Diasteroselective structure directing effect of (1 S,2 S)-2-hydroxymethyl- 1-benzyl-1-methylpyrrolidinium in the synthesis of ZSM-12

Article abstract of DOI:10.1021/cm903095q

The chiral cation (1S,2S)-2-hydroxymethyl-1-benzyl-1-methylpyrrolidinium (bmpm) and a 50% mixture of this with its diastereoisomer (1R,2S)-2- hydroxymethyl-1-benzyl-1-methylpyrrolidinium have been prepared and tested as structure directing agents (SDAs) i

Full text of DOI:10.1021/cm903095q

2276 Chem. Mater. 2010, 22, 2276–2286
DOI:10.1021/cm903095q
Diasteroselective Structure Directing Effect of
(1S,2S)-2-Hydroxymethyl-1-benzyl-1-methylpyrrolidinium
in the Synthesis of ZSM-12
,†
Raquel Garcıa,* Luis Gomez-Hortiguela, Felix Sanchez, and Joaquın Perez-Pariente
†,‡
§
†
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ꢀ
†
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Instituto de Catalisis y Petroleoquımica (CSIC), C/Marie Curie 2, 28049 Cantoblanco, Madrid, Spain,
‡Department of Chemistry, Third Floor, Kathleen Lonsdale Building, University College London, Gower
§
Street, WC1E 6BT, London, United Kingdom, and Instituto de Quımica Organica General (CSIC), C/Juan
´
de la Cierva, 3, 28006, Madrid, Spain
ꢀ
Received October 6, 2009. Revised Manuscript Received February 8, 2010
The chiral cation (1S,2S)-2-hydroxymethyl-1-benzyl-1-methylpyrrolidinium (bmpm) and a 50%
mixture of this with its diastereoisomer (1R,2S)-2-hydroxymethyl-1-benzyl-1-methylpyrrolidinium
have been prepared and tested as structure directing agents (SDAs) in the synthesis of pure-silica
zeolites in fluoride medium. The S,S isomer has been shown to efficiently direct the crystallization of
zeolite ZSM-12 (MTW); in contrast, the use of a mixture of the two diastereoisomers as a SDA does
not lead to the formation of the ZSM-12 structure under the same synthesis conditions, thus
suggesting a lower efficiency of the R,S isomer to direct the crystallization of the structure.
A computational study based on molecular mechanic simulations allowed explanation of the efficient
structure directing role of the S,S isomer in terms of a high host-guest interaction due to a strong
structural relationship between the MTW topology and the molecular geometry of the S,S isomer.
However, the simulations revealed that the interaction developed by the R,S diasteroisomer with the
MTW framework is smaller due to a worse fitting of its molecular structure with the zeolite topology,
providing an explanation for the experimental observations.
Introduction
of chiral catalytic reactions or result in enantioselective
sorption or separation processes, therefore allowing for
obtaining optically pure chiral products.3
Nowadays, there is an increasing demand for enantio-
merically pure compounds in the pharmaceuticals and
fine chemicals industries which prompts a strong interest
in processes able to differentiate chiral enantiomers, such
as the resolution of racemic mixtures and asymmetric
synthesis reactions. The design of solid sorbents and
heterogeneous catalysts with combined shape selectivity
and enantioselectivity represents a particularly attractive
option, where microporous materials (including zeolites
and zeotypes) are excellent candidates to achieve this
goal. Zeolites are a class of crystalline microporous
molecular sieves whose network is comprised of corner-
sharing SiO4 and AlO4 tetrahedral units, giving place to a
periodic three-dimensional microporous framework. The
structure of these materials is comprised of pores and
cavities of molecular dimensions, which together with
their wide structural and compositional chemistry and
their stability provides a range of potential applications to
these materials, which are used as shape selective cata-
lysts, adsorbents, and ion exchangers.1,2 In this context,
chirality is one of the most desirable properties for a
zeolite structure since the constrained geometry of its
framework could eventually control the stereoselectivity
Several approaches have been attempted to introduce
chirality in zeolite materials. The most promising ap-
proach to date is the immobilization of homogeneous
chiral catalysts inside the inorganic solid matrix,4 thus
easing the processes of separation, handling, and recovery
of the chiral catalysts. Some enantioselectivity has also
been achieved by anchoring chiral modifiers to the micro-
porous materials, in the vicinity of the active sites.5 In
these cases, the zeolitic host might also give additional
selectivity by molecular sieving effects.6 However, in both
cases the chiral information is contained in the molecular
component attached to an otherwise achiral solid. A more
interesting approach comes from the synthesis of an
intrinsically chiral framework, in which chirality is imprinted
in the inorganic solid. Among the known zeolite structures,
only a few of them are known to contain chiral channels,7
though in a recent paper 20 more zeolite structures have
been recognized as possessing chiral networks;8 indeed,
(3) Davis, M. E. Top. Catal. 2003, 25, 3.
(4) Mc Morn P.; Hutchings, G. J. Chem. Soc. Rev., 2004, 33, 108, and
references therein.
(5) Davis, M. E. Microporous Mesoporous Mater., 1998, 21, 173, and
references therein.
(6) Bedioui, F. Coord. Chem. Rev. 1995, 144, 39.
(7) Yu, J.; Xu, R. J. Mater. Chem. 2008, 18, 4021.
(8) Dryzun, C.; Mastai, Y.; Shvalb, A.; Avnir, D. J. Mater. Chem.
2009, 19, 2062.
*Corresponding author. Phone: þ 34 91 5854796. E-mail: rgs@icp.csic.es.
(1) Davis, M. E. Nature 2002, 417, 813.
(2) Corma, A. J. Catal. 2003, 216, 298.
r
pubs.acs.org/cm
Published on Web 03/04/2010
2010 American Chemical Society

Article
Chem. Mater., Vol. 22, No. 7, 2010 2277
in this work the authors demonstrated that chiral zeolites
are actually able to perform enantioselective operations.
Very recently, a new chiral zeolite topology has been
discovered.9
in the synthesis of SSZ-56;17 the polycyclic SDA used in
the synthesis of zeolite SSZ-73 (SAS);18 or the cis and
trans isomers of N,N-diethyldecahydroquinolinium, which
direct the crystallization of several different zeolite struc-
tures for each of them.19
Zeolite beta is the commonly cited example of a chiral
zeolite structure. This zeolite is a heavily intergrown
material constituted of at least three closely related
structures, polymorphs A, B, and C. Polymorph A is in
the form of two enantiomorphs containing a helical pore
along the c-axis,10 while polymorphs B and C do not show
chirality. In recent years, polymorphs B and C have been
synthesized as pure phases,11,12 but to date, it has not been
possible to obtain polymorph A as a pure phase. It was
reported that a zeolite beta enriched in polymorph A was
obtained by using a chiral SDA, and this sample of zeolite
beta was capable of performing enantioselective adsorp-
tion and catalysis, yielding a low enantiomeric excess.13
The hydrothermal synthesis of zeolite materials often
requires the presence of organic molecules, usually called
structure directing agents (SDAs), which organize the
inorganic tetrahedral units into a particular topology
around themselves, therefore providing the initial build-
ing blocks for further crystallization of a particular
structure type.14 These organic molecules are encapsu-
lated within the void space of the nascent frameworks,
thus keeping occluded after the crystallization process.
Hence the size and shape of the SDA plays an important
role in determining the outcome of zeolite syntheses;
actually, there is usually some correlation between the
shape of the molecule and that of the pores crystallized in
its presence.15 In this context, the main strategy tradi-
tionally followed to synthesize a chiral zeolite framework
is the use of an asymmetric organic molecule as a structure
directing agent to impart chirality into the inorganic
framework. For a transfer of the chirality from the
SDA molecule to the inorganic framework to occur, a
close structural relationship between the host and the
guest species should exist. In this regard, it is worth
mentioning that, in some cases, the structure directing
effect of organic molecules in the synthesis of zeolite
materials is so strong that different isomers of the same
organic molecule can show different phase selectivities.
Some examples of this behavior are the different structure
directing effect that exert the diastereoisomers of the
cation 4,40-trimethylenebis(1-benzyl-1-methylpiperidinium)
on the synthesis of zeolite beta;16 the specificity of the
transisomerofN,N-diethyl-2-methyldecahydroquinolinium
Recent work in our group has demonstrated the effi-
cient structure directing role of (S)-N-benzyl-2-pyrrolidi-
nemethanol in the synthesis of AFI-type microporous
aluminophosphates.20,21 In these works, we observed that
the use of this molecule as a SDA provides a rich
supramolecular chemistry that can enhance its molecular
chiral nature and thus the eventual transfer of the chir-
ality to the microporous framework. On the basis of these
grounds, we have studied in this work the structure
directing effect of a related molecule, 2-hydroxymethyl-
1-benzyl-1-methylpyrrolidinium (bmpm), in the synthesis
of all-silica zeolites. In this case, the attachment of a
methyl group to the tertiary amine provides a more rigid
asymmetric atom in the SDA molecule, what could
eventually enhance the chiral character of the SDA,
favoring in principle the transfer of chirality to the frame-
work. Besides, the presence of two rings (phenyl and
pyrrolidine) provides to this molecule a high rigidity, a
feature that is also required for a transfer of the chirality
to the nascent framework, provided a strong structure
directing effect occurs. In this work we report the results
we have obtained using the S,S diasteroisomer alone as
well as a mixture of the S,S and R,S diastereisomers of the
chiral cation bmpm as SDA. The synthesis and charac-
terization of the materials are complemented with a
molecular modeling study aimed to understand the dif-
ferent structure directing efficiency of the S,S and R,S
diasteroisomers for the synthesis of the zeolite. A second-
ary aim of this study is to experimentally validate the
theoretical predictions provided by the computational
simulations by using a single diasteroisomer and a mix-
ture of both diastereoisomers in the synthesis of the
zeolite.
Experimental Section
Synthesis of SDA Cation. Both the pure S,S diastereoisomer
and the mixture of R,S and S,S diastereoisomers were prepared
according to Figure 1. As shown in this figure, the different
products are obtained depending on the initial tertiary amine,
making use of the different steric constraint provided by the
methyl or benzyl groups.
To prepare the pure S,S bmpm diastereoisomer (route 1), the
starting amine (S)-1-benzyl-2-pyrrolidinemethanol was methy-
lated in order to obtain the quaternary ammonium cation,
(1S,2S)-2-hydroxymethyl-1-benzyl-1-methylpyrrolidinium (bmpm)
iodide. In a typical preparation, 50.0 g of (S)-1-benzyl-2-pyrro-
lidinemethanol (Aldrich, 97%) were added over a solution
of 55.66 g of CH3I (50% exc., Fluka) in ethanol. After stirring
~
(9) Sun, J.; Bonneau, C.; Cantın, A.; Corma, A.; Dıaz-Cabanas, M. J.;
Moliner, M.; Zhang, D.; Li, M.; Zhou, X. Nature 2009, 458, 1154.
(10) Treacy, M. M. J.; Newsam, J. M. Nature 1988, 332, 249.
~
(11) Corma, A.; Moliner, M.; Cantin, A.; Dıaz-Cabanas, M. J.; Jorda,
J. L.; Zhang, D.; Sun, J.; Jansson, K.; Hovmoller, S.; Zou, X. Chem.
€
Mater. 2008, 20, 3218.
(12) Cantin, A.; Corma, A.; Dıaz-Cabanas, M. J.; Jorda, J. L.; Moliner,
~
(18) Kim, C.; Hwang, S.-J.; Burton, A. W.; Zones, S. I. Microporous
Mesoporous Mater. 2008, 116, 227.
M.; Rey, F. Angew. Chem., Int. Ed. 2006, 45, 8013.
(13) Davis, M. E.; Lobo, R. F. Chem. Mater. 1992, 4, 756.
(14) Cundy, C. S.; Cox, P. A. Chem. Rev. 2003, 103, 663.
(15) Gies, H.; Marler, B. Zeolites 1992, 12, 42.
(16) Tsuji, K.; Beck, L. W.; Davis, M. E. Microporous Mesoporous
Mater. 1999, 28, 519.
(19) Lee, G. S.; Nakagawa, Y.; Hwang, S.-J.; Davis, M. E.; Wagner, P.;
Beck, L.; Zones, S. I. J. Am. Chem. Soc. 2002, 124, 7024.
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J. Phys. Chem. Chem. Phys. 2006, 8, 486.
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(21) Gomez-Hortiguela, L.; Blasco, T.; Perez-Pariente, J. Microporous
(17) Elomari, S.; Burton, A.; Medrud, R. C.; Grosse-Kunstleve, R.
Microporous Mesoporous Mater. 2009, 118, 325.
Mesoporous Mater. 2007, 100, 55.

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2278 Chem. Mater., Vol. 22, No. 7, 2010
Figure 1. Schematic view of the two attacks that take place in the synthesis of (1) the pure S,S diasteroisomer (route 1, top) and (2) the mixture of
diasteroisomers (route 2, bottom), showing the diasteroisomers that are formed depending on the initial reactant used.
The amount of each isomer was determined from the integral
1
measures of the H NMR spectrum of the iodide salt of the
mixture of isomers (see the Supporting Information). The iodide
form of the mixture of isomers was obtained by stirring an
equimolecular amount of the chloride salt previously synthe-
sized and potassium iodide (Aldrich) in acetone. The potassium
chloride is separated by filtration, and the acetone is evaporated
to yield the final solid product quantitatively.
The hydroxide forms of the quaternary ammonium salts,
(1S,2S)-2-hydroxymethyl-1-benzyl-1-methylpyrrolidinium (bmpm)
iodide, and the mixture of (1S,2S)- and (1R,2S)-2-hydroxy-
methyl-1-benzyl-1-methylpyrrolidinium (bmpm) chloride were
obtained by ion exchange with an anionic resin (Amberlite
IRN-78; exchange capacity, 4 meq/g; Supelco). The hydroxide
concentration of the SDA solution was determined by titration
with a 0.05 M HCl solution (Panreac) using phenolphthalein
(Aldrich) as an indicator.
Figure 2. 13C NMR spectrum of the product from synthesis route 1, the
iodide salt of the pure S,S-bmpm (a) or route 2, the chloride salt of the
mixture of diastereoisomers SS and RS of bmpm (b).
Zeolite Synthesis. The S,S pure bmpm isomer or the mixture
of isomers were employed as SDAs in pure silica preparations in
fluoride medium. In a typical experiment, 9.79 g of tetraethyl-
orthosilicate (TEOS, Aldrich, 98%) were hydrolyzed over 15.41 g
of the hydroxide aqueous solution (36%) of the SDA. The
mixture was stirred until the excess of water over that required
to reach the desired composition was evaporated, and then 1.04 g
of HF (Panreac, 48%) was added and mixed to create a
homogeneous gel of composition 0.54 bmpmOH/0.54 HF/1
SiO2/4.7 H2O. The gel was introduced into 20 mL Teflon-lined
stainless steel autoclaves, which were heated statically under
autogenous pressure for selected periods of time (Table 1). The
solid products were recovered by filtration, washed with water
and ethanol, and dried at room temperature overnight. Selected
samples were calcined at 550 °C under a continuous flow of N2
(100 mL/min) for 1 h followed by air (100 mL/min) for 6 h in
order to remove the occluded organic material.
for 5 days at room temperature, the ethanol was removed under
vacuum at 60 °C. The final solid product (∼81% yield) was
exhaustively washed with diethyl ether, recrystallized from acetone
(mp 143-144 °C), and characterized by 13C and 1H nuclear
magnetic resonance (NMR) (Figure 2) and chemical CHN analy-
sis. (Calculated for C13H20NOI: C = 46.8, H = 6, N = 4.2.
Found: C = 47.1, H = 5.9, N = 4.3).
A mixture of the S,S and R,S diastereoisomers was prepared
according to route 2 by benzylation of (S)-1-methyl-2-pyrrolidine-
methanol. A total of 13.02 g of (S)-1-methyl-2-pyrrolidinemethanol
(96%, Aldrich) was added over a solution of 20.57 g (50% exc.) of
benzylchloride (99%, Aldrich) in ethanol. After 24 h of stirring at
room temperature, the ethanol was removed under vacuum to yield
the final solid product (∼89% yield). The solid was exhaustively
washed with diethyl ether, dried, and characterized by 13C NMR
and chemical CHN analysis. (Calculated for C13H20NOCl: C =
64.6, H = 8.3, N = 5.8. Found: C = 63.7, H = 8.3, N = 5.7).
Characterization. Powder X-ray diffraction (XRD) patterns
were recorded on a Panalytical X’Pro diffractometer using Cu
KR radiation. Thermogravimetric analyses (TGA) were carried
out on a Perkin-Elmer TGA7 instrument. The samples were

Article
Chem. Mater., Vol. 22, No. 7, 2010 2279
Table 1. Syntheses Conditions and Products of Hydrothermal Synthesis
Performed with the Pure SS bmpm Isomer and the Mixture of the RS and
SS Isomers, For a Gel Composition of 0.54 bmpmOH/0.54 HF/
1 SiO2/4.7 H2O
SDA-SDA interactions. The atomic charges for the organic
molecules were calculated by the charge-equilibration method,28
setting the total net molecular charge to þ1. In the true synth-
esis, the positive charge of the organic SDA molecules is
compensated by the presence of the negatively charged frame-
work (and/or fluoride ions) defects. However, because of the ill-
defined nature of these defects as well as the unability of CVFF
to model them, charge compensation was provided in our
models by the framework by using a related version of the
uniform charge background method,29 where the atomic charge
for every silicon framework atom was reduced until charge
neutrality. Framework oxygen charges were kept fixed to -1.2.
The most stable location for the SDA molecules was obtained
by means of simulated annealing calculations, which consisted
of heating of the system from 300 to 700 K with temperature
increments of 10 K and then cooling to 300 K again in the same
way. A total of 500 MD steps of 1.0 fs (for a total of 0.5 ps) were
run in every heating/cooling step. This cycle was repeated 10
times, and at the end of each cycle the system was geometry
optimized. Then, the most stable situation was taken as repre-
sentative for subsequent analysis of the location and interaction
energy. The interaction energies were calculated by subtracting
the energy of the molecules in vacuo to the total energy of the
system.
gel
T (°C)
t (days)
product
SS-150-25
SS-150-37
SS-135-25
SS-135-37
SS-135-6
SS-135-12
SS-135-16
SS-135-26
RSSS-135-13
RSSS-135-16
RSSS-1-11b
RSSS-1-22b
RSSS-2-14c
150
150
135
135
135
135
135
135
135
135
135
135
135
25
37
25
37
6
12
16
26
13
16
11
22
14
ZSM-12
ZSM-12
ZSM-12
ZSM-12
Aa
ZSM-12þA
ZSM-12
ZSM-12
A
A
A
A
mixture
a Amorphous. b 0.54 bmpmCl were added to this gel. c Gel seeded with
5 wt % of ZSM-12.
heated in air, and the temperature ramp was 20 °C/min.
Chemical analyses were obtained from a Perkin-Elmer 2400
CHN analyzer. Scanning electron microscopy and EDX ana-
lyses were carried out using a JEOL JSM 6400 Philips XL30
operating at 20 kV. 1H and 13C NMR spectra of organic
compounds were recorded on a Bruker200. Chemical shifts
are quoted relative to tetramethylsilane (TMS) as an internal
reference. Solid state nuclear magnetic resonance magic angle
spinning (MAS) NMR spectroscopy was performed on a Bruker
AV 400 spectrometer using a BL7 probe for 13C and a BL2.5
Results and Discussion
1. Synthesis and Characterization of the Diastereo-
isomers. The use of the related achiral 1-benzyl-1-methyl
pyrrolidinium (bmp) as SDA in pure silica preparations
in fluoride medium is known to yield zeolite beta,30 which
as commented above possesses one chiral polymorph.
Therefore, in an attempt to direct the crystallization of
this zeolite toward the chiral polymorph A, we decided to
replace bmp with a related but chiral cation, bmpm, in
which the presence of two asymmetric atoms provides a
chiral environment that could eventually favor the crys-
tallization of the chiral polymorph of zeolite beta.
There are two asymmetric atoms in the bmpm mole-
cule: one is the CR of the pyrrolidine ring where the
methanol substituent is attached, and the other one is
the N atom that becomes asymmetric after the attach-
ment of the methyl group (Figure 1). The absolute con-
figuration of the former is certainly S in all salts, since the
SDA molecule is synthesized starting from the pure chiral
reactants (S)-(-)-N-benzylpyrrolidine-2-methanol or (S)-
1-methyl-2-pyrrolidinemethanol, both with C in the S
configuration (which indeed are derived from the L-pro-
line amino acid); such an absolute configuration will
remain in the final SDA product, since the organic
reactions carried out in order to yield the final SDA
molecule do not involve any transformation on the
asymmetric C atom that is conformationally stable in
proline derivatives.
1
1
probe for F. H to 13C cross-polarization (CP) spectra were
recorded using π/2 rad pulses for the proton of 4.5 μs and a
recycle delay of 3 s; the samples were span at the magic angle at a
rate of 5-5.5 kHz. The 19F spectra were measured using pulses
of 4.5 μs to flip the magnetization π/2 rad, with delays of 80 s
between two consecutive pulses and spinning rates of approxi-
mately 20 kHz.
Computational Details. A computational study was carried
out in order to study the most stable location of both diaster-
oisomers within the MTW structure. The computational meth-
odology employed in this work is based on similar protocols that
we have been recently using for studying structure directing
effects in the crystallization of the FER or AFI structures.20,22-24
The geometry of the MTW structure has been kept fixed during
all the calculations. Molecular structures and the interaction
energies of the organic SDAs with the framework are described
with the consistent valence forcefield (CVFF);25 this force field
was originally developed for small organic molecules but has
been extended for materials science applications including the
simulation of zeolite and related structures, for which it has been
successfully applied recently.21-23,26,27 van der Waals and elec-
trostatic interactions were calculated by the Ewald summation.
Periodic boundary conditions (PBC) were applied in all the
calculations in order to ensure the complete inclusion of
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Besides, if the methyl group is attached in the last step
(route 1), once the benzyl group is already attached to the
molecule, methylation of the N atom to produce the final
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J. J. Am. Chem. Soc. 2004, 126, 12097.
(25) Dauger-Osguthorpe, P.; Roberts, V. A.; Osguthorpe, D. J.; Wolff,
J.; Genest, M.; Hagler, A. T. Proteins: Struct., Funct., Genet. 1988,
4, 21.
(28) Rappe, A. K.; Goddard, W. A., III. J. Phys. Chem. 1995, 95, 3358.
(29) De Vita, A.; Gillan, M. J.; Lin, J. S.; Payne, M. C.; Stich, I.; Clarke,
J. L. Phys. Rev. B 1992, 46, 12964.
(26) Moloy, E. C.; Cygan, R. T.; Bonhomme, F.; Teter, D. M.;
Navrotsky, A. Chem. Mater. 2004, 16, 2121.
(27) Williams, J. J.; Smith, C. W.; Evans, K. E.; Lethbridge, Z. A. D.;
Walton, R. I. Chem. Mater. 2007, 19, 2423.
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2280 Chem. Mater., Vol. 22, No. 7, 2010
quaternary ammonium goes through only one side of the
N atom, the opposite one to the benzyl group, due to
steric reasons, thus giving place to the S absolute config-
uration for the N atom in the final bmpm molecule31
(Figure 1, top). Therefore, only the S,S-bmpm diastero-
isomer (hereinafter, the first letter refers to the N absolute
configuration and the second one to the C absolute
configuration) is obtained. However, when the quatern-
ary ammonium cation is synthesized by benzylation of the
pure chiral reactant (S)-(-)-N-methylpyrrolidine-2-met-
hanol, due to the smaller size of the methyl substituent,
the attack of benzyl chloride to the N atom can take place
through both sides of the pyrrolidine ring, thus leading to
a mixture of both the S,S- and the R,S-bmpm diastero-
isomers (Figure 1, bottom).
The quaternary ammonium products synthesized by
both routes possess CHN compositions that are close to
the expected values: calculated for C13H20NOI: C = 46.8,
H = 6.0, N = 4.2. Found: C = 47.1, H = 5.9, N = 4.3
and calculated for C13H20NOCl: C = 64.6, H = 8.3, N =
5.8. Found: C = 63.7, H = 8.3, N = 5.7. Figure 2
compares the 13C NMR spectra of the products. In the
case of the product obtained by methylation (route 1),
there is only one type of carbon atom, evidencing the
presence of a unique isomer, while in the spectrum of the
product obtained by benzylation, there are more peaks
corresponding to analogous carbons in different isomers.
These results show that the product obtained by route 2 is
a mixture of both the S,S and the R,S isomers. From the
1H NMR spectra, we estimated the approximate ratio of
the two isomers in this product as ∼50% (see the Sup-
porting Information).
Figure 3. X-raydiffractionpatternofcrystallizationofZSM-12 at 135°C
with the S,S bmpm isomer (a) 6 days, (b) 12 days, (c) 16 days, (d) 26 days,
and (e) with the mixture of S,S- and R,S-bmpm isomers after 16 days of
crystallization (RSSS-135-16).
2. Structure Directing Effect of S,S-bmpm. 2.a. Mole-
cular-Sieve Synthesis and Characterization. We initially
studied the structure directing effect of the pure S,S-
bmpm isomer in the synthesis of all-silica zeolites in
fluoride medium. Table 1 shows the synthesis conditions
and the products obtained. Hereafter, the samples will be
referred to with the isomer used in the synthesis, followed
by the temperature and time of crystallization. The XRD
patterns of the as-prepared samples indicate that this
isomer efficiently directs the formation of highly crystal-
line ZSM-12 at temperatures of 135 and 150 °C; indeed,
the zeolite is stable at both temperatures at least for as
long as 25 days. It is noticeable that while the related
cation bmp in similar preparations yielded zeolite beta as
the only product,30 the samples obtained with S,S-bmpm
under similar conditions do not even show the presence of
traces of beta at any time. Zeolite beta is considered to be
a “default” phase in pure silica preparations in fluoride
medium since it has been obtained with numerous
SDAs.32 However, bmpm does not yield this phase, sug-
gesting that small changes in the molecular structure of
the organic SDA have a profound effect in the products
of crystallization. ZSM-12 (MTW) is a high-silica zeolite
Figure 4. 13C MAS NMR spectra of the (a) iodide salt of (1S,2S)-
2-hydroxymethyl-1-benzyl-1-methylpyrrolidinium and (b) sample
SS-135-25.
that possesses a monodimensional 12-ring channel system
along the b-axis of the structure.33 Indeed, beta and ZSM-
12 have in common the projection of the structure along
this channel, i.e., the projection of the structure of ZSM-
12 along the 12-ring channel is the same as the projection
along the a and b axes of the structure of zeolite beta.34
In order to study the kinetics of crystallization of this
zeolite with the S,S-bmpm isomer, we prepared a second
batch and heated the autoclaves at 135 °C for shorter
crystallization times. Figure 3 shows the X-ray diffraction
patterns of the products obtained after 6, 12, 16, and 26 d.
We can clearly observe that zeolite ZSM-12 starts to
crystallize at 12 days of heating (only amorphous material
is observed in the sample heated for 6 days). After 16 days,
the zeolite has crystallized almost completely, and no
€
(31) Dehmlow, E. V.; Klauck, R.; Duttmann, S.; Neumann, B.; Stamm-
(33) Baerlocher, C.; McCusker, L. B. Database of Zeolite Structures,
1996, http://www.iza-structure.org/databases/.
(34) Lobo, R. F.; Zones, S. I.; Davis, M. E. J. Inclusion Phenom. Mol.
Recognit. Chem. 1995, 21, 47.
ler, H. Tetrahedron: Asymmetry 1998, 9, 2235.
(32) Villaescusa, L. A.; Camblor, M. A. Recent Res. Dev. Chem. 2003, 1,
93.

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Chem. Mater., Vol. 22, No. 7, 2010 2281
Figure 5. (1) SEM micrograph of sample SS-135-25, (2) 19F MAS NMR spectrum, and (3) 29Si MAS NMR spectrum of sample SS-135-25.
significant change is observed when further increasing the
crystallization time.
below 200 °C evidences the lack of water in the sample
and thus the high hydrophobicity of the material, as
usually found for pure silica zeolites prepared in fluoride
medium.32 The total weight loss measured in the TGA
(∼12%) is close to the amount of organic content calcu-
lated by CHN analysis and indicates that there are two
molecules of bmpm per unit cell. Since the unit cell of
ZSM-12 contains four channels, this indicates that the
organic cation spans to two unit cells along the b direc-
tion, as found for other ZSM-12 materials synthesized
with a related cation.35
The presence of fluoride in the samples was studied by
19F MAS NMR (Figure 5-2). The spectrum displayed in
Figure 5-2 shows a signal at a chemical shift of ∼-80 ppm,
which can be assigned to fluoride within the ZSM-12
zeolite 36 and a second signal at ∼-121 ppm, which can be
attributed to the presence of an impurity of SiF62- in the
sample.37 The relative intensities of these two signals
obtained by spectral deconvolution (93:7, respectively)
demonstrate that the presence of the hexafluorosilicate
phase is minor.
Sample SS-135-25 was then characterized in detail by
different techniques. Scanning electron microscopy (SEM)
images of the sample, Figure 5-1, revealed a crystalline
morphology of the samples as isolated large and well-
defined needles, which is charasteristic for ZSM-12 crystals.
The organic content of the MTW sample (SS-135-25)
was determined by CHN analysis. The observed C, H,
and N contents were 7.83, 1.18, and 0.75%, respectively,
giving a C/N ratio of 12.2, a value which is very close to
that of the isolated SDA (C/N = 13), thus suggesting that
the organic molecule resists the hydrothermal treatment
and is indeed incorporated intact within the zeolite. The
total organic content occluded in the material, estimated
from the N content and taking F as the counterbalance
ion, is 12% of SDAF.
The integrity of the S,S-bmpm molecule inside the
zeolite framework was further assessed by 13C CP MAS
NMR spectroscopy. Figure 4 displays the spectrum of the
iodide salt of S,S-bmpm and of the sample SS-135-25,
showing the resonances corresponding to the different
carbon environments in the organic molecules. All the
signals of the organic cation can be distinguished in the
spectrum of the zeolite, and no additional signals are
observed, which confirms that the organic cation is
incorporated intact within the zeolite.
The 29Si MAS NMR spectrum of the calcined material
(Figure 5-3) shows several signals in the range from -107
to -117 ppm, which are assigned to Si(OSi)4 (Q4) silicate
species in different crystallographic sites;38 no signals
(35) Shantz, D. F.; Fild, C.; Koller, H.; Lobo, R. F. J. Phys. Chem. B
1999, 103, 10858.
€
~
(36) Koller, H.; Wolker, A.; Villaescusa, L. A.; Dıaz-Cabanas, M. J.;
Valencia, S.; Camblor, M. A. J. Am. Chem. Soc. 1999, 121, 3368.
(37) Camblor, M. A.; Barrett, P. A.; Diaz-Cabanas, M.-J.; Villaescusa,
L. A.; Puche, M.; Boix, T.; Perez, E.; Koller, H. Microporous
Mesoporous Mater. 2001, 48, 11.
Thermogravimetric analysis of sample SS-135-25
shows a gradual weight loss of 11.5% in the temperature
range between 200 and 900 °C, which corresponds to the
removal of the organic molecules from the inner surface
of the zeolite. The absence of a noticeable weight loss
(38) Fyfe, C. A.; Gies, H.; Kokotailo, G. T.; Marler, B.; Cox, D. E.
J. Phys. Chem. 1990, 94, 3718.

´
Garcıa et al.
2282 Chem. Mater., Vol. 22, No. 7, 2010
the 12 MR channels of the MTW structure. For this set of
calculations, one S,S-bmpm molecule was loaded in a 1 ꢀ
1 ꢀ 4 MTW supercell. There are two possible orientations
for the bmpm molecules within the MTW channels, which
are related by rotating the pyrrolidine ring around the
N-CH2 bond, whose respective interaction energies with
the MTW framework are -134.5 and -108.6 kcal/mol
per S,S-bmpm molecule, respectively, evidencing that
the occluded molecules will only orient as the former.
Figure 6-3 shows the most stable orientation of the
molecule, where the pyrrolidine ring is roughly aligned
with the channel direction, with the most outermost
group, which is the methanol substituent, pointing to-
ward the larger 10-ring side-cavities of the channel. The
two bmpm molecular rings, the pyrrolidine and the
phenyl rings, are oriented with the ring axis parallel to
the larger cross section of the elliptical channel, this is,
parallel to “a”.
We then studied the energy diagram for the location of
the molecule in different positions along the channel axis,
searching for stable positions along the channel. The
molecules were manually displaced along the c axis by
˚
1 A steps and then geometry optimized. Only two stable
positions were identified (positions 1 and 2): all the
different molecular locations along the 12 MR channel
direction reverted to one of these two positions. Position 1
is clearly more stable than position 2, with the energy
difference around 12 kcal/mol, due to a better fitting
of the molecular groups with the channel topology
(Figure 6-3). The high energy difference evidences that
the S,S-bmpm molecule will be occluded in the MTW
structure during the synthesis mostly in position 1. These
energy results demonstrate the existence of one preferred
well-defined site along the channel axis for accommodat-
ing the S,S-bmpm molecule, where the methanol substi-
tuent and the benzyl rings are pointing toward the side
cavities while the methyl group is pointing toward the
center of a six-ring (Figure 6-3).
A detailed analysis of the molecular structure of S,S-
bmpm and of the MTW void volume available revealed a
clear structural relationship between them, as shown in
Figure 6, which explains the high efficiency of this mole-
cule in directing the MTW synthesis. There are two types
of side pockects along the MTW channel: one delimited
by 10-rings, which are on opposite sides in the “a”
direction (referred to as A cavities in Figure 6-2), and
other two delimited by 6-rings, on opposite sides of the
“c” direction (referred to as B), smaller than the previous;
both types of cavities are arranged perpendicularly and
alternatively (B-A-B). Meanwhile, a related molecular
structure can be found in the S,S-bmpm molecule: there
are two longer molecular axis parallel to “b”, one corres-
ponding to the axis crossing the pyrrolidine ring with the
methanol subsituent and the other through the benzyl
ring (these are referred to as A in Figure 6-4); these axes
will align within the A cavities in MTW due to their larger
cross-section. In addition, we can define another perpen-
dicular molecular axis, though of a lower length, perpen-
dicular to the previous ones, going through the methyl
Figure 6. (1, left) Projection of the MTW structure and (right) channel
walls. (2) MTW channel structure, showing the free volume (left) and the
VdW surface (right), highlighting the side-cavities. (3) Two views of the
most stable location of S,S-bmpm (position 1) inside the MTW channel.
(4) Structural relationship between the S,S-bmpm isomer and MTW (2).
associated with connectivity defects are observed, as
usually found in samples obtained in fluoride medium
since the charge of the organic cations is compensated by
fluoride rather than by negatively charged connectivity
defects. The overall spectrum displays three broad sig-
nals, three of which are in turn split into two signals, in
agreement with the seven independent T-sites of the
asymmetric unit of the MTW structure.38
2.b. Computational Study. The experimental results
previously presented demonstrate that the S,S-bmpm
isomer directs the crystallization of ZSM-12 instead of
the zeolite beta. In this section we try to understand the
structure directing efficiency of this SDA with the aid of
computational simulation techniques.
Figure 6 shows a projection of the MTW structure (1),
the channel walls and two different views of the MTW
channel system (2); one with the van der Waals surface
(right) and the other one showing the free volume inside
the channel (left). The 12 MR channels are one-dimen-
sional, elliptical, and not interconnected. The channel
walls are formed by 6 MR and 10 MRs which form side-
cavities.
2.b.1. Location of S,S-bmpm along the MTW Channel.
In order to understand the structure directing effect of the
bmpm molecule in the synthesis of ZSM-12, first we
studied the location and interaction energies of the SDA
molecule by docking one single S,S-bmpm molecule within

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Chem. Mater., Vol. 22, No. 7, 2010 2283
Figure 7. Location of S,S-bmpm molecules in the different orientations, with methanol groups oriented toward the same side and phenyl rings facing each
other (phfac-ohss, A-top, two views are shown) or benzyl rings in opposite sides (phopp-ohss, A-bottom), with methanol in opposite sides and benzyl rings
facing each other (phfac-ohop, B-top) or benzyl rings in opposite sides (phopp-ohop, B-bottom). (C) Two views of the most stable location of R,S-bmpm
isomers, with methanol groups in the same side and benzyl rings facing each other (phfac-ohss). Dashed green lines indicate H-bonds, while dashed circles
highlight the fitting of methyl groups with the six rings; dashed green and blue arrows indicate the intermolecular interactions between S,S-bmpm (H-bonds
and π π-type, respectively) that gives place to a chain molecular arrangement.

´
Garcıa et al.
2284 Chem. Mater., Vol. 22, No. 7, 2010
and methylene groups (referred as B) that will locate in
the smaller B-type cavities of the structure. Such A and B
molecular axes are also arranged perpendicularly and
alternatively (B-A-B) and with a similar distance be-
tween them as in the MTW structure. Therefore, this close
structural relationship between the molecular structure of
S,S-bmpm and the MTW topology explains the high
ability of this molecule to direct the synthesis of this
framework.
2.b.2. Packing of S,S-bmpm. Once understood the
preferential siting of the S,S-bmpm isomers in the chan-
nel, we studied the packing between consecutive S,S-
bmpm molecules. Because of the noninterconnection
between different channels, molecules sited in different
MTW channels will not interact among each other; hence,
only molecules in one channel have been studied. Four
molecules were initially loaded in a single channel in a 1 ꢀ
1 ꢀ 8 MTW supercell. This gives an organic content of
two molecules per unit cell, which is in good agreement
with the experimental value. The obtained energies were
then multiplied by 4 (since there are 4 channels per unit
cell) and normalized to one unit cell. Consecutive bmpm
molecules can be packed in different relative orientations:
with phenyl rings of consecutive molecules facing each
other (“phfac”) or in opposite sides (“phopp”). In addi-
tion, methanol substituents of consecutive molecules can
be oriented in the same side (“ohss”) or in opposite sides
(“ohopp”). Overall, four different relative orientations of
the molecules were studied by means of simulated anneal-
ing calculations.
The most stable location of the molecules is shown in
Figure 7. The associated interaction energies for these
orientations were calculated as -245.3 and -237.6 kcal/
mol for phfac-ohss and phfac-ohopp orientations, and
-241.1 and -233.0 kcal/mol for phopp-ohss and phopp-
ohopp orientations, respectively. These energy results
show that the orientation where the methanol groups of
consecutive molecules are in the same side is more stable
than when they are pointing in opposite directions,
regardless of the relative orientation of the aromatic
rings. This might be due to a better fitting between
consecutive rings (benzyl-benzyl in “phfac” or benzyl-
pyrrolidine in “phopp” orientations) and also to a better
adjustment with the channel topology (with the side
pockets). In addition, the orientation with benzyl rings
facing each other is more stable (by ∼4 kcal/mol per
MTW unit cell (u.c.)). Overall, the most stable orientation
hence is with benzyl rings facing each other and methanol
groups pointing toward the same side (Figure 7-A, top).
The higher stability of this organic arrangement (S,S-
bmpm-phfac-ohss) is due to, first, a good fitting between
the molecular arrangement and the channel topology in
terms of the structural relationship as previously com-
mented (Figure 6); second, to a stabilizing interaction
between consecutive aromatic rings through π-π inter-
actions, and finally, to the development of a double H-
bond between the methanol groups of consecutive mole-
cules. These two types of interactions between consecu-
tive molecules, π-π type interactions between aromatic
rings, and double H-bonds between methanol groups,
generate a molecular chain arrangement of self-assembled
S,S-bmpm molecules along the MTW channel, which
is detailed in Figure 7A-top. It is worth noting that in
this most stable orientation, the methanol groups are
always located in the same side all along each 12MR
channel, thus generating an asymmetric environment in
the channels.
A higher packing value of 2.5 molecules per unit cell
was also tried. In this case, the only possible molecular
orientation able to reach such a high packing value is with
benzyl rings facing each other and methanol groups
oriented toward the same side. The interaction energy
developed under this molecular arrangement was -174.9 kcal/
mol per MTW u.c., evidencing a high unstability for this
packing value compared to the previous interaction energy
(under a packing of 2 molecules per u.c., ∼-245 kcal/
mol), thus evidencing that the most stable molecular
packing is of 2 molecules per unit cell, in agreement with
the experimental observations.
3. Structure Directing Effect of R,S-bmpm. So far, the
experimental and computational results have demon-
strated the existence of a true templating effect of the S,
S-bmpm molecule when directing the synthesis of the
MTW structure due to a close structural complementary
relationship between the molecular and the channel
structures. Such strong templating effect led us to wonder
if a subtle modification of the molecular geometry such as
the inversion of the absolute configuration of the N atom,
giving place to the R,S-bmpm diasteroisomer, could have
an important influence over the structure directing ability
of this molecule. We then first studied computationally
the interaction energy of this new isomer with the MTW
structure and then tried to experimentally validate the
observations of the simulation study.
3.a. Computational Study. 3.a.1. Interaction of R,S-
bmpm with the MTW Structure. The same set of calcula-
tions as in the previous sections (with S,S-bmpm) have
been performed for the R,S-bmpm isomer. When study-
ing one molecule in a 1 ꢀ 1ꢀ 4 u. c. MTW, i. e., without
considering packing effects, we observed that again the
most stable orientation was the same as for the previous
diasteroisomer, developing an interaction energy with the
framework of -132.5 kcal/mol per molecule. Interest-
ingly, this interaction energy of one single molecule of the
R,S-diasteroisomer is slightly lower than that of the S,S
(R,S, -132.5 kcal/mol; S,S, -134.5 kcal/mol).
When packing effects were considered (four molecules
in the same channel in a 1ꢀ1ꢀ4 u.c. MTW supercell),
the interaction energy was calculated as -233.2 kcal/mol
per MTW u.c. in the most stable configuration (same
orientation as S,S, with benzyl rings facing each other and
methanol groups oriented in the same side, phfac-ohss).
This energy is much lower than the corresponding for S,S
(-245.3 kcal/mol per MTW u.c.), suggesting a more
efficient structure directing ability of the S,S diastero-
isomer for the synthesis of the MTW structure. The most
stable location of the R,S-bmpm molecules is shown in
Figure 7C. The lower interaction of the R,S-bmpm isomer

Article
Chem. Mater., Vol. 22, No. 7, 2010 2285
with the MTW structure is due to a worse fitting of the
R,S molecular geometry within the channel topology; if
we compare with the location of S,S-bmpm, we can
observe that the fitting of the methyl groups with the 6-
rings of the channel is better in the S,S isomer, where they
point to the center of the ring, than in the R,S one, where
they are bent, as highlighted in parts A and C of Figure 7
by dashed circles; this is due to the different relative
configuration of the methyl and methanol substituents,
which are in syn (in the same side) or anti (opposite sides)
configurations in S,S and R,S isomers, respectively (see
Figure 1-right). Besides, the lower interaction of R,S-
bmpm might also be due to a less effective packing of
these isomers along the channel, since in this case only one
H-bond is developed between consecutive molecules, in
contrast to the double H-bond observed for the S,S
isomer.
Figure 8. X-ray diffraction pattern of (a) ZSM-12 synthesized with the S,
S-bmpm isomer at 16 days (sample SS-135-16), (b) physical mixture of
ZSM-12 (5 wt %) in amorphous silica, and (c) sample RSSS-2-14.
3.a.2. Interaction of an Equimolar Mixture of S,S- and
R,S-bmpm with MTW. Our simulation study thus sug-
gests a much lower structure directing efficiency of the R,
S isomer in the synthesis of the MTW structure; we now
attempted to experimentally validate this theoretical ob-
servation. However, as commented in the introduction,
only an equimolar mixture of both diasteroisomers rather
than the isolated R,S isomer is obtained by direct synth-
esis following the approach described here. Hence, we
finally simulated the interaction of an equimolar mixture
of diasteroisomers by the same computational methodo-
logy. The two diasteroisomers were arranged alterna-
tively (note: other arrangements were tried but lower
interaction energies were found). The most stable orien-
tation involved the molecules with benzyl rings facing
each other but due to the different absolute configuration
of consecutive molecules, in this case, methanol subsitu-
ents were located in opposite sides, hence letting the
aromatic rings of consecutive molecules to arrange par-
allel to each other, developing strong π-π type inter-
actions. The interaction energy observed for this system
was -240.9 kcal/mol per MTW u.c., which is in between
that for the pure systems (S,S, -245.3 kcal/mol; R,S:
-233.2 kcal/mol). Therefore, these results also suggest a
lower efficiency of the mixture of isomers to direct the
crystallization of the MTW structure.
3.b. Molecular-Sieve Synthesis. Finally, we performed
a set of zeolite synthesis experiments by using the mixture
of diastereoisomers (R,S) and (S,S) bmpm (RSSS-135,
Table 1). The experiments were performed with a similar
gel composition and at 13 and 16 days where the crystal-
lization of ZSM-12 with the pure S,S-bmpm isomer had
already finished. The XRD patterns of the new samples
(Figure 3) clearly show that when the mixture of isomers
is employed in the synthesis of ZSM-12, a dramatic effect
over the crystallization of the ZSM-12 zeolite is observed.
An amorphous material is obtained with the mixture of
isomers after 13 days of crystallization, while ZSM-12
had already started to crystallize after 12 days when the S,
S isolated isomer was used as the SDA. In addition, while
after 16 days the S,S isomer yields well-crystallized ZSM-
12, the sample obtained with the mixture of isomers is still
mostly amorphous. Therefore these results evidence that
the mixture of isomers, and so the R,S isomer, is not able
to direct the crystallization of ZSM-12, in contrast to the
S,S isomer itself, in good agreement with the predictions
suggested by the computational study.
The lower efficiency of the structure directing ability of
the mixture of isomers might be due either to the incor-
poration of the two isomers within the MTW structure
during crystallization, with the consequent decrease of
the interaction with the framework due to the occlusion of
R,S-bmpm, to the lowering of the concentration of the S,
S isomer in the synthesis gel, or to the combination of
both factors together.
In order to answer the above questions, we performed
subsequent experiments (RSSS-1-and RSSS-2, Table 1).
In one of them, we increased the total organic content in
the synthesis gel to 1.08 by adding 0.54 mol of the
chloride salt of the mixture of bmpm isomers, so that
the total content of 1S,2S was equivalent to that in the
pure form that leads to ZSM-12. The resulting product
was an amorphous material even at long crystallization
times (22 days), therefore suggesting that the presence of
the 1R,2S impedes the nucleation of ZSM-12. In a
second experiment (RSSS-2-14), the gel with the mixture
of isomers was seeded with a small amount of ZSM-12
(∼5 wt % of zeolite). In this case, the XRD pattern of the
product (Figure 8) showed the crystallization of a mix-
ture of phases, though some diffractions of ZSM-12 can
be identified. Comparing the intensity of these diffrac-
tion peaks with those of a 5 wt % physical mixture of
zeolite ZSM-12 and amorphous silica indicates that
there has been some crystalline growth. Therefore, the
above results suggests that the low structure directing
ability of the mixture of isomers is due to a blocking of
the ZSM-12 nucleation provoked by the presence of
1R,2S-bmpm molecules, which compete to be incorpo-
rated within the nascent MTW structure, thus prevent-
ing further growth of the zeolite. The effect of the (1R,
2S) isomer is mainly exerted over the nucleation of ZSM-
12 rather than over crystal growth, though both are
disfavored.

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Garcıa et al.
2286 Chem. Mater., Vol. 22, No. 7, 2010
The fact that such a subtle change in the molecular
structure of the SDA molecule can dramatically alter the
structure directing ability of a molecule suggests that the
S,S-bmpm plays a true templating effect in the synthesis
of this zeolite, as previously mentioned.
Our results opens up a new possible application of
zeolites in enantioselective/diasteroselective processes.
Indeed, the diasteroespecificity in the synthesis of zeolite
structures by using chiral SDA molecules, as the example
studied in this work, could eventually be used as a
diasteroselective separation process, in which the prefer-
ential structure directing ability of one of the diastero-
isomers would lead to a partial enrichment of the zeolite
in a specific diasteroisomer (and the opposite in the
mother liquors), provided the other isomer does not have
a blocking effect on the zeolite crystallization, as occurred
in the present case.
these isomers within the MTW channels involves the
development of a molecular chain where the SDAs are
self-assembled through π-π type interactions between
the aromatic rings and double H-bonds between metha-
nol attached to pyrrolidine groups, thus generating a
chiral molecular arrangement which efficiently stabilizes
the MTW structure by developing strong nonbonded
interactions. However, experiments trying to synthesize
the same zeolite with a ∼1:1 mixture of the 1S,2S and
1R,2S isomers failed in producing crystalline ZSM-12,
which is explained by the low interaction that the latter
isomer develops with the MTW framework, thus block-
ing the structure directing effect of the efficient SS-
isomer. Therefore, our results provide a new example of
a true templating effect, which in turn is diasterospecific,
observed in the synthesis of zeolite materials.
Acknowledgment. We are thankful for the financial sup-
port of the Spanish Ministry of Science and Innovation
(MICINN, former MEC), Projects CTQ2006-06282 and
MAT2006-14274-C02-02. R. Garcıa acknowledges CSIC
Conclusions
This work describes experimental and theoretical studies
about the structure directing efficiency of two diastero-
isomers [(1S,2S) and (1R,2S)] of the cation 2-hydroxy-
methyl-1-benzyl-1-methylpyrrolidinium in the synthesis
of pure silica zeolites in fluoride medium. Experimental
results indicate that the 1S,2S diastereoisomer directs very
efficiently the crystallization of ZSM-12. Such a highly
efficient structure directing role of this isomer is due to a
close structural relationship between the SDA and the
framework, whose molecular geometries are indeed com-
plementary. Interestingly, the most stable arrangement of
ꢀ
€
for a JAE contract. L. Gomez-Hortiguela is grateful to the
Spanish Ministry of Science and Innovation for a postdoc-
toral fellowship. We thank Accelrys for providing their
ꢀ
software and Centro Tecnico de Informatica for running
ꢀ
the calculations.
Supporting Information Available: 1H NMR spectra of the
organic salts of the pure 1S,2S-bmpm isomer and of the mixture
of the 1S,2S and 1R,2S-bmpm isomers (PDF). This material is
available free of charge via the Internet at http://pubs.acs.org.