Crystal Structure of (2-Picolinato)bis(2,2′-bipyridine)ruthenium(II) Chloride

Abstract

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...

Characterization of a Mixed-Valence Ru(II)/Ru(III) Ion-Pair Complex. Unexpected High-Frequency Electron Paramagnetic Resonance Evidence for Ru(III)–Ru(III) Dimer Coupling

“…There are only two entries containing [Ru II (bipy) 2 (pic)] + , but with different simple counterions, such as Cl − and PF 6 − . 21,30 Also, only four structures with the same [cis-Ru III Cl 2 (pic) 2 ] − anion were found in the CSD database. 12,13 The following analyses were performed to check the homogeneity and purity of the bulk material.…”

“…A search in the CSD database revealed that no similar mixed-valence Ru­(II)/Ru­(III) ion-pair complex of the structure described here could be found. There are only two entries containing [Ru II (bipy) 2 (pic)] + , but with different simple counterions, such as Cl – and PF 6 – . , Also, only four structures with the same [ cis -Ru III Cl 2 (pic) 2 ] − anion were found in the CSD database. , …”

“…The proton signals of the diamagnetic [Ru II (bipy) 2 (pic)] + complex are observed within the 7.3–8.8 ppm range. Signals reported in the literature for [Ru II (bipy) 2 (pic)]­PF 6 and [Ru II (bipy) 2 (pic)]­Cl appeared within the same chemical shift range. The total integration corresponds to 20 protons, which is in agreement with the total number of protons in the diamagnetic cationic species (Figure S7a).…”

“…H 2 pic­[ cis -Ru III Cl 2 (pic) 2 ] was prepared according to a procedure reported by us before . [Ru II (bipy) 2 (pic)]­Cl­·5.5H 2 O was synthesized using a slight modification of the synthesis described in the literature (for further details on the structure of this complex, see Supporting Information, Figure S1 and Tables S1–S3) . [Ru­(bipy) 2 Cl 2 ]·2H 2 O (52 mg, 0.1 mmol) dissolved in water (5 mL) was refluxed for 1 h under an argon atmosphere.…”

“…12 [Ru II (bipy) 2 (pic)]Cl•5.5H 2 O was synthesized using a slight modification of the synthesis described in the literature (for further details on the structure of this complex, see Supporting Information, Figure S1 and Tables S1−S3). 21 [Ru(bipy) 2 Cl 2 ]•2H 2 O 22 (52 mg, 0.1 mmol) dissolved in water (5 mL) was refluxed for 1 h under an argon atmosphere. Then picolinic acid (13.7 mg, 0.1 mmol) dissolved in ethanol (5 mL) was added, and the reaction mixture was refluxed for further 4 h. The obtained solution was evaporated under argon to dryness, and the solid was dissolved in water (18 mL).…”