Self-assembled molecular magnets from discrete dimer to one-dimensional helical chain: Syntheses, crystal structures and magnetic properties

The reaction of the deprotonated tridentate N-(8-quinolyl)salicylaldimine anionic ligand (L) and CuX₂ (X = ClO₄^-, Ac^-, N₃^- and SCN^-) in DMF gave four new complexes 1-4 which contain the architecture CuL⁺. The Cu²⁺ center is surround by a tridentate ligand (L) and counter anions (or DMF) to adopt a similar square-pyramidal coordination environment in 1-4, however their crystal packing structures are distinct. The tectons of CuL⁺ form discrete [CuL(DMF)]₂ dimers in 1 and (CuLX)₂ in 2 and 3 and a 1D helical chain of ⋯CuL(SCN)⋯ in 4. It is observed that the binding ability and structural features of the counter anion play an important role in controlling the final packing structures for these complexes. The variations of the magnetic susceptibility as a function of temperature in the range of 2-350 K obey the simple Curie-Weiss law with a weak AFM coupling feature in 1-4; and at room temperature the EPR spectra of 1-3 show axially symmetrical signals with small linewidths, even when g_∥ and g_⊥ are not well resolved in the spectra of 1 and 2, and the EPR spectrum of 4 displays an isotropic feature.