Electron Paramagnetic Resonance Spectroscopic Study of Trinuclear Manganese Complex

• Main Authors: Mang-Lun Wu, 吳孟倫
• Other Authors: Ping-Yu Chen
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/19102956477794731882

碩士 === 國立中興大學 === 化學系所 === 105 === In this study, the EPR spectra of the reactions of the trimanganese complexes, including [MnII(OAc)2MnII(µ-OAc)MnII(7-Dipy)](OAc) (1) and [MnIIMnIIMnII(7-Dipy)](ClO4)4 (3), with TBHP or TBA-OX are reported. Althougth the oxidations induced by TBHP or TBA-OX will all give rise to higher oxidation states, including detectable Mn3(III, III, IV), Mn3(III, IV, IV) or Mn3(IV, IV, IV), Complex 3 can be raised to ever higher state, namely Mn3(IV, IV, V) with S = 1 spin state evidenced by parallel mode EPR g ~ 4.01 signal. The high-valent Mn(IV, IV, IV) species is rationally proposed based on its efficient oxo-transfer to C-H bonds of alkane, and is further confirmed by the prependicular mode EPR with addition of ethylene glycol. However, ethylene glycol is commonly used as an antifreeze for improving the glass of the freezed solution, obviously it can also effectively stablilize the Mn3(IV, IV, IV) species no matter using TBHP or TBA-OX at -50 oC, and PhIO as oxidants. A signal with 6 ~ 8 distinct splitting lines at g ~ 5 in prependicular mode EPR spectroscopy will appear immediately, which is similar to the typical monomanganese(IV)-oxo complex. At the same time, another 11-lines signal at g ~ 2 is observed in parallel mode, which is conjectured as Mn3(III, IV, IV). For the Complex 3, it appears a g ~ 7 signal in prependicular mode, presumably resulting from coupling among multiple manganese ions, and a g ~ 4.01 characteric signal in parallel mode, referring to a S = 1 Mn(V) formation. Based on the EPR study of these distinct manganese species and their interdependence in the formation, a clear oxidative mechanism for the trimanganese complexes is thus depicted.