Synthesis, temperature-controlled structures and polyphenol oxidase activities of dinuclear manganese(II) complexes with N,N,N′,N′-tetrakis(2′-benzimidazolylmethyl)-1,4-diethylene amino glycol ether

Three dinuclear Mn(II) complexes, [Mn2(EGTB)(NO3)2(H2O)4](NO3)2 (1), [Mn2(EGTB)(NO3)4] (2) and [Mn2(EGTB)(NO3)(H2O)](NO3)3 (3) (EGTB = N,N,N′,N′-tetrakis(2′-benzimidazolylmethyl)-1,4-diethylene amino glycol ether) were prepared and characterized. Their crystal structures revealed a relationship between synthesis temperature and structure. With increasing the reaction temperature from 60 to 120 °C or 160 °C, the Mn–Mn distances are shortened from 14.019 Å in 1, 7.662 Å in 2 to 5.662 Å in 3. Additionally, polyphenol oxidase (PPO) activity of those three complexes was studied by measuring the rate of increase in absorbance at 320 nm of pyrogallol substrate. At pH 7.8 and 30 °C, the turnover numbers are 5.58 h−1 for 1, 11.38 h−1 for 2 and 13.97 h−1 for 3, respectively. Furthermore, in pH 7.8–8.2, their catalytic activity increased with rising pH.