Tuning the Electronic Coupling in Cyclometalated Diruthenium Complexes through Substituent Effects: A Correlation between the Experimental and Calculated Results

Abstract

A common bridging ligand, 3,3',5,5'-tetrakis(N-methylbenzimidazol-2-yl)biphenyl, and four terpyridine terminal ligands with various substituents (amine, tolyl, nitro, and ester groups) have been used to synthesize ten cyclometalated diruthenium complexes 1(2+) -10(2+) . Among them, compounds 1(2+) -6(2+) are redox nonsymmetric, and others are symmetric. These complexes show two Ru(III/II) processes and an intervalence charge transfer (IVCT) transition in the one-electron oxidized state. The potential separation (ΔE) of 1(2+) -10(2+) has been correlated to the energy difference ΔG(0) , the energy of the IVCT band Eop , and the ground-state delocalization coefficient α(2) . Time-dependent (TD)DFT calculations suggest that the absorptions in the visible region of 1(2+) -6(2+) are mainly associated with the metal-to-ligand charge-transfer transitions from both ruthenium ions and to both terminal ligands and the bridging ligand. However, the energies of these transitions vary significantly. DFT calculations have been performed on 1(2+) -6(2+) and 1(3+) -6(3+) to give information on the electronic structures and spin populations of the mixed-valent compounds. The TDDFT-predicted IVCT excitations reproduce well the experimental trends in transition energies. In addition, three monoruthenium complexes have been synthesized for a comparison study.

Long-Range Ruthenium-Amine Electronic Communication through the para-Oligophenylene Wire

“…The involved electron transfer is believed to occur via a hole-transfer superexchange mechanism 40 41 , as has been proposed in symmetric mixed valent compounds with either triarylamine 23 24 25 or cyclometalated ruthenium 26 27 28 29 as the charge-bearing sites. This assertion is also supported by DFT calculations.…”

“…1 ). Mixed-valent compounds with either amine 23 24 25 or cyclometalated ruthenium complexes 26 27 28 29 as the redox sites have been previously investigated. The asymmetric structures of 1 – 6 and their proligands 13 – 18 will be helpful in improving the solubility of these compounds and thus making easier the synthesis, characterization, and analysis of these materials.…”

Exploring the localized to delocalized transition in non-symmetric bimetallic ruthenium polypyridines

“…The lack of symmetry in mixed-valence systems can have two origins. It may arise from different chemical environments around the moieties involved in the electron transfer 10,11 , or from non-symmetric bridges connecting those moieties, like in the case of the cyanide anion, which is one of the most thoroughly explored. [12][13][14][15] Most of this studies conclude that cyanide is able to promote strong electronic coupling between metal centers, 13,[16][17][18] although very few of these complexes have been described as Class III systems.…”

Synthesis, Photophysics, and Switchable Luminescence Properties of a New Class of Ruthenium(II)–Terpyridine Complexes Containing Photoisomerizable Styrylbenzene Units

“…Cyclometalated ligands can often destabilize the 3 MC state. 55−58 Replacement of pyridine ring by different heterocyclic moieties may sometime give rise to less distorted octahedral configuration. 59−63 The important point for improving their emission behaviors is to extend the electron delocalization for minimizing nonradiative deactivation channels.…”