配体分子结构对Pd(Ⅱ)-Phen-PCA体系堆积作用的影响

Dependence of the Aromatic-ring Stacking Interactions in the Ternary Complexes on Ligand Structure

用pH电位滴定法测定了含1,10-邻菲咯啉(Phen)和羧酸(CA)配体的三元混配配合物Pd(Phen)(cA)+体系的稳定常数,比较和讨论了各种三元混配配合物之间的稳定性差异.实验结果表明,在三元混配配合物Pd(Phen)(PCA)+中(PCA为苯基羧酸)存在分子内芳环堆积作用,堆积程度依赖于苯基和配位的羧酸根之间的亚甲基数目,其中以2-苯乙酸和3-苯丙酸与邻菲咯啉为最佳堆积.

The stability constants of ternary mixed-ligand complexes of the type Pd(Phen) (CA)(+), where Phen(1,10-phenanthroline) and CA(-)(carboxylate), have been determined by potentiometric pH titration in aqueous solution (ionic strength, I = 0.1 mol (.) L-1, adjusted with KNO3; 25 degreesC), and compared with the stabilities of the corresponding binary complexes. It reveals that the ternary complexes containing phenylalkanecarboxylates ligands (PCA(-)) are much more stable than those formed with formate and acetate. The results indicate that there exist the intramolecular aromatic-ring interactions between the phenanthroline ring of Phen and the phenyl moiety of the ligand PCA(-) in the ternary mixed-ligand Pd(Phen) (PCA)(+) complexes. The extent of the stacking interactions was calculated which depends on the number of methylene groups between the phenyl moieties and the coordinated carboxylate groups. The best-fit stacks are reached with 2-phenylacetate and 3-phenylpropionate.