Substitution reactions between aquatetracyanonitridorhenate(V) ions and different bidentate ligands containing N, O-donor atoms

[摘要] English: The aim of this study was to determine the products as well as the mechanism for thereaction between [ReN(H2O)(CN)4]2- complex and different bidentate ligands(pyridine-2-carboxylate (pic-), quinoline-2-carboxylate (quin-) and pyridine-2,3-dicarboxylate (2,3-dipic-)). Solid state and solution studies, which investigatedifferent aspects of these systems, were performed. Elucidation of the mechanismwas achieved by utilizing X-ray crystallography and reaction kinetics.X-ray crystallographic structure determinations show that all the complexes studiedcrystallize in the triclinic space group Pī. The different bond distances and angles ofall the complexes studied were determined, as well as the significant mode ofdistortion of the coordinated octahedron in these complexes. The large transinfluenceof the nitrido ligand was also evidenced in the bond distances of the transbonded ligands. For bidentate substituted complexes, the carboxylato oxygen of picandquin- anions are bonded trans to the nitrido ligand while the cyano ligand isbonded trans to one of the cyano ligands. Small bite angles for chelation were alsodetected. A cyano-bridged binuclear rhenium(V) complex was isolated for the firsttime.Kinetic studies of all the ligands studied show the same tendency towards substitutionreactions. A two-step reaction process was spectrophotometrically observed andkinetically investigated. The first fast reaction was regarded as the aqua substitution(reaction C, in Scheme A) while the second slow reaction resulted in the cyanosubstitution during the ring-closure step (reaction E, in Scheme A). A reactionmechanism (Scheme A) was proposed for all the reactions that were possible with theconditions that prevailed during the study. The acid dissociation constants weredetermined spectrophotometrically and kinetically. Negative entropy of activationwas determined for the second step of the reactions and points to an associativemechanism.See Scheme A in full text.The aim of this study was to determine the products as well as the mechanism for thereaction between [ReN(H2O)(CN)4]2- complex and different bidentate ligands(pyridine-2-carboxylate (pic-), quinoline-2-carboxylate (quin-) and pyridine-2,3-dicarboxylate (2,3-dipic-)). Solid state and solution studies, which investigatedifferent aspects of these systems, were performed. Elucidation of the mechanismwas achieved by utilizing X-ray crystallography and reaction kinetics.X-ray crystallographic structure determinations show that all the complexes studiedcrystallize in the triclinic space group Pī. The different bond distances and angles ofall the complexes studied were determined, as well as the significant mode ofdistortion of the coordinated octahedron in these complexes. The large transinfluenceof the nitrido ligand was also evidenced in the bond distances of the transbonded ligands. For bidentate substituted complexes, the carboxylato oxygen of picandquin- anions are bonded trans to the nitrido ligand while the cyano ligand isbonded trans to one of the cyano ligands. Small bite angles for chelation were alsodetected. A cyano-bridged binuclear rhenium(V) complex was isolated for the firsttime.Kinetic studies of all the ligands studied show the same tendency towards substitutionreactions. A two-step reaction process was spectrophotometrically observed andkinetically investigated. The first fast reaction was regarded as the aqua substitution(reaction C, in Scheme A) while the second slow reaction resulted in the cyanosubstitution during the ring-closure step (reaction E, in Scheme A). A reactionmechanism (Scheme A) was proposed for all the reactions that were possible with theconditions that prevailed during the study. The acid dissociation constants weredetermined spectrophotometrically and kinetically. Negative entropy of activationwas determined for the second step of the reactions and points to an associativemechanism.

[发布机构] University of the Free State