摘要：

In this work we report on the synthesis, crystal structure, and physicochemical characterization of the novel dinuclear [Fe ~IIICd ~II(L)(μ-OAc) _2]ClO _4?0.5H _2O (1) complex containing the unsymmetrical ligand H _2L = 2-bis[{(2-pyridyl-methyl)-aminomethyl}-6-{(2-hydroxy-benzyl)-(2-pyridyl-methyl)} -aminomethyl]-4-methylphenol. Also, with this ligand, the tetranuclear [Fe _2 ~IIIHg _2 ~II(L) _2(OH) _2](ClO _4) _2?2CH _3OH (2) and [Fe ~IIIHg ~II(L)(μ-CO _3)Fe ~IIIHg ~II(L)](ClO _4) _2?H _2O (3) complexes were synthesized and fully characterized. It is demonstrated that the precursor [Fe ~III _2Hg ~II _2(L) _2(OH) _2](ClO _4) _2?2CH _3OH (2) can be converted to (3) by the fixation of atmospheric CO _2 since the crystal structure of the tetranuclear organometallic complex [Fe ~IIIHg ~II(L)(μ-CO _3)Fe ~IIIHg ~II(L)] (ClO _4) _2?H _2O (3) with an unprecedented {Fe ~III(μ-O phenoxo) _2(μ-CO _3)Fe ~III} core was obtained through X-ray crystallography. In the reaction 2 → 3 a nucleophilic attack of a Fe ~III-bound hydroxo group on the CO _2 molecule is proposed. In addition, it is also demonstrated that complex (3) can regenerate complex (2) in aqueous/MeOH/NaOH solution. Magnetochemical studies reveal that the Fe ~III centers in 3 are antiferromagnetically coupled (J = - 7.2 cm ~(- 1)) and that the Fe ~III-OR-Fe ~III angle has no noticeable influence in the exchange coupling. Phosphatase-like activity studies in the hydrolysis of the model substrate bis(2,4-dinitrophenyl) phosphate (2,4-bdnpp) by 1 and 2 show Michaelis-Menten behavior with 1 being ~ 2.5 times more active than 2. In combination with k _H/k D isotope effects, the kinetic studies suggest a mechanism in which a terminal Fe ~III-bound hydroxide is the hydrolysis-initiating nucleophilic catalyst for 1 and 2. Based on the crystal structures of 1 and 3, it is assumed that the relatively long Fe ~III...Hg ~II distance could be responsible for the lower catalytic effectiveness of 2.

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