Coordination Reactivity of a Tautomeric Thiosemicarbazone Schiff Base for Open-Dicubane Cu4 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 L2- 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 kcat 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%.