What is the possible origin of the 195Pt NMR shielding in the solid state? X-ray diffraction, solid-state NMR studies of deceptively simple C2[PtX6] salts (C = various cations, X = Cl- and Br-)

Odendal, James Arthur (2015-03)

Thesis (DSc)--Stellenbosch University, 2015.

Thesis

ENGLISH ABSTRACT: The primary objective of the work presented in this thesis is to investigate the sensitivity and nature of the 195Pt chemical shift in the solid-state, as a function of temperature. We have carried out a series of experimental single crystal X-ray diffraction (SCXRD), solid state nuclear magnetic resonance (SSNMR) and density functional theory (DFT) experiments and calculations on various dication hexachloridoplatinate(IV) salts to paint a picture of the nature of the 195Pt shielding in the solid state. The results obtained from SCXRD analyses performed as a function of temperature on Rb2PtCl6, (NH4)2PtCl6 and [(N(CH3)4]2PtCl6 salts give a detailed account on the changing inter- and intramolecular interactions in dication hexachloridoplatinate(IV) salts upon lattice expansion, as a function of increasing temperature. The 195Pt SSNMR measurements of these salts have a peculiar 195Pt chemical shift sensitivity to changes in temperature. The 195Pt chemical shift trends performed as a function of temperature of the Rb2PtCl6 salt resulted in a linear-like trend with the slope of δ195Pt/T = 0.362 (0.008) ppm/K. The (NH4)2PtCl6 salt trend showed some non-linear characteristics at lower temperatures and tended towards linearity at a higher temperature with the slope δ195Pt/T = 0.228 (0.0126) ppm/K. The 195Pt chemical shift of the [(N(CH3)4]2PtCl6 had quite a different trend due to its well-known structural phase transitions as a function of temperature. The expected sensitivity range of the 195Pt chemical shift, predicted from experimental temperature dependent (100 K and 400 K) SCXRD measurements of Rb2PtCl6 and (NH4)2PtCl6 salts coincide well with that of experimental 195Pt chemical shift sensitivity. The atomic coordinates obtained from SCXRD analyses performed as a function of temperature were used to conduct DFT calculations to extract SSNMR parameters together with electrostatic potentials in order to study the local molecular and electronic structures of Rb2PtCl6 and (NH4)2PtCl6 salts. The computed 195Pt SSNMR parameters gave an account of chemical shift parameters and quadrupolar coupling parameters, which show excellent agreement with experimental 195Pt chemical shift SSNMR measurements. These calculations shed some light on the 35Cl SSNMR parameters, which to date are still unobtainable by means of conventional experimental SSNMR measurements. The computed 35Cl SSNMR shielding parameters showed that the electronic environments of the Cl- ion in dication hexachloridoplatinate(IV) salts are central to the understanding and interpretion of experimental 195Pt chemical shift sensitivity. These computational analyses gave the means to propose a theory whereby the : “polarization of electronic charge density from the PtIV ion towards the Cl- ion as the interaction between the anion and cation are being weakened due to lattice expansion as a function of increasing temperature”. This thesis shows that the combination of these three usually independently used analytical techniques are crucial in understanding the behaviour of experimental 195Pt chemical shift dication hexachloridoplatinate(IV) salts in the solid state.

AFRIKAANSE OPSOMMING: Die primêre doel van die werk wat in hierdie tesis beskryf word was om die sensitiwiteit en die aard van die 195Pt chemiese afskerming tensor in die vaste toestand as 'n funksie van temperatuur te ondersoek. Ons het 'n reeks enkelkristal X-straal diffraksie (SCXRD) en vastestof kernmagnetiese resonansie (SSNMR) eksperimente asook (kwantum meganiese) DFT (density functional theory) berekeninge op verskeie dikatioon heksachloroplatinaat (IV) soute uitgevoer ten einde 'n beeld te vorm van die aard van die 195Pt kern in die vaste toestand. Die resultate verkry deur SCXRD ontledings van die soute Rb2PtCl6, (NH4)2PtCl6 en [(N(CH3)4]2PtCl6, uitgevoer as ’n funksie van temperatuur, gee gedetailleerde informasie rakende die veranderende inter-en intramolekulêre interaksies in hierdie heksachloroplatinaat (IV) soute tydens uitsetting van die kristalstruktuur as ’n funksie van toenemende temperatuur. Die 195Pt SSNMR metings van hierdie soute toon ’n eienaardige 195Pt chemiese afskerming sensitiwiteit tot temperatuurveranderinge. Die 195Pt chemiese afskerming in die sout Rb2PtCl6 bepaal as 'n funksie van die temperatuur lei tot 'n effektief lineêre tendens; die tendens vir die (NH4)2PtCl6 sout toon 'n aantal nie-lineêre eienskappe by laer temperature en neig tot lineariteit by hoër temperatuur. Die 195Pt chemiese afskerming van [(N(CH3)4]2PtCl6 het ’n merkbaar verskillende tendens as gevolg van sy welbekende strukturele faseveranderinge as 'n funksie van temperatuur. Die verwagte sensitiwiteit van die 195Pt chemiese afskerming soos voorspel vanaf eksperimentele temperatuur afhanklikheid (100 K en 400 K) SCXRD metings van Rb2PtCl6 en (NH4)2PtCl6soute stem goed ooreen met die eksperimentele 195Pt chemiese afskerming sensitiwiteit. Die atoomkoördinate verkry vanaf SCXRD ontledings uitgevoer as 'n funksie van temperatuur is gebruik om DFT berekeninge van SSNMR parameters en elektrostatiese potensiale uit te voer en sodoende die plaaslike molekulêre en elektroniese struktuur van die Rb2PtCl6 en (NH4)2PtCl6soute te bestudeer. Die berekende 195Pt SSNMR parameters verskaf ’n rekening van chemiese afskerming parameters en quadrupoolkoppeling parameters wat oortuigende ooreenkomste toon met eksperimentele 195Pt SSNMR metings. Hierdie berekeninge werp ook lig op die 35Cl SSNMR parameters, tot dusver nog onbekombaar deur middel van konvensionele eksperimentele SSNMR metings. Die berekende 35Cl SSNMR parameters het getoon dat die elektroniese omgewings van die Cl-ioon in dikatioon heksachloroplatinaat (IV) soute sentraal staan in die begrip en interpretasie van 195Pt chemiese afskerming sensitiwiteit. Hierdie kwantum meganiese berekeninge fasiliteer ’n voorstel van "polarisering van elektroniese ladingsdigtheid van die Pt-ioon na die Cl-ioon as die interaksie tussen die anioon en katioon verswak weens kristalstruktuuruitsetting as 'n funksie van die toenemende temperatuur". Hierdie tesis toon dat die kombinasie van hierdie drie analitiese tegnieke, wat meestal onafhanklik gebruik word, van kardinale belang is in die begrip van die gedrag van 195Pt chemiese afskerming in dikatioon heksachloroplatinaat (IV) soute in die vaste toestand.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/96596
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