (0.067 V) for 2 and -0.490 V (0.076 V) for 3, while the E-1/2 (Delta E-p) values (in mV) for the (CuCuI)-Cu-II/(CuCuI)-Cu-I couple is -0.953 V (0.060 V) for 2 and -0.985 V (0.069 V) for 3. Variable-temperature (2-300K) magnetic susceptibility measurements of the two compounds reveal that the metal centers in both of the complexes are coupled by strong antiferromagnetic interactions with 2f values (H = -JS(1).S-2) of -780 and -820 cm(-1) for 2 and 3, respectively. (C) 2012 Elsevier B.V. All rights reserved.