Substitution reactions between aquatetracyanonitridorhenate(V) ions and different bidentate ligands containing N, O-donor atoms
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Date
2006-05
Authors
Mtshali, Thato Nicholas
Journal Title
Journal ISSN
Volume Title
Publisher
University of the Free State
Abstract
English: 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.
Afrikaans: Hierdie studie het die identifikasie van produkte, asook die meganisme waarvolgens die reaksie tussen die [ReN(H2O)(CN)4]2- kompleks en verskillende bidentate ligande (piridien-2-karboksilaat- (pic-), kinolien-2-karboksilaat- (quin-) en piridien-2,3- dikarboksilaat anione (2,3-dipic-) plaasvind, ten doel. Navorsing is op die vaste toestand en verskeie oplossingseienskappe van die verskillende produkte uitgevoer. Die suksesvolle daarstelling van die meganisme vir hierdie substitusiereaksies is met behulp van X-straalkristallografie en reaksiekinetika uitgevoer. Die kristalstruktuurbepalings wat tydens hierdie studie onderneem is, het aangetoon dat al die produkte in die trikliniese Pī ruimtegroep kristalliseer. Belangrike bindingsafstande en –hoeke, asook die mate van oktaëdriese verwringing wat in hierdie verbindings teenwoordig is, is bepaal. Die relatiewe groot trans-invloed van die nitridoligand is duidelik sigbaar in die verskillende groepe en ligande wat trans ten opsigte van die nitridoligand teenwoordig is. Die karboksilatosuurstofatoom vir beide pic- en quin- is trans ten opsigte van die nitridogroep in die verskillende komplekse gebind terwyl die piridienstikstof trans ten opsigte van 'n sianiedgroep gebind is. Relatiewe klein bythoeke is vir die gecheleerde ligande waargeneem. Tydens hierdie studie is die eerste sianiedgebrugde bikernige renium(V) kompleks geïsoleer. Die kinetiese studies wat tydens hierdie studie onderneem is het almal dieselfde substitusiegedrag openbaar. 'n Tweestap-substitusieproses is spektrofotometries asook kineties waargeneem. Die eerste reaksie word as die akwasubstitusiestap beskou (reaksie C, in Skema A), terwyl die stadiger tweede stap die substitusie van 'n sianiedgroep met die gepaardgaande ringsluiting van die bidentate ligand behels (reaksie E, in Skema A). Skema A word vir al die moontlike reaksies wat onder die gegewe reaksiekondisies kan plaasvind, voorgestel. Die suurdissosiasiekonstantes vir die metaalkompleks asook die verskillende ligande is spektrofotometries asook kineties bepaal. 'n Negatiewe aktiveringsentropie dui op assosiatiewe aktivering tydens die finale stappe van die substitusieproses. Sien Skema A in volteks. Hierdie strukturele en kinetiese data is dan ook met dié van ander isolektroniese groep 6 en 7 metaalkomplekse vergelyk en goeie ooreenkomste is tussen die verskillende okso- en nitridokomplekse verkry.
Afrikaans: Hierdie studie het die identifikasie van produkte, asook die meganisme waarvolgens die reaksie tussen die [ReN(H2O)(CN)4]2- kompleks en verskillende bidentate ligande (piridien-2-karboksilaat- (pic-), kinolien-2-karboksilaat- (quin-) en piridien-2,3- dikarboksilaat anione (2,3-dipic-) plaasvind, ten doel. Navorsing is op die vaste toestand en verskeie oplossingseienskappe van die verskillende produkte uitgevoer. Die suksesvolle daarstelling van die meganisme vir hierdie substitusiereaksies is met behulp van X-straalkristallografie en reaksiekinetika uitgevoer. Die kristalstruktuurbepalings wat tydens hierdie studie onderneem is, het aangetoon dat al die produkte in die trikliniese Pī ruimtegroep kristalliseer. Belangrike bindingsafstande en –hoeke, asook die mate van oktaëdriese verwringing wat in hierdie verbindings teenwoordig is, is bepaal. Die relatiewe groot trans-invloed van die nitridoligand is duidelik sigbaar in die verskillende groepe en ligande wat trans ten opsigte van die nitridoligand teenwoordig is. Die karboksilatosuurstofatoom vir beide pic- en quin- is trans ten opsigte van die nitridogroep in die verskillende komplekse gebind terwyl die piridienstikstof trans ten opsigte van 'n sianiedgroep gebind is. Relatiewe klein bythoeke is vir die gecheleerde ligande waargeneem. Tydens hierdie studie is die eerste sianiedgebrugde bikernige renium(V) kompleks geïsoleer. Die kinetiese studies wat tydens hierdie studie onderneem is het almal dieselfde substitusiegedrag openbaar. 'n Tweestap-substitusieproses is spektrofotometries asook kineties waargeneem. Die eerste reaksie word as die akwasubstitusiestap beskou (reaksie C, in Skema A), terwyl die stadiger tweede stap die substitusie van 'n sianiedgroep met die gepaardgaande ringsluiting van die bidentate ligand behels (reaksie E, in Skema A). Skema A word vir al die moontlike reaksies wat onder die gegewe reaksiekondisies kan plaasvind, voorgestel. Die suurdissosiasiekonstantes vir die metaalkompleks asook die verskillende ligande is spektrofotometries asook kineties bepaal. 'n Negatiewe aktiveringsentropie dui op assosiatiewe aktivering tydens die finale stappe van die substitusieproses. Sien Skema A in volteks. Hierdie strukturele en kinetiese data is dan ook met dié van ander isolektroniese groep 6 en 7 metaalkomplekse vergelyk en goeie ooreenkomste is tussen die verskillende okso- en nitridokomplekse verkry.
Description
Keywords
Kinetics, Crystallography, Bidentate ligands, Acid dissociation constant, Stability constant, Entropy and enthalpy of activation, Cyano complexes, Chelation, Rhenium, Substitution reactions, Ligands, Thesis (Ph.D. (Chemistry))--University of the Free State, 2006