Charge Delocalization in a Cyclometalated Bisruthenium Complex Bridged by a Noninnocent 1,2,4,5-Tetra(2-pyridyl)benzene Ligand

Abstract

Two ruthenium atoms are covalently connected to the para positions of a phenyl ring in 1,2,4,5-tetra(2-pyridyl)benzene (tpb) to form a linear Ru-tpb-Ru arrangement. This unique structure leads to appealing electronic properties for the biscyclometalated complex [(tpy)Ru(tpb)Ru(tpy)](2+), where tpy is 2,2';6',2″-terpyridine. It could be stepwise oxidized at substantially low potential (+0.12 and +0.55 V vs Ag/AgCl) and with a noticeably large comproportionation constant (1.94 × 10(7)). In addition to the routinely observed metal-to-ligand charge-transfer transitions, [(tpy)Ru(tpb)Ru(tpy)](2+) displays a separate and distinct absorption band at 805 nm with appreciable absorptivity (ε = 9000 M(-1) cm(-1)). This band is assigned to the charge transition from the Ru-tpb-Ru motif to the pyridine rings of tpb with the aide of density functional theory (DFT) and time-dependent DFT calculations. Complex [(tpy)Ru(tpb)Ru(tpy)](2+) was precisely titrated with 1 equiv of cerium ammonium nitrate to produce [(tpy)Ru(tpb)Ru(tpy)](3+), which shows intense multiple NIR transitions. The electronic coupling parameters H(ab) of individual NIR components are determined to be 5812, 4942, 4358, and 3560 cm(-1). DFT and TDDFT calculation were performed on [(tpy)Ru(tpb)Ru(tpy)](3+) to elucidate its electronic structure and spin density population and the nature of the observed NIR transitions. Electron paramagnetic resonance studies of [(tpy)Ru(tpb)Ru(tpy)](3+) exhibit a discernible rhombic signal with the isotropic g factor of ⟨g⟩ = 2.144. These results point to the strong orbital interaction of tpb with metal centers and that tpb behaves as a redox noninnocent bridging ligand in [(tpy)Ru(tpb)Ru(tpy)](2+). Complex [(tpy)Ru(tpb)Ru(tpy)](3+) is determined to be a Robin-Day class III system with full charge delocalization across the Ru-tpb-Ru motif.

Experimental and Theoretical Studies of Charge Delocalization in Biruthenium–Alkynyl Complexes Bridged by Thiophenes

“…[16,26] Herein, we report the oxidation titration of complexes 1 a-1 c by using ferrocenium hexafluorophosphate as an oxidant, after which the in situ generated radical species were characterized by using IR spectroscopy, without isolation. Continuing the one-electron oxidation into [8] in the crystal structure of compound 1 c and in DFT-optimized structures [1 cÀH] n < M + > (n = 0, 1, 2). The nA C H T U N G T R E N N U N G (C C) bands of neutral complexes 1 a-1 c appeared at 2056, 2055, and 2046 cm À1 , respectively.…”

Conformational Tuning of the Intramolecular Electronic Coupling in Molecular‐Wire Biruthenium Complexes Bridged by Biphenyl Derivatives

“…The large number of compounds that has been synthesized allows the study of variousf actors, including distance, solvent effect, molecular topology,m etal complex, the nature of the bridge, and tuning the degree of charge delocalization between the terminal redox sites in the MV state. [21][22][23][24][25][26][27][28][29][30][31][32][33] Since the bridging ligands play an important role in tuning the ET properties of MV complexes, ranging from localization to delocalization, the synthesis of such compounds with various bridgingl igands has attracted considerable interest. [19] Recently,a ni mportant aspect of developing the [ML n (bridge)ML n ] system is controlling the electronic delocalization in the ground state of the MV form and the metal-versus-ligand character of the redox processes to yield am etal-centered or bridge-centered process.…”

A mercuric ensemble based on a cycloruthenated complex as a visual probe for iodide in aqueous solution

“…dcbpy(p ⁄ ) and Ru(dp) ? bthiq(p ⁄ ) bridging ligand transitions, respectively [31,32]. It is notable that there was no emissive spectrum observed upon excited at room temperature [32].…”

“…In view of long-wavelength absorptions of cyclometallated ruthenium complexes [31][32][33][34] for easy visualization, a new water soluble cycloruthenated complex Ru(bthiq)(dcbpy) 2 + (1, Hbthiq = 1-(2-benzo[b]thiophenyl)isoquinoline, dcbpy = 4,4 0 -dicarboxylate-2,2 0 -bipyridine) was designed to form its mercuric(II) ensemble (1-Hg 2+ ) (Scheme 1). Subsequently, 1-Hg 2+ was further used to recognize iodide visually in aqueous solutions, which resulted in an apparent color change from yellow to deep-red.…”