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

Abstract

• [Co(bpy) 2 (OH 2 ) 2 ][OTf] 3 ·H 2 O ( 1 ·[OTf] 3 ·H 2 O) prepared by simple reaction in aqueous acid. • 1 ·[OTf] 3 ·H 2 O is a promising material for preparing heteroleptic bidentate complexes. • 1 ·[OTf] 3 ·H 2 O unstable in alcohols and acetonitrile but stable in water and acetone. • [Co(bpy) 2 (pic)][OTf] 2 and [Co 2 (bpy) 4 (μ-O 2 )(μ-OH)][PF 6 ] 3 prepared from 1 ·[OTf] 3 ·H 2 O. • 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 (OH 2 ) 2 ][OTf] 3 ·H 2 O ( 1 ·[OTf] 3 ·H 2 O; OTf − = CF 3 SO 3 − ), was obtained from the reaction of [Co(bpy) 2 (CO 3 )][OTf]·0.5H 2 O with aqueous HOTf (HOTf = HCF 3 SO 3 , trifluoromethanesulfonic acid). The prepared complex was characterized by single-crystal X-ray crystallographic and elemental analyses, and its solution behavior was investigated by 1 H NMR spectroscopy. Our study of 1 ·[OTf] 3 ·H 2 O 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 ·H 2 O 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 ·H 2 O, NaOH, and H 2 O 2 in water at room temperature produced the dinuclear complex [Co 2 (bpy) 4 (μ–O 2 )(μ–OH)][PF 6 ] 3 ( 3 ·[PF 6 ] 3 ) in good yield (92%) and with excellent purity. The structures of 1 ·[OTf] 3 ·H 2 O and 2 ·[PF 6 ] 2 were determined by single-crystal X-ray crystallographic analysis.