Unusual slow magnetic relaxation in a sulfate-bridged copper(II) complex with 1-(2-pyridylazo)-2-naphthol ligand.

We report an unprecedented one-pot route synthesis and in-depth characterizations of a new binuclear copper(II) complex with the tridentate PAN ligand (1-(2-pyridylazo)-2-naphthol). The compound of formula [Cu2(μ-SO4)(PAN)2(H2O)2] was isolated as a highly crystalline material, where the two copper(II) centers are connected by a sulfate bridge. Single-crystal X-ray diffraction (SC-XRD) combined with UV-Vis spectroscopy confirms a square-pyramidal coordination around each Cu(II) center in both the solid state and solution. Remarkably, magnetic studies revealed an unconventional slow magnetic relaxation under applied dc fields, characterized by three field-dependent processes spanning more than four orders of magnitude in frequency. These findings broaden the design space of transition-metal molecular magnets by showing that simple sulfate bridging and π-conjugated ligands can engender complex relaxation dynamics in Cu(II) dimers.