The magnetic exchange interaction in bi- and tetranuclear copper(II) complexes with the bis-azomethine of 1,3-diaminopropano1-2 and 4-hydroxy-3-formylcoumarin with an azide exogenous bridge

By the reaction of Cu(II) perchlorate with the condensation product of 1,3-diamino-2-propanol and 4-hydroxy-3-formylcoumarin (H3L) in the presence of sodium azide, a tetranuclear copper(II) complex with the composition [Cu2L(mu(2-1,1)-N-3)](2) (I) was obtained. On crystallization from a pyridine solution, the crystalline adduct [Cu2L(mu(2)-N-3)(PY)(2)] (PY = pyridine) was obtained and further characterized by XRD. The copper ions in (II) are coordinated by ONO'NO donor atoms of the triply deprotonated pentadentate ligand and the azide anion is coordinated in an asymmetric mu 2-1,1 fashion, favoring a "roof" like conformation of the molecule. The pyridine molecules are coordinated to each copper center, completing the distorted square-pyramidal coordination environment, but in a different way - for one copper ion the solvent molecule populates an apical position, for the other - a position in the basal plane. The tetranuclear complex is formed by linking two binuclear [Cu2L] units by two bridging mu(2-1,1)-N-3\groups in a head-to-tail fashion. The temperature dependence of the magnetic susceptibility was studied for both I and II samples, showing a medium strength overall antiferromagnetic exchange for I and a weak ferromagnetic one with 2J = +5 cm(-1) for II. Two major superexchange pathways in I - through an alkoxide oxygen atom of the polydenate ligand and through the bridging azide-anion are characterized by opposite magnetic interaction characters - antiferromagnetic (2Jo = -328 cm(-1)) and ferromagnetic (2J(N) = +132 cm(-1)), correspondingly. Quantum-chemical modeling using the broken symmetry approach was performed for II and possible binuclear isomers of I, differing in the azide-anion coordination mode and conformation of the polydentate ligand, and for two possible tetranuclear dimers. (C) 2017 Elsevier Ltd. All rights reserved.