Magnetostructural Studies on Ferromagnetically Coupled Copper( II ) Cubanes of Schiff‐Base Ligands

Three cubane copper( II ) clusters, namely [Cu 4 (HL′) 4 ] ( 1 ), [Cu 4 L 2 (OH) 2 ] ( 2 ), and [Cu 4 L 2 (OMe) 2 ] ( 3 ), of two pentadentate Schiff‐base ligands N , N ′‐(2‐hydroxypropane‐1,3‐diyl)bis(acetylacetoneimine) (H 3 L′) and N , N ′‐(2‐hydroxypropane‐1,3‐diyl)bis(salicylaldimine) (H 3 L), are prepared, structurally characterized by X‐ray crystallography, and their variable‐temperature magnetic properties studied. Complex 1 has a metal‐to‐ligand stoichiometry of 1:1 and it crystallizes in the cubic space group P $\bar 4$ 3 n with a structure that consists of a tetranuclear core with metal centers linked by a μ 3 ‐alkoxo oxygen atom to form a cubic arrangement of the metal and oxygen atoms. Each ligand displays a tridentate binding mode which means that a total of eight pendant binding sites remain per cubane molecule. Complexes [Cu 4 L 2 (OH) 2 ] ( 2 ) and [Cu 4 L 2 (OMe) 2 ] ( 3 ) crystallize in the orthorhombic space group Pccn and have a cubane structure that is formed by the self‐assembly of two {Cu 2 L} + units. The variable‐temperature magnetic susceptibility data in the range 300–18 K show ferromagnetic exchange interactions in the complexes. Along with the ferromagnetic exchange pathway, there is also a weak antiferromagnetic exchange between the copper centers. The theoretical fitting of the magnetic data gives the following parameters: J 1 =38.5 and J 2 =−18 cm −1 for 1 with a triplet ( S =1) ground state and quintet ( S =2) lowest excited state; J 1 =14.7 and J 2 =−18.4 cm −1 for 2 with a triplet ground state and singlet ( S =0) lowest excited state; and J 1 =33.3 and J 2 =−15.6 cm −1 for 3 with a triplet ground state and quintet lowest excited state, where J 1 and J 2 are two different exchange pathways in the cubane {Cu 4 O 4 } core. The crystal structures of 2 ⋅6 H 2 O and 3 ⋅2 H 2 O⋅THF show the presence of channels containing the lattice solvent molecules.