Ferromagnetic coupling in trinuclear, partial cubane Cu^II complexes with a μ₃-OH core: magnetostructural correlations

Abstract

Three new trinuclear copper (II) complexes, [(CuL¹)₃(μ₃-OH)][ClO₄]₂⋅3 H₂O (1), [(CuL²)₃(μ₃-OH)][ClO₄]₂⋅H₂O (2) and [(CuL³)₃(μ₃-OH)][ClO₄]₂⋅7 H₂O (3) have been synthesized from the three tridentate Schiff bases HL¹, HL² and HL³ (HL¹ = 6- aminomethyl-3-methyl-1-phenyl-4-azahex-2-en-1-one, HL² = 6-aminoethyl-3-methyl-1-phenyl-4-azahex-2-en-1-one and HL³ = 6-aminodimethyl-3-methyl-1-phenyl-4-azahex-2-en-1-one). They have been characterized by X-ray crystallography and IR and UV spectroscopy, and their magnetic properties have been investigated. All the compounds contain a partial cubane [Cu₃O₄] core consisting of the trinuclear unit [(CuL)₃(μ₃-OH)]²⁺, perchlorate ions and water molecules. In each of the complexes, the copper atoms are five-coordinate with a distorted square-pyramidal geometry except complex 1, in which one of the Cu^II of the trinuclear unit is weakly coordinated to one of the perchlorate ions. Magnetic measurements performed in SQUID MPMS-XL7 using polycrystalline samples at an applied field of 2 kOe indicate a global intramolecular ferromagnetic coupling. Magnetostructural correlations have been calculated on the basis of theoretical models without symmetry restriction. Continuous shape measurements are an appropriate tool for establishing the degree of distortion of the Cu^II from square-planar geometry. Structural, theoretical and experimental magnetic data indicate that the higher the degree of distortion, the greater the ferromagnetic coupling.