11The coordination chemistry of ruthenium(II) complexes with polypyridyl ligands has been an area of great interest, because of their redox properties and photochemistry. 1 We reported on the syntheses, crystal structures, and isomerization reactions of the ruthenium(II) complexes bearing a di-2-pyridyl ketone (dpk);
trans(Cl),cis(S)-[RuCl2(dpk-κ 2 N,O)(dmso-S)2] and cis(Cl),cis(S)-[RuCl2(dpk-κ2 The crystal structure of the trans(Cl),cis(S)-isomer revealed that the oxygen of the ketone group on the dpk ligand was able to act as an effective donor atom to from a N,O-coordination mode, which was kinetically more favorable than the N,N mode, but was thermodynamically unstable. In view of the hemilabile coordination ability of the N,O bidentate ligand, the 2-picolinic acid (Hpic) has great interest for us. One of the popular and typical Ru(II)N5O type complexes that includes a pic ligand is [Ru(pic)(bpy)2] + (bpy = 2,2′-bipyridine), which has been synthesized. [3][4][5] The crystal structure and 1 H NMR spectrum of [Ru(pic)(bpy)2](PF6) have been repotrted. 3,4 In the crystal structure, the dihedral angles between two pyridine rings within each 2,2′-bipyridyl ligand (10.3(3) and 14.4(2) ), are significantly larger than that in [Ru(bpy)3](PF6)2 (2.2(1) ).
6Although a greater twisting of bpy ligands has not been noticed in the literature, 3 we take notice of the greater twisting and the hydrogen-bonding interactions between two oxygen atoms of a pic in a Ru(II) complex cation and 3,3′-protons of a bpy ligand in a neighboring complex cation; Fig. S1 in which the hydrogen-bonding diagram is drawn according to the CIF file of [Ru(pic)(bpy)2](PF6). That is to say, the four O···H-C interactions between two Ru(II) complex cations allow the cations to come close to each other so that the bpy ligands are twisted. Similar O···H-C interactions between two O atoms of a ClO4 -ion and 3,3′-protons of a bpy ligand in {(μ-H2L)[Ru(bpy)2]2}(ClO4)2 (H4L = 1,5-diamino-9,10-anthraquinone) have also been observed, 7 in which the dihedral angles of the bpy ligands (9.9 and 10.4 ) are similar to those in [Ru(pic)(bpy)2](PF6). We thus feel a great interest in the structure of [Ru(pic)(bpy)2] + with another counter anion. Warren et al. isolated the Cl salt by converting it from PF6 salt using the ion-exchange resin. 5 We directly isolated a Ru(II) complex as Cl salt, [Ru(pic)(bpy)2]Cl, from the reaction mixture, and determined the crystal structure, as shown in Fig. 1 To the homogeneous dark-purple hydrolysis solution, a solution of Hpic (1.1 mmol) in ethanol (20 mL) was added, and the mixture was refluxed for 3 h. While refluxing, the solution turned from dark-purple to wine-red. The resulting wine-red solution was evaporated to dryness under a vacuum, and the residue was dissolved in 2 mL of water. An aqueous solution of HCl (1 M, 2 mL) was added to precipitate a brown-red solid.The brown-red solid, [Ru(pic)(bpy)2]Cl was collected by filtration, washed with a small amount of cold water, and dried in vacuo (0.93 mmol, 96%). The 1 H NMR spectr...