Solvent switchable Cu^II complexes

A new tetranuclear complex Cu₄, [Cu₂L(OH)] ₂·2CH₃OH·H₂O (1), with the functionalized Schiff base ligand 2,6-bis((2-(acetylamino)phenylimino)methyl)-4- tert-butylphenol (H₃L) has been obtained and characterized in the solid state by X-ray diffraction. The formation of the tetranuclear species is solvent dependent, the presence of water being a determinant in its isolation. Based on the mass-spectrometric evidence, the behaviour of the H ₃L-Cu^II system in the presence of water was investigated. Namely, water can switch the nuclearity of the Cu^II cluster from dinuclear to tetranuclear. The redox behaviour of this species in DMSO solution, showing two cathodic metal-centred peaks at E_P = -0.80 and -1.35 V and an irreversible ligand-centred anodic peak at E_P = 1.03 V, was found to be similar to that of a pristine dinuclear complex. The tetranuclear species was also characterized in the solid state by magnetic measurements, showing a dominating bulk antiferromagnetic behaviour, with a singlet ground state at approximately 2 K. DFT calculations permitted us to estimate the strong intradimer antiferromagnetic exchange interaction (J₁ = -440 cm ^-1), together with two weak interdimer ferromagnetic exchange interactions (J₂ = +0.5 and J₃ = +1.7 cm^-1).