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Structural and thermodynamic aspects of water–carbonate exchange equilibrium for MIII/IV–EDTA–carbonate systems†
Inorganic Chemistry Frontiers ( IF 7 ) Pub Date : 2018-11-27 00:00:00 , DOI: 10.1039/c8qi01062e
Rafał Janicki 1, 2, 3, 4 , Anna Mondry 1, 2, 3, 4
Affiliation  

The results of a thermodynamic description of ternary M–EDTA–carbonate (where M = Er(III), Th(IV)) complex formation are presented. The crystal structures of the novel [C(NH2)3]3[Er(EDTA)(CO3)]·H2O (I) and [C(NH2)3]4[Th(EDTA)(CO3)2]·5H2O (II) compounds were determined. The structural and UV-vis-NIR spectroscopic results of crystal I served as the model data to analyze the stoichiometry and stability of the Er(III)–EDTA–carbonate system in aqueous solutions. The formation of the [Er(EDTA)(CO3)]3– complex in solution under different conditions was examined by complementary techniques including temperature dependent UV-vis-NIR and NMR spectroscopy as well as potentiometry. It was established that the affinity of the carbonate for the Er(III)–EDTA chelate is strongly pH dependent. Thus reaction (A) [Er(EDTA)(H2O)2] + CO32– ⇄ [Er(EDTA)(CO3)]3– + 2H2O is more favoured at near neutral pH, while reaction (B) [Er(EDTA)(OH)(H2O)2]2– + CO32– ⇄ [Er(EDTA)(CO3)]3– + 2H2O + OH occurs under more basic conditions. The log β values were found to be 3.66 ± 0.07 and 0.20 ± 0.12 for reactions (A) and (B), respectively. The temperature dependence of log β allowed the determination of the enthalpy and entropy changes of both reactions for the first time (ΔH(A) = −2.8 ± 0.8 kJ mol−1, ΔS(A) = 62 ± 3 J mol−1 K−1 and ΔH(B) = 28.1 ± 4.6 kJ mol−1, ΔS(B) = 92 ± 15 J mol−1 K−1). These data indicate that the carbonate anion more readily displaces H2O than the OH ligand. The obtained results are important not only from the point of view of environmental lanthanide and actinide mobility, but also for designing MRI contrast agents.

中文翻译:

M III / IV –EDTA–碳酸盐系统中水-碳酸盐交换平衡的结构和热力学方面

给出了M-EDTA-碳三元碳酸盐(其中M = Er(III),Th(IV))配合物形成的热力学描述结果。新型[C(NH 23 ] 3 [Er(EDTA)(CO 3)]·H 2 O(I)和[C(NH 23 ] 4 [Th(EDTA)(CO 3)2 ]·5H 2 O(II)的化合物被确定。晶体I的结构和UV-NIR光谱结果作为模型数据,用于分析Er(III)的化学计量和稳定性)–水溶液中的EDTA –碳酸盐系统。通过补充技术,包括依赖于温度的UV-vis-NIR和NMR光谱以及电位计,研究了在不同条件下溶液中[Er(EDTA)(CO 3)] 3–络合物的形成。已经确定,碳酸盐对Er(III)-EDTA螯合物的亲和力强烈依赖于pH值。因此,反应(A)[Er(EDTA)(H 2 O)2 ] - + CO 3 2- ⇄[Er(EDTA)(CO 3)] 3- + 2H 2 O在接近中性pH时更有利, (B)[Er(EDTA)(OH)(H 2 O)2 ]2- + CO 3 2- ⇄[二(EDTA)(CO 3)] 3- + 2H 2 O + OH -更基本的条件下发生。日志 β发现值分别为3.66±0.07和用于反应(A)和(B)0.20±0.12。日志的温度依赖性 β允许的两个反应的首次(焓和熵的变化的确定Δ ħ (A) = -2.8±0.8千焦耳摩尔-1,Δ小号(A) = 62±3Ĵ摩尔- 1 K -1ΔH (B) = 28.1±4.6 kJ mol -1,ΔS (B)= 92±15J mol -1 K -1)。这些数据表明,碳酸根阴离子更容易位移ħ 2 ö比OH -配位体。所获得的结果不仅从环境镧系元素和act系元素迁移率的观点来看是重要的,而且对于设计MRI造影剂也很重要。
更新日期:2018-11-27
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