Coordination Reactivity of a Tautomeric Thiosemicarbazone Schiff Base for Open‐Dicubane Cu ₄ Complexes: Synthesis, Structures, Catalytic Functions, and Magnetic Behavior

Two tetranuclear Cu(II) complexes [Cu₄L₂(μ₃-OCH₃)₂](ClO₄)₂∙2H₂O (1) and [Cu₄L₂(H₂O)₂(μ₃-OH)₂](NO₃)₂∙H₂O (2) (H₂L = 2,6-diformyl-4-methylphenol bis(thiosemicarbazone)) have been synthesized. Two types of sulfur atom-bearing L^2- scaffolds were obtained through tautomerization of the thiosemicarbazone arms. Geometric arrangements of [Cu₂(μ₃-OMe)₂Cu₂] and [Cu₂(μ₃-OH)₂Cu₂] are found for tetranuclear complexes. Reactions of Cu(ClO₄)₂∙6H₂O and Cu(NO₃)₂∙3H₂O with H₂L were utilized with linkers HO^- and MeO^-. These synthesized complexes have been characterized by x-ray crystallography, and their magnetic properties have been examined. Complexes 1 and 2 showed fluorescence quenching behavior with respect to the free H₂L. Complexes 1 and 2 exhibit catalytic oxidation reactivity for the 2-aminophenol and 3,5-ditertbutyl catechol, effectively mimicking the enzymes catechol oxidase and phenoxazinone synthase, respectively. The turnover numbers k_cat for 3,5-DTBCH₂ and AP are 13.32 (1), 25.56 (2) and 23.04 (1), 13.35 (2). From the variable temperature magnetic susceptibility measurements, the obtained J values ranged between -200 and -500 cm^-1 and were found to be highly correlated, which indicates the strong antiferromagnetic interactions between the interlinked copper(II) centers. For complex 1, the values are g = 2.13, J = -470 cm^-1, ρ = 1.4% and for compound 2 these are g = 2.08, J = -480 cm^-1, ρ = 2.5%.