Self‐Assembled Arene–Ruthenium‐Based Rectangles for the Selective Sensing of Multi‐Carboxylate Anions

Abstract

Novel arene-ruthenium [2+2] metalla-rectangles, 4 and 5, were synthesized by the self-assembly approach using a dipyridyl amide ligand (3) and arene-ruthenium acceptors (arene: benzoquinone (1); naphthacenedione (2)), and characterized by NMR and ESI-MS. The solid-state structure of 5 determined by X-ray diffraction shows the encapsulated diethyl ether molecules in the rectangular cavity of 5. The luminescent 5 was further utilized for anion sensing where the amidic linkage serves as a hydrogen bond donor site for anions, and the ruthenium moiety serves as a signaling unit. A UV-vis titration study demonstrates that, while 5 interacts very weakly with the common mono anions as well as flexible dicarboxylate anions such as malonate and succinate, it displays significant binding affinity (K > 103 in MeOH) for the rigid multi-carboxylate anions such as oxalate, citrate, and tartrate in a 1:1 fashion. It is suggested that the 1:1 bidentate hydrogen bonding assisted by the proper geometrical complementarities is mainly responsible for the increased affinity of 5 towards such anions. In particular, a fluorescence titration study reveals a large fluorescence enhancement of 5 upon binding with multi-carboxylate anions. This indicates that the fluorescence enhancement is attributed to the blocking of the photo-induced electron transfer process from the arene-Ru moiety to the amidic donor in 5 as a result of hydrogen bonding between the donor and the anion.

Colorimetric and optical discrimination of halides by a simple chemosensor

“…Certain receptors incorporated with transition metal ions such as copper, 17–23 nickel, 24 zinc 25–27 and ruthenium 28, 29 often respond to an analyte by displaying distinct color or optical changes through metal-anion interactions in a solution under neutral condition. Fabbrizzi and coworkers reported a furan-based dinuclear copper complex leading to the selective binding of chloride in water.…”

Self-assembled metal–organic polyhedra: An overview of various applications

“…Chi, Stang, and co-workers reported two arene-Ru-based SCCs via [2+2] assembly of molecular clips (B2 and B4) and diamide ligand (L5). The amidic linkage SCC (B4+L5) has a hydrogen bond sites for effective interaction with rigid dianionic species such as oxalate, citrate, and tartrate, with a Stern-Volmer constant of 5×10 4 , 1.4×10 5 , and 1.8×10 4 M -1 respectively [176]. However, minimal spectral change was observed for monoanionic species such as halide or acetate.…”

Chromogenic and fluorogenic chemosensors and reagents for anions. A comprehensive review of the years 2010–2011

“…151). 197 NIR-emissive alkynylplatinum(II) terpyridyl complex 320 (see Fig. 153) was used as a turn-on selective probe for heparin.…”