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

The aim of this study was to determine the products as well as the mechanism for the reaction 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 investigate different aspects of these systems, were performed. Elucidation of the mechanism was achieved by utilizing X-ray crystallography and reaction kinetics. X-ray crystallographic structure determinations show that all the complexes studied crystallize in the triclinic space group Pī. The different bond distances and angles of all the complexes studied were determined, as well as the significant mode of distortion of the coordinated octahedron in these complexes. The large transinfluence of the nitrido ligand was also evidenced in the bond distances of the trans bonded ligands. For bidentate substituted complexes, the carboxylato oxygen of picand quin- anions are bonded trans to the nitrido ligand while the cyano ligand is bonded trans to one of the cyano ligands. Small bite angles for chelation were also detected. A cyano-bridged binuclear rhenium(V) complex was isolated for the first time. Kinetic studies of all the ligands studied show the same tendency towards substitution reactions. A two-step reaction process was spectrophotometrically observed and kinetically investigated. The first fast reaction was regarded as the aqua substitution (reaction C, in Scheme A) while the second slow reaction resulted in the cyano substitution during the ring-closure step (reaction E, in Scheme A). A reaction mechanism (Scheme A) was proposed for all the reactions that were possible with the conditions that prevailed during the study. The acid dissociation constants were determined spectrophotometrically and kinetically. Negative entropy of activation was determined for the second step of the reactions and points to an associative mechanism. See Scheme A in full text. The aim of this study was to determine the products as well as the mechanism for the reaction 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 investigate different aspects of these systems, were performed. Elucidation of the mechanism was achieved by utilizing X-ray crystallography and reaction kinetics. X-ray crystallographic structure determinations show that all the complexes studied crystallize in the triclinic space group Pī. The different bond distances and angles of all the complexes studied were determined, as well as the significant mode of distortion of the coordinated octahedron in these complexes. The large transinfluence of the nitrido ligand was also evidenced in the bond distances of the trans bonded ligands. For bidentate substituted complexes, the carboxylato oxygen of picand quin- anions are bonded trans to the nitrido ligand while the cyano ligand is bonded trans to one of the cyano ligands. Small bite angles for chelation were also detected. A cyano-bridged binuclear rhenium(V) complex was isolated for the first time. Kinetic studies of all the ligands studied show the same tendency towards substitution reactions. A two-step reaction process was spectrophotometrically observed and kinetically investigated. The first fast reaction was regarded as the aqua substitution (reaction C, in Scheme A) while the second slow reaction resulted in the cyano substitution during the ring-closure step (reaction E, in Scheme A). A reaction mechanism (Scheme A) was proposed for all the reactions that were possible with the conditions that prevailed during the study. The acid dissociation constants were determined spectrophotometrically and kinetically. Negative entropy of activation was determined for the second step of the reactions and points to an associative mechanism.