Structural and magnetic characterization of two tetranuclear Cu(II) complexes with closed‐cubane‐like core framework

Abstract

Two novel tetranuclear Cu(II) complexes [Cu4(L1)4]·3(H2O) (1) and [Cu4(H2L2)4(H2O)4] (2) ( H2L1 = (E)-2-((1-hydroxybutan-2-ylimino)methyl)phenol; H4L2 = 2-((2-hydroxy-3-methoxybenzylidene)amino)-2-hydroxymethylpropane-1,3-diol) were synthesized from the self-assembly of copper(II) perchlorate and the tridentate Schiff base ligands. Both complexes crystallize in the tetragonal system with space group I 41/a and form tetranuclear species with closed-cubane like core framework. Both the complexes possess a S4 axis but of different stereochemistry due to the different arrangement of the ligands about the copper ions. Variable temperature magnetic susceptibility measurements indicate an overall weak antiferromagnetic exchange coupling in 1, while ferromagnetic exchange coupling in 2. In agreement with their closed-cubane structure, the magnetic behavior of the two complexes have been studied by employing the isotropic spin Hamiltonian of type H = J1 (S1S3 + S1S4 + S2S3 + S2S4) - J2 (S1S2 + S3S4) (J1 describes the magnetic exchange coupling between the four Cu(II) pairs with short Cu···Cu distances, while J2 characterizes the magnetic exchange coupling between the remaining two intermetallic pairs with long distances). The PHI program was used to study their magnetic behavior. A good agreement between the experimental and fitted curves was found with the following parameters: g = 2.14, J1 = -20.3 cm-1 and J2 = 0 cm-1 for 1 and g = 2.10, J1 = 101.1 cm-1 and J2 = -51.5 cm-1 for 2.