Two new tetranuclear cationic metalla-bowls 4 and 5 were self-assembled from a bis-pyridine amide ligand (H2L) (1) and arene-ruthenium acceptors, [(Ru2(μ-η4-C2O4)(η6-p-cymene)2](O3SCF3)2 (2) and [Ru2(dhnd)(η6-p-cymene)2](O3SCF3)2 (dhnd = 6,11-dihydroxy-5,12-naphthacenedionato) (3), respectively. The metalla-bowls were characterized by multinuclear NMR, ESI-MS, UV-Vis spectroscopy, and single crystal X-ray diffraction study of 4. The crystal structure of 4 reveals unambiguous proof for the molecular shape of the metalla-bowl and the encapsulation of one triflate anion in the cavity through hydrogen bonding. The metalla-bowl 5 has been evaluated for anion binding studies by use of amide ligand as a hydrogen bond donor and arene-Ru acceptor as a signalling unit. UV-Vis titration studies showed that 5 selectively binds with multi-carboxylate anions such as oxalate, tartrate and citrate in a 1 : 1 fashion with high binding constants of 4.0–5.5 × 104 M−1. Furthermore, the addition of multi-carboxylate anions into a solution of 5 gave rise to a large enhancement of fluorescence intensity attributable to the blocking of a photo-induced electron transfer process from the arene-ruthenium moiety to the amidic donor in 5. However, the fluorescence intensity almost remains unchanged upon addition of other anions including F−, Cl−, PF6−, MeCOO−, NO3− and PhCOO−, as identically seen in the UV-Vis titration experiments, pointing to the high selectivity of 5 for the sensing of multi-carboxylate anions.
两个新的四核阳离子
金属碗4和5是通过双
吡啶酰胺
配体(H2L)(1)和
芳烃-
钌受体[(Ru2(μ-η4-
C2O4)(η6-p-cymene)2](O3SCF3)2(2)以及[Ru2(dhnd)(η6-p-cymene)2](O3SCF3)2(dhnd = 6,11-二羟基-5,12-
萘烯二酸酯酸盐)(3)自组装而成。这些
金属碗通过多核NMR、ESI-MS、紫外-可见光光谱以及对4的单晶X射线衍射研究进行了表征。4的晶体结构清楚地证明了
金属碗的分子形状,并通过氢键合在腔体内包裹了一个
三氟甲磺酸根阴离子。
金属碗5的阴离子结合研究评估利用酰胺
配体作为氢键供体以及
芳烃-
钌受体作为信号单元。紫外-可见光滴定研究表明,5以1:1的比例选择性结合多
羧酸阴离子,如
草酸、
酒石酸和
柠檬酸,结合常数高达4.0–5.5 × 10^4 M−1。此外,向5的溶液中添加多
羧酸阴离子会显著增强荧光强度,这归因于阻止了从
芳烃-
钌部分到5中的酰胺供体的光诱导电子转移过程。然而,在添加其他阴离子时,包括F−、Cl−、PF6−、MeCOO−、
NO3−和PhCOO−,荧光强度几乎保持不变,与紫外-可见光滴定实验中观察到的相同,表明5对多
羧酸阴离子的传感具有高选择性。