Tamal Kanti Ghosh and Pradyut Ghosh, Department of Inorganic Chemistry, Indian Association for the Cultivation of Science, 2A & 2B Raja S. C. Mullick Road, Kolkata 700032, India.
Dalton Trans. 2018 Jun 5;47(22):7561-7570. doi: 10.1039/c8dt01023d.
Two new RuII-based bis-heteroleptic ditopic receptors 1[PF6]2 (C44H34F12N10OP2Ru) and 2[PF6]2 (C40H27F17N10OP2Ru), decorated with a 1-naphthyl and pentafluorophenyl urea pendant arm, respectively, along with the previously reported 3[PF6]2 (C40H31F13N10OP2Ru), containing a pendant 4-fluorophenyl urea unit and 4[PF6]2, devoid of a pendant urea arm, have been studied to establish the role of urea proton acidity on the sensing and extraction of oxyanions in the presence of triazole C-H as an additional hydrogen bonding motif. 1H-NMR, isothermal titration calorimetry (ITC) and photophysical experiments show selective binding of 1[PF6]2 and 2[PF6]2 toward oxyanions such as phosphates (e.g., H2PO4- and HP2O73-) and carboxylates (e.g., CH3CO2- and PhCO2-) like 3[PF6]2. This generalizes the role of triazole C-H and urea in the RuII-based bis-heteroleptic ditopic receptors towards recognition of such anions. Interestingly, complex 1[PF6]2 having intermediate acidic urea -NH protons showed the highest binding affinity with phosphates as compared to the other urea analogues 2[PF6]2 and 3[PF6]2 as well as the non-urea analogue, 4[PF6]2 (C32H24F12N8P2Ru). Moreover, 2[PF6]2 having the most acidic -NH protons showed higher binding affinity towards carboxylates as compared to that of 1[PF6]2/3[PF6]2. Detailed photo-physical studies revealed that 1[PF6]2 is a farsuperior and more selective H2PO4- sensor compared to 2[PF6]2/3[PF6]2/4[PF6]2, as evidenced by the higher degree of amplification of RuII center-based MLCT emission, greater change in excited state lifetime, lower detection limit and higher degree of selectivity. Furthermore, 1[PF6]2 also acts as a moderate liquid-liquid extraction agent of H2PO4-, CH3CO2- and PhCO2- anions, which was comparable to 3[PF6]2 and much higher as compared to 2[PF6]2/4[PF6]2.
两个新的 RuII 基双杂双位受体 1[PF6]2（C44H34F12N10OP2Ru）和 2[PF6]2（C40H27F17N10OP2Ru），分别用 1-萘基和五氟苯基脲侧臂修饰，以及之前报道的 3[PF6]2（C40H31F13N10OP2Ru），含有 4-氟苯基脲单元和 4[PF6]2，没有侧臂脲，已被研究以确定脲质子酸度在三唑 C-H 作为额外氢键模体存在下对阴离子的传感和提取的作用。1H-NMR、等温滴定量热法（ITC）和光物理实验表明，1[PF6]2 和 2[PF6]2 对阴离子（如磷酸盐（如 H2PO4-和 HP2O73-）和羧酸盐（如 CH3CO2-和 PhCO2-）具有选择性结合，就像 3[PF6]2 一样。这将三唑 C-H 和脲在基于 RuII 的双杂双位受体中识别此类阴离子的作用推广。有趣的是，与其他脲类似物 2[PF6]2 和 3[PF6]2 以及非脲类似物 4[PF6]2（C32H24F12N8P2Ru）相比，具有中等酸性脲-NH 质子的配合物 1[PF6]2 对磷酸盐表现出最高的结合亲和力。此外，具有最酸性-NH 质子的 2[PF6]2 对羧酸盐表现出比 1[PF6]2/3[PF6]2 更高的结合亲和力。详细的光物理研究表明，1[PF6]2 是比 2[PF6]2/3[PF6]2/4[PF6]2 更好、更具选择性的 H2PO4-传感器，这是由基于 RuII 中心的 MLCT 发射更高程度的放大、激发态寿命更大的变化、更低的检测限和更高的选择性所证明的。此外，1[PF6]2 还可以作为 H2PO4-、CH3CO2-和 PhCO2-阴离子的中等液-液萃取剂，与 3[PF6]2 相当，比 2[PF6]2/4[PF6]2 高得多。
