取代锰卟啉的轴向配位反应及平衡常数的测定

Axial Coordination Reactions of Substitutive Derivates of Manganese Porphyrins and Determination of Equilibrium Constants

研究了4种具有不同取代基的锰卟啉在三氯甲烷溶剂中与咪唑(Im)、4-甲基咪唑(4-MeIm)、吡啶(Py)、4-甲基吡啶(4-MePy)等4种客体小分子的轴向配位反应,并采用微量紫外-可见光谱滴定法测定了反应的平衡常数。结果表明:每种锰卟啉均可以与咪唑及吡啶类客体分子发生轴向配位反应,轴向配合物的形成能力和稳定性与锰卟啉所含有的取代基有关,在β位上含有强吸电子硝基取代基的锰卟啉与客体分子能够形成更稳定的配合物;客体分子的性质对轴向配合物的形成也有显著的影响,锰卟啉与吡啶以物质的量之比为1∶1反应生成五元配位化合物;每一种锰卟啉与其他3种客体分子均以物质的量之比为1∶2反应生成六元配位化合物。客体的轴向配位反应能力由大到小依次为Im、4-MeIm、4-MePy、Py。

Axial coordination reactions between 4 substitutive derivates of manganese porphyrins and 4small molecular ligands of imidazole（Im）,4-methylimidazole（4-MeIm）,pyridine（Py）and 4-methylpyridine（4-MePy）in CHCl_3 medium were studied and the equilibrium constants of the coordination reactions were determined by micro UV-Vis spectrophotometric titration.It was found that each of the 4 manganese porphyrins with different substitution forms coordination complex with either of the 4 guest ligands,with their formation ability and stability related to the position of substituents in the manganese porphyrin molecules.The manganese porphyrins with substitution of-NO_2^- group at theβposition,form more stable complexes with the guest ligands due to the strong electron affinity of the NO_2^- group;different structures of the guest ligands also show significant effects on the coordination reaction.A 5-membered complex with mole ratio of manganese porphyrins and pyridine of 1 to 1 is formed;and 6-membered complexes with mole ratio of manganese porphyrins and the remainder 3guest ligands of 1 to 2 are formed.Reaction abilities of the 4guest ligands in the coordination reactions have the following order：Im〉4-MeIm〉4-MePy〉Py.