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RELA~IONSHrps BETWEEN MAS NMR

AND MINERAL STRUCTURE

By

BARBARA LUCY SHERRIFF. B.A .• B.Sc .• H.Sc.

A Th~sis. ,

Submitted to the school of Graduate Studies

In Partfal Fulfilment of the Requirements

for the Degree

Doctor of Phi losophy"

McMaster University

September 1988,

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MASNMR AND MINERAL STRUCTURE

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DOCTOR OF PHILOSOPHY (1988) MCMASTER UNIVERSITY.

o (Geology) Hamilton. Onta~io.

TITLE: Relationships between MAS NMR and Mineral Structure

AUTHOR: Barbara Lucy Sherriff, B.A. (The Open University)

B.Sc. (Leicester University)

M.Sc. (Brock University)

SUPERVISOR:Professor H. D. Grundy

NUMBER OF PAGES: xv. 214 /

i i

ABSTRACT

29S '. 1 magic angle spinning nuclear magnetic

resonance (MAS nmr) has been used extensively to study the.

structure, properties. and reactions of sflicate minerals,

ceramics and glasses. Despite many attempts to relate

chemical shift with crystal structure the factors governing

29Si chemical shift are not weI I understood.

This study investigates the effect of local

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structural environment of the silicate tetrahedron on 29Si

chemical shift. A simple relationship is found between the

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atomic positions of the cations bonded to the terminal

oxygens of the tetrahedron and 29Si chemical shift. which

can be used to calculate chemical shift from atomic

positions. A plot of calculated against experimental

chemical shift has a correlation coefficient of 0.986 for

124 sets of date from all groups of sil icates.

29S ' h . I1 C emlca shifts calculated from diffraction

data, are used to interpret MAS nmr spectra of scapolite, a

partially disordered mineral system. Models are devised for

cation ordering throughout the sol id solution series. in

which the charge on the cavities are balanced locally by

the requisite number of AI04 tetrahedra.

29Si , 27 AI • 23 Na , 7Li and 9Se MAS nmr spectroscopy

is used to inveseigate the difference in atomic sites

iii

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between beryls with slightly different compositions. 9 Be

and 2951 MAS nmr results agree wfth the ,presence of. domains

In the Li-Cs beryis with the structure of low-alkal I

beryls. Lack of a tetrahedral peak in the 27Al spectra of

Li-Cs beryls eliminates the coupled sUbstitution of LI for

AT and A1 for Be. Peaks in 'the,23 Na spectra of LI-Cs beryls

from NaCI in solutiori In fluid Inclusions show the'

potential of nmr to study fluid Inclusions.

Models of theoretical structures based on a

symmetrical 5i04 -tetrahedron with AI'· or Si 1 i gands show

that chemical shift is linearly proportional to cation~

oxygen distance (r) a~d ~xponential ly proportional to~_

siT f con-oxygen-cat ion angle (0). The possible ranges of

chemical shift for each type of silicate are more extensive

than those of Lippmaa et ale (1980) •

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ACKNOWLEDGEMENTS

. . .I would like to thank' my' superyfsor Dr. H. D•

. Grundy For' instructing me fn the art of carrying out·

'scientfFic research and for his help with computing. Thanks

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at so go to Dr. r. D. Brown, Dr. M. J. McG I i nchey, Dr A. D.:

Sain, Dr. F. C. Hawthorne, Or. J. R. Kramer, Dr. J. S.

Hartman and Dr. D. M. Shaw for helpful discussions. Dr D.

M. Shaw is especially thanked for constructive criticism

and readfng of the manuscript and Dr. J. S. Hartman for

....providing the

Fyfe.

MAS nmr probes from the design of~r. C.. A.

I'am grateful to Dr R. E.. Lenkinski. W. Klimstra.

Dr C. A. Fyfe, and Dr. S. Johnson at Guelph University and

B. Sayer of McMaster

instrumentation.

University for he 1p w.fth Iilmr

This project was supported by NsERC Funding and.

also by Hooker and Sherman scholarships From McMaster

University. The time on the nmr spectrometers at the South

Western Ontario Nmr Centre was paid For by Brock University

through Dr. J. S. Hartman.

F i na I Iy would like to thank all my Friends at.

McMaster UnIversity especially Kathy Teeter. ·Jil I Gleed and

'Dr. Marilyn Truscott and my children Barry and Jackie For

their friendship and support.

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CONTENTS,.,..' ....1

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Abstract

Acknowledgements

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Chapter 1.•

Introductfon to nuclear magneticresonance qf sflicate minerals

t 1•. 1 Introduction

1.2 Nuclear Magnetfc Resonance...,

Chapter 2

. ·29 '.'1.. 3 " 5 i· MAS nmr. " -- ...' , ~

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. .·:: ..~L •.~:.;·""re~·~ous:. work on the ·re.l at f ~nshi p~:~,:::;:. <~.·o.F::. .... 5 f MAS nmr chern fca 1 s h i ft . .' .."" .,:·w~~~· mf nera' st~uc;:ture

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Cor.~2~a~Jon b~tween atomic structureand .. , . 5 i MAS nmr chem fca I sh f ft

. 2. 1 Introduct f"on

2.2 Nmr and diffraction data

2.2.1 Disorder of cations in acrystallographic site

2.2.2 Difference In compositionor ordering between mineralsamples 24

2.2.3 Inaccurate structural data

2.2.4 Errors in nmr data

2.3 Calculations

2.3.1 The first term; magneticanisotropy

2.3.2 Second term; bond valence

2.3.3 Third term; Si-O-X angle.

2.3.4 Resultant equation

vi

26

27

32

34

38

44

46

Page

4.4.2 A1Limfnum-27 127

4.4.3 Sodfum-23 129

4~4.4 Beryllfum-9 '136: :

, .4.4.5 Lfthfum-7 140

4.5 Conclusfons " 143

Chapter 5 ModellIng theoretical silicate structuresand thoughts For the future 145

5. 1 Introduction 145

5.2 Sf04 tetrahedral model 146r

5.3 Results and discussion 149

5.4 Present state of chemical shiFtcalculations 153

) 5.5 Ideas For the future 153

.'

ReFerences

Appendix I

157

The theory of nuclear magnetic resonance 172

1.1 General theory of nmr spectroscopy 172

1.2 Pulse Fourier Transrorm 176

1.3 ChemIcal shift 178

1.4 High Reso I ut ion nmr of .§.o lids 180

1.5 MAS nmr spectra or quadrupolar nuclei 184

1.6 Relaxatfon times

Appendix. II Mineral samples

Appendix III Dum.For

Appendix IV Len.for

Appendfx V Chfsi.For

vi f f

188

190

191

194

197

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Appendix VI

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Values of n For SiD? polymorphs summedat _1/2 A intervals ~o 10 A

Page

202

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209

204

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Appendix VII Summations or-geometric terms ror Si02polymorphs averaged rrom 6 - 10 A 203, ',~" . ~

Append i x VI I I 295 f chemf cal -shrft or sf 1i catemJn~rals1 eXperfmental values, and valuescat cu I~t'ed \~rc:>m equatJ ops- .3, a~d 4.

. ,. . ,.Appendix IX Calculated chemical" shiFts From

theoretical models (angle a variedbetween'I25 and '180°)

Appendix X Calculated cnemieal shfFts rromtheoretical models (distaflce r variedbetween l~75 and 1.55 A) 210

of ','

-Appendix XI The relationship between the McConnellequation and equations 3 and 4 212

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FIGURESPage

1.1 Ranges of 2951 MAS nmr chemIcal shiFt Fors 111~~t.es" and Framework ,:atum:f nos' 1" cates

1.2-:· ~9S"~~'\'~~6~:~opiC ~hemfcal':;-~'h'f';':'~ plotted" against; 'the: 'mean~~'number oFs f 1fcor{ 'atoms 'for' ', (a ) For', 52 zeolf"tes' wi th"fauJas f.t Jc framework

(b>' for 26 Zeo 1fte-A Framewor,k" mater fa 1s .. '.. ' .~ "' .. ,: ,".j," '

1•3 ,2951 , chernf cal. sh f ft l versus' "':.:0',:, .. '(a)average Sf-O, bond:length, ,','(b rtota 1 cat f On-aXi9~~~:bbnd stre~th for theFo.u r oxygen' at'oms,,~~r~oundfng eac~ 5.1 ,.5 f \e

... -:z:" .. ", _~ . ,-.' " I

I .4 Re 1at ion be'tween' chernf ca 1 sh,f Ft and structura 1parameters

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7

9

10

1.5

1.6

1.7

1 .8

2. 1

Bond direction related,shieldfng versus 5f-0bond distances For s 111 ca po:l Yfl]0rphs

Relationship between 29~t'c~emfcal shiFt andmean oxygen ~ characterof:s,f I'f ca po Iyrnorphsand zepl ites " ",", '

Experimental 2951 nmr ~hemfcal shfFt ofzeal ites and sit ica polymorphs plottedagainst calculated chemfcal shiFts.

Graph showing correlatfon between 295f MASS ~mrchemical shiFt and chemical, shfFt predicted on'the basis of the group electronegatfvfty sum.

Diagram showing the deFinitions of angles eand a and the leng~hs rand R.

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13

15

17

33

2.2 Summations of n, using equation (1), at 1/2 Aintervals From 51, plotted against distanceFrom 51 For the SfQ2 polymorphs

2.3 The ~n of summatlo~s, at 1/2 A Intervals,From 6 to2 10 A, F~r the geometric termt«1-3cos e )/3R ) plotted againstexperimental 0 Fbr the silica polymorphs.

2.4 Experimental 2951 MAS nmr chemical shiFtplotted agafnst chemical shift calculatedFrom equations 3 and 4.

36

38

47

nmr spectrum of white kyanfte

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51

Page

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2.6 29Si HAS nmr spectrum of pfemontfte

2.7 29Si HAS nmr spectrum of wollastonfte

2.8 29Sf HAS nmr spectra of albfte/mfcroclfneperthftes

2.9 29Sf HAS nmr spectra of the plagioclase'feldspar series.

2.10 2951 HAS nmr spectrum of nephe line

3;1 The structure of ~capolfte viewedalong the c-axfs

3.2 The structure of scapolite viewedalong the a-axis

3.3 29Si ~ASnmr spectra of scapol ite samples

3.4 Peak Fitting to the 29Si HAS nmr spectrumof GL (34.1~ He)

3.5 27A1 HAS nmr spec~a of scapollte samples

3.6 A graph of 27A1 peak width plotted againstmelonite content

3. 7 ConF 1gurat fon of the Na-O po 1yhedror.

54

58

61

64

66

76

77

84

86

96

98

100

3.8 A plot of (Na.Ca)-O distances as a runction'of me i on f tecontent 101

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":3':~9" 23 Na HAS nmr spectra of scapo lite samples

\3. 1q 13C HAS nmr spectrum of scapo lite sample Q13

3. 11 Model of cation ordering In 371- Me scapollte

3.12 Hodel of cation ordering in 201- Me scapo 1 ite

3. 13 Model of Cqtfon orderlll1g in 751- He scapol ite.:.--, .........

103

107

109

I 12

114

4.1. Photographs of computer simulated models of"the structure of Lf-Cs beryl viewed along(a) the c-axis; (b) the a-axis. :)20

4.2 29 51 MAS nmr spectra" of (a) T-24 Li-Cs.beryl(b) S~EE-l~6 low alkal i beryl 124

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