Cyclometalated Diruthenium Complexes Bridged by 3,3′,5,5′‐Tetra(pyrid‐2‐yl)biphenyl: Tuning of Electronic Properties and Intervalence Charge Transfer by Terminal Ligand Effects

Six cyclometalated diruthenium complexes bridged by 3,3′,5,5′‐tetra(pyrid‐2‐yl)biphenyl have been prepared, in which 1 2+ , 3 2+ , and 5 2+ are symmetric complexes with different terminal ligands [2,6‐bis( N ‐methylbenzimidazolyl)pyridine (Mebip), 4′‐tolyl‐2,2′:6′,2″‐terpyridine (ttpy), and trimethyl‐4,4′,4″‐tricarboxylate‐2,2′:6′,2″‐terpyridine (Me 3 tctpy), respectively]. Three other complexes with mixed terminal ligands (Mebip‐Me 3 tctpy for 6 2+ ; Mebip‐ttpy for 7 2+ ; ttpy‐Me 3 tctpy for 8 2+ ) are structurally nonsymmetric. These complexes display two consecutive Ru(III/II) redox couples between 0.20 and 0.90 V vs. Ag/AgCl, with the potential splitting ranging from 150 (for 5 2+ ) to 280 mV (for 6 2+ ). The mixed‐valent states of these complexes have been generated by stepwise electrolysis. The symmetric complexes show intervalence charge transfer (IVCT) transitions at similar energy ( E op ≈ 5750 cm –1 ), with the electronic coupling parameter V ab of 1240, 1220, and 970 cm –1 for 1 3+ , 3 3+ , and 5 3+ , respectively. The nonsymmetric series show significantly different E op (7600, 5850, and 6650 cm –1 for 6 3+ , 7 3+ , and 8 3+ , respectively) but V ab values that were comparable to that of 1 3+ . DFT and TDDFT calculations have been performed to complement these experimental results.