A unique example of structural and magnetic diversity in four interconvertible copper (II)−azide complexes with the same schiff base ligand: a monomer, a dimer, a chain and a layer

Abstract

Four new Cu (II)-azido complexes of formula [CuL(N₃)] (1), [CuL(N₃)]₂ (2), [Cu₇L₂(N₃)₁₂]_n (3) and [Cu₂L(dmen)(N₃)₃]_n (4) (dmen = N,N-dimethylethylenediamine) have been synthesized using the same tridentate Schiff base ligand HL (2-[1-(2-dimethylaminoethylimino)ethyl]phenol, the condensation product of dmen and 2-hydroxyacetophenone). The four compounds have been characterized by X-ray structural analyses and variable-temperature magnetic susceptibility measurements. Complex 1 is mononuclear, whereas 2 is a single μ-1,1 azido-bridged dinuclear compound. The polymeric compound 3 possesses a 2D structure in which the Cu (II) ions are linked by phenoxo oxygen atoms and two different azide bridges (μ-1,1 and μ-1,1,3). The structure of complex 4 is a double helix in which two μ-1,3-azido-bridged alternating one-dimensional helical chains of CuL(N₃) and Cu(dmen)(N₃)₂ are joined together by weak μ-1,1 azido bridges and H-bonds. The complexes interconvert in solution and can be obtained in pure form by carefully controlling the conditions. The magnetic properties of compounds 1 and 2 show the presence of very weak antiferromagnetic exchange interactions mediated by a ligand π overlap (J = −1.77) and by an asymmetric 1,1-N₃ bridge (J = −1.97 cm⁻¹), respectively. Compound 3 presents, from the magnetic point of view, a decorated chain structure with both ferro- and antiferromagnetic interactions. Compound 4 is an alternating helicoidal chain with two weak antiferromagnetic exchange interactions (J = −1.35 and −2.64 cm⁻¹).