Coordination chemistry of niobium(v) and tantalum(v) with hard o-donor ligands: a solution and solid state investigation
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Date
2018-02
Authors
Belay, Alebel Nibret
Journal Title
Journal ISSN
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Publisher
University of the Free State
Abstract
English: This thesis describes the study directed towards the synthesis, characterization and substitution kinetics of novel niobium(V) and tantalum(V) complexes containing selected O,O’-bidentate ligands that could potentially be used for the separation of niobium from tantalum. There is also a search for complexes that will be attractive and useful as advanced materials for high technology applications and in the nuclear power environment. The study included systematic assessment of the physical and chemical behaviour of the free ligands, co-crystals and complexes as well as the factors which govern their stability, reactivity, coordination geometry, bond lengths and angles, π-π stacking interaction and inter- and intramolecular networks of hydrogen bonds. It became evident that the crystal stabilization was influenced by intermolecular π-π interactions and inter- and intramolecular hydrogen and halogen bond networks, producing a stabilized crystal lattice. A range of Nb(V) and Ta(V) complexes such as cis-(Et4N)[NbO(ca)2(H2O)OPPh3]·3H2O-·THF (5), (Et4N)4[Nb4O4(ca)2(μ2-O)2C18]·2CH3CN (6), [NbO(cupf)3] (7), [NbO(hopo)3]. MeOH (8), [TaO(hopo)3]·MeOH (9), [Ta(hopo)4]C1·2MeCN·2H2O (10) (where ca = 2,5-dichloro-3,6-dihydroxy-1,4-benzoquinonato, cupf = N-nitroso-N-phenylhydroxylaminato, hopo = 2-hydroxypyridinato-N-oxide) as well as two co-crystals [OPPh3½(caH2)] (2) and [(2½(caH2)(DMAP)6·11H2O)] (4) were prepared and characterised by IR (ATR), NMR (1H, 13C and 31P), UV-Vis spectroscopy and single crystal X-ray diffraction. Additionally, two free ligands, [½(caH2)·H2O] (1) and [hopoH] (3), were characterised by single crystal X-ray diffraction. The six-, seven- and eight coordinate geometries show different coordination modes as observed in complexes (5) and (7) (D5h pentagonal bipyramidal geometry), (6) (a regular octahedral coordination mode), (8) (C3v-capped octahedral geometry), (9) (C2-capped trigonal prismatic geometry) and (10) (D2-square antiprismatic geometry). Therefore, these different geometries found in complexes (5), (6), (7), (8), (9) and (10) describe the shape of complexes with six, seven and eight oxygen atoms bound to the niobium(V) and tantalum(V) metal centres, with the differences playing a possible key role to increase the potential of a new type of separation of niobium from tantalum. Starting with the selected complex, cis-[NbO(ca)2(H2O)(OPPh3)]-, the substitution of the triphenyl-phosphineoxide by pyridine-type ligands such as pyridine (py), 4-N,N-dimethyl-aminopyridine (DMAP), 4-methylpyridine (4-Mepy), 3-chloropyridine (3-Clpy) and 3-bromopyridine (3-Brpy) in acetonitrile media at 31.2°C were determined and evaluated. These entering monodentate ligands could be arranged in terms of their increasing reactivity values: 3-Brpy < 3-Clpy < 4-Mepy < py < DMAP, defined by the values of kf = 0.147(4) x 10-2; 0.206(7) x 10-2; 0.181(6) x 10-2; 0.131(2) x 10-2 and 2.032(2) x 10-2 M-1s-1 respectively. The pseudo first-order rate constants were dependent on concentration and temperature. From the observed kinetic results a suitable mechanism was proposed. Activation parameters were determined for the reaction of the complex, cis-[NbO(ca)2(H2O)(OPPh3)]-, with 4-N,N-dimethylaminopyridine (DMAP) as entering ligand. The activation parameters for these triphenylphosphineoxide substitution reactions were calculated as 51.5(9) k J mol-1 and -108(3) J K-1 mol-1 for the standard change of enthalpy (ΔH≠(kf)) and the standard change of entropy (ΔS≠(kf)) respectively. The negative entropy of activation implies a more ordered state and presumably this substitution reaction could involve an associative ligand substitution mechanism. Although only part of a preliminary study, a range of novel Nb(V) and Ta(V) complexes with O,O’-, O,N- and N,N’-bidentate ligands were synthesised and characterised by IR (ATR), NMR (1H and 13C) and UV-Vis spectroscopy. The reaction of [NbCl6]- with chloranilic acid (caH2) in solution gave cis-[NbO(ca)2(H2O)]-, which react further with added triphenylphosphineoxide (OPPh3) to give the final product, cis-[NbO(ca)2(H2O)OPPh3]-. Knowledge obtained from this study should contribute to the understanding of the chemical and physical properties of the various Nb(V) and Ta(V) complexes and identify possible differences to apply in future for developing potential separation methods for niobium from tantalum.
Afrikaans: Hierdie tesis beskryf die studie wat gerig was op die sintese, karakterisering en substitusie-kinetika van nuwe niobium(V) en tantalum(V) komplekse wat geselekteerde O,O’-bidentate ligande bevat wat moontlik gebruik kan word vir die skeiding van niobium en tantalum. Daar is ook ‘n soektog na komplekse wat aanloklik en nuttig as gevorderde stowwe vir hoë tegnologie toepassings en in die kernkrag omgewing sal wees. Die studie het ‘n sistematiese beoordeling van die fisiese en chemiese gedrag van die vry ligande, ko-kristalle en komplekse asook die faktore wat hulle stabiliteit, reaktiwiteit, koördinasiegeometrie, bindingslengtes- en hoeke, π-π stapelingsinteraksie en inter- sowel as intramolekulêre netwerke van waterstofbindings ingesluit. Dit het duidelik geword dat die kristalstabilisasie beïnvloed is deur intermolekulêre π-π interaksies asook inter- en intramolekulêre netwerke van waterstof- en halogeenbindings, wat ‘n gestabiliseerde kristalrooster tot gevolg het. ‘n Reeks van Nb(V) en Ta(V) komplekse soos cis-(Et4N)[NbO(ca)2(H2O)OPPh3]·3H2O- ·THF (5), (Et4N)4[Nb4O4(ca)2(μ2-O)2Cl8]·2CH3CN (6), [NbO(cupf)3] (7), [NbO(hopo)3]- ·MeOH (8), [TaO(hopo)3]·MeOH (9), [Ta(hopo)4]Cl·2MeCN·2H2O (10) (waar ca = 2,5-dichloro-3,6-dihidroksi-1,4-bensokwinonato, cupf = N-nitroso-N-fenielhidroksielaminato, hopo = 2-hydroksipiridinato-N-oksied) sowel as twee ko-kristalle, [OPPh3½(caH2)] (2) en [(2½(caH2)(DMAP)6·11H2O)] (4) is berei en gekarakteriseer deur IR (ATR), KMR (1H, 13C en 31P), UV-Vis spektroskopie en enkelkristal X-straaldiffraksie. Bykomend is twee vry ligande, [½(caH2)·H2O] (1) en [hopoH] (3), gekarakteriseer deur enkelkristal X-straaldiffraksie. Die ses-, sewe- en agtgekoordineerde geometrieë vertoon verskillende wyses van koördinering soos waargeneem in komplekse (5) en (7) (D5h pentagonale bipiramidale geometrie), (6) (‘n gewone oktahedriese koördinering), (8) (C3v-gekroonde oktahedriese geometrie), (9) (C2-gekroonde trigonale prismatiese geometrie) en (10) (D2-vierkantig antiprismatiese geometrie). Die verskillende geometrieë soos waargeneem in komplekse (5), (6), (7), (8), (9) en (10) beskryf die vorm van komplekse met ses, sewe en agt suurstofatome gebonde aan die niobium(V) en tantalum(V) metaalsentrums, waar die verskille ‘n moontlike sleutelrol kan speel om die potensiaal van ‘n nuwe tipe skeiding van niobium van tantalum te vergroot. Beginnende met die gekose kompleks, cis-[NbO(ca)2(H2O)(OPPh3)]-, is die substitusie van trifenielfosfienoksied deur piridien tipe ligande soos piridien (py), 4-N,N-dimetiel-aminopiridien (DMAP), 4-metielpiridien (4-Mepy), 3-chloropiridien (3-Clpy) en 3-bromopiridien (3-Brpy) in asetonitrielmedium by 31.2 oC bepaal en ge-evalueer. Hierdie inkomende monodentate ligande kan gerangskik word in terme van hulle toenemende reaktiwiteitswaardes: 3-Brpy < 3-Clpy < 4-Mepy < py < DMAP, gedefinieer deur die waardes van kf = 0.147(4) x 10-2; 0.206(7) x 10-2; 0.181(6) x 10-2; 0.131(2) x 10-2 en 2.032(2) x 10-2 M-1s-1 respektiewelik. Die pseudo eerste-orde tempokonstantes was afhanklik van konsentrasie en temperatuur. Vanaf die waargenome kinetiese resultate kon ‘n toepaslike meganisme voorgestel word. Aktiveringsparameters is bepaal vir die reaksie van die kompleks, cis-[NbO(ca)2(H2O)(OPPh3)]- met 4-N,N-dimetielaminopiridien (DMAP) as inkomende ligand. Die aktiveringsparameters vir hierdie trifenielfosfienoksied substitusiereaksies is bereken as 51.5(9) k J mol-1 en -108(3) J K-1 mol-1 vir die standaard entalpieverandering (ΔH≠(kf)) en die standaard entropieverandering (ΔS≠(kf)) respektiewelik. Die negatiewe aktiveringsentropie impliseer ‘n meer geordende toestand en dat hierdie substitusiereaksie moontlik volgens ‘n assosiatiewe meganisme van ligandsubstitusie plaasvind. Alhoewel slegs deel van ‘n voorlopige studie, is ‘n reeks nuwe Nb(V) en Ta(V) komplekse met O,O’-, O,N- en N,N’-bidentate ligande berei en gekarakteriseer met behulp van IR (ATR), KMR (1H and 13C) en UV-Vis spektroskopie. Die reaksie van [NbCl6]- met chlooranilieksuur (caH2) in oplossing lewer cis-[NbO(ca)2(H2O)]-, wat verder met bygevoegde trifenielfosfienoksied (OPPh3) reageer om die finale produk cis-[NbO(ca)2(H2O)OPPh3]- te lewer. Kennis wat met hierdie studie ingewin is behoort te lei tot ‘n beter insig en begrip van die chemiese en fisiese eienskappe van die verskeie Nb(V) en Ta(V) komplekse en om moontlike verskille te identifiseer om in die toekoms toe te pas vir die ontwikkeling van metodes vir die skeiding van niobium en tantalum.
Afrikaans: Hierdie tesis beskryf die studie wat gerig was op die sintese, karakterisering en substitusie-kinetika van nuwe niobium(V) en tantalum(V) komplekse wat geselekteerde O,O’-bidentate ligande bevat wat moontlik gebruik kan word vir die skeiding van niobium en tantalum. Daar is ook ‘n soektog na komplekse wat aanloklik en nuttig as gevorderde stowwe vir hoë tegnologie toepassings en in die kernkrag omgewing sal wees. Die studie het ‘n sistematiese beoordeling van die fisiese en chemiese gedrag van die vry ligande, ko-kristalle en komplekse asook die faktore wat hulle stabiliteit, reaktiwiteit, koördinasiegeometrie, bindingslengtes- en hoeke, π-π stapelingsinteraksie en inter- sowel as intramolekulêre netwerke van waterstofbindings ingesluit. Dit het duidelik geword dat die kristalstabilisasie beïnvloed is deur intermolekulêre π-π interaksies asook inter- en intramolekulêre netwerke van waterstof- en halogeenbindings, wat ‘n gestabiliseerde kristalrooster tot gevolg het. ‘n Reeks van Nb(V) en Ta(V) komplekse soos cis-(Et4N)[NbO(ca)2(H2O)OPPh3]·3H2O- ·THF (5), (Et4N)4[Nb4O4(ca)2(μ2-O)2Cl8]·2CH3CN (6), [NbO(cupf)3] (7), [NbO(hopo)3]- ·MeOH (8), [TaO(hopo)3]·MeOH (9), [Ta(hopo)4]Cl·2MeCN·2H2O (10) (waar ca = 2,5-dichloro-3,6-dihidroksi-1,4-bensokwinonato, cupf = N-nitroso-N-fenielhidroksielaminato, hopo = 2-hydroksipiridinato-N-oksied) sowel as twee ko-kristalle, [OPPh3½(caH2)] (2) en [(2½(caH2)(DMAP)6·11H2O)] (4) is berei en gekarakteriseer deur IR (ATR), KMR (1H, 13C en 31P), UV-Vis spektroskopie en enkelkristal X-straaldiffraksie. Bykomend is twee vry ligande, [½(caH2)·H2O] (1) en [hopoH] (3), gekarakteriseer deur enkelkristal X-straaldiffraksie. Die ses-, sewe- en agtgekoordineerde geometrieë vertoon verskillende wyses van koördinering soos waargeneem in komplekse (5) en (7) (D5h pentagonale bipiramidale geometrie), (6) (‘n gewone oktahedriese koördinering), (8) (C3v-gekroonde oktahedriese geometrie), (9) (C2-gekroonde trigonale prismatiese geometrie) en (10) (D2-vierkantig antiprismatiese geometrie). Die verskillende geometrieë soos waargeneem in komplekse (5), (6), (7), (8), (9) en (10) beskryf die vorm van komplekse met ses, sewe en agt suurstofatome gebonde aan die niobium(V) en tantalum(V) metaalsentrums, waar die verskille ‘n moontlike sleutelrol kan speel om die potensiaal van ‘n nuwe tipe skeiding van niobium van tantalum te vergroot. Beginnende met die gekose kompleks, cis-[NbO(ca)2(H2O)(OPPh3)]-, is die substitusie van trifenielfosfienoksied deur piridien tipe ligande soos piridien (py), 4-N,N-dimetiel-aminopiridien (DMAP), 4-metielpiridien (4-Mepy), 3-chloropiridien (3-Clpy) en 3-bromopiridien (3-Brpy) in asetonitrielmedium by 31.2 oC bepaal en ge-evalueer. Hierdie inkomende monodentate ligande kan gerangskik word in terme van hulle toenemende reaktiwiteitswaardes: 3-Brpy < 3-Clpy < 4-Mepy < py < DMAP, gedefinieer deur die waardes van kf = 0.147(4) x 10-2; 0.206(7) x 10-2; 0.181(6) x 10-2; 0.131(2) x 10-2 en 2.032(2) x 10-2 M-1s-1 respektiewelik. Die pseudo eerste-orde tempokonstantes was afhanklik van konsentrasie en temperatuur. Vanaf die waargenome kinetiese resultate kon ‘n toepaslike meganisme voorgestel word. Aktiveringsparameters is bepaal vir die reaksie van die kompleks, cis-[NbO(ca)2(H2O)(OPPh3)]- met 4-N,N-dimetielaminopiridien (DMAP) as inkomende ligand. Die aktiveringsparameters vir hierdie trifenielfosfienoksied substitusiereaksies is bereken as 51.5(9) k J mol-1 en -108(3) J K-1 mol-1 vir die standaard entalpieverandering (ΔH≠(kf)) en die standaard entropieverandering (ΔS≠(kf)) respektiewelik. Die negatiewe aktiveringsentropie impliseer ‘n meer geordende toestand en dat hierdie substitusiereaksie moontlik volgens ‘n assosiatiewe meganisme van ligandsubstitusie plaasvind. Alhoewel slegs deel van ‘n voorlopige studie, is ‘n reeks nuwe Nb(V) en Ta(V) komplekse met O,O’-, O,N- en N,N’-bidentate ligande berei en gekarakteriseer met behulp van IR (ATR), KMR (1H and 13C) en UV-Vis spektroskopie. Die reaksie van [NbCl6]- met chlooranilieksuur (caH2) in oplossing lewer cis-[NbO(ca)2(H2O)]-, wat verder met bygevoegde trifenielfosfienoksied (OPPh3) reageer om die finale produk cis-[NbO(ca)2(H2O)OPPh3]- te lewer. Kennis wat met hierdie studie ingewin is behoort te lei tot ‘n beter insig en begrip van die chemiese en fisiese eienskappe van die verskeie Nb(V) en Ta(V) komplekse en om moontlike verskille te identifiseer om in die toekoms toe te pas vir die ontwikkeling van metodes vir die skeiding van niobium en tantalum.
Description
Keywords
Niobium(V), Tantalum(V), Coordination geometry, O,O’-bidentate ligands, Pyridine derivatives, Separation, Substitution kinetics, Spectroscopic studies and X-ray crystallography, Thesis (Ph.D. (Chemistry))--University of the Free State, 2018