Synthesis and proton transfer-linked redox tuning of ruthenium(II) complexes with tridentate 2,6-bis(benzimidazol-2-yl)pyridine ligands

Abstract

New ruthenium complexes of two tridentate ligands 2,6-bis( benzimidazol-2-yl)pyridine ( L7) and 2,6bis( 1 -methylbenzimidazol-2-yl)pyridine (La) have been synthesised. Proton and 13C NM R spectroscopy served well for their characterization, and the observed change. Proton chemical shift yields information about the electron distribution accompanying deprotonation of the ligands. The [ RuL7Jn+ chelate acts as a tetrabasic acid, with pK, ranging from 2.5 to 10.7, depending on the ruthenium oxidation state. The absorption spectra and oxidation potentials are consequently sensitive to solution pH and to solvent. The proton-coupled oxidative electron-transfer reactions of the complexes afford stable higher oxidation states such as Ru'". The properties of the complexes are discussed in comparison to those of previously reported bis(tridentate 1igand)ruthenium compounds.

Synthesis, crystal structure determination, spectroscopic and electrochemical studies of trans-[Ru(PPh3)2(bbpH2)Cl]Cl·CHCl3·H20 (bbpH2=2,6-bis(benzimidazolyl) pyridine) – an infinite double columnar supramolecule in the solid state

“…The absorption in the visible region is then expected to be due to HOMO fi LUMO + 1, LUMO + 2, and HOMO)1 fi LUMO + 1. Again these energy gaps are higher for (1) than for (2), in agreement with the observation that in the visible region k max for (2) is [12] higher than that for (1). 118A 119A (C 1 point group) (optimized geometry) )11.71 eV )11.85 eV )12.12 eV )12.14 eV )9.58 eV )9.54 eV…”

“…This behavior is comparable to that of [Ru(terpy) 2 ] 2+ , which is weakly fluorescent at room temperature, and at LNT the fluorescence lifetime increases [2]. It may be noted that although the bbpH 2 ligand is known to be fluorescent, its bis complex [Ru(bbpH 2 ) 2 ] 2+ was found to be non-fluorescent [12]. Thus, the luminescence behavior of (1) is similar to that of [Ru(terpy) 2 ] 2+ , but different from that of [Ru(bbpH 2 ) 2 ] 2+ .…”

“…Thus, the luminescence behavior of (1) is similar to that of [Ru(terpy) 2 ] 2+ , but different from that of [Ru(bbpH 2 ) 2 ] 2+ . (5) [Ru(terpy) 2 ] 2+ 1.28 c (6) [Ru(bpy) 3 ] 2+ 1.27 d (7) [Ru(bpy) 2 (BibzImH 2 )] 2+ 1.12 d (8) [Ru(bpy)(BibzImH 2 ) 2 ] 2+ 0.91 d (9) [Ru(BibzImH 2 ) 3 ] 2+ 0.80 d (10) [Ru(BiImH 2 ) 3 ] 2+ 0.54 d (11) [Ru(bpy)(BiImH 2 ) 2 ] 2+ 0.80 d (12) [Ru(bpy) 2 …”

Reactions of rhodium and iridium salts with multidentate N-heterocycles

“…The 'H NMR spectra of bBzlH2py and bBzlMe2py in DMSO-d~ exhibited resonances due to phenylene and pyridine ring protons (Table 2) and the assignments are in consonance with those reported by Addison and coworkers [11]. The spectra of the complexes illustrated both positive and negative coordination induced shifts (c.i.s =6~,,mp~x-6t,g,,,d), the appreciable one being for H-4'.…”

“…According to the earlier report on bBzlMe2py, the phenylene carbons 7' and 4' are magnetically equivalent, so also are the quaternary carbons 8' and 9". Thus, two resonances, one at 6 115.72 lbr C-7',4' and another at 6 139.23 for C-8'.9', have been reported [11], A similar finding has been made for bBzlMe2py. Surprisingly in the present investigation, the four carbons 7', 4', 8' and 9' are seen to be magnetically nonequivalent in the same solvent and thus four resonances at 0 112.1, 119.9, 134.5 and 144.2, respectively, have been observed (Fig.…”