The stability constants of ML-type complexes of the two linear triphosphate ligand anion analogues triphosphate ($$ {\text{P}}_{ 3} {\text{O}}_{10}^{5 - } $$P3O105-) and diimidotriphosphate ($$ {\text{P}}_{ 3} {\text{O}}_{ 8} ( {\text{NH}})_{2}^{5 - } $$P3O8(NH)25-) were investigated thermodynamically using potentiometric titrations according to Schwarzenbach’s procedure. The stability constants of the ML-type complexes of different divalent metal ions with $$ {\text{P}}_{ 3} {\text{O}}_{ 8} ( {\text{NH}})_{2}^{5 - } $$P3O8(NH)25- are larger than those of the corresponding complexes with $$ {\text{P}}_{ 3} {\text{O}}_{10}^{5 - } $$P3O105- because of the greater basicity of the imino group. The order of the stability constants for the ML-type complexes follows the Irving–Williams order, indicating that only non-bridging oxygen atoms are coordinated directly to the different metal ions in both ligands, and that the imino groups cannot participate in coordination to the metal ions. In the complexation reactions of the Ca2+, Sr2+, Ba2+–$$ {\text{P}}_{ 3} {\text{O}}_{10}^{5 - } $$P3O105- and Cu2+, Zn2+, Ni2+–$$ {\text{P}}_{ 3} {\text{O}}_{ 8} ( {\text{NH}})_{2}^{5 - } $$P3O8(NH)25- systems, each metal ion forms an enthalpically stable complex, and there was no suggestion of a conspicuous entropic effect based on the chelate effect. Monodentate complexes that are strongly coordinated with the ligands were therefore formed, whereas entropically stable bidentate complexes were formed in the complexation reactions of the Cu2+, Zn2+, Ni2+–$$ {\text{P}}_{ 3} {\text{O}}_{10}^{5 - } $$P3O105- and Ca2+, Ba2+, Sr2+–$$ {\text{P}}_{ 3} {\text{O}}_{ 8} ( {\text{NH}})_{2}^{5 - } $$P3O8(NH)25- systems. According to the HSAB concept, hard metal cations such as Ca2+, Ba2+ and Sr2+ should bind to the harder oxygen atoms rather than the softer nitrogen atoms of the imidopolyphosphate anions, preventing direct coordination to the imino nitrogen atom.Graphical Abstract

中文翻译：

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短链聚磷酸盐及其亚氨基衍生物的二价金属离子络合物的稳定性

两种线性三磷酸配体阴离子类似物三磷酸 ($$ {\text{P}}_{ 3} {\text{O}}_{10}^{5 - } $$P3O105 -) 和二亚胺三磷酸 ($$ {\text{P}}_{ 3} {\text{O}}_{ 8} ( {\text{NH}})_{2}^{5 - } $$P3O8 (NH)25-) 根据施瓦岑巴赫程序使用电位滴定法进行热力学研究。$$ {\text{P}}_{ 3} {\text{O}}_{ 8} ( {\text{NH}})_{ 不同二价金属离子的ML型配合物的稳定性常数2}^{5 - } $$P3O8(NH)25- 大于对应的配合物 $$ {\text{P}}_{ 3} {\text{O}}_{10}^{ 5 - } $$P3O105- 因为亚氨基的碱性更强。ML 型配合物的稳定常数顺序遵循 Irving-Williams 顺序，表明只有非桥接氧原子直接与两个配体中的不同金属离子配位，并且亚氨基不能参与与金属离子的配位。在 Ca2+、Sr2+、Ba2+–$$ {\text{P}}}_{ 3} {\text{O}}_{10}^{5 - } $$P3O105- 与 Cu2+、Zn2+ 的络合反应中， Ni2+–$$ {\text{P}}}_{ 3} {\text{O}}_{ 8} ( {\text{NH}})_{2}^{5 - } $$P3O8(NH) 25-系统，每个金属离子形成一个焓稳定的络合物，并且没有基于螯合效应的显着熵效应的暗示。因此形成了与配体强烈配位的单齿配合物，而在 Cu2+、Zn2+、Ni2+–$$ {\text{P}}_{ 3} {\text{O }}_{10}^{5 - } $$P3O105- 和 Ca2+, Ba2+, Sr2+–$$ {\text{P}}_{ 3} {\text{O}}_{ 8} ( {\text{NH}})_{2}^{5 - } $$P3O8(NH) 25-系统。根据 HSAB 概念，Ca2+、Ba2+ 和 Sr2+ 等硬金属阳离子应与较硬的氧原子结合，而不是与亚氨基多磷酸盐阴离子的较软的氮原子结合，从而防止与亚氨基氮原子直接配位。