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

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).