Tuning of Metal–Metal Interactions in Mixed-Valence States of Cyclometalated Dinuclear Ruthenium and Osmium Complexes Bearing Tetrapyridylpyrazine or -benzene

Abstract

New dinuclear ruthenium or osmium complexes with cyclometalated bonds in either tridentate bridging (BL) or ancillary ligands (L), [(L)M(BL)M(L)] (where M = Ru, Os; L = bis(N-methylbenzimidazolyl)pyridine, -benzene; BL= tetrapyridylpyrazine (tppz), -benzene (tpb)), were synthesized, and their mixed-valence-state characteristics were investigated. All of the complexes showed successive one-electron redox processes, each of which correspond to M(II/III) (M = Ru, Os) or ligand reduction waves. In addition, an M(III/IV) couple was observed in cyclometalated [M2(bis(benzimidazolyl)benzene)2(BL)] complexes (M = Ru, Os). Effects of the cyclometalated bonds on the redox behaviors and the accessibility to the mixed-valence M(II)–M(III) dinuclear complexes are discussed. Introduction of a cyclometalated bond induced a large negative potential shift in the redox potentials of dinuclear ruthenium and osmium complexes, depending on either bridging or ancillary sites of the cyclometalated bonds: the change falls within the range of −1.0 to −1.2 V for the bridging sites and −0.65 to −0.7 V for the ancillary ones. This large negative potential shift arises from the strong electron-donating property of the phenyl anion in a metal–C bond. Replacing the ruthenium by osmium in the dinuclear complexes with the same bridging ligand results in an increase of the potential separation (ΔE(1)) and the comproportionation constant (K com) of the mixed-valence complexes having the tppz bridging ligand (ΔE(1) and K com values: Os > Ru); however, complexes having the tpb bridging ligand showed the opposite trend (ΔE(1) and K com: Os < Ru). In addition to the results of EPR and DFT calculation, it was found that the orbital energy levels of the central metal ion (namely, either Ru or Os) in the mixed-valence complex determines the degree of orbital mixing between metal dπ orbitals and bridging-ligand π or π* orbitals, which leads to either hole- or electron-transfer exchange mechanisms.

Photoresponsive Molecular Memory Films Composed of Sequentially Assembled Heterolayers Containing Ruthenium Complexes

“…Eur.J.2016, 22,1658 -1667 www.chemeurj.org tion of the ethyl group with trimethylsilylbromide.T he UV/Vis/ NIR spectralf eatures and redox potentials of Ru-NP and Ru-CP are almost identicalt ot hose of the reported Ru-N and Ru-C complexes. [57] Steady-state rotatingd isk voltammetry measurements for the isolated Ru complexes in CH 3 CN revealed Ru IIRu II and Ru II -Ru III oxidations tates for Ru-NP and Ru-CP,r espectively.T he surfacec overage of these Ru complexes duringt he surfacei mmobilization on ITO electrodes strongly depends on the pH value of the solution containing the Ru complex. [56] Therefore, the Ru complexes were dissolved in water ([Ru] = 50 mm)a nd the pH value wasadjusted to pH 6( Ru-NP)orp H4 (Ru-CP).…”

“…, (EtL = 2,6-bis(N-(2,4,6-methyl-3,5-diethylphosphonatomethyl-benzyl)-benzimidazole-2-yl)-pyridine), as well as the EtL ligand with ethylphosphonate anchor groups were synthesized according to previously published literature procedures. [55,57] Abbreviations for ligands and Ru complexes are reported in the Supporting Information. Electronic absorption spectra (200-2500 nm) were obtained from aH itachi U-4000 spectrometer.N MR spectra were recorded on a5 00 MHz Jeol JNM-ECX500 spectrometer.I Rs pectra were recorded on aN icolet FT-IR Magna 560 spectrometer.M ass spectra for the Ru complexes were measured using aM icromass LCT electrospray mass spectrometer equipped with an electrospray interface (ESI) system.…”

“…When the potentialw as set at À0.54 V, the appearance of the characteristic IVCT band at 1140 nm and the decreaseo ft he band at 521 nm (Figure 3) coincided which the spectroelectrochemicalc hange for the reduction of ITO jj(Ru-CP) 4 ( Figure S9 in the Supporting Information) and were comparable to the spectral change fort he corresponding Ru-C complex in CH 3 CN solution ( Figure S10 in the Supporting Information). [57] This change was attributed to the formation of the mixed-valent Ru II -Ru III state in the outer Ru-CP layers. Since no direct ET from the ITOe lectrode to the outer Ru-CP layers was observed in the CV measurements, this reduction should have occurredd ue to ET mediation via low-lying orbitals in the inner Ru-NP layers.…”

Synthesis and Single‐Molecule Conductance Study of Redox‐Active Ruthenium Complexes with Pyridyl and Dihydrobenzo[b]thiophene Anchoring Groups

“…The two reduction waves of complex 2 at −1.63 and −1.87 V versus Fc + /Fc correspond to one‐electron reductions of each ancillary ligand L2 centered. The large spike peak at E pa =−1.71 V versus Fc + /Fc arises from the desorption of the complex 2 adsorbed on the electrode after the reductions . Complex 3 exhibits two successive one‐electron oxidation waves at 1.06 and 1.39 V versus Fc + /Fc corresponding to (Ru II –Ru II )/(Ru II –Ru III ) and (Ru II –Ru III )/(Ru III –Ru III ) processes, and two one‐electron reduction waves at −0.74 and −1.23 V versus Fc + /Fc derived from tppz/tppz − and tppz − /tppz 2− processes, respectively.…”

Poly[6‐(2,6‐bis(1′‐methylbenzimidazolyl)pyridin‐4‐yloxy)hexyl acrylate] (PBIP) and its terbium (III) complex (PBIP‐Tb3+): Homopolymerization, optical, and magnetic performance

“…They have strong coordinating capability and can chelate with both transition metal ions and lanthanide ions . Their complexes display good biocompatibility, excellent catalytic activity, high sensitivity and selectivity to specific matter, special optical and electrical property, and interesting magnetism, so they have aroused a great of interest for their potential applications. Up to now, several small molecular magnets containing BIP complexes have been reported .…”