Ruthenium(II) 2,2′-Bibenzimidazole Complex as a Second-Sphere Receptor for Anions Interaction and Colorimeter

Abstract

A ruthenium(II) complex [Ru(bpy) 2(H 2bbim)](PF 6) 2 ( 1) as anions receptor has been exploited, where Ru(II)-bpy moiety acts as a chromophore and the H 2bbim ligand as an anion binding site. A systematic study suggests that 1 interacts with the Cl (-), Br (-), I (-), NO 3 (-), HSO 4 (-), and H 2PO 4 (-) anions via the formation of hydrogen bonds. Whereas 1 undergoes a stepwise process with the addition of F (-) and OAc (-) anions: formation of the monodeprotonated complex [Ru(bpy) 2(Hbbim)] with a low anion concentration, followed by the double-deprotonated complex [Ru(bpy) 2(bbim)], in the presence of a high anion concentration. These stepwise processes concomitant with the changes of vivid colors from yellow to orange brown and then to violet can be used for probing the F (-) and OAc (-) anions by naked eye. The deprotonation processes are not only determined by the basicity of the anion but also related to the strength of hydrogen bonding, as well as the stability of the formed compounds. Moreover, a double-deprotonated complex [Ru(bpy) 2(bbim)].CH 3OH.H 2O ( 3) has been synthesized, and the structural changes induced by the deprotonation has also been investigated. In addition, complexes [Ru(bpy) 2(Hbbim)] 2(HOAc) 3Cl 2.12H 2O ( 2), [Ru(bpy) 2(Hbbim)](HCCl 3CO 2)(CCl 3CO 2).2H 2O ( 4), and [Ru(bpy) 2(H 2bbim)](CF 3CO 2) 2.4H 2O ( 5) have been synthesized to observe the second sphere coordination between the Ru(II)-H 2bbim moiety and carboxylate groups via hydrogen bonds in the solid state.

Functional Dimming of Pincer‐Shaped Bibenzimidazole‐Ruthenium(II) Complexes with Improved Anion‐Sensitive Luminescence

“…The general observation of hydrogen bonds with monodentate Hbond acceptors is peculiar, as previously reported structures of bibenzimidazole-ruthenium(II) complexes often show bifurcated H-bond frameworks with bidentate or multiple acceptors. [18,22,28,29] Scheme 2. Bibenzimidazole-ruthenium(II) complexes presented in this work; complexes K1 and K2 are pincer-shaped owing to anisyl substituents at the 4,4′-positions, and the latter is sterically confined.…”

“…On the basis of previous reports, we concluded that the loss of emission indicates subsequent deprotonation of the amine functions, as deprotonated bibenzimidazole ruthenium complexes are generally nonluminescent. [16,18,20,24,28,33] As the mono-deprotonated and fully deprotonated bibenzimidazole ruthenium complexes are usually well-distinguishable even with the naked eye through a transition from bright red to brown to deep violet, the UV/Vis spectra of K0, K1, and K2 were recorded in acetonitrile upon the addition of either TBAF (for K0, cf. Figure 5, right) or TBAOH (for K0, Figure 6).…”

“…[18][19][20][21] Also, several synthetic modifications have been reported for the manipulation of the electronic and steric properties of these ligands. [22][23][24][25][26] Manipulations of the 4,4′-positions are of particular interest as they define a pincerlike pocket around the hydrogen-bond moiety.…”

Protonation‐Dependent Luminescence of an Iridium(III) Bibenzimidazole Chromophore

“…[24] In the solid-state structure of Ir(tmBBI)-H two water molecules are hydrogen bonded to the secondary amine functions of the bibenzimidazole core in a conventional manner. [1,5,22,[25][26][27][28] Owing to the good quality of the data obtained, we were able to locate the protons accurately in the hydrogen-bond framework. The position of the amine proton was assigned with respect to a well-defined Q-peak in an early stage of the refinement.…”

“…Ye and coworkers have confirmed the capability of biimidazole complexes to act as hydrogen-bond donors through NMR and UV/Vis spectroscopy. [5][6][7] The absorption features in the visible region change significantly upon deprotonation or hydrogen bonding to fluoride or acetate ions. In their fully deprotonated state, these complexes act as metalloligands, that is, the deprotonated biimidazole sphere can bind a second metal center such as zinc(II), nickel(II), or copper(I).…”