Dieter Freude, Institut für Experimentelle Physik I der Universität Leipzig Skiseminar in the Dortmunder Hütte in Kühtai, Sunday 30 March 2008, 7:308:30 p.m.

Principles of NMR spectroscopyPrinciples of NMR spectroscopyPrinciples of NMR spectroscopyPrinciples of NMR spectroscopy

NMR is far from nuclear spectroscopyNMR is far from nuclear spectroscopyNMR is far from nuclear spectroscopyNMR is far from nuclear spectroscopy

NMR is near to Nobel PrizesNMR is near to Nobel PrizesNMR is near to Nobel PrizesNMR is near to Nobel Prizes

Physics 1952 Chemistry 1991 2002 Medicine 2003  

 

 

 

 

 

 

 Felix Bloch and Edward Purcell Richard R. Ernst Kurt Wüthrich Paul Lauterbur and Peter Mansfield

Stanford Harvard University ETHZ ETHZ Urbana NottinghamUSA USA Switzerland Switzerland USA England

Some of the 130 NMR isotopesSome of the 130 NMR isotopesSome of the 130 NMR isotopesSome of the 130 NMR isotopes

WEB of Science: 35% of NMR studies focus to the nuclei 1H, 25% to 13C, 8% to 31P, 8% to 15N, 4% to 29Si,and 2% to 19F. In these nuclei, we have a nuclear spin I = ½.

If we look at nuclei with a quadruple moment and half-integer spin I > ½, we find 27Al in 3% of all the NMR papers and 1% for each of the nuclei 11B, 7Li, 23Na and 51V.

For even numbered spin, only the I = 1-nuclei are frequently encountered: 2H in 4% and 14N and 6Li in 0.5% of all NMR papers.

nucleus natural abundance

/%

spin quadrupole moment Q/fm2

gyromagnetic ratio

/107 T s

-frequency 100 MHz

(1H)

rel. sensitivity at natural

abundance

1H 99.985 1/2 26.7522128 100.000000 1.000 2H 0.015 1 0.2860 4.10662791 15.350609 1.45 10 6 6Li 7.5 1 0.0808 3.9371709 14.716106 6.31 10 4 7Li 92.5 3/2 4.01 10.3977013 38.863790 0.272 11B 80.1 3/2 4.059 8.5847044 32.083974 0.132 13C 1.10 1/2 6.728284 25.145020 1.76 10 4 14N 99.634 1 2.044 1.9337792 7.226330 1.01 10 3 15N 0.366 1/2 2.71261804 10.136784 3.85 10 6 17O 0.038 5/2 2.558 3.62808 13.556430 1.08 0 5 19F 100 1/2 25.18148 94.094008 0.834

23Na 100 3/2 10.4 7.0808493 26.451921 9.25 10 2 27AI 100 5/2 14.66 6.9762715 26.056890 0.21 29Si 4.67 1/2 5.3190 19.867187 3.69 10 4 31P 100 1/2 10.8394 40.480742 6.63 10 2 51V 99.750 7/2 5.2 7.0455117 26.302963 0.38

Chemical shift of the NMRChemical shift of the NMRChemical shift of the NMRChemical shift of the NMR

H+

external magnetic field B0

shielded magnetic

fieldB0(1)

OH

electronshell

We fragment hypothetically a water molecule into hydrogen cation plus hydroxyl anion. Now the 1H in the cation has no electron shell, but the 1H in the hydroxyl anion is shielded (against the external magnetic field) by the electron shell. Two signals with a distance of about 35 ppm appear in the (hypothetical) 1H NMR spectrum.

Chemical shift and Chemical shift and JJ-coupling-couplingChemical shift and Chemical shift and JJ-coupling-coupling

1 2 3 4 0

10 20 30 40 50 60 70 0

t/ms

t/s

0 1 2 3 4 5 / ppm

The figure shows at left the free induction decay (FID) as a function of time and at right the Fourier transformed 1H NMR spectrum of alcohol in fully deuterated water. The individual spikes above are expanded by a factor of 10. The singlet comes from the OH groups, which exchange with the hydrogen nuclei of the solvent and therefore show no splitting. The quartet is caused by the CH2 groups, and the triplet corresponds to the CH3 group of the ethanol. The splitting is caused by J-coupling between 1H nuclei of neighborhood groups via electrons.

An NMR spectrum is not shown as a function of the frequency = ( / 2) B0(1),

but rather on a ppm-scale of the chemical shift = 106 (ref ) /L, where the

reference sample is tetramethylsilane (TMS) for 1H, 2H, 13C, and 29Si NMR.

Chemical shift rangeChemical shift rangeof some nucleiof some nucleiChemical shift rangeChemical shift rangeof some nucleiof some nuclei

Ranges of the chemical shifts of a few nuclei and the reference substances, relative to which shifts are related.

1, 2H TMS

6, 7Li 1M LiCl

11B BF3O(C2H5)2

13C MS = (CH3)4Si

14, 15N NH4+

19F CFCl3

23Na 1M NaCl

27Al [Al(H2O)6]3+

29Si TMS = (CH3)4Si

31P 85% H3PO4

51V VOCl3

1000 100 10 0 10 100 1000/ ppm

129, 131Xe XeOF4

NMR spectrometer NMR spectrometer NMR spectrometer NMR spectrometer

H. Pfeifer: Pendulum feedback receiverDiplomarbeit, Universität Leipzig, 1952

Bruker'shome page

AVANCE 750 wide-bore in

Leipzig

NMR spectrometer for liquidsNMR spectrometer for liquidsNMR spectrometer for liquidsNMR spectrometer for liquids

Campher

H3C CH3

CH3

O

1.0

0

0.9

4

1.0

9

0.9

8

1.1

2

2.1

0

3.1

43

.01

3.2

0

Inte

gra

l

2.5 2.0 1.5 1.0 ppm

H

4 5 4 0 3 5 3 0 2 5 2 0 1 5 1 0 5p p m2.5 2 .0 1 .5 1 .0p p m

2.5

2.0

1.5

1.0

pp

m

2.52.0

1.51.0

pp

m

45 40 35 30 25 20 15 10 5ppm

2.5 2.0 1.5 1.0p p m

0.8

0.9

1.0

p p m

Structure NMR-Spektrum

CHHH

1H-NMR13C-NMRHH-COSYHC-COSYHETCORNOESY

R. Meusinger, A. M. Chippendale, S. A. Fairhurst, in “Ullmann’s Encyclopedia of Industrial Chemistry”, 6 th ed., Wiley-VCH, 2001

Structure determination by NMRStructure determination by NMRStructure determination by NMRStructure determination by NMR

How works NMR: a nuclear spin How works NMR: a nuclear spin I I = 1/2 in an magnetic field = 1/2 in an magnetic field BB00How works NMR: a nuclear spin How works NMR: a nuclear spin I I = 1/2 in an magnetic field = 1/2 in an magnetic field BB00 B0, z

y

x

L

B0, z

y

x

L

Many atomic nuclei have a spin, characterized by the nuclear spin quantum number I. The absolute value of the spin angular momentum is

The component in the direction of an applied field is

  Lz = Iz  m = ½ for I = 1/2.

.)1( IIL

Atomic nuclei carry an electric charge. In nuclei with a spin, the rotation creates a circular current which produces a magnetic moment µ.

An external homogenous magnetic field B results in a torque T = µ B  with a related energy of  E =  µ·B.

The gyromagnetic (actually magnetogyric) ratio is defined by

µ =  L.

The z component of the nuclear magnetic moment is

µz =  Lz =  Iz    m .

The energy for I = 1/2 is split into 2 Zeeman levels

Em =  µz B0 =  mB0 = B0/2 = L/2.Pieter Zeeman observed in 1896 the splitting of optical spectral lines in the field of an electromagnet.

Larmor frequencyLarmor frequencyLarmor frequencyLarmor frequency

Joseph Larmor described in 1897 the precession of electron orbital magnetization in an external magnetic field.

Classical model: the torque T acting on a magnetic dipole is defined as the time derivative of the angular momentum L. We get

By setting this equal to T = µ B , we see that

The summation of all nuclear dipoles in the unit volume gives us the magnetization. For a magnetization that has not aligned itself parallel to the external magnetic field, it is necessary to solve the following equation of motion:

.dd1

dd

ttμL

T

.dd

Bμμ

t

.dd

BMM t

B0, z

M

y

x L

We define B  (0, 0, B0) and choose M(t  0)  |M| (sin, 0, cos). Then we obtain

Mx  |M| sin cosLt, My  |M| sin sinLt, Mz  |M| cos with L = B0.

The rotation vector is thus opposed to B0 for positive values of . The Larmor frequency

is most commonly given as an equation of magnitudes: L =  B0 or.

2 0L B

Macroscopic magnetizationMacroscopic magnetizationMacroscopic magnetizationMacroscopic magnetization energy Em = ½

E = hL

Em = ½

Nm = ½

Nm = ½

hL « kT applies at least for temperatures above 1 K

and Larmor frequencies below 1 GHz. Thus,

spontaneous transitions can be neglected, and the

probabilities P for absorption and induced emission

are equal. It follows P = B+½,½ wL= B½,+½ wL, where B

refers to the Einstein coefficients for inducedtransitions and wL is the spectral radiation density at the Larmor frequency.

A measurable absorption (or emission) only occurs if there is a difference in the two

occupation numbers N. In thermal equilibrium, the Boltzmann distribution applies to

N and we have .expexp L0

2/1

2/1

kTh

kTB

NN

If L  500 MHz and T  300 K, hL/kT 8 10 is very small, and the exponential

function can be expanded to the linear term:

.108 5L

2/1

2/12/1

kTh

NNN

Longitudinal relaxation time Longitudinal relaxation time TT11Longitudinal relaxation time Longitudinal relaxation time TT11

All degrees of freedom of the system except for the spin (e.g. nuclear oscillations,

rotations, translations, external fields) are called the lattice. Setting thermal

equilibrium with this lattice can be done only through induced emission. The

fluctuating fields in the material always have a finite frequency component at the

Larmor frequency (though possibly extremely small), so that energy from the spin

system can be passed to the lattice. The time development of the setting of

equilibrium can be described after either switching on the external field B0 at time

t  0 (difficult to do in practice) with,1 1

0

T

t

enn

T1 is the longitudinal or spin-lattice relaxation time an n0 denotes the difference in

the occupation numbers in the thermal equilibrium. Longitudinal relaxation time

because the magnetization orients itself parallel to the external magnetic field.

T1 depends upon the transition probability P as 

1/T1 = 2P  2B½,+½ wL.

TT1 1 determination by IRdetermination by IRTT1 1 determination by IRdetermination by IR

The inversion recovery (IR) by -/2

1210Tenn

By setting the parentheses equal to zero, we get 0  T1 ln2 as the passage of

zero.

0

Line width and Line width and TT22Line width and Line width and TT22

A pure exponential decay of the free induction (or of the envelope of the echo, see next page) corresponds to

G(t) = exp(t/T2).

The Fourier-transform gives fLorentz = const. 1 / (1 + x2) with x = ( 0)T2,

see red line. The "full width at half maximum" (fwhm) in frequency units is

.1

22/1 T

Note that no second moment exists for a Lorentian line shape. Thus, an exact Lorentian line shape should not be observed in physics.

Gaussian line shape has the relaxation function G(t) = exp(t2 M2 / 2) and a line

form fGaussian = exp (2/2M2), blue dotted line above, where M2 denotes the

second moment. A relaxation time can be defined by T22 = 2 / M2. Then we get

21/2=2/T2=1/2

0

fLorentz

1

1/2

( ) ( ) ( ) .Hz/×12.74ln

Hz/=s/

2=s/ 2

2/1

22

2/122

2-2

≈

TM

Correlation time Correlation time cc, relaxation times , relaxation times TT11 and and TT22Correlation time Correlation time cc, relaxation times , relaxation times TT11 and and TT22

tftfG

c

GG

exp0

2

L

2

L06

24

1 21

8

1

2

4

1

5

11

c

c

c

cII

rT

2

L

2

L06

24

2 21

2

1

53

4

1

5

11

c

c

c

cc

II

rT

T1

T2

ln T1,2

1/T

T1 min

T2 rigid

The relaxation times T1 and T2 as a function of the reciprocal absolute temperature

1/T for a two spin system with one correlation time. Their temperature dependency

can be described by c  0 exp(Ea/kT).

It thus holds that T1  T2 1/c when Lc « 1 and T1 L2 c when Lc » 1.

T1 has a minimum of at Lc 0,612 or Lc 0,1.

Rotating coordinate system and the offsetRotating coordinate system and the offsetRotating coordinate system and the offsetRotating coordinate system and the offset

For the case of a static external magnetic field B0 pointing in z-

direction and the application of a rf field Bx(t) = 2Brf cos(t) in x-

direction we have for the Hamilitonian operator of the external interactions in the laboratory sytem (LAB)

H0 + Hrf = LIz + 2rf cos(t)Ix,

where L = 2L = B0 denotes the Larmor frequency, and the

nutation frequency rf is defined as rf = Brf.The transformation from the laboratory frame to the frame rotating with gives, by neglecting the part that oscillates with the twice radio frequency,

H0 i + Hrf i = Iz +

rf Ix,

where = L denotes the resonance offset

and the subscript i stays for the interaction representation.

B0

M

x

y

z

B0

M x’

y

z

Magnetization phases develop in this interaction representation in the rotating coordinate system like = rf or = t.

Quadratur detection yields value and sign of .

Bloch Bloch equation and stationary solutionsequation and stationary solutions Bloch Bloch equation and stationary solutionsequation and stationary solutions

We define Beff  (Brf, 0, B0 /) and introduce the Bloch equation:

1

0

2

effd

d

T

MM

T

MM

tzx zyyx eee

BMM

Stationary solutions to the Bloch equations are attained for dM/dt  0:

.

1

1

,21

,21

0

212rf

222

2

L

22

2

L

rf0rf

212rf

222

2

L

2

rf0rf

212rf

222

2

L

22L

MTTBT

TM

HMBTTBT

TM

HMBTTBT

TM

z

y

x

Hahn echoHahn echoHahn echoHahn echo

B0

M

x

y

z B0

M x

y

z B0

x

y

z

5 4

1 2

3

B0

x

y

z

1 2

5 4

3

B0

M x

y

z

/2 pulse FID, pulsearound the dephasing around the rephasing echo y-axis x-magnetization x-axis x-magnetization

(r,t) = (r)·t (r,t) = (r,) + (r)·(t )

TT2 2 and and TT22**TT2 2 and and TT22**

( ) 2

2

e= TG

( ) 2e= Tt

tG

EXSY, NOESY, stimulated spin echoEXSY, NOESY, stimulated spin echoEXSY, NOESY, stimulated spin echoEXSY, NOESY, stimulated spin echo

stimulated echo

0

t1 t2 tmix

t1

time

FID FID

after mixing

Pulsed field gradient NMR diffusion measurements base on NMR pulse sequences that generate a spin echo, like the Hahn echo (two pulses) and the stimulated spine echo (three pulses). At right, the 13-intervall sequence for alternating gradients consisting of 7 rf pulses, 4 gradient pulses of duration , intensity g, and diffusion time and 2 eddy current quench pulses is described.

NMR diffusometry (PFG NMR)NMR diffusometry (PFG NMR)NMR diffusometry (PFG NMR)NMR diffusometry (PFG NMR)

free induction decay

rf pulses

gradient pulses

g

ecd

p

gDSS

2

4exp

2

0

The self-diffusion coefficient D of molecules in bulk phases, in confined geometries and in biologic materials is obtained from the amplitude S of the free induction decay in dependence on the field gradient intensity g by the equation

Application of MAS technique in addition to PFG (pulsed field gradient) improves drastically the spectral resolution, allowing the study of multi-component diffusion in soft matter or confined geometry.

The difference between solid-state and liquid NMR,The difference between solid-state and liquid NMR,the lineshape of waterthe lineshape of water

The difference between solid-state and liquid NMR,The difference between solid-state and liquid NMR,the lineshape of waterthe lineshape of water

10 20 30 400

/ kHz

-30 -20 -10-40

0.1 0.2 0.3 0.40

/ Hz

-0.3 -0.2 -0.1-0.4

solid water (ice)

liquid water

Fast rotation (160 kHz) of the sample about an axis oriented at 54.7° (magic-angle) with respect to the static magnetic field removes all broadening effects with an angular dependency of

o7.543

1cosarc

That means chemical shift anisotropy,dipolar interactions,first-order quadrupole interactions, and inhomogeneities of the magnetic susceptibility.

It results an enhancement in spectral resolution by line narrowing also for soft matter studies.

High-resolution solid-state MAS NMRHigh-resolution solid-state MAS NMRHigh-resolution solid-state MAS NMRHigh-resolution solid-state MAS NMR

2

1cos3 2

rotor with samplein the rf coil zr

rot

θ

gradient coils forMAS PFG NMR

B0

Laser supported high-temperature MAS NMRLaser supported high-temperature MAS NMRfor time-resolvedfor time-resolved in situ in situ studies of reaction stepsstudies of reaction steps

in heterogeneous catalysis: the NMR batch reactorin heterogeneous catalysis: the NMR batch reactor

Laser supported high-temperature MAS NMRLaser supported high-temperature MAS NMRfor time-resolvedfor time-resolved in situ in situ studies of reaction stepsstudies of reaction steps

in heterogeneous catalysis: the NMR batch reactorin heterogeneous catalysis: the NMR batch reactor

MAS Rotor 7 mm

CO2 Laser

Cryo Magnet

B0

Dieter Freude, Institut für Experimentelle Physik I der Universität Leipzig Skiseminar in the Dortmunder Hütte in Kühtai, 31 March 2008, 7:308:30 p.m.

Some applications of solid-state Some applications of solid-state NMR spectroscopyNMR spectroscopy

Some applications of solid-state Some applications of solid-state NMR spectroscopyNMR spectroscopy

NMR on the topNMR on the topNMR on the topNMR on the top

WEB of Science refers for the year 2006 to about 16 000 NMR studies, mostly on liquids, but including also 2500 references to solid-state NMR.

Near to 12 000 studies concern magnetic resonance imaging (MRI).

The next frequently applied technique, infrared spectroscopy, comes with about 9 000 references in

the WEB of Science.

Solid-state NMR on porous materialsSolid-state NMR on porous materialsSolid-state NMR on porous materialsSolid-state NMR on porous materials

1H MAS NMR spectra including TRAPDOR 29Si MAS NMR 27Al 3QMAS NMR 27Al MAS NMR 1H MAS NMR in the range from 160 K to 790 K

11H MAS NMR on molecules H MAS NMR on molecules adsorbed in porous materialsadsorbed in porous materials

11H MAS NMR on molecules H MAS NMR on molecules adsorbed in porous materialsadsorbed in porous materials

Hydrogen exchange in bezene loaded H-zeolites In situ monitoring of catalytic conversion of molecules

in zeolites by 1H, 2H and 13C MAS NMR MAS PFG NMR studies of the self-diffusion

of acetone-alkane mixtures in nanoporous silica gel

11H MAS NMR spectra, TRAPDORH MAS NMR spectra, TRAPDOR11H MAS NMR spectra, TRAPDORH MAS NMR spectra, TRAPDOR

0

t2

time

FID echo

t1 t1

1H MAS NMR with 27Al dephasing

11H MAS NMR spectra, TRAPDORH MAS NMR spectra, TRAPDOR11H MAS NMR spectra, TRAPDORH MAS NMR spectra, TRAPDOR

H-ZSM-5 activated at 550 °C

420246 8 10 / ppm

20 468 10 / ppm

4

4.2 ppm 2.9 ppm2.9 ppm

2.2 ppm

1.7 ppm

2.2 ppm1.7 ppm2.9 ppm2.9 ppm

with dephasing

without dephasing

difference spectra

2

Without and with dipolar dephasing by 27Al high power irradiation and difference spectra are shown from the top to the bottom. The spectra show signals of SiOH groups at framework defects, SiOHAl bridging hydroxyl groups, AlOH group.

H-ZSM-5 activated at 900 °C

4.2 ppm

4.2 ppm

4.2 ppm

11H MAS NMR of porous materialsH MAS NMR of porous materials11H MAS NMR of porous materialsH MAS NMR of porous materials

4 2 0 2 4 6 7 5 ppm

3 1 1 2

Bridging OH groups in small channels and cages of zeolites SiOHAl

Disturbed bridging OH groups in zeolite H-ZSM-5 and H-Beta SiOH

Bridging OH groups in large channels and cages of zeolites SiOHAl

Cation OH groups located in sodalite cages of zeolite Y and in channels of ZSM-5 which are involved in hydrogen bonds

CaOH, AlOH, LaOH OH groups bonded to extra-framework aluminium species which are located in cavities or channels and which are involved in hydrogen bonds

AlOH Silanol groups at the external surface or at framework defects

SiOH

Metal or cation OH groups in large cavities or at the outer surface of particles MeOH

2929Si MAS NMR spectrum of silicalite-1Si MAS NMR spectrum of silicalite-12929Si MAS NMR spectrum of silicalite-1Si MAS NMR spectrum of silicalite-1

SiO2 framework consisting of 24 crystallographic different silicon sites per unit cell (Fyfe 1987).

2929Si MAS NMRSi MAS NMR2929Si MAS NMRSi MAS NMR

130 110 90 70 60 80 ppm

100 120

Si(1 Zn)

Si(2 Zn)

zincosilicate-type zeolites VP-7, VPI-9 Q4

alkali and alkaline earth

silicates

Q0

Q2

Q1

Q4

Si(1 Al)

Si(0 Al)

Si(2 Al)

Si(3 Al)

Si(4 Al)

Si(3Si, 1OH)

aluminosilicate-type zeolites

Q3

Q4

Q3

Determination of the Si/Al ratio by Determination of the Si/Al ratio by 2929Si MAS NMRSi MAS NMRDetermination of the Si/Al ratio by Determination of the Si/Al ratio by 2929Si MAS NMRSi MAS NMR

For Si/Al = 1 the Q4 coordination represents a SiO4 tetrahedron that is surrounded by four AlO4-tetrahedra, whereas for a very high Si/Al ratio the SiO4 tetrahedron is surrounded mainly by SiO4-tetrahedra. For zeolites of faujasite type the Si/Al-ratio goes from one (low silica X type) to very high values for the siliceous faujasite. Referred to the siliceous faujasite, the replacement of a silicon atom by an aluminum atom in the next coordination sphere causes an additional chemical shift of about 5 ppm, compared with the change from Si(0Al) with n = 0 to Si(4Al) with n = 4 in the previous figure. This gives the opportunity to determine the Si/Al ratio of the framework of crystalline aluminosilicate materials directly from the relative intensities In (in %) of the (up to five) 29Si MAS NMR signals by means of the equation

4

0

400Al

Si

nnnI

Take-away message from this page:

Framework Si/Al ratio can be determined by 29SiMAS NMR. The problem is that the signals for n = 04 are commonly not well-resolved and a signal of SiOH (Q3) at about 103 ppm is often superimposed to the signal for n = 1.

2929Si MAS NMR shift and Si-O-Si bond angle Si MAS NMR shift and Si-O-Si bond angle 2929Si MAS NMR shift and Si-O-Si bond angle Si MAS NMR shift and Si-O-Si bond angle Considering the Q4 coordination alone, we find a spread of 37 ppm for zeolites in the previous figure. The isotropic chemical shift of the 29Si NMR signal depends in addition on the four Si-O bonding lengths and/or on the four Si-O-Si angles i, which occur between neighboring tetrahedra. Correlations between the chemical shift and the arithmetical mean of the four bonding angles i are best described in terms of

The parameter describes the s-character of the oxygen bond, which is considered to be an s-p hybrid orbital. For sp3-, sp2- and sp-hybridization with their respective bonding angles  = arccos(1/3)  109.47°, = 120°,  = 180°, the values  = 1/4, 1/3 and 1/2 are obtained, respectively. The most exact NMR data were published by Fyfe et al. for an aluminum-free zeolite ZSM-5. The spectrum of the low temperature phase consisting of signals due to the 24 averaged Si-O-Si angles between 147.0° and 158.8° (29Si NMR linewidths of 5 kHz) yielded the equation for the chemical shift

1coscos

44.216.287ppm Take away message from this page:

Si-O-Si bond angle variations by a distortion of the short-range-order in a crystalline material broaden the 29Si MAS NMR signal of the material.

2727Al MAS NMRAl MAS NMR2727Al MAS NMRAl MAS NMR

0 10 20 30 40 50 60 70 80 90 100 10 110 120 ppm

aluminates

aluminosilicates

aluminoborates

aluminophosphates

aluminates

aluminosilicates

aluminoborates

aluminophosphates

aluminates

aluminosilicates

aluminoborates

aluminophosphates

aluminosilicates

3-f

old

co

ord.

4-f

old

co

ordi

nate

d

5-f

old

co

ordi

nate

d

6-f

old

co

ordi

nate

d

20

2727Al MAS NMR shift and Al-O-T bond angleAl MAS NMR shift and Al-O-T bond angle2727Al MAS NMR shift and Al-O-T bond angleAl MAS NMR shift and Al-O-T bond angle

Aluminum signals of porous inorganic materials were found in the range -20 ppm to 120 ppm referring to Al(H2O)6

3+. The influence of the second coordination sphere can be demonstrated for tetrahedrally coordinated aluminum atoms: In hydrated samples the isotropic chemical shift of the 27Al resonance occurs at 7580 ppm for aluminum sodalite (four aluminum atoms in the second coordination sphere), at 60 ppm for faujasite (four silicon atoms in the second coordination sphere) and at 40 ppm for AlPO4-5 (four phosphorous atoms in the second coordination sphere).

In addition, the isotropic chemical shift of the AlO4 tetrahedra is a function of the mean of the four Al‑O‑T angles (T = Al, Si, P). Their correlation is usually given as

 /ppm = -c1  + c2.

c1 was found to be 0.61 for the Al-O-P angles in AlPO4 by Müller et al. and 0.50 for the Si-O-Al angles in crystalline aluminosilicates by Lippmaa et al. Weller et al. determined c1-values of 0.22 for Al-O-Al angles in pure aluminate-sodalites and of 0.72 for Si-O-Al angles in sodalites with a Si/Al ratio of one.

Aluminum has a nuclear spin I = 5/2, and the central transition is broadened by second-order quadrupolar interaction. This broadening is (expressed in ppm) reciprocal to the square of the external magnetic field. Line narrowing can in principle be achieved by double rotation or multiple-quantum procedures.

/

2727Al 3QMAS NMR study of AlPOAl 3QMAS NMR study of AlPO44-14 -14 2727Al 3QMAS NMR study of AlPOAl 3QMAS NMR study of AlPO44-14 -14

40 30 20 10 0

40

30

20

10

0

1/ ppm

2/ ppm

position 1

position 2

position 3

position 5

AlPO4-14, 27Al 3QMAS spectrum (split-t1-whole-echo, DFS pulse) measured at 17.6 T with a rotation frequency of 30 kHz.

The parameters CS, iso = 1.3 ppm, Cqcc = 2.57 MHz, = 0.7 for aluminum nuclei at position 1, CS, iso = 42.9 ppm, Cqcc = 1.74 MHz, = 0.63, for aluminum nuclei at position 2, CS, iso = 43.5 ppm, Cqcc = 4.08 MHz, = 0.82, for aluminum nuclei at position 3, CS, iso = 27.1 ppm, Cqcc = 5.58 MHz, = 0.97, for aluminum nuclei at position 5, CS, iso = 1.3 ppm, Cqcc = 2.57 MHz, = 0.7 were taken from Fernandez et al.

2277Al MAS NMR spectra Al MAS NMR spectra of a hydrothermally treated zeolite ZSM-5of a hydrothermally treated zeolite ZSM-5

2277Al MAS NMR spectra Al MAS NMR spectra of a hydrothermally treated zeolite ZSM-5of a hydrothermally treated zeolite ZSM-5

L = 195 MHz

Rot = 15 kHz

/ ppm

60 40 20 0 20 40 60 80 100

L = 130 MHz

Rot = 10 kHz

four-fold coordinated

five-fold coordinated

six-fold coordinated

Take-away message:

A signal narrowing by MQMAS or DOR is not possible, if the line broadening is dominated by distributions of the chemical shifts which are caused by short-range-order distortions of the zeolite framework.

Mobility of the Brønsted sites Mobility of the Brønsted sites and hydrogen exchange in zeolitesand hydrogen exchange in zeolites

Mobility of the Brønsted sites Mobility of the Brønsted sites and hydrogen exchange in zeolitesand hydrogen exchange in zeolites

O O O OO

OOO OO OO

Al SiSi Al

H

O

NH4+

OO

OO

Al

H

OO

OO

Al

H

OO

OO

Al

H

OO

OO

Al

H O O O OO

OOO OO OO

Al SiSi Al

H

O

Proton mobility of bridging hydroxyl groups in zeolites H-Y and H-ZSM-5 can be monitored in the temperature range from 160 to 790 K. The full width at half maximum of the 1H MAS NMR spectrum narrows by a factor of 24 for zeolite H-ZSM-5 and a factor of 55 for zeolite 85 H-Y. Activation energies in the range 20-80 kJ mol have been determined.

one-site jumps around one aluminum atom

O O O OO

OOO OO OO

Al SiSi Al

H

O

multiple-site jumps along several aluminum atoms

Narrowing onset and correlation timeNarrowing onset and correlation timeNarrowing onset and correlation timeNarrowing onset and correlation time

2,5 3,0 3,5 4,0 4,5 5,0 5,5 6,0

1

10

1000 T 1/ K 1

20

1,5 0,1

1

10

2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 1000 T 1/ K 1

fwh

m o

f th

e s

ide

ba

nd

en

velo

pe

/ kH

z

40 °C

120°C

3,2 kHz

17 kHz

The correlation time corresponds to the mean residence time of an ammonium ion at an oxygen ring of the framework.

2H NMR, H-Y: at50 °Cc=5 µs 1H NMR, H-Y: at 40 °C c=20 µs 2H NMR, H-ZSM-5: at 120 °C c=3,8 µs

 = rigid/2

rigidc 1

1

 = rigid/2

2H MAS NMR, deuterated zeolite H-ZSM-5, loaded with 0.33 NH3 per crossing

1H MAS NMR, zeolite H-Y, loaded with mit 0.6  NH3 per cavity

The correlation time corresponds to the mean residence time of an ammonium ion at an oxygen ring of the framework.

1D 1D 11H EXSY (exchange spectroscopy)H EXSY (exchange spectroscopy)1D 1D 11H EXSY (exchange spectroscopy)H EXSY (exchange spectroscopy)

Evolution time t1 = 1/4 .

denotes the frequency difference of the exchanging species.

MAS frequency should be a multiple of

Two series of measurements should be performed at each temperature: Offset  right of the right signal and offset  left of the left signal.

0

tm

time

/2

FID t1

/2 /2t2

EXSY pulse sequence

Result of the EXSY experimentResult of the EXSY experimentResult of the EXSY experimentResult of the EXSY experiment

Stack plot of the spectra of zeolite H-Y loaded with 0.35 ammonia molecules per cavity. Mixing times are between tm = 3 s and15 s.

0 2 4 6 8 10 12

ammonium ions

OH

Intensity

0 2 4 6 8 10 12

mixing time tm / s

/ ppm 10 0

97 °C

Intensities of the signals of ammonium ions and OH groups for zeolite H-Y loaded with 1.5 ammonia molecules per cavity. Measured at 87 °C in the field of 9,4 T. The figure on the top and bottom correspond to offset on the left hand side and right hand side of the signals, respectively.

Basis of the data processingBasis of the data processingBasis of the data processingBasis of the data processing

0AmmmAA exp1exp12

1)( MD

DtD

DtI

t

0BmmmBB exp1-exp12

1)( MD

DtD

DtI

t

D

MtDσtDσ

DMtDσtDσtItI

A0Bmm

B0AmmmBAmAB

1expexp

2

1

1expexp

2

1)()(

BBAA2

1LL 2

1

ABAB2 LLD BBAA2

1LL

diagonal peaks

cross peaks

BA

BA

B1

A1

BBBA

ABAA

11

11

10

01KRL

T

T

LL

LL

dynamic matrix (without spin diffusion):

Laser supported Laser supported 11H MAS NMR of H-zeolitesH MAS NMR of H-zeolitesLaser supported Laser supported 11H MAS NMR of H-zeolitesH MAS NMR of H-zeolites

Spectra (at left) and Arrhenius plot (above) of the temperature dependent 1H MAS NMR measurements which were obtained by laser heating. The zeolite sample H-Y was activated at 400 °C.

20 0 20 40 40 / ppm

297 K

723 K

773 K

673 K

423 K

573 K

623 K

1.0 1.5 2.0 2.5 3.0 3.5 0.1

1

10

1000 T / K

1/

2 /

kHz

Proton transfer between Brønsted sites and Proton transfer between Brønsted sites and benzene molecules in zeolites H-Ybenzene molecules in zeolites H-Y

Proton transfer between Brønsted sites and Proton transfer between Brønsted sites and benzene molecules in zeolites H-Ybenzene molecules in zeolites H-Y

In situ 1H MAS NMR spectroscopy of the proton transfer between bridging hydroxyl groups and benzene molecules yields temperature dependent exchange rates over more than five orders of magnitude.

H-D exchange and NOESY MAS NMR experiments were performed by both conventional and laser heating up to 600 K.

Exchange rate Exchange rate as a dynamic measure of Brønsted acidityas a dynamic measure of Brønsted acidity

Exchange rate Exchange rate as a dynamic measure of Brønsted acidityas a dynamic measure of Brønsted acidity

Arrhenius plot of the H-D and H-H exchange rates for benzene molecules in the zeolites 85 H-Y and 92 H-Y. The values which are marked by blue or red were measured by laser heating or conventional heating, respectively.

The variation of the Si/Al ratio in the zeolite H-Y causes a change of the deprotonation energy and can explain the differences of the exchange rate of one order of magnitude in the temperature region of 350600 K. However, our experimental results are not sufficient to exclude that a variation of the pre-exponential factor caused by steric effects like the existence of non-framework aluminum species is the origin of the different rates of the proton transfer.

10

10

10

10

1.5 2.71.9 2.3

92 H-Y

85 H-Y

1000

T/K

k /min

In situ monitoring of catalytic conversion of In situ monitoring of catalytic conversion of molecules in zeolites by molecules in zeolites by 11H, H, 22H and H and 1313C MAS NMRC MAS NMR

In situ monitoring of catalytic conversion of In situ monitoring of catalytic conversion of molecules in zeolites by molecules in zeolites by 11H, H, 22H and H and 1313C MAS NMRC MAS NMR

Kinetics of a double-bond-shift reaction, hydrogen exchange and 13C-label scrambling of n-butene in H-ferrierite

6 4 2 0 / ppm

–CH= 5.6

CH3– 1.7

65 min

4 min

1H MAS NMR spectra of n-but-1-ene-d8 adsorbed on H-FER2 (T=360K). Hydrogen transfer occurs from the acidic hydroxyl groups of the zeolite to the deuterated butene molecules. Both methyl and methene groups of but-2-ene are involved in the H/D exchange. The ratio between the intensities of the CH3 and CH groups in the final spectrum is 3:1.

*

**

*

**

*

126

200 160 120 80 40 0 / ppm

17

13

*

17 min at 323 K

20 h at 323 K

*

**

*

**

*

126

200 160 120 80 40 0 / ppm

17

13

*

17 min at 323 K

20 h at 323 K

13C CP/MAS NMR spectra of [2-13C]-n-but-1-ene adsorption on H-FER in dependence on reaction time. Asterisks denote spinning side-bands. The appearance of the signals at 13 and 17 ppm and decreasing intensity of the signal at 126 ppm show the label scrambling.

1.7

5.0 2.0

0 2 4 6 / ppm

1.0

5.9

5 min

18.5 h

2H MAS NMR spectra of n-but-1-ene-d8 adsorbed on H‑FER (T = 333K). n-But-1-ene undergoes readily a double-bond-shift reaction, when it is adsorbed on ferrierite. The reaction becomes slow enough to observe the kinetics , if the catalyst contains only a very small concentration of Brønsted acid sites.

MAS PFG NMR for NMR diffusometryMAS PFG NMR for NMR diffusometryMAS PFG NMR for NMR diffusometryMAS PFG NMR for NMR diffusometry

1.02.0 / ppmΔδ

CH3 (n-but)CH3 (iso)

CH2 (n-but)

CH (iso)

Δδ = 0.4 ppm

gradientstrength

MAS PFG NMR diffusion experiment

om 54.7

3

1cosarcθ

rotor with samplein the rf coil zr

g gradient pulses

rot

θm

gradient coil

B0

3

4exp/

2

0g

DSS

0.51.01.52.0

δ = 0.02 ppm

ppm

-2024ppm

* * ****

ωr = 0 kHzωr = 1 kHz

ωr = 10 kHz

FAU Na-X , n-butane + isobutane

rf pulses

g pulses

FID

g

Gz

r. f.

T

ecd

MAS PFG NMR studies of the self-diffusion MAS PFG NMR studies of the self-diffusion of acetone-alkane mixtures in nanoporous silica gelof acetone-alkane mixtures in nanoporous silica gel

MAS PFG NMR studies of the self-diffusion MAS PFG NMR studies of the self-diffusion of acetone-alkane mixtures in nanoporous silica gelof acetone-alkane mixtures in nanoporous silica gel

The self-diffusion coefficients of mixtures of acetone with several alkanes were studied by means of magic-angle spinning pulsed field gradient nuclear magnetic resonance (MAS PFG NMR). Silica gels with different nanopore sizes at ca. 4 and 10 nm and a pore surface modified with trimethylsilyl groups were provided by Takahashi et al. (1). The silica gel was loaded with acetone –alkane mixtures (1:10). The self-diffusion coefficients of acetone in the small pores (4 nm) shows a zigzag effect depending on odd or even numbers of carbon atoms of the alkane solvent as it was reported by Takahashi et al. (1) for the transport diffusion coefficient.

(1) Ryoji Takahashi, Satoshi Sato, Toshiaki Sodesawa and Toshiyuki Ikeda: Diffusion coefficient of ketones in liquid media within mesopores;Phys. Chem. Chem. Phys.5 (2003) 2476–2480

0,00 0,05 0,10 0,15 0,20 0,250,01

0,1

1 = 600 ms = 2 ms

Em / acetone + alkane (C6,C

7,C

8,C

9)

S /

S0

g 2 / T 2m-2

nonane C9

octane C8

heptane C7

hexane C6

Semi-logarithmic plot of the decay of the CH3 signal of ketone in binary mixture with acetone at 298 K. The diffusion time is = 600 ms and a gradient pulse length is = 2 ms:

/ ppm0.40.81.

21.62.02.42.8

CH3

CH3

CH2

acetone

octane

gradient

strength

Stack plot of the 1H MAS PFG NMR spectra at 10 kHz of the 1:10 acetone and octane mixture absorbed in Em material as function of increasing pulsed gradient strength for a diffusion time = 600 ms:

6 7 8 9 10

8,0x10-12

1,0x10-11

1,2x10-11

1,4x10-11

Acetone diffusivity in alkane mixture

D /

m2 s-1

Carbon number of alkane solvent

% ( = 600 ms) % ( = 800 ms) % ( = 1200 ms) Diffusion coefficient of acetone in mixture within Em

in dependence of the number of carbons in the alkane solvent. The measurements were carried out with diffusion time = 600 ms, = 800 ms and = 1200 ms and the gradient pulse length = 2 ms.

Horst ErnstMoisés FernándezClemens Gottert

Johanna KanellopoulosBernd Knorr

Thomas LoeserToralf Mildner

Lutz MoschkowitzDagmar Prager

Denis SchneiderAlexander Stepanov

Deutsche ForschungsgemeinschaftMax-Buchner-Stiftung

I acknowledge

support from