Diastereoisomerically pure pyrazole-3,5-dicarboxylate-bridged dinuclear ruthenium(II) and osmium(II) complexes of 2,2'-bipyridine: structural, electrochemical and spectral studies

Abstract

Pyrazole-3,5-dicarboxylate-bridged dinuclear ruthenium(II) and osmium(II) complexes of 2,2'-bipyridine of composition [(bpy)₂Ru(pzdc)Ru(bpy)₂](ClO₄)·H₂O (1) and [(bpy)₂Os(pzdc)Os(bpy)₂](ClO₄)·H₂O (2) have been obtained in high yield and have been separated to their homochiral (ΛΛ/ΔΔ) rac (1a, 2a) and heterochiral (ΛΔ/ΔΛ) meso (1b, 2b) diastereoisomers. The distinctive structural features of these diastereoisomers have been characterized by 1-D and 2-D ¹H NMR spectroscopy. The X-ray crystal structure of rac-[(bpy)₂Os(pzdc)Os(bpy)₂](ClO₄)·H₂O (2a) has been determined. The electrochemical and electronic spectral studies have established that there remain difference in properties and hence difference in intermetallic communication between the diastereoisomeric forms in each case. Dinuclear ruthenium(II) and osmium(II) complexes [(bpy)₂M(pzdc)M(bpy)₂](ClO₄) · H₂O containing 2,2'-bipyridine and pyrazole-3,5-dicarboxylate(pzdc^3-) as the bridging ligand have been separated to their homochiral (ΛΛ/ΔΔ) rac and heterochiral (ΛΔ/ΔΛ) meso forms. The physicochemical properties of the diastereoisomers have been compared by ¹H NMR, electronic spectroscopies and electrochemistry. The structure of the rac form of the diosmium(II) complex cation is shown.