Doubly phenoxide-bridged binuclear copper(II) complexes with ono tridentate schiff base ligand: Synthesis, structural, magnetic and theoretical studies

The tridentate ONO-donor Schiff base ligand H2L, derived from the condensation of 1-anisyl-1,3-butanedione and 2-aminophenol, was generated in situ and reacted with Cu(NO3)2•3H2O to yield two doubly phenoxo bridged di-copper(II) complexes depending on the nitrogenous base used. [Cu2L2] (1) is obtained in 85% and 75% yield in the presence of pyridine or 4-picoline, respectively, and [(py-tBu)2Cu2L2] (2) is isolated in 75% yield in the presence of 4-tert-butylpyridine. Compounds 1 and 2 were characterized in the solid-state by elemental analysis and FT-IR spectroscopy. Single crystal X-ray diffraction study reveals that in 1 the two four-coordinated copper atoms adopt a square planar geometry, whereas in 2 each Cu(II) metal ion shows a five coordinate square pyramidal (ONO,N + O) geometry. In each dimer, two μ-phenolic oxygen atoms bridge the two half-units forming a planar Cu2O2 core. EPR studies in fluid solutions indicate that the dimeric structure of 1 and 2 is destroyed upon dissolution. In the solid-state, 1 is EPR silent, whereas 2 presents an unresolved broad resonance (H peak-to-peak = 71.5 G) with g = 2.071 at 298 K, along with the triplet state (S = 1) signature at g = 4.181. Variable temperature (2-300 K) magnetic susceptibility measurements exhibit strong antiferromagnetic interactions between the Cu(II) centers with a J value of -397 cm -1 for 1, while no interaction operates between the two spins localized on Cu(II) metal ions in 2. Ab initio calculations were also performed to supplement the experimental results.