Heterometallic CuCd and Cu ₂ Zn complexes with <i>o</i> -vanillin and its Schiff-base derivative: slow magnetic relaxation and catalytic activity associated with Cu( <scp>ii</scp> ) centres

In this work, two novel heterometallic mixed-ligand mixed-anion complexes [Cu^IICd^IIClL(<i>o</i>-Van)(OAc)]·3H₂O (1) and [CuII2Zn^IICl₂L₂(<i>o</i>-Van)(OAc)] (2) were prepared by reacting fine copper powder and Cd(II) or Zn(II) acetate with an ethanol solution of the Schiff-base ligand HL formed <i>in situ</i> in the condensation reaction of 2-hydroxy-3-methoxy-benzaldehyde (<i>o</i>-VanH) and CH₃NH₂·HCl. The compounds were thoroughly characterized by elemental analysis, FT-IR, UV/Vis and EPR spectroscopy, cyclic voltammetry, and single-crystal X-ray diffraction, revealing the neutral molecular nature of both the compounds. Catalytic properties of 1 and 2 were studied in the oxidation of hydrocarbons with H₂O₂ under mild conditions, showing the maximum reaction rate of 4 × 10^-5 M s^-1 and TOF up to 640 h^-1. Both compounds undergo complex transformations in solution as evidenced by kinetic analysis and time-dependent UV/Vis spectroscopy, indicating that the reduced Cu(I) form of 1 is unexpectedly unfavorable. Complex 1 demonstrates slow magnetic relaxation dominated by the direct relaxation process between <i>T</i> = 1.8 and 7 K under an external DC field of 0.2 and 0.4 T, a very rarely observable effect in the coordination compounds of Cu(II). Complex 2 possesses weak ferromagnetism (<i>J</i> = 4.50 cm^-1, <i>zJ</i>' = -0.201 cm^-1 for <i>H</i> = -<i>JS</i>₁<i>S</i>₂ formalism) occurring through the Cu-O-Cu pathways. Theoretical CASSCF, DFT and TDDFT calculations were applied to investigate the electronic structures of 1 and 2 and rationalize their behavior in solution.