Dicarboxylate Recognition Properties of a Dinuclear Copper(II) Cryptate

A ditopic polyamine macrobicyclic compound with biphenylmethane spacers was prepared, and its dinuclear copper­(II) complex was studied as a receptor for the recognition of dicarboxylate anions of varying chain length in H2O/MeOH (50:50 (v/v)) solution. The acid–base behavior of the compound, the stability constants of its complexes with Cu2+ ion, and the association constants of the copper­(II) cryptate with succinate (suc2–), glutarate (glu2–), adipate (adi2–), and pimelate (pim2–) were determined by potentiometry at 298.2 ± 0.1 K in H2O/MeOH (50:50 (v/v)) and at ionic strength 0.10 ± 0.01 M in KNO3. The association constants of the same cryptate as receptor for aromatic dicarboxylate substrates, such as phthalate (ph2–), isophthalate (iph2–), and terephthalate (tph2–), were determined through competition experiments by spectrophotometry in the UV region. Remarkably high values of association constants in the range of 7.34–10.01 log units were found that are, to the best of our knowledge, the highest values of association constants reported for the binding of dicarboxylate anions in aqueous solution. A very well defined peak of selectivity was observed with the binding constant values increasing with the chain length and reaching the maximum for substrates with four carbon atoms between the carboxylate groups. Single-crystal X-ray diffraction determinations of the cascade complexes with adi2– and tph2– assisted in the understanding of the selectivity of the cryptate toward these substrates. The Hirshfeld surface analyses of both cascade complexes suggest that the establishment of several van der Waals interactions between the substrates and the walls of the receptor also contributes to the stability of the associations.本研究合成了一种带有二苯甲烷间隔基的双位点多胺大环双环化合物（ditopic polyamine macrobicyclic compound），并以其双核铜(II)配合物作为受体，用于在水/甲醇（体积比50:50）混合溶剂中识别不同链长的二羧酸根阴离子。 本研究通过电位滴定法，在298.2±0.1 K、以硝酸钾（KNO3）为支持电解质且离子强度为0.10±0.01 M的水/甲醇（50:50 v/v）混合溶剂体系中，测定了该化合物的酸碱解离行为、其与Cu²+离子形成配合物的稳定常数，以及该铜(II)穴合物（copper(II) cryptate）与丁二酸根（suc²⁻）、戊二酸根（glu²⁻）、己二酸根（adi²⁻）和庚二酸根（pim²⁻）的结合常数。 针对邻苯二甲酸根（ph²⁻）、间苯二甲酸根（iph²⁻）和对苯二甲酸根（tph²⁻）等芳香族二羧酸底物，本研究通过紫外区分光光度法的竞争实验，测定了该穴合物作为受体时的结合常数。 研究发现其结合常数高达7.34~10.01对数单位，据我们所知，这是目前水溶液中二羧酸根阴离子结合反应所报道的最高结合常数数值。 实验观察到十分明确的选择性峰：结合常数随底物羧基之间的碳链长度增加而升高，当羧基相隔四个碳原子时达到最大值。 对与己二酸根（adi²⁻）和对苯二甲酸根（tph²⁻）形成的级联配合物进行单晶X射线衍射表征，有助于阐明该穴合物对上述底物的选择性识别机制。 对这两种级联配合物的赫尔施费尔德表面分析表明，底物与受体空腔壁之间形成的多重范德华相互作用，同样对配合物的稳定性具有贡献。