Crystal structure of chloro(2,2':6',2"-terpyridine)(2-phenylazopyridine)-ruthenium(II) chloride.

complexes (where tpy = 2,2′:6′,2′′-terpyridine, L = bidentate ligand, n = 0 or 1), because they are used as precursors of aquo complexes, which can finally be converted to oxo compounds. Oxo-ruthenium complexes are useful as catalysts in different reactions, particularly in the catalytic oxidation of water to dioxygen.1,2 As a part of serial studies on the properties of oxoruthenium complexes, we synthesized the title complex, [Ru(tpy)(L)Cl]Cl (where L = 2-(phenylazo)pyridine = azpy). 2-(Phenylazo)pyridine (azpy) and [Ru(tpy)Cl3] were prepared by methods reported in the literatures.3,4 Ru(tpy)Cl3 (0.2 g) and azpy (0.09 g) were refluxed for 3 h in 25 mL of ethanol–water containing LiCl (0.07 g) and triethylamine (0.06 mL). A hot solution was filtered and the filtrate was allowed to stand for 10 days. Crystals suitable for an X-ray technique were selected from the obtained solid. Details concerning the X-ray structure determination are given in Tables 1 – 3. Ru(II) is in a distorted octahedral environment bonded to three nitrogen atoms of the tpy ligand, two nitrogen atoms of the azpy ligand and one chlorine atom. The four nitrogen atoms (N3, N4, N5, N6) define the equatorial plane, whereas the Cl1 and N1 atoms occupy the trans-axial sites. The longest bond, Ru–Cl1, is comparable to those in cis-Ru(azpy)2Cl2. It is noted that the N(6)–Ru–N(3) angle is 104.82(16) ̊, greater than that (99.4(3) ̊) in [Ru(tpy)(azpy)(CH3CN)](ClO4)2. The bite angle of the azpy ligand, N(3)–Ru–N(1), is 76.70(15) ̊, smaller than that in cis-[Ru(bpy)2Cl2]. The Ru–N(azo) (1.999(4)Å) bond distance is longer compared to the value 1.971(7)Å in [Ru(tpy)(azpy)(CH3CN)](ClO4)2. However, the Ru–N(azo) bond distance is still shorter than that of Ru–N(pyridine), as expected. This is due to the greater πbackbonding, d(Ru) → π*(azo). The tpy ligand is planar with the maximum deviation being 0.086 Å for C13 from the best 683 ANALYTICAL SCIENCES MAY 2001, VOL. 17 2001 © The Japan Society for Analytical Chemistry