Crystal structure and redox potentials of the tppz-bridged {RuCl(bpy)}+ dimer

Abstract

We report the structural and electrochemical characterization of the binuclear complex [μ-(C24H16N6){RuCl(C10H8N2)}2](PF6)2, which contains the bis-tridentate bridging ligand 2,3,5,6-tetrakis(pyridin-2-yl)pyrazine (tppz), the monodentate ligand Cl−, and the bidentate ligand 2,2′-bipyridine (bpy) {systematic name: μ-2,3,5,6-tetrakis(pyridin-2-yl)pyrazine-bis[(2,2′-bipyridine)chloridoruthenium(II)] bis(hexafluoridophosphate)}. The complete [(bpy)(Cl)Ru(tppz)Ru(Cl)(bpy)]2+ dication is generated by crystallographic twofold symmetry; the tppz bridging ligand has a significantly twisted conformation, with an average angle of 42.4° between the mean planes of adjacent pyridyl rings. The metal-coordinated chloride ligands are in a trans configuration relative to each other across the {Ru(tppz)Ru} unit. The RuII ion exhibits a distorted octahedral geometry due to the restricted bite angle [160.6 (3)°] of the tppz ligand. For bpy, the bond lengths of the Ru—N bonds are 2.053 (8) and 2.090 (8) Å, with the shorter bond being opposite to Ru—Cl. For the tridentate tppz, the Ru—N distances involving the outer N atoms trans to each other are 2.069 (8) and 2.072 (9) Å, whereas the Ru—N bond involving the central N atom has the much shorter length of 1.939 (7) Å as a result of the geometric constraints and stronger π-acceptor ability of the pyrazine-centered bridge. The Ru—Cl distance is 2.407 (3) Å and the intramolecular distance between Ru centers is 6.579 (4) Å. In the crystal, weak C—H...Cl and C—H...F interactions consolidate the packing.

Keywords

• crystal structure
• dinuclear complex
• electrochemistry
• tetra(pyridyl)pyrazine
• ruthenium precatalyst