Crystal structures and solution behavior of cis-di(aqua)bis(2,2ʹ-bipyridine)cobalt(III) and related complexes

• Published in: Journal of molecular structure 2021-11, Vol.1244, p.130938, Article 130938
• Main Authors: Toyama, Mari, Yamamoto, Yu, Yoshimoto, Takuya, Katagiri, Kosuke
• Format: Article
• Language: English
• Subjects: Aqua ligand; Heteroleptic cobalt(III) complex; NMR spectroscopy; Polypyridyl ligand; X-ray crystal structure
• ISSN: 0022-2860; 1872-8014
• DOI: 10.1016/j.molstruc.2021.130938

•[Co(bpy)2(OH2)2][OTf]3·H2O (1·[OTf]3·H2O) prepared by simple reaction in aqueous acid.•1·[OTf]3·H2O is a promising material for preparing heteroleptic bidentate complexes.•1·[OTf]3·H2O unstable in alcohols and acetonitrile but stable in water and acetone.•[Co(bpy)2(pic)][OTf]2 and [Co2(bpy)4(μ-O2)(μ-OH)][PF6]3 prepared from 1·[OTf]3·H2O.•Full NMR, elemental, and X-ray structural analyses of Co(III) complexes carried out. A cobalt(III) complex bearing two 2,2ʹ-bipyridine (bpy) ligands and two aqua ligands, cis-[Co(bpy)2(OH2)2][OTf]3·H2O (1·[OTf]3·H2O; OTf− = CF3SO3−), was obtained from the reaction of [Co(bpy)2(CO3)][OTf]·0.5H2O with aqueous HOTf (HOTf = HCF3SO3, trifluoromethanesulfonic acid). The prepared complex was characterized by single-crystal X-ray crystallographic and elemental analyses, and its solution behavior was investigated by 1H NMR spectroscopy. Our study of 1·[OTf]3·H2O revealed that it is stable in water and acetone upon heating; however, in methanol and ethanol, the complex was unstable upon heating, forming [Co(bpy)3]3+. In addition, upon the reaction of 1·[OTf]3·H2O with picolinic acid (Hpic) in acetone at 295 K, [Co(bpy)2(pic)][OTf]2 (2·[OTf]2) was gradually and selectively precipitated from the reaction solution in 82% yield. Moreover, the reaction between 1·[OTf]3·H2O, NaOH, and H2O2 in water at room temperature produced the dinuclear complex [Co2(bpy)4(μ–O2)(μ–OH)][PF6]3 (3·[PF6]3) in good yield (92%) and with excellent purity. The structures of 1·[OTf]3·H2O and 2·[PF6]2 were determined by single-crystal X-ray crystallographic analysis.