Thesis (PhD)--Stellenbosch University, 2013. / ENGLISH ABSTRACT: In this work a robust reversed phase ion-pairing high performance liquid chromatographic
(RP-HPLC) method has been developed for the separation, characterization and quantification of
all possible [PtCl6-nBrn]2- (n = 0 – 6) and [PtCl4-nBrn]2- (n = 0 – 4) complex anions using UV-Vis
detection. High resolution 195Pt NMR of more concentrated PtII/IV solutions served to validate the
relevant species assignments, particularly those of the stereoisomer species, cis- and trans-
[PtCl4Br2]2-, [PtCl2Br4]2- and mer- and fac-[PtCl3Br3]2-. Quantification of the PtII/IV species was
achieved by means of IP-RP-HPLC coupled to either ICP-MS or ICP-OES, and together with the
UV-Vis absorption spectra obtained by photodiode array (PDA) recording of all eluted species,
allowed for the determination of the photometric characteristics (λmax and ε) of all the PtII/IV
species. This data enables practical speciation studies of such PtII/IV complex anions using
standard analytical equipment.
The hyphenation of ion-pairing RP-HPLC to ICP-OES allows for the successful determination
of the Pt to halide mole ratios of individually separated species in order to characterize these
species in a novel manner. The Pt to chloride and/or Pt to bromide mole ratio of the [PtCl4]2- and
the series of [PtCl6-nBrn]2- (n = 0 – 6) complexes were determined using HPLC-ICP-OES based
on the 177.708 nm Pt, 134.724 nm Cl and 148.845 nm Br emission lines and served as a
technique for the unambiguous chemical speciation of such complexes.
An increase in sensitivity of the developed method was achieved by the use of an ion-pairing
reversed phase ultra high performance liquid chromatography electrospray ionization quadrupole
time-of-flight mass spectrometry (UHPLC-ESI-Q-TOF-MS) method. This method proved
capable of separating and characterizing the homoleptic and heteroleptic [PtIVCl6-nBrn]2-
(n = 0 – 6) and mono-aquated [PtIVCl5-nBrn(H2O)]- (n = 0 – 5) complex anions in well defined
acidic aqueous solutions. Ion-pairing ultra high performance liquid chromatography separation based on the volatile ion-pairing reagent, tributylamine, provided adequate chromatographic
resolution as well as sufficiently low background noise for high resolution ESI-Q-TOF-MS
detection. The wealth of structural information contained in the mass spectra obtained for each
PtIV species simplified the identification of individual species. Moreover, the general
fragmentation trends encompassing a constant incremental change of 44 Da (79/81Br - 35/37Cl)
resulting from the successive substitution of Cl- by Br-, in combination with the observed elution
order, facilitated the relevant species assignments. The developed method enabled the relative
rapid (<13 min) characterization of all 22 [PtCl6-nBrn]2- (n = 0 – 6) and mono-aquated
[PtCl5-nBrn(H2O)]- (n = 0 – 5) species.
Quantification of each individual [PtCl6-nBrn]2- (n = 0 – 6) species by means of ion-paring
HPLC-UV-Vis allowed for the determination of all 17 stability constants for the PtIV chloridobromido
halide exchange reaction network. Determination of the associated Gibbs free energies
for each ligand exchange reaction step, o
rxnK ΔG
n
(n = 1 - 17), together with energy conservation
relationships, served to validate the accuracy of the experimentally calculated stability constants.
The experimentally determined overall formation constant, or ΔGo
rxn, and those calculated using
the standard reaction half cell reduction potentials of [PtCl6]2- and [PtBr6]2- were in good
agreement, further confirming the experimentally obtained thermodynamic parameters. The
thermodynamic driving force for the PtIV chloride-bromido exchange reactions is attributed to
the hydration of the halide ligands, which drives the reaction towards the bromido PtIV species in
aqueous solutions, even though the chlorido PtIV complexes are energetically favoured in this
reaction network. Evaluation of other metal cation halido exchange reactions shows that all metal
halido complexes exhibit the F- >> Cl- > Br- > I- order of thermodynamic stability and is only
inverted due to the solvation of the relevant halide ligands. Furthermore, density functional
theory (DFT) was used to predict the thermodynamic stabilities with respect to the isodesmic
reactions involving chlorido-bromido PtIV stereoisomer pairs and chlorido-bromido PtIV ligand
exchange reactions of the [PtCl6-nBrn]2- (n = 0 – 6) species and confirm the F- >> Cl- > Br- > I-
order of thermodynamic stability as well as determining the ΔΔGo
rxn within the range of 8 - 20
kJ.mol-1 to the experimentally determined ΔΔGo
rxn. / AFRIKAANSE OPSOMMING: Tydens hierdie studie is „n robuuste “reverse-phase” ioonparing hoë-verrigting vloeistof
chromatografie, RP-IP-HPLC, metode ontwikkel vir die skeiding, karakterisering en
kwantifisering van alle moontlike [PtCl6-nBrn]2- (n = 0 – 6) en [PtCl4-nBrn]2- (n = 0 – 4) kompleks
anione waar UV-Vis as detektor gebruik word. Die relavante spesies toedelings wat gemaak is,
veral ten opsigte van die cis- en trans-[PtCl4Br2]2-, [PtCl2Br4]2- en mer- en fac-[PtCl3Br3]2-
stereo-isomeerpare, is deur middel van hoë-resolusie 195Pt KMR van meer gekonsentreerde PtII/IV
oplossings bevestig. Die PtII/IV spesies was gekwantifiseer deur die IP-RP-HPLC aan of „n ICPMS
of „n ICP-OES te koppel. Daarenbowe was dit moontlik om die fotometriese eienskappe
(λmax en ε) van elke individuele PtII/IV komplex anion te bepaal deur die UV-Vis absorpsie
spektrum van elke elueerende spesies met PDA op te neem. Die nuwe metode wat tydens hierdie
studie ontwikkel is het dit dus moontlik gemaak om sulke PtII/IV komplek sanione met standaard
analitiese toerusting prakties te skei.
Verder is gevind dat deur IP-RP-HPLC aan ICP-OES te koppel dit moontlik is om die Pt tot
halied mol verhoudings van elke individueel geskeide spesies te bepaal en dus hierdie spesies op
„n oorspronklike, nuwe manier te karakteriseer. Die Pt tot chloried en/of Pt tot bromied mol
verhoudings van die [PtCl4]2- en die reeks van [PtCl6-nBrn]2- (n = 0 – 6) kompleks anione, soos
bepaal deur gebruik te maak van HPLC-ICP-OES, is gebasseer op die 177.708 nm Pt, 134.724
nm Cl en 148.845 nm Br emissie lyne. Hierdie metode kan gebruik word vir die eenduidige
chemiese skeiding van hierdie komplekse.
Die sensitiwiteit van hierdie metode was egter verder verbeter deur gebruik te maak van
ioonparing “reverse-phase” ultra hoë-verrigting vloeistof chromatografie gekoppel met
elektrosprei ionisasie quadropool “time-of-flight” massa spektrometrie (UHPLC-ESI-Q-TOFMS).
Deur dit te doen is dit nou selfs moontlik om die homoleptiese en heteroleptiese [PtIVCl6-nBrn]2- (n = 0 – 6) spesies, asook die “mono-aqauted” [PtIVCl5-nBrnH2O]- (n = 0 – 5)
spesies in „n goed gedefinieërde aangesuurde waterige oplossings te skei en te karakteriseer. Die
vlugtige ioon-paringsreagent, tributielamien, is vir die skeidingsproses op die IP-UHPLC gebruik
om te verseker dat voldoende chromatografiese resolusie, so wel as lae genoeg agtergrondgeraas,
verkry word vir hoë-resolusie ESI-Q-TOF-MS deteksie. Die rykdom informasie vervat in die
massaspektrum van elke PtIV spesies het die indentifikasie van elke spesies vergemaklik.
Daarenbowe het die fragmentasie tendens, aanduidend van „n konstante inkrementele
verandering van 44 amu (71/81Br – 35/37Cl) weens die opeenvolgende substitusie van Cl- met
Br-, tesame met die elusie volgorde, die spesies-toedelings gefasiliteer. Met hierdie nuut
ontwikkelde metode is dit nou moontlik om al 22 [PtCl6-nBrn]2- (n = 0 – 6) en “mono-aquated”
[PtCl5-nBrnH2O]- (n = 0 – 5) spesies in „n relatiewe kort tydperk (< 13 min) te karakteriseer.
Deurdat elke [PtCl6-nBrn]2- (n = 0 – 6) spesies nou individueel met IP-HPLC-UV-Vis
gekwantifiseer kan word, is dit moontlik om al 17 stabiliteitskonstantes vir die PtIV chloridobromido
halied uitruilingsreaksienetwerk te bepaal. Die geassosieerde Gibbs vrye energie,
ΔG°rxnKn (n = 0 – 17), wat vir elke stap in die uitruilingsreaksienetwerk bepaal is, tesame met die
energiebewaring verhoudings, was gebruik om die akkuraatheid van die eksperimenteel bepaalde
stabiliteitskonstantes te bekragtig. Verdermeer was die waarde van die algehele formasie
konstante wat eksperimenteel bepaal is, ΔG°rxn, in goeie ooreenstemming met dit wat bereken is
deur die standaard reaksie halfsel reduksie potensiale van [PtCl6]2- en [PtBr6]2-. Dus is die
eksperimenteel verkrygde termodinamiese parameters bevestig. Die termodinamiese dryfkrag vir
die PtIV chloried-bromied uitruilingsreaksies is toegereken aan die hidrasie van die halied
ligande, wat in waterige oplossings die reaksie na die bromied PtIV spesies dryf, al is die chloried
PtIV spesies energeties bevoordeel in hierdie reaksienetwerk. Evaluering van ander metaalkatioon-
halied-uitruilreaksies wys dat alle metaal-halied komplekse die F- >> Cl- > Br- > I- orde
van termodinamiese stabiliteit volg en dat hierdie volgorde slegs omgekeer sal word weens
solvasie van hierdie halied ligande. Darenbowe digtheids funksionele teorie (DFT) gebruik om
die termodinamiese stabiliteit met betrekking tot isodesmiese reaksies wat chloried-bromied PtIV
stereoisomeer pare behels te voorspel, sowel as van chloried-bromied PtIV
liganduitruilingsreaksies van die [PtCl6-nBrn]2- (n = 0 – 6) spesies, en bevestig die F- >> Cl- > Br-
> I- volgorde van termodinamiese stabiliteit. Verder was dit ook moontlik om met DFT die
ΔΔG°rxn tot so naby as 8 – 20 kJ.mol-1 te bereken.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/80099 |
| Date | 03 1900 |
| Creators | Van Wyk, Pieter-Hugo |
| Contributors | Koch, Klaus R., Gerber, Wilhelmus J., Stellenbosch University. Faculty of Science. Dept. of Chemistry and Polymer Science. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | xi, 97 p. : ill. |
| Rights | Stellenbosch University |
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