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.

Graphical abstractThree new dinuclear manganese(II) complexes assembled with N,N,N′,N′-tetrakis(2′-benzimidazolylmethyl)-1,4-diethylene amino glycol ether (EGTB) have been synthesized through temperature-dependent synthesis. Interestingly, in the three complexes, the Mn–Mn distances are shortened with increase in temperature. Additionally, the study on the polyphenol oxidase (PPO) activity of the three complexes toward pyrogallol reveals that, in the pH range 7.8–8.2, catalytic activities of all three complexes increase with increasing of pH values.Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Three dinuclear Mn(II) complexes were prepared and characterized. ► Interestingly, there is a relationship between synthesis temperature and structure. ► In pH 7.8–8.2, the polyphenal oxidase activity of the complexes increased with rising pH.