Variations of structures and phenoxazinone synthase-like activity of the complexes based on (CuII)2MnII node and dicyanamide spacer

Article abstract of DOI:10.1021/acs.cgd.7b01407

Three new heterometallic Cu(II)?Mn(II) complexes, [((CuL)₂Mn)₂(μ_1,5-N(CN)₂)(CH₃CN)₂](ClO₄)₃ (1), [(CuL)₂Mn(N(CN)₂)₂]·(H₂O) (2), and [(CuL)₂Mn-(μ_1,5-N(CN)₂)₂]_n (3), have been synthesized using a Cu(II)metalloligand of an asymmetrically dicondensed Schiff base ligand (where H₂L = N-α-methylsalicylidene-N′-salicylidene-1,3-propanediamine). Complex 1 was formed when the ratio of [CuL]/Mn(ClO₄)₂/NaN(CN)₂ was 2:1:1, whereas complexes 2 and 3 were obtained with a 2:1:2 ratio of the same reactants on varying the reaction conditions. Single-crystal structural analyses reveal that complex 1 possesses a hexanuclear structure in which two (Cu^II)₂Mn^II units are connected by one μ_1,5-N(CN)₂^? bridge, 2 is a discrete trinuclear species with two terminally coordinated N(CN)₂^? ions to the Mn(II), whereas complex 3 is a polymeric form of 2 with μ_1,5-N(CN)₂^? bridges between Cu(II) and Mn(II) centers. The thermal variations of dc magnetic susceptibilities suggest that all three complexes (1?3) are antiferromagnetically coupled with comparable exchange coupling constants (?25.4, ?22.8, and ?22.0 cm^?1, respectively) which are expected from the Cu?O?Mn angles. All the complexes show biomemitic phenoxazinone synthase-like activity for the aerial oxidation of o-aminophenol to amino phenoxazinone. The turnover numbers (k_cat) for the process are 4966, 2021, and 1107 h^?1 for complexes 1?3 respectively. The mass spectral evidence on intermediates suggests that the cooperative activity of the two different metal ions, i.e., coordination of substrate to Mn(II) and shuttling of oxidation state of Cu between I and II, is possibly operative in the oxidation process. The highest catalytic activity of 1 is attributed to the presence of one coordinating solvent molecule to Mn(II).