The synthesis and characterization of mixed ligand Ru(II) complexes with dipyrido(2,3-a:3′,2′-j)phenazine (dpop′) and 2,3,5,6-tetra(2-pyridyl)-pyrazine (tppz)

The synthesis of the mixed ligand mono metallic [Ru(dpop′)(tppz)]2+ and bimetallic [(dpop′)Ru(tppz)Ru(dpop′)]4+ (dpop′ = dipyrido(2,3-a:3′,2′-j)phenazine; tppz = 2,3,5,6 tetra-(2-pyridyl)pyrazine) complexes is described. The [Ru(dpop′)(tppz)]2+ complex display an intense absorption at 518 nm which is assigned to a Ru(dπ) → dpop′ (π∗) MLCT transition, and at 447 nm which is assigned to a Ru(dπ) → tppz(π∗) MLCT transition. It undergoes emission at RT in CH3CN with λem = 722 nm. The bimetallic [(dpop′)Ru(tppz)Ru(dpop′)]4+ complex shows a low energy absorption shoulder near 635 nm assigned to a Ru(dπ) → tppz(π∗) MLCT transition and an intense peak at 542 nm due to Ru(dπ) → dpop′ (π∗) MLCT transition. The bimetallic complex also emits at RT in CH3CN with λem = 785 nm. Cyclic voltammetry shows reversible Ru+2/+3 oxidations at 1.68 V for the monometallic complex and Ru+2/+3 oxidation couples at +1.94 and +1.70 V for the bimetallic complex.