Enantioselective recognition and separation by a homochiral porous lamellar solid based on unsymmetrical schiff base metal complexes

Article abstract of DOI:10.1002/chem.200900037

A homochiral lamellar supramolecular host system has been developed by treating 3-[(E)-{[(1R,2R)-2-aminocyclohexyl]imino}methyl]-4-hydroxybenzoic acid (H₂L) with copper nitrate and characterized by a variety of techniques including microanalysi

Full text of DOI:10.1002/chem.200900037

DOI: 10.1002/chem.200900037
Enantioselective Recognition and Separation by a Homochiral Porous
Lamellar Solid Based on Unsymmetrical Schiff Base Metal Complexes
Guozan Yuan, Chengfeng Zhu, Weimin Xuan, and Yong Cui*[a]
Abstract: A homochiral lamellar supra-
molecular host system has been devel-
oped by treating 3-[(E)-{[(1R,2R)-2-
aminocyclohexyl]imino}methyl]-4-hy-
droxybenzoic acid (H2L) with copper
nitrate and characterized by a variety
of techniques including microanalysis,
IR spectroscopy, thermogravimetric
analysis (TGA), circular dichroism
(CD) spectroscopy, and powder and
single-crystal X-ray diffraction. Triden-
tate Schiff base L ligands link adjacent
metal centers to form 1D coordination
polymeric chains using tridentate N2O
donors and carboxylate groups, while
interchain metal–oxygen and hydro-
gen-bonding interactions further link
1D polymeric chains to a porous lamel-
lar solid. The host features a flexible
helical framework for guest inclusions
and chiral amphiphilic channel surfaces
lined with amine hydrogen atoms and
aliphatic groups capable of multiple in-
teractions with guest species. It allows
for the development of an efficient ap-
proach for highly enantioselective sep-
aration of racemic secondary alcohols
by inclusion crystallization followed by
distillation (>99.5% ee). In addition,
the host including different alcohols ex-
hibits guest-responsive ferroelectric be-
havior.
Keywords: chirality · coordination
polymers · crystallization · separa-
tion · supramolecular chemistry
Introduction
With few notable exceptions, such a highly chiral recogni-
tion system has not yet been developed.[3–5]
Recent advances in the field of solid-state supramolecular
chemistry have led to many chiral coordination frameworks
exhibiting important properties such as asymmetric recogni-
tion, separation, catalysis, and nonlinear optics.[1–3] Signifi-
cantly, flexibility without loss of crystallinity can be expected
for structures containing deformable organic building blocks
in response to guest removal or exchange, which may induce
extensive and highly selective recognition and inclusion abil-
ities.[4] It has been demonstrated that porous polymeric net-
works bearing amphiphilic channel surfaces have strong af-
finities for amphiphilic guest molecules. Those chiral matrix-
es therefore hold great promise for separation of racemic al-
cohols with a suitable pore size and shape for target mole-
cules generated from the specific framework flexibility.[1a,5]
Of particular interest to us are elegant works on “bioin-
spired” amino acid and peptide based metal–organic materi-
als with the aim of generating well-defined enzymelike
chiral cavities and functions for enantioselective processes.[6]
It was suggested that the placement of hydrophilic function-
alities (such as an amine and hydroxyl groups) accessible to
guest molecules or available for chemical modification in
flexible chiral networks represents the key step toward
highly porous biomimetic solids for application in heteroge-
neous chiral processes.[3a,6] To create biomimetic coordina-
tion assemblies, we have focused on chiral metal Schiff base
complexes,[7] which have successfully been applied in many
asymmetric reactions and recognitions as excellent chiral
scaffolds and, more interestingly, can be readily designed
and modified to be biomimetic in character.[8] We report
here the assembly of a flexible homochiral porous lamellar
solid based on chiral unsymmetrical Schiff base copper com-
plexes using a combination of coordination and hydrogen
bonds that features amphiphilic internal channel surfaces
lined with amine hydrogen atoms and aliphatic groups. It
allows for the development of an efficient approach to
highly enantioselective separation of racemic alcohols by in-
clusion crystallization and distillation (>99.5% ee). The fer-
roelectric properties of the host including different alcohols
were also studied.
[a] G. Yuan, C. Zhu, W. Xuan, Prof. Y. Cui
School of Chemistry and Chemical Technology
State Key Laboratory of Metal Matrix Composites
Shanghai Jiao Tong University
Shanghai 200240 (China)
Fax : (+86)21-5474-1297
E-mail: yongcui@sjtu.edu.cn
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.200900037.
6428
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 6428 – 6434

FULL PAPER
Results and Discussion
Synthesis considerations and spectroscopic characterization:
Tridentate ligand (R,R)-H2L was synthesized by the 1:1 con-
densation of (1R,2R)-(À)-1,2-diaminocyclohexane with 4-(3-
hydroformyl-4-hydroxy)benzoic acid, which was obtained by
the Reimer–Tiemann reaction of 4-hydroxybenzoic acid
with chloroform.[9] Heating Cu
ACHTUNRTGNEUNG(NO3)2·3H2O and H2L (1:1
molar ratio) in basic MeOH afforded blue, rodlike crystals
(Scheme 1). The product is stable in air and insoluble in
Scheme 1. Synthesis of the ligand H2L and polymer 1.
Figure 1. a) View of a 1D polymeric chain in 1·2MeOH; b) view of 1D
intertwined supramolecular helical polymeric chains in 1 along the b axis.
water as well as common organic solvents such as acetone,
THF, and MeCN. It was formulated as [Cu2L2]·2MeOH
(1·2MeOH) on the basis of X-ray crystallography, elemental
analysis, IR spectroscopy, and thermogravimetric analysis
(TGA). The phase purity of the bulk sample was established
by comparison of their observed and simulated powder X-
ray diffraction (PXRD) patterns.
Two intertwined right-handed helical chains are thus gen-
erated around the crystallographic 2(1) axis as shown in Fig-
ure 1b. The two helices have an identical pitch of
7.2490(14) ꢁ (equal to the b axis length). The hydrophobic
cyclohexane groups of the L ligands are oriented toward the
outside of the helix, whereas the hydrophilic coordinated
amines are buried in the chain accessible to guest molecules.
The grooves inside the helices are thus amphiphilic, which is
reminiscent of those of amphiphilic b-sheet peptides.[10]
Highly directional supramolecular interactions in 1 thus lead
to a chiral 2D corrugated network (Figure 2a). Such 2D heli-
cal grids stack along the b axis through interdigitation of the
cyclohexane rings from the adjacent layers (Figure 2b).
There is, however, significant void space formed between
the lamellae, and a space-filling model of 1 viewed along the
a axis clearly indicates the presence of large asymmetric
channels with a largest dimension of 6.93 ꢁ.
Calculations using PLATON software indicated that 1 has
14.5% of its total volume occupied by solvent molecules.[11]
TGA revealed that the guest molecules could be removed at
140–3008C. A combination of TGA (Figure 3) and PXRD
(see Figure S7 in the Supporting Information) experiments
indicated that the framework and crystallinity of 1 remained
intact upon complete removal of guest molecules. The hand-
edness of 1 is determined by the enantiomer of the L ligand
used, as evidenced by the fact that (S)-1 adopts a left-
handed layer structure, whereas (R)-1 adopts a right-handed
structure.[10] CD spectra of 1 (Figure 4) made from R and S
enantiomers of the L ligand are mirror images of each
other, which indicates their enantiomeric nature.
Structural description: A single-crystal X-ray diffraction
study revealed that 1·2MeOH exhibits a hydrogen-bonded
chiral helical layered structure that crystallizes in the mono-
clinic chiral space group P21. The asymmetric unit contains
two [CuL] units and two methanol guest molecules. Both Cu
centers adopt a distorted square-planar geometry by coordi-
nating to an N2O donor set of one L ligand and one carbox-
ylate oxygen atom of another L ligand. Each L ligand uses
one tridentate N2O donor site to bind one Cu center and
uses one monodentate carboxylate group to bind another
Cu. The aromatic ring is practically coplanar with the basal
CuN2O2 plane (dihedral angles of 5.68 for Cu1 and 2.18 for
Cu2). Adjacent Cu centers are thus linked by L ligands to
form 1D zigzag chains running along the b axis as shown in
Figure 1a. The Cu centers have weak interchain interactions
with uncoordinated carboxylate oxygen atoms of the L li-
gands at the axial site (Cu···O, 2.6171(4) and 2.6956(8) ꢁ)
due to the Jahn–Teller effect. The two hydrogen atoms of
the coordinated amine of the L ligand in the polymeric
chains are pointing outward and are well positioned to form
strong hydrogen bonds either with the coordinated depro-
tonated phenolic oxygen atoms (O···N, 3.0614(6) and
3.1737(5) ꢁ) of adjacent chains or with guest methanol mol-
ecules (O···N, 3.0163(15) and 2.9373(5) ꢁ).
Chem. Eur. J. 2009, 15, 6428 – 6434
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6429

Y. Cui et al.
Figure 2. a) View of the 2D lamellar structure in 1a; b) view of the
porous 3D lamellar structure of 1 along the b axis (Cu, purple; C, deep
gray; O, red; N, blue; H, light gray).
Figure 3. TGA curves of 1·2Guest.
Ethanol and isopropanol molecules can also be included
in host 1 by using the same crystallization procedure as de-
scribed above. Single-crystal X-ray structure analyses
showed that the two adducts 1·2EtOH and 1·2ACHTNUTRGNE(UNG iPrOH) are
isostructural to 1·2MeOH (Table 1). Although the frame-
works are intact, the supramolecular polymer undergoes a
guest-responsive structural change. In particular, the pitches
of the characteristic intertwined helices increase from
7.2490(14) ꢁ in 1·2MeOH to 7.3952(15) ꢁ in 1·2EtOH and
7.4236(15) ꢁ in 1·2ACHTUNGTRENNUNG(iPrOH) to accommodate larger guest
molecules. The layer-to-layer separation increases from
3.0706(2) ꢁ in 1·2MeOH to 3.1268(1) ꢁ in 1·2EtOH and
3.1970(4) ꢁ in 1·2ACHTUNGTRENNUNG(iPrOH). This self-adjustment of helical
Figure 4. CD spectra of (R)-1·2MeOH (a) and (S)-1·2MeOH (c).
pitches is realized mainly by adaptive variation of direction-
al hydrogen bonds within polymer chains between coordi-
nated amines of L and coordinated phenolic oxygen atoms
(O···N, 3.0688(6) and 3.1978(6) ꢁ in 1·2EtOH; 3.0657(6)
the host structure can be readily achieved through crystalli-
zation of host (R)-1 with racemic alcohols. Chiral gas chro-
matography (GC) analysis of the desorbed 2-butanol from
(R)-1 by distillation showed that the enantiomeric excess
(ee) value was 99.8% (Figure 5a), whereas the absolute con-
figuration of (R)-2-butanol was confirmed by comparing its
GC retention time with that of the standard sample. Similar
enantioselective inclusion behaviors are observed for race-
mic 3-methyl-2-butanol and 2-pentanol, whereby compound
(R)-1 exhibited remarkable inclusion toward the R enantio-
and 3.1987(6) ꢁ in 1·2
tions (Cu···O, 2.6510(4) and 2.7622(5) ꢁ in 1·2EtOH;
2.6421(4) and 2.7272(5) ꢁ in 1·2(iPrOH)).
ACHTUNGTRNE(NUNG iPrOH)) and weak Cu···O interac-
AHCTUNGTRENNUNG
Enantioselective recognition and separation: The flexible
helical framework and multiple chiral points exhibited by 1
have prompted us to explore its application in enantiomeric
recognition and resolution. This inclusion of 2-butanol by
6430
www.chemeurj.org
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 6428 – 6434

Enantioselective Recognition and Separation
FULL PAPER
Table 1. Crystal data and structure refinement for 1·Guest.
of the helical pitch in single
crystals of 1 is very small and
can be readily overcome by the
inclusion of C1 to C5 alcohols.
Whereas the size of the includ-
ed guest is mainly determined
by the intrinsic pore shape and
size of the host, the ability of 1
to tune helical pitches and in-
terlayer separations in accord-
ance with guest molecules is
limited and hence the longer
C6 and C7 alcohols were ex-
cluded. The differentiation of
substrates on the basis of multi-
ple weak interactions and coop-
1·2MeOH
1·2EtOH
1·2
(iPrOH)
1·2
(2-BuOH)
1·4H2O
formula
Mr
C30H40Cu2N4O8 C32H44Cu2N4O8 C34H48Cu2N4O8 C36H52Cu2N4O8 C28H40Cu2N4O10
711.74
739.79
767.84
795.90
293(2)
0.71073
monoclinic
P21
13.110(3)
7.5040(15)
16.520(3)
105.88(3)
1563.2(5)
2
719.72
293(2)
0.71073
monoclinic
P21
13.1340(8)
7.2566(4)
16.4929(10)
106.0710(10)
1510.48(15)
2
T [K]
293(2)
293(2)
293(2)
l [ꢁ]
0.71073
0.71073
0.71073
crystal system
space group
a [ꢁ]
b [ꢁ]
c [ꢁ]
monoclinic
P21
monoclinic
P21
monoclinic
P21
13.137(3)
7.2490(14)
16.286(3)
105.85(3)
1492.0(5)
2
13.023(3)
7.3952(15)
16.597(3)
106.31(3)
1534.1(5)
2
13.090(3)
7.4236(15)
16.431(3)
105.92(3)
1535.4(5)
2
b [8]
V [ꢁ3]
Z
1calcd [MgmÀ3
]
1.584
1.484
1.602
1.446
1.704
1.451
1.691
1.426
1.582
1.471
m [mmÀ1
]
q range [8]
limiting
indices
3.13 to 25.00
À15ꢀhꢀ15
À8ꢀIꢀ8
À19ꢀIꢀ19
11604
3.04 to 25.00
À15ꢀhꢀ15
À8ꢀIꢀ8
À19ꢀIꢀ19
12010
3.14 to 25
À15ꢀhꢀ15
À8ꢀIꢀ8
À19ꢀIꢀ19
11971
3.03 to 25.00
À15ꢀhꢀ15
À8ꢀIꢀ8
À19ꢀIꢀ19
12359
1.61 to 25.00
À15ꢀhꢀ15
À8ꢀkꢀ8
À19ꢀIꢀ19
10919
erative interactions within
a
reflns collected
independent
reflns
final R indices
[I>2s(I)]
compositionally complex chiral
groove is reminiscent of the se-
lective function of enzymes.[12]
Crystallization, along with
adsorption, is one of the most
important methods for the re-
covery of pure enantiomers.[13]
5007
4805
5161
5070
5106
(Rint =0.0707)
R1=0.0475
wR2=0.1052
(Rint =0.0442)
R1=0.0587
wR2=0.1533
(Rint =0.0384)
R1=0.0708
wR2=0.1982
(Rint =0.0360)
R1=0.0657
wR2=0.1871
(Rint =0.0235)
R1=0.0350
wR2=0.0971
mer over the S enantiomer as well. The inclusion com-
pounds can be formulated as 1·2(3-methyl-2-butanol) and
1·2(2-pentanol), respectively, based on elemental analysis
and TGA. The ee values of the desorbed guests were 99.6
and 99.5% (Figure 5b and c), respectively. The chiral nature
of the included molecule is determined by the handedness
of the host, as further evidenced by the fact that (S)-1
showed remarkable inclusion toward the S enantiomer over
the R enantiomer as well (99.6% ee) (Figure S8 in the Sup-
porting Information). 2-Heptanol and 2-octanol could not
produce inclusion crystals with 1 under otherwise identical
crystallization conditions, both of which yielded crystals of
1·4H2O, probably due to fact that the two alcohols are too
large to be trapped in the frameworks (Table 1).
The structural arrangement of the host/guest revealed by
single-crystal X-ray analysis provides insight into the origin
of the stereoselectivity of the system. The adduct complex is
isostructural to 1·2MeOH as well (Table 1). The guest (R)-
2-butanol is located in the groove of the supramolecular
helices and adopts an extended conformation, with the OH
group hydrogen bonded to the coordinated amine of L in
the polymer (Figure 6). This enforces a chiral P21 symmetric
cavity in which inclusion of (R)-2-butanol evades steric in-
teractions between the terminal alkyl group and the cyclo-
hexane groups of L, which an included S enantiomer could
not evade. Both the helical pitches of the intertwined supra-
molecular chains (7.5040(15) ꢁ) and the layer-to-layer sepa-
ration increase (3.2637(2) ꢁ) further for entrapping 2-buta-
nol molecules. The stretch of intertwined helices is also ac-
companied by the self-adjustment variation of hydrogen
bonds (O···N, 3.1295(6) and 3.2050(6) ꢁ) and Cu···O interac-
tions (Cu···O, 2.6845(4) ꢁ and 2.7459(5) ꢁ) within the infin-
ite chains. Therefore, the potential barrier for the expansion
However, it is generally difficult to perform optical resolu-
tion of small secondary alkyl alcohols, the key building
blocks for many chiral drugs and fine chemicals,[14] due to
the subtle structural difference between the enantiomers as
methyl groups and hydrogen atoms attached to the chiral
carbon have to be discriminated. Although the optical reso-
lution of organic substrates by lattice inclusion compounds
using a pure organic host has received significant atten-
tion,[15] the crystallization process involved in the synthesis
of coordination polymers has not in itself been explored as a
tool for chiral separation.[1,7] The high enantioselectivities
described here are in sharp contrast to those based on crys-
tallization separation methods using pure organic deriva-
tives,[15] but are comparable to those based on adsorptive
methods using metal–organic assemblies.[3b,7] In the latter
cases, formation of a chiral hydrophobic cavity with the
right size and shape for guests is vital for the optical discrim-
ination of the alcohols. Our success arises from the flexible
host framework coupled with an amphiphilic channel, which
leads to bioanalogous recognition behavior during interac-
tion with guest species. Note that the H2L Schiff base ligand
is relatively cheap and easily prepared on a large scale as
compared with the reported ligands for optical resolu-
tion.[3b,7,15] Moreover, the H2L ligand can be easily recycled
by using dilute HCl to dissociate the used powder and by
extraction with chloroform, an approach that has been
proven useful elsewhere.[16] This separation has the potential
to be run on an industrial scale.
Ferroelectric properties: The ferroelectric behavior of 1
could be examined given that its point group P2 is one of
the 10 polar point groups required for such materials. All al-
cohol-inclusion compounds exhibited a similar hysteresis
Chem. Eur. J. 2009, 15, 6428 – 6434
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6431

Y. Cui et al.
Figure 6. View of the arrangement of a) (R)-2-butanol guest molecules
around the intertwined helical chains (space-filling mode colored in blue
and orange, respectively) along the b axis and b) in the channels of 1
(Cu, purple; C, black; O, red; N, blue; H, gray).
spontaneous polarization, whereas 1·MeOH displays the
weakest spontaneous polarization (see Figure S10 in the
Supporting Information). This is consistent with the fact
that host 1 has a flexible crystal structure and may take up
different guests to modulate charge transfer among 1D
chains so as to generate adequate electronic asymmetry
through cooperative supramolecular interactions.[19]
Conclusions
In the present work, we have developed a well-defined la-
mellar supramolecular host system based on tridentate
Schiff base metal complexes that features a flexible helical
framework and amphiphilic channel surfaces and exhibits
guest-responsive ferroelectric properties and a high enantio-
selective ability to separate racemic alcohols. With a precise
knowledge of their single-crystal structures and the facile
tunability of the building blocks, the present research holds
great promise in the development of novel chiral lamellar
solids that are especially capable of separation and catalysis
with a practical enantioselectivity.
Figure 5. Chiral GC results of the desorbed a) (R)-2-butanol, b) (R)-3-
methyl-2-butanol, and c) (R)-2-pentanol from (R)-1, as well as the corre-
sponding racemic alcohols [bottom lines in a) and c); top line in b)].
loop, which is a typical ferroelectric feature. Compounds
1·2MeOH, 1·2EtOH, 1·2ACTHNUTRGENNU(G iPrOH), and 1·2ACHTUNGTNER(NUGN 2-BuOH) exhib-
ited a remnant polarization (Pr) of 1.13, 4.54, 5.33, and
6.41 nCcmÀ2, a coercive field (Ec) of 0.85, 2.85, 4.63, and
4.79 kVcmÀ1, and a saturated polarization (Ps) of approxi-
mately 1.39, 16.73, 19.94, and 24.19 nCcmÀ2, respectively.
The saturation spontaneous polarization values (Ps) are
smaller than that of the typical ferroelectric compound “Ro-
chelle salt” (KOOCCH(OH)CH(OH)COONa·4H2O, Ps=
0.25 mCcmÀ2)[17] but are comparable with those found in co-
Experimental Section
ordination compounds.[18] Compound 1·2
hibits an enhanced E–P hysteresis loop with the strongest
ACHTUNGTREN(NGNU 2-BuOH) thus ex-
Chemicals, reagents, and analyses: All of the chemicals are commercially
available and were used without further purification. 4-(3-Hydroformyl-
6432
www.chemeurj.org
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 6428 – 6434

Enantioselective Recognition and Separation
FULL PAPER
4-hydroxy)benzoic acid was obtained by the Reimer–Tiemann reaction of
4-hydroxybenzoic acid with chloroform. Elemental analyses of C, H, and
N were performed using an EA1110 CHNS-0 CE elemental analyzer.
The IR (KBr pellet) spectra were recorded (400–4000 cmÀ1 region) using
a Nicolet Magna 750 FT–IR spectrometer. The solid-state CD spectra
were recorded on a J-800 spectropolarimeter (Jasco, Japan). Thermogra-
vimetric analyses (TGA) were carried out in air with a heating rate of
108CminÀ1 using a STA449C integration thermal analyzer. Powder X-ray
diffraction (PXRD) data were collected using a DMAX2500 diffractome-
ter using CuKa radiation. The calculated PXRD patterns were produced
using the SHELXTL-XPOW program and single-crystal reflection data.
Gas chromatography was conducted using a Lunan Ruihong SP-6890
equipped with a flame ionization detector. The measurement of the po-
larization–voltage curves was carried out on a pellet of the powder
sample with an aixACCT TF Analyzer 2000 system at room temperature.
The pellet (with a diameter of 6 mm and thickness of 1.3 mm) was sand-
wiched between silver electrodes and immersed in insulating oil while
being measured.
Synthesis of 1·2(3-methyl-2-butanol): Following the same procedure as
the synthesis of 1·2MeOH, except that MeOH was replaced by 3-methyl-
2-butanol. This afforded 1·2(3-methyl-2-butanol) as blue, rodlike crystals.
Yield: 33.3 mg, 81%; IR (KBr): v˜ =3230 (s), 3138 (m), 2932 (s), 2857
(m), 2360 (w), 1651 (s), 1609 (s), 1565 (s), 1478 (w), 1450 (w), 1384 (s),
1312 (s), 1250 (m), 1193 (m), 1118 (m), 1038 (m), 948 (w), 792 (m), 711
(m), 651 (m), 591 (w), 523 (w), 446 cmÀ1 (w); elemental analysis calcd
(%) for C38H56Cu2N4O8: C 55.39, H 6.85, N 6.80; found: C 55.14, H 6.81,
N 6.80.
Synthesis of 1·2(2-pentanol): Following the same procedure as the syn-
thesis of 1·2MeOH, except that MeOH was replaced by 2-pentanol. This
afforded 1·2(2-pentanol) as blue, rodlike crystals. Yield: 32.9 mg, 80%;
IR (KBr): v˜ =3231 (s), 3143 (m), 2933 (s), 2858 (m), 2365 (w), 1651 (s),
1610 (s), 1563 (s), 1531 (m), 1478 (w), 1450 (w), 1371 (s), 1312 (s), 1250
(m), 1194 (w), 1119 (m), 1046 (m), 950 (w), 838 (w), 793 (m), 712 (m),
651 (m), 591 (w), 523 (w), 446 cmÀ1 (w); elemental analysis calcd (%) for
C38H56Cu2N4O8: C 55.39, H 6.85, N 6.80; found: C 55.07, H 6.78, N 6.86.
Synthesis of 1·4H2O: Following the same procedure as the synthesis of
1·2MeOH, except that MeOH was replaced by 2-heptanol and 2-octanol.
This afforded 1·4H2O as blue, rodlike crystals. Yield: 30.5 mg, 85%; IR
(KBr): v˜ =3323 (m), 3229 (s), 3138 (m), 2857 (m), 2668 (w), 1649 (s),
1609 (s), 1563 (s), 1477 (m), 1449 (m), 1370 (s), 1312 (s), 1250 (m), 1193
(m), 1118 (m), 1038 (m), 930 (w), 837 (w), 792 (s), 711 (m), 650 (s), 560
(m), 522 (w), 445 cmÀ1 (w); elemental analysis calcd (%) for
C28H40Cu2N4O10: C 46.73, H 5.60, N 7.78; found: C 46.55, H 5.52, N 7.73.
X-ray crystallography: Single-crystal XRD data for the compounds was
collected using a Bruker Smart 1000 CCD diffractometer with MoKa radi-
ation (l=0.71073 ꢁ) at room temperature. The empirical absorption cor-
rection was applied by using the SADABS program.[20] The structure was
solved by using direct methods and refined by full-matrix least-squares
using F2.[21] In all compounds, the guest molecules and hydrogen atoms
were refined isotropically, whereas all other atoms were refined aniso-
tropically. Crystal data and details of the data collection are given in
Table 1, whereas the selected bond distances and angles are presented in
Tables S1–S5 in the Supporting Information.
Synthesis of (R,R)-H2L:[22] A mixture of (1R,2R)-(À)-1,2-diaminocyclo-
hexane (0.32 g, 2.74 mmol) and 4-(3-hydroformyl-4-hydroxy)benzoic acid
(0.44 g, 2.68 mmol) in methanol (100 mL) was heated to reflux for 1 h.
The resulting precipitate was filtered and washed with hot methanol (
ꢁ508C, 5ꢂ10 mL) and dried under vacuum to give a pale yellow solid
(R,R)-H2L (0.67 g, 95%).
Separation and chiral GC analysis of guest molecules from inclusion crys-
tals: The inclusion crystals of 1·2Guest (200 mg; Guest=2-butanol, 3-
methyl-2-butanol, or 2-pentanol) were filtered, washed with diethyl ether
to remove surface solvent molecules, and then loaded into a distillation
setup and gently heated at 408C under vacuum for 1 h while the volatiles
were collected with a liquid nitrogen bath. In addition, the guest alcohols
can also be readily removed from inclusion crystals of 1·2Guest by wash-
ing it 5 times with chloroform.
The enantiomeric excess of the 2-butanol was determined to be 99.5%
by using gas chromatography (GC). Conditions: column: CHIRALDEX
G-TA by ASTEC Company (30 mꢂ0.25 mm i.d.); column temperature:
248C; carrier gas: N2 (0.5 mLminÀ1), H2 (0.5 mLminÀ1); retention time:
minor compound (S) 25.84 min, major compound (R) 26.70 min.
Synthesis of 1·2MeOH:
A mixture of CuCAHTUNGTRNUEGN(NO3)·3H2O (24.2 mg,
0.1 mmol), H2L (26.2 mg, 0.1 mmol), MeOH (1 mL), and 1% NaOH
aqueous solution (3 mL) was sealed in a 10 mL vial with a screw cap and
heated at 808C for 12 h. The mixture was then cooled to room tempera-
ture and blue, rodlike crystals were collected, washed with diethyl ether,
and dried in air. Yield: 29.5 mg, 83%; IR (KBr): v˜ =3229 (s), 3136 (m),
2932 (s), 2855 (m), 2362 (w), 1651 (s), 1610 (s), 1564 (s), 1477 (w), 1369
(s), 1313 (s), 1252 (w), 1192 (w), 1117 (m), 1039 (m), 793 (m), 712 (m),
650 (m), 592 cmÀ1 (w); elemental analysis calcd (%) for C30H40Cu2N4O8:
C 50.62, H 5.66, N 7.87; found: C 49.91, H 5.60, N 7.81.
The enantiomeric excess of the desorbed 3-methyl-2-butanol was deter-
mined to be 99.6% by using GC. Conditions: column: CHIRALDEX G-
TA by ASTEC Company (30 mꢂ0.25 mm i.d.); column temperature:
288C; carrier gas: N2 (1.0 mLminÀ1), H2 (1.0 mLminÀ1); retention time:
minor compound (S) 25.19 min, major compound (R) 26.28 min.
The enantiomeric excess of the desorbed 2-pentanol was determined to
be 99.5% by using GC. Conditions: column: CHIRALDEX G-TA by
ASTEC Company (30 mꢂ0.25 mm i.d.); column temperature: 408C; car-
rier gas: N2 (1.0 mLminÀ1), H2 (1.0 mLminÀ1); retention time: minor
compound (S) 19.70 min, major compound (R) 20.93 min.
Synthesis of 1·2EtOH: Following the same procedure as the synthesis of
1·2MeOH, except that MeOH was replaced by EtOH. This afforded
1·2EtOH as blue, rodlike crystals. Yield: 30.3 mg, 82%; IR (KBr): v˜ =
3230 (s), 3138 (m), 2931 (s), 2857 (m), 2361 (w), 1650 (s), 1610 (s), 1565
(s), 1531 (m), 1478 (w), 1450 (w), 1371 (s), 1313 (s), 1252 (m), 1193 (m),
1118 (m), 1049 (m), 793 (m), 713 (m), 651 (m), 593 (w), 523 cmÀ1 (w); el-
emental analysis calcd (%) for C32H44Cu2N4O8: C 51.95, H 5.99, N 7.57;
found: C 51.11, H 5.91, N 7.52.
Synthesis of 1·2
of 1·2MeOH, except that MeOH was replaced by iPrOH. This afforded
1·2(iPrOH) as blue, rodlike crystals. Yield: 30.6 mg, 80%; IR (KBr): v˜ =
3229 (s), 3138 (m), 2932 (s), 2858 (m), 1651 (s), 1609 (s), 1564 (s), 1478
(w), 1450 (w), 1372 (s), 1312 (s), 1250 (m), 1193 (w), 1134 (m), 1118 (m),
1046 (m), 950 (w), 862 (w), 837 (w), 792 (m), 712 (m), 651 (m), 591 (m),
522 (w), 470 (w), 444 cmÀ1 (w); elemental analysis calcd (%) for
C34H48Cu2N4O8: C 53.18, H 6.30, N 7.30; found: C 53.30, H 6.27, N 7.22.
ACHTUNGTRENNUNG(iPrOH): Following the same procedure as the synthesis
Acknowledgements
ACHTUNGTRENNUNG
This work was supported by NSFC-20671062, “973” Programs
(2007CB209701 and 2009CB930403), NCET-05–0395, Shuguang Program
(06SG12) and the Scientific Research Foundation for the Returned Over-
seas Chinese Scholars, the State Education Ministry, and the Key Project
of the Chinese Ministry of Education.
Synthesis of 1·2(2-butanol): Following the same procedure as the synthe-
sis of 1·2MeOH, except that MeOH was replaced by 2-butanol. This af-
forded 1·2(2-butanol) as blue, rodlike crystals. Yield: 31.8 mg, 80%; IR
(KBr): v˜ =3230 (s), 3138 (m), 2932 (s), 2857 (m), 2668 (w), 2360 (w),
1651 (s), 1610 (s), 1564 (s), 1531 (m), 1478 (m), 1450 (m), 1371 (s), 1312
(s), 1250 (m), 1193 (m), 1118 (m), 1038 (m), 792 (m), 711 (m), 650 (m),
561 (w), 523 (w), 445 cmÀ1 (w); elemental analysis calcd (%) for
C36H52Cu2N4O8: C 54.33, H 6.59, N 7.04; found: C 54.08, H 6.55, N 6.97.
[1] a) D. Bradshaw, J. B. Claridge, E. J. Cussen, T. J. Prior, M. J. Ros-
seinsky, Acc. Chem. Res. 2005, 38, 273; b) B. Kesanli, W. Lin, Coord.
Chem. Rev. 2003, 246, 305; c) B. Moulton, M. J. Zaworotko, Chem.
Rev. 2001, 101, 1629; d) O. M. Yaghi, M. OꢃKeeffe, N. W. Ockwig,
H. K. Chae, M. Eddaoudi, J. Kim, Nature 2003, 423, 705; e) B. J.
Holliday, C. A. Mirkin, Angew. Chem. 2001, 113, 2076; Angew.
Chem. Int. Ed. 2001, 40, 2022.
Chem. Eur. J. 2009, 15, 6428 – 6434
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
6433

Y. Cui et al.
[2] a) J. Kepert, T. J. Prior, M. J. Rosseinsky, J. Am. Chem. Soc. 2000,
122, 5158; b) J. D. Ranford, J. J. Vittal, D. Wu, X. Yang, Angew.
Chem. 1999, 111, 3707; Angew. Chem. Int. Ed. 1999, 38, 3498;
c) D. N. Dybtsev, A. L. Nuzhdin, H. Chun, K. P. Bryliakov, E. P.
Talsi, V. P. Fedin, K. Kim, Angew. Chem. 2006, 118, 930; Angew.
Chem. Int. Ed. 2006, 45, 916; d) J. Zhang, S. Chen, H. Valle, M.
Wong, C. Austria, M. Cruz, X. Bu, J. Am. Chem. Soc. 2007, 129,
14168; e) J. S. Seo, D. Whang, H. Lee, S. L. Jun, J. Oh, Y. J. Jeon, K.
Kim, Nature 2000, 404, 982.
[3] a) C. D. Wu, A. Hu, L. Zhang, W. Lin, J. Am. Chem. Soc. 2005, 127,
8940; b) R.-G. Xiong, X.-Z. You, B. F. Abrahams, Z. Xue, C.-M.
Che, Angew. Chem. 2001, 113, 4554; Angew. Chem. Int. Ed. 2001,
40, 4422; c) D. Bradshaw, T. J. Prior, E. J. Cussen, J. B. Claridge,
M. J. Rosseinsky, J. Am. Chem. Soc. 2004, 126, 6106–6114; d) S.
Cho, B. Ma, S. Nguyen, J. T. Hupp, T. E. Albrecht-Schmitt, Chem.
Commun. 2006, 2563; e) Y. Liu, X. Xu, Y. Cui, Angew. Chem. 2008,
120, 4614; Angew. Chem. Int. Ed. 2008, 47, 4538.
[4] a) S. Kitagawa, R. Matsuda, Coord. Chem. Rev. 2007, 251, 2490;
b) C. Serre, C. Mellot-Draznieks, S. Surblꢄ, N. Audebrand, Y. Fili-
nchuk, G. Fꢄrey, Science 2007, 315, 1828; c) H. J. Choi, M. P. Suh, J.
Am. Chem. Soc. 2004, 126, 15844; d) G. J. Halder, C. J. Kepert, B.
Moubaraki, K. S. Murray, J. D. Cashion, Science 2002, 298, 1762.
[5] K. Tanaka, S. Odaa, M. Shirob, Chem. Commun. 2008, 820.
[6] a) R. Vaidhyanathan, D. Bradshaw, J. N. Rebilly, J. P. Barrio, J. A.
Gould, N. G. Berry, M. J. Rosseinsky, Angew. Chem. 2006, 118, 6645;
Angew. Chem. Int. Ed. 2006, 45, 6495; b) A. Mantion, L. Massꢅger,
P. Rabu, C. Palivan, L. B. McCusker, A. Taubert, J. Am. Chem. Soc.
2008, 130, 2517; c) E. V. Anokhina, A. J. Jacobson, J. Am. Chem.
Soc. 2004, 126, 3044; d) M. J. Ingleson, J. Bacsa, M. J. Rosseinsky,
Chem. Commun. 2007, 3036.
2006, 106, 3987; d) S. J. Wezenberg, A. W. Kleij, Angew. Chem. 2008,
120, 2388; Angew. Chem. Int. Ed. 2008, 47, 2354.
[9] H. Wynberc, J. Am. Chem. Soc. 1954, 76, 4998.
[10] R. P. Cheng, S. H. Gellman, W. F. DeGrado, Chem. Rev. 2001, 101,
3219.
[11] A. L. Spek, J. Appl. Crystallogr. 2003, 36, 7.
[12] O. Pꢆmies, J. E. Bꢇckvall, Chem. Rev. 2003, 103, 3247.
[13] J. W. Schroer, C. Wibowo, K. M. Ng, AIChE J. 2001, 47, 369.
[14] S. C. Stinson, Aarsb. Soc. Sci. Fenn. Chem. Eng. News 2000, 78, 55.
[15] a) Y. Imai, T. Sato, R. Kuroda, Chem. Commun. 2005, 328; b) M.
Periasamy, N. S. Kumar, S. Sivakumar, V. D. Rao, C. R. Ramana-
than, L. Venkatraman, J. Org. Chem. 2001, 66, 3828; c) F. Toda,
Pure Appl. Chem. 2001, 73, 1137.
[16] A. M. Pivovar, K. T. Holman, M. D. Ward, Chem. Mater. 2001, 13,
3018.
[17] J. Valasek, Phys. Rev. 1921, 17, 475.
[18] a) D. W. Fu, Y. M. Song, G. X. Wang, Q. Ye, R. G. Xiong, T. Akuta-
gawa, T. Nakamura, P. W. H. Chan, S. D. Huang, J. Am. Chem. Soc.
2007, 129, 5346; b) W. W. Zhou, J. T. Chen, G. Xu, M. S. Wang, J. P.
Zou, X. F. Long, G. J. Wang, G. C. Guo, J. S. Huang, Chem.
Commun. 2008, 2762.
[19] a) S. Horiuchi, R. Kumai, Y. Tokura, Angew. Chem. 2007, 119, 3567;
Angew. Chem. Int. Ed. 2007, 46, 3497; b) H. Sun, J. Steeb, A. E.
Kaifer, J. Am. Chem. Soc. 2006, 128, 2820; c) R. Yerushalmi, A.
Brandis, V. Rosenbach-Belkin, K. K. Baldridge, A. Scherz, J. Phys.
Chem. A 2006, 110, 412.
[20] G. M. Sheldrick, SADABS, Program for Empirical Absorption Cor-
rection of Area Detector Data, University of Gçttingen, Gçttingen
(Germany), 1996.
[21] G. M. Sheldrick, SHELXTL97, Program for Crystal Structure Re-
finement, University of Gçttingen (Germany), 1997.
[22] Y. M. Jeon, J. Heo, C. A. Mirkin, Tetrahedron Lett. 2007, 48, 2591.
[7] a) G. Li, W. Yu, J. Ni, T. Liu, Y. Liu, E. Sheng, Y. Cui, Angew.
Chem. 2008, 120, 1265; Angew. Chem. Int. Ed. 2008, 47, 1245; b) G.
Li, W. Yu, Y. Cui, J. Am. Chem. Soc. 2008, 130, 4582.
[8] a) E. G. Jager, J. Knaudt, M. Rudolph, M. Rost, Chem. Ber. 1996,
129, 1041; b) B. Sreenivasulu, F. Zhao, S. Gao, J. J. Vittal, Eur. J.
Inorg. Chem. 2006, 2656; c) C. Baleiz¼o, H. Garcia, Chem. Rev.
Received: January 7, 2009
Published online: May 21, 2009
6434
www.chemeurj.org
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2009, 15, 6428 – 6434