Synthesis of Structurally Diverse Ferrimagnetically and Antiferromagnetically Coupled M-II -Mn-II (M = Cu, Ni) Heterometallic Schiff Base Compounds with a Dicyanamide Spacer and Study of Biomimetic Catalytic Activity

摘要

The two heterometallic Schiff base compounds {[(CuL)Mn(N(CN)(2))(2)]center dot CH3CN}infinity (1) and [(NiL)(4) Mn-2 (N(CN)(2))(2) ](ClO4)(2) (2) have been synthesized using the N2O2 , donor ligand 2,2'-((1E,1'E)-((2,2-dimethylpropane-1,3-diyObis (azanylylidene))bis(methanylylidene))-diphenol (H2L) and a dicyanamide spacer. Single-crystal X-ray structural analyses reveal that compounds 1 and 2 have a one-dimensional zigzag polymeric structure and a discrete hexanuclear structure, respectively. Magnetic studies of 1 reveal the presence of intrachain ferrimagnetic coupling between Cu(II) and Mn(II) spins. Alternating interactions in an F-AF-F sequence (F, ferromagnetic; AF, antiferromagnetic) of 1 impose the ideal situation of noncompensation in spin moments considering intrachain magnetic interactions. On the other hand, an antiferromagnetic interaction between neighboring Mn(II) ions is observed for 2. ESI-MS and EPR studies help to predict the solution-phase structures of the two compounds. Between them, 1 dissociates to form Cu(II)-Mn(III) species with three N(CN)(2-) and one CH3OH, making it catalytically active in mimicking the two well-known proteins phenoxazinone synthase and phosphatase. The calculated turnover numbers (k(cat)) for the aerial oxidation of o-aminophenol and hydrolysis of 4-nitrophenylphosphate (4-NPP) are 5129 h(-1) and 25.052 s(-1), respectively. However, in the solution state 2 behaves as a discrete structure, which causes its inability to catalyze reactions. A probable mechanistic pathway has been studied by using experimental tools such as ESI-mass spectra, cyclic voltammetry, and EPR measurements, suggesting the formation of an imine radical during the catalytic reaction of phenoxazinone synthase like activity.