1D tubular and 2d metal-organic frameworks based on a flexible amino acid derived organic spacer

Article abstract of DOI:10.1002/asia.200900078

The organic ligand bgxH₄, resulting from the condensation of two glutamate moieties on a xylene core, has been designed to generate chiral metal-organic frameworks with increased metal-metal distances in order to favor their potential porosity.

Full text of DOI:10.1002/asia.200900078

FULL PAPERS
DOI: 10.1002/asia.200900078
1D Tubular and 2D Metal–Organic Frameworks Based on a Flexible Amino
Acid Derived Organic Spacer
Jean-Noꢀl Rebilly, John Bacsa, and Matthew J. Rosseinsky*[a]
Dedicated to Professor C. N. R. Rao on the occasion of his 75th birthday
Abstract: The organic ligand bgxH4, re-
sulting from the condensation of two
glutamate moieties on a xylene core,
has been designed to generate chiral
metal–organic frameworks with in-
creased metal–metal distances in order
to favor their potential porosity. The in
situ reactivity of the ligand, through
cyclization, led to the bpgxH2 ligand,
which displays an extremely rich archi-
tectural potential. Under formate-gen-
erating conditions, two 1D tubular and
one 2D MOFs based on bpgxH2 have
been obtained, incorporating up to
three different organic linkers, and or-
ganized in an exquisite hierarchical
way by the combined effects of the
flexibility, the coordinating groups, and
the H-bonding groups of the ligand.
Furthermore, the tubular structures dis-
play pockets where water molecules
are encapsulated.
Keywords: amino acids · chirality ·
encapsulated water · metal–organic
frameworks · tubular structures
Introduction
mochiral systems that can find applications in enantioselec-
tive separation and asymmetric catalysis, which remains a
difficult goal to achieve with pure inorganic porous sys-
tems.[18,19]
Chiral MOFs can be crystallized from achiral building
blocks,[20] but this generally leads to a racemate, thus limit-
ing the possibility of enantioselective applications. Two main
synthetic approaches can be used to generate homochiral
porous frameworks. Porosity can be generated by means of
an achiral organic spacer while chirality is located on an
auxiliary chiral ligand.[21] A second strategy consists of using
chiral organic spacer to introduce both properties within the
framework.[10]
Naturally occurring chiral ligands are interesting starting
materials as they are readily available in enantiopure form
and on a gram scale. Several coordination polymers have
been reported with natural chiral ligands.[22–25] As protein
pockets play a crucial role in the selectivity of metalloen-
zymes, chiral aminoacids as ligands[24–37] are good candidates
to generate enantioselectivity in porous MOFs. Aspartic
Metal–organic frameworks (MOFs) have been the subject
of an increasing number of studies over the last fifteen
years.[1–4] The topology and internal surface functionality can
be controlled by the choice of the metal ions and network-
forming ligands. This synthetic approach thus permits the in-
corporation of specific properties within the material, such
as magnetism,[5,6] luminescence,[7] chirality,[8,9] and catalytic
centers.[10] The introduction of permanent porosity within
these coordination polymer materials turned them into alter-
native candidates for applications ranging from separation
and catalysis to gas storage,[11–14] with figures of merit that
are competitive with zeolites in those fields.[15–17] The weaker
framework-forming coordinate bonds in the MOF case per-
mits synthesis under milder conditions compared with zeo-
lites. This has a series of advantages — this paper addresses
the assembly of homochiral networks from chiral building
blocks and under relatively mild synthesis conditions, race-
mization of these units can be avoided, giving access to ho-
acid was used to form the NiACHTNUTGRNENG(U l-Asp)CAHUTNGTREN(NUGN bipy)0.5 framework and
a family of related derived systems.[27,28,38] Remarkable sorp-
tion enantioselectivity was observed in this porous chiral
system, and channel dimensions could be tuned in one direc-
tion by the choice of the achiral 4,4’-bipyridine type linker.
The other dimension is limited by the distance between the
chiral centers which is set by the dimensions of the amino
acid linker. In order to gain control over this dimension
[a] Dr. J.-N. Rebilly, Dr. J. Bacsa, Prof. M. J. Rosseinsky
Department of Chemistry
University of Liverpool
Liverpool L69 7ZD (UK)
Fax : (+44)151-794-3587
E-mail: m.j.rosseinsky@liv.ac.uk
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/asia.200900078.
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Chem. Asian J. 2009, 4, 892 – 903

while retaining a ligand based on natural starting materials
from the chiral pool, we adopted a related strategy to
extend the pore dimensions, which are limited by the sepa-
ration between the ligating groups of the amino acid, by
using a network-forming ligand easily derived from amino
acids by functionalizing them with a rigid aromatic separat-
ing platform. This paper will focus on the glutamic acid de-
rivative, which displays a specific reactivity.
ability owing to the amide group generated during cycliza-
tion.
Structural Description of 1–3
Reaction of lanthanum triflate with 0.75 equivalent of
bgxH4 in Water/EtOH/DMF (v/v/v 2:3:3) at 1008 for 18 h
leads to very small white needles of [La
ACHUTGTNNERNUG(bpgx)ACHTUNGTRENNUNG(HCO2)
Herein, we report the synthesis of a chiral spacer derived
from an amino acid and its use to generate framework struc-
tures. In the course of the reaction, the ligand undergoes in-
ternal cyclization, forming a chiral dicarboxylate ligand that
generates 1D tubular structures with lanthanum and praseo-
dymium and a 2D framework with copper and 4,4’-bipyri-
dine. Furthermore, the solvent conditions used here allowed
us to incorporate up to three different ligands in these struc-
tures by means of in situ generation of formate ions during
the reaction.
N
ACHTUNGTRENNUNG
The structure is made of tubular structures of [La
ACHTUNGTRENNUNG(bpgx)-
ACHTUNGTRENNUNG
Results and Discussion
Ligand a,a’-bis(N-glutamyl)-p-xylene (bgxH4) was obtained
from condensation of two equivalents of sodium glutamate
and one equivalent of terephthalaldehyde in water/MeOH,
followed by in situ reduction of imine bonds by sodium bor-
ohydride. This synthetic scheme generates a ligand which
displays two amino acid moieties covalently linked by a
xylene spacer core. Each amino acid moiety retains the co-
ordination abilities of its original natural amino acid, the
main difference being the nature of the amine function
which is now secondary rather than primary in the natural
amino acid. Metal–organic assemblies based on such ligands
are thus expected to be less compact than their natural
amino acid analogues. The presence of the xylene spacer be-
tween chiral centers imposes a minimum distance between
metal centers, which is a key factor to generate porosity in
these materials.
a,a’-bis(N-pyroglutamyl)-p-xylene (bpgxH2) forms in situ
during the solvothermal reaction with metal salts from cycli-
zation of bgxH4 and was not isolated (Scheme 1). The a-
amino acid pattern disappears and bpgxH2 can be consid-
ered as a chiral dicarboxylic acid ligand, acting as a flexible
spacer owing to its xylene core, and displaying H-bonding
Scheme 2. Construction of the tubular structures. a) Views of the two
chains of La ions (spheres) and the two sets of ꢂstaple-likeꢃ bpgx2À ligands
(rectangles). b) The carboxylates bridge the La ions to generate two
chains that are connected by the organic backbone of the ligand repre-
sented as a rectangle (dark grey at the front, light grey at the back) to
form the tubular structure. c) The formate ligands bridge metals on the
outside of the tube (dark grey) and bind to La in a bidentate fashion
inside the tube (light grey). They complete balancing the charge of La
and make the structure neutral. d) the coordination sphere of La ions is
completed by water molecules (dots).
À
Scheme 1. Synthetic scheme for ligand bpgxH2. Rotations about the CAr
À
CCH2 and CCH2 N bonds (curved arrows) are responsible for the relative
orientation of the two carboxylate functions of bpgxH2.
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M. J. Rosseinsky et al.
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mation where the two carboxylate groups are oriented in
the same direction (Schemes 2a and 2b). The carboxylates
bridge successive metal centers generating the two chains of
La ions. The organic backbone of the ligands links the two
chains to generate the metal–organic tube (Scheme 2b). To
balance the charge of the metal, formate ions are present,
bridging La ions on the outside of the tube, and bidentate to
single La centers on the inside of the tube (Scheme 2c). Fi-
nally, water molecules complete the La coordination sphere
(Scheme 2d). The inner formates are regularly spaced along
the tube in such a way that they divide the tubular structure
into pockets where two water molecules are encapsulated
and held by a local H-bonding network involving coordinat-
ed water molecules. The asymmetric unit contains four non
equivalent lanthanum ions. Two of these ions are eight coor-
dinate (Figure 1a) and display the same type of coordina-
tion sphere (La1, La4) and two are nine coordinate (Fig-
ure 1b) with similar coordination environments (La2, La3).
The coordination sphere is fully oxygenated in all cases. In
the case of La1 and La4, the eight oxygen atoms come from
one bidentate non-bridging formate function (2O), one
bridging formate acting as a monodentate ligand (1O) to-
wards La1 (or La4), four bridging carboxylate functions
from four bpgx2À ligands (1O each), and one water molecule
(Figure 1c). They form a distorted square antiprismatic envi-
ronment (Figure 1a). La2 and La3 are coordinated by one
oxygen atom from a bridging formate, three oxygen atoms
from three bridging carboxylate functions of bpgx2À ligands
(1O each), two oxygen atoms from a bridging carboxylate of
a bpgx2À ligand bound in a bidentate fashion (2O) and three
water molecules. They are in a distorted tricapped trigonal
prismatic geometry (Figure 1b).
The chains which make up the tubes consist of lanthanum
centers with two alternating geometries along the chain axis.
Each La1 ion is connected to two neighboring La3 ions by
four bridging carboxylates from four bpgx2À ligands, gener-
ating a chain structure based on alternating La1 and La3
(Figures 1c and 1d). The same pattern is observed for the
(La2, La4) pair, generating a chain of alternating La2 and
La4 (Figures 1c and 1d). Three of the bpgx2À carboxylates
bridge La1 and La3 (respectively La2 and La4) in a syn anti
(h1 h1 m2) fashion (Figures 1c and 1d). The last one bridges
them in a chelato-bridging (h2 h1 m2) mode. In order to bal-
ance the charge of the metal, a formate ion is present in the
coordination sphere of each metal center. In the asymmetric
unit, two of the formates act as bidentate non bridging (1,3)
ligands towards La1 and La4 (Figure 1c). The other two are
bridging ligands in a syn syn (h1 h1 m2) fashion, and connect
La1a to only one of its neighbors (La3b via O4 and O3, but
not La3a) on the one hand, and La4b to La2b (but not
La2a) via O9, and O10 on the other hand. Water molecules
complete the coordination sphere making La1 and La4 8 co-
ordinate square antiprisms and La2 and La3 9 coordinate
Figure 1. a) Polyhedron view of the square antiprismatic coordination
sphere of La4 (similar for La1), showing the bending induced by the bi-
dentate formate. b) Polyhedron view of the tricapped trigonal prismatic
coordination sphere of La2 (similar for La3). Eight O atoms form a dis-
torted square antiprism similar to the case of La4. The ninth atom (the
second O atom of the bidentate carboxylate of bpgx2À, on top) sits above
the top square forming the summit of a square pyramid. c) Views of the
1D chains based on La1 and La3 ions (top), La2 and La4 ions (bottom),
showing the coordination sphere of metal centers and the binding modes
of the different carboxylate functions. d) Same views as in (c) with La
polyhedral representation. Carboxylates from the bpgx2À ligands are rep-
resented bearing one more C than formates. La1, La4: light grey; La2,
La3: dark grey.
their two La neighbors in the chains by two bpgx2À carboxy-
lates. However, only one out of the four bpgx2À carboxylates
present in the coordination sphere is chelato-bridging, the
other three are simply bridging. As a consequence, La poly-
hedra share one corner with only one of their two La poly-
hedra neighbors in the chains. They are thus grouped along
the chains as pairs of corner-sharing polyhedra (Figure 1d).
The two 1D chains based on (La1, La3) and (La2, La4)
are both oriented along the a axis of the structure (Fig-
ure 1c) and are connected together by the organic backbone
À
tricapped trigonal prisms. Most La O bond lengths are be-
tween 2.415 and 2.605 ꢁ. The chelato-bridging mode is the
only mode that creates a shared corner between the two
bridged La octahedra. All La ions are linked to each of
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1D Tubular and 2D Metal–Organic Frameworks
of the bpgx2À ligands to lead to 1D tubular structures (Fig-
ures 2 and 3).
The bpgx2À carboxylates define a pseudo-equatorial plane
for La ions. The bridging formate ligands are located on the
Figure 2. Partial view of a tubular structure in 1 showing the connectivity
of the bpgx2À ligands. Three different bpgx2À ligands are highlighted in
medium grey, dark grey, and black. They share a maximum of three
metal centers. One of their carboxylate groups is involved in the bridging
within the (La1, La3) chain, the other in the bridging within the (La2,
La4) chain. The particular ꢂcisꢃ conformation of bpgx2À (carboxylates pro-
jecting in the same mean direction) limits the dimensionality to 1D. All
other ligands are omitted for clarity.
Figure 3. a) Views of the partial tubular structure formed by coordination
of La to bpgx2À linkers. Section of the tube in the (a, b+c) plane (left),
cross section of the tube in the (b,c) plane (right). bpgx2À linkers are de-
picted in black. All other ligands have been erased in these views.
b) Views of the full tubular structure formed by coordination of La to
bpgx2À linkers (in black), formate ligands (outer ligands in light grey,
inner ligands in medium grey), and water molecules. Section of the tube
in the (a, b+c) plane (left), cross section of the tube in the (b,c) plane
(right). The inner formates act as windows and divide the tube into pock-
ets, that each encapsulate two water guest molecules, held by hydrogen
bonding to the coordinated water molecules and formates present inside
the tube. c) Polyhedral view of a tube (section of the tube in the (a, b+c)
plane), showing the O atoms involved in the pockets hydrogen bonding
network. The guest water molecules (O3S and O6S) interact essentially
external side of the tube. They occupy one coordination site
on each La ion. The other external pseudo-axial sites are oc-
cupied by one (La1 and La4) or two (La2 and La3) of the
oxygen atoms of water molecules (Scheme 2d, Figure 3b).
The pseudo-axial coordination sites on La1 and La4 locat-
ed inside the tube are occupied by the two oxygen atoms of
the bidentate chelating formates, while one water molecule
sits on the pseudo-axial site of La2 and La3 (Scheme 2d,
Figure 3).
À
together (O3S O6S=3.338 ꢁ) and with the oxygen atoms of carboxy-
À
À
À
lates (O3S O1=3.338 ꢁ, O6S O61=3.256 ꢁ, O6S O6=3.393 ꢁ) and
À
À
coordinated water (O3S O2W=2.594 ꢁ, O6S O5W=2.373 ꢁ). La1 and
La4 are light grey spheres, La2 and La3 are dark grey spheres. The
oxygen atoms of the water molecules are depicted in dark grey, and hy-
drogen atoms are white.
In each bpgx2À ligand, one of the carboxylate function is
involved in the generation of the (La1, La3) chain and the
other in the generation of the (La2, La4) one. The two car-
boxylate functions are oriented almost in the same mean di-
rection and thus generate 1D tubular structures (Figures 2
and 3).
bpgx2À ligands, and the other two edges corresponding to
the xylene core of bpgx2À (Figures 3a and 3b). The axis de-
fined by the two benzylic C atoms of bpgx2À forms a 448
angle with the a axis (Figure 3c).
The xylene moities are twisted about their axis in such a
way that they all stack along the a direction, creating CH–p
interactions between the aromatic ring of one bpgx2À ligand
and the xylene CH2 group of its neighbor. This conforma-
tion of the aromatic ring reduces the inner volume of the
tube (Figures 3a and 3b). The channels arising from this
tubular structure are partially obstructed by the inner li-
gands (Figure 3b). Indeed, the La1 and La4 ions that bear
the bidentate formates on both sides of the inner surface of
There are four different bpgx2À ligands in the asymmetric
unit. Two correspond to mode A (the two carboxylates are
syn anti (h1 h1 m2) bridging, Scheme 3b), and two to mode B
(one carboxylate is syn anti (h1 h1 m2) bridging, the second is
chelato-bridging (h2 h1 m2), Scheme 3c) .
Each bpgx2À linker shares a maximum of three metal cen-
ters with another bpgx2À linker (Figure 2). This arrangement
of bpgx2À ligands generates a tubular structure, with a
pseudo-square cross-section, with two opposite edges based
on the lanthanum ions and two pyroglutamate moieties of
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The tubular structures in 1 are all oriented along a in the
crystal. Each tube has four nearest neighbor tubes. The
mean plane formed by La ions of a tube is rotated by 768
about a with respect to the mean plane of its neighboring
tubes (Figure 4a). The space between them is occupied by
Scheme 3. a) Binding modes of bpgx2À ligands in compounds 1, 2, and 3.
The carboxylate groups are both syn anti (h1 h1 m2) bridging in type A li-
gands. In type B ligands, one function is syn anti (h1 h1 m2) bridging and
the second is chelato-bridging (h2 h1 m2). In type C ligands, both functions
are bidentate non-bridging. b) Type B ligands found in 1. Left: one car-
boxylate is chelato-bridging and creates a pair of corner-sharing poly-
hedra, the other is simply bridging the two La ions belonging to another
pair. Right: Again, one carboxylate creates a pair of corner-sharing poly-
hedra via the chelato-bridging mode, the other, simply bridging, links two
La ions belonging to two different polyhedra pairs. c) Type A ligands
found in 1. None of the carboxylates is chelato-bridging: Thus, they donꢃt
create the polyhedra pairs. Left: one of the carboxylate connects two La
ions belonging to the same pair of corner-sharing polyhedra, the other
two La ions belonging to two different pairs. Right: both carboxylates
connect two La ions belonging to different pairs. d) Type C ligands found
in 3. All bpgx2À carboxylates are bidentate and non-bridging. La1, La4:
light grey; La2, La3: dark grey; Cu: medium grey polyhedra; O: dark
grey dots; C: medium grey; N: black.
Figure 4. a) View of two neighboring tubes showing the 768 angle formed
by the mean plane of their La ions. b) View along a of the packing of
tubular structures in 1. Two neighboring 1D substructures are highlighted
in green and purple. Interstitial water molecules connect three tubes by
hydrogen bonding to amide units and coordinated water molecules (high-
lighted in dotted lines).
the tubes, have coordinates along the a axis (tube axis) that
are only separated by 2.237 ꢁ. As a consequence, their for-
mate ligands are very close to each other and tend to close
the channels by dividing them into pockets (Figures 3b and
3c). This window pattern is repeated by a translation of a=
9.5208 ꢁ along the tube axis and leaves enough space in be-
tween to accommodate two water molecules (Figures 3b
and 3c), which interact by hydrogen bonding with the coor-
dinated water and, in a weaker way, with oxygen atoms of
the coordinated carboxylates and with one another.
water molecules (four per asymmetric unit). Each of them
sits in a pseudo-tetrahedral environment and is interacting
with three tubes through three hydrogen bonds involving
water molecules coordinated to La on the first tube, and an
oxygen atom of an amide function of bpgx2À on each of the
other two tubes (Figure 4b). The neutral amide bond, which
does not bind metal centers unlike the charged carboxylates,
is involved in the hydrogen bonding network and is thus re-
sponsible for the relative orientation of neighboring tubes
resulting from their mutual hydrogen bonding to a set of
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1D Tubular and 2D Metal–Organic Frameworks
mediating water molecules. These amide functions, intro-
duced in order to extend the amino acid core of the ligand,
thus organize the tubes within the crystal, giving the net-
work-forming ligand two roles stemming from the two dif-
ferent functional groups it supports.
A related compound 2 can be obtained in similar condi-
tions by replacing lanthanum triflate by praseodymium ni-
trate in the procedure described for 1. Structurally, 2 dis-
plays a building motif that is similar to the one described in
Schemes 2a and 2b. However, unlike 1, where formates bal-
ance the charge inside and outside the tubes (Scheme 2c), in
the structure of 2, the charge is balanced by three formates
(two outside and one inside the tubes) for one nitrate
(inside the tubes). Formally, one out of two inner formates
is replaced by a nitrate in the structure of 2 and consequent-
ly reduces the inner volume of the tubeꢃs pockets (see the
Supporting Information). Nevertheless, as evidenced by ele-
mental analysis of the bulk material, this structure is not
representative of the bulk phase, which corresponds, to a Pr
equivalent to 1 (see the Supporting Information). Reaction
of copper nitrate with one equivalent of bgxH4 and two
equivalents of 4,4’-bipyridine in water/EtOH/DMF (v/v/v
2:3:3) at 1008 for 18 h affords small blue crystals of [Cu-
ACHTUNGTRENNUNG(bpgx)0.5ACHTUNGTRENNUNG(HCO2)ACHTUNGTRENNUNG(bipy)]CAHTNUGTREN(UNNG H2O) 3. 3 crystallizes in the chiral
space group P21 (a=9.9916 (64) ꢁ, b=22.5295 (141) ꢁ, c=
10.0941 (62) ꢁ, b=113.163 (7)). 3 is remarkable as it is built
from three distinct framework forming ligands — bpgx and
bipy form an extended network from dimers bridged by for-
mate. The asymmetric unit contains two crystallographically
non equivalent copper ions, which however both play the
same chemical role in forming the structure. Both are six co-
ordinate and their coordination sphere is a distorted octahe-
dron based on two oxygen atoms of a (1,3) bidentate car-
boxylate function of a bpgx2À ligand, two nitrogen atoms
from bipyridine ligands, and two oxygen atoms from two
(1,1) h2 bridging formates. For both Cu1 and Cu2, the short-
est bonds form a square plane made of the two pyridine ni-
Figure 5. a) Views of the dimeric structure in 3 and the coordination
sphere of the Cu2+ ions. Cu: medium grey, N: black, O: dark grey, C:
light grey. Top: The shortest bonds forming a square plane and perpen-
dicular to the Jahn–Teller axis of Cu are highlighted in bold dark grey.
Bottom: Copper octahedra view showing the edge-sharing of the two Cu
centers within the dimeric unit bridged by formate. b) View of three 1D
substructures along the (a+c) direction, showing that each dimeric Cu
unit is connected to two neighbors by bpgx2À ligands and that each
bpgx2À ligand connects one Cu1 center to one Cu2 center. Along (a+c),
the angle between the carboxylate functions of bpgx2À is 1298, while the
angle formed by the mean plane of copper centers of two neighboring
double chains is 608.
À
trogen atoms sitting trans to each other (Cu1 N2=2.024 ꢁ,
À
À
À
Cu1 N1=2.025 ꢁ, Cu2 N4=2.030 ꢁ, Cu2 N5=1.965 ꢁ,
Figure 5a), one of the oxygen atoms of the bidentate car-
boxylate of bpgx2À (Cu1 O1=1.943 ꢁ, Cu2 O8=2.302 ꢁ,
À
À
Figure 5a), and the bridging oxygen atom of one of the
À
À
bridging formates (Cu1 O4=1.981 ꢁ, Cu2 O6=1.935 ꢁ,
ously an angular distortion and a bond length elongation
(Figure 5a). This arises from the bite angle of the chelate
À
À
Figure 5a). The O Cu N angles within those square planes
À
À
À
À
À
À
are close to 908, the highest deviations being N4 Cu2 O6=
92.438 and N1 Cu1 O4=89.738, and the O Cu O and N
Cu N angles are confined above 168.578. A fifth coordina-
carboxylate (O8 Cu2 O9=58.688, O1 Cu2 O2=56.638)
that prevents coordination near the axial position. The sixth
À
À
À
À
À
À
À
bonds are the longest of the coordination sphere (Cu1 O2=
À
tion site is occupied on one of the axial positions by the
bridging oxygen atom of the formate that is not involved in
the square planar coordination (O6 for Cu1, O4 for Cu2).
The corresponding bonds are much longer than the equato-
rial ones ((Cu1 O6=2.332 ꢁ, Cu2 O4=2.452 ꢁ, Fig-
ure 5a), which can be attributed to the Jahn–Teller distor-
tion along these directions. The final coordination site is oc-
cupied by the second oxygen atom of the bidentate carbox-
ylate of bpgx2À and is responsible for the main distortion
with respect to the octahedral geometry, which is simultane-
2.592 ꢁ, Cu2 O9=2.410 ꢁ). Atoms O4 and O6 are the
bridging atoms of formates that bind metals in a (1,1) h2
mode. Each of them is involved in equatorial coordination
on one site with a short bond and axial coordination on the
other site with a longer bond arising from the Jahn–Teller
elongation. As a consequence, the bridging is asymmetric
and a dimeric structure based on a highly distorted diamond
À
À
À
À
À
arrangement (Cu1 O4 Cu2 O6) is generated (Figure 5a).
This structure can also be viewed as two edge-sharing octa-
À
hedra, the shared edge being O4 O6.
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The oxygen atoms of the formates, being bridging atoms
boxylates of one bpgx2À ligand form an angle of 1298. The
conformation adopted by bpgx2À in 3 is thus different from
the ꢂcisꢃ one observed in 1. This will thus create an angle be-
tween the mean plane of the dimer pair of Cu ions of two
neighboring 1D substructures linked by the bridging bpgx2À.
However, owing to the asymmetry of the bidentate binding
À
in a diamond arrangement, define a common plane (Cu1
À
À
O4 Cu2 O6) for Cu1 and Cu2 that also includes all the
other coordinating oxygen atoms (O8, O9, O1, O2, Fig-
À
ure 5a). Consequently, the Cu N bonds of both Cu1 and
Cu2 are perpendicular to this plane and thus parallel to
each other. As the connectivity of 4,4’-bipyridine is linear, a
one-dimensional substructure is generated by connecting the
dimeric copper units with the bipy linker in the direction
À
mode of the carboxylate (one Cu O bond is far longer than
the other), this angle is only 608 and not the expected 1298
(Figure 5b). Along the (a+c) direction (principal axis),
neighboring double chains displays an offset of 6.56 ꢁ corre-
sponding to the distance between the planes of the two car-
boxylate functions of bpgx2À (Figure 6b). From a symmetry
point of view, the arrangement of neighboring double chains
linked by bpgx2À ligands produces a 21 screw axis of space
group P21 along b.
À
À
À
perpendicular to the (Cu1 O4 Cu2 O6) plane. Bipy linkers
connect one Cu1 center to another Cu1, or one Cu2 center
À
to another Cu2. This 1D Cu bipy substructure is thus made
of two parallel Cu–bipy chains, one made of Cu1 centers,
the other of Cu2 centers, linked by the bridging formates
(Figure 6a). The last two copper coordination sites that are
The arrangement of double chains connected by bpgx2À li-
gands generates a 2D structure of [CuACHTUNGTREN(NUNG bpgx)ACHNUTRTGEG(NUNN HCO2)ACHTUNGTRENNUNG(bipy)]
that looks like a folded sheet due to the 608 angle formed
by the mean plane of copper centers in neighboring double
chains (Figure 5b). All sheets have a mean plane that is par-
allel to the (a+c, b) plane. They are ꢂfoldedꢃ along the (a+c)
direction, and the zone of folding is located on the aromatic
ring of the bpgx2À ligands (Figure 7). Neighboring sheets are
generated by translation along a and c. They are thus piled
up on top of one another in such a way that the convex part
of one sheet fills the concave part of its neighbors, leaving a
limited intersheet space (Figure 7a). Nevertheless, this space
represents 12.8% of the cell volume. PLATON locates two
voids per unit cell. They are located between the aromatic
rings of bpgx2À ligands belonging to two neighboring sheets
and each account for 144 electrons (Figure 7b). This residu-
al electronic density was attributed to solvent molecules (for
water molecules only, it would correspond to 14H2O per
unit cell). The presence of the oxygen atoms of the bpgx2À
amide bond and the formate ligand in the vicinity of the
voids determined by PLATON suggests these functions are
involved in hydrogen bonding with the interstitial water
molecules and play a role in the organisation of sheets in
the crystal.
Figure 6. a) View of one double chain in 3 showing how two sets of bipy
linkers connects the Cu1 and Cu2 centers into parallel chains bridged by
formate. b) View of two neighboring bridged parallel chains in 3 showing
the offset of 6.56 ꢁ between them.
not involved in the formation of this double chain are occu-
pied by the oxygen atoms of a bidentate carboxylate of
bpgx2À (O8 and O9 for Cu2 centers, O1 and O2 for Cu1
centers, Figure 5b). The second carboxylate of this bpgx2À
ligand binds a copper center of a neighboring chain of bipy-
linked dimers in a similar manner (bpgx2À adopts binding
mode ꢂCꢃ, Schemes 3a and 3d, Figure 5b). They only act as
terminal ligands to lock two coordination sites on each Cu
center (Schemes 3a and 3d). The principal axes of all
double chains are oriented along the same direction (a+c)
in the crystal structure. Consequently, each 1D substructure
is connected to two neighbors by two sets of parallel bpgx2À
ligands. Each bpgx2À ligand binds one Cu1 and one Cu2
center (Figure 5b). Each of the two carboxylate functions
Synthesis and Characterisation
1 can be obtained as a pure phase using a slightly different
ratio of reagents and solvents than the one used to obtain
the single crystals used in structure determination. Stoichio-
metric reaction of lanthanum triflate and bgxH4 in Water/
EtOH/DMF (v/v/v 3:3:2) at 1008 for 18 h leads to the isola-
tion of 1 as a homogeneous solid made of very thin white
needles. Phase purity is shown by a LeBail fit to powder X-
ray diffraction data, indicating a single phase with cell pa-
rameters close to those of the single crystal determined at
150 K a=26.64323 (78) ꢁ, b’=17.71220 (50) ꢁ, c=9.04766
(39) ꢁ, b=97.69128 (273) in space group P21 (Figure S1 in
the Supporting Information). The b’ parameter is very close
to the b parameter of the crystal structure.
À
À
À
are included in a (Cu1 O4 Cu2 O6) plane (i.e., perpendic-
ular to (a+c)). The distance between the planes of the two
carboxylate functions of one bpgx2À ligands (along (a+c)) is
6.56 ꢁ. Within those planes, the directions of the two car-
Elemental analysis is in agreement with the crystal struc-
ture formula [LaCAHTNUGTRNE(NNGU bpgx)ACUHTTGNERNNU(GN HCO2)AHCTNUTRGEGN(NNU H2O)2]ATHCNUGTREN(NUGN H2O)ACHNUTRGTENG(UNN EtOH)0.33.
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1D Tubular and 2D Metal–Organic Frameworks
isolated as small blue crystals. Phase purity is evidenced by
LeBail fit of the powder data (Figure S4 in the Supporting
Information) which yields cell parameters, a=10.22455
(75) ꢁ, b=22.583 (1) ꢁ, c=10.0612 (8) ꢁ, b=113.724 (3) in
space group P21, which is very close to the cell obtained
from single crystal diffraction.
Elemental analysis is in agreement with the crystal struc-
ture formula [CuCAHTUGNTERN(UNNG bpgx)0.5ACHTUNGTRENG(NU HCO2)ACHUTNGERTG(NNUN bipy)]ACHTNGUTRENUN(GN H2O). The first
weight loss observed in TGA (Figure S5 in the Supporting
Information), attributed to solvent loss, starts at room tem-
perature up to 1608C (observed 3%, calc. 3.9%) and is fol-
lowed by a gradual decomposition to CuO between 1808C
and 5008C (observed weight loss 79.3%, calculated from
analysis formula 79%). The solvent content (one water mol-
ecule per copper) is significantly smaller than the one evalu-
ated from the intersheet residual electronic density in the
crystal structure. This is consistent with desolvation as soon
as the crystals are removed from the mother liquor, as TGA
shows a solvent loss starting at room temperature.
Discussion
Amino acids as ligands display at least two potentially coor-
dinating functions, the amino and the carboxylate groups,
which usually coordinate to metals in a chelate binding
mode generating a 5 membered ring. The carboxylate can
become bridging within a coordination polymer, with the re-
sulting 1,3 syn-anti bridging mode imposing a typical separa-
tion of 5.5 ꢁ between connected metal centers. Further co-
ordinating functions can be located on the side chain (as in
the cases of cysteine and aspartic acid) extending the con-
nectivity of the ligand and thus the dimensionality of the
metal–organic framework. In order to introduce porosity
within the framework, we synthesized spacers derived from
amino acids by condensation of amino acids and terephtha-
laldehyde followed by in situ reduction. In this way, two che-
lating chiral sites are gathered in one ligand and separated
by a xylene moiety, creating a distance of approximately
7.5 ꢁ between the nitrogen atoms of the amino acids. A re-
lated approach has been used very recently to generate
chiral ligands from amino-acids via the formation of an
amide bond between terephthaloyl chloride and the amino
group of aminoacids.[39] The approach described here retains
the whole amino acid functionality on both sides of a ter-
ephthalic core. The glutamic acid derivative bgxH4
(Scheme 1) was thus reacted with different metal salts and
neutral organic linkers to generate extended structures.
In the three structures reported here, bgxH4 undergoes in
situ cyclization to generate bpgxH2. This cyclization is a
common feature of glutamic acid.[40] Pyroglutamic acid is
generated by intramolecular reaction of the amino group
with the carboxylic acid of the side chain of glutamic acid,
forming an amide bond and a thermodynamically favored
five membered ring. The reaction is catalyzed by Brønsted
or Lewis acids. During the formation of 1, 2, and 3, the
metal probably acts as a Lewis catalyst to turn bgxH4 into
bpgxH2 which can then react with the metal as a dicarboxy-
Figure 7. a) View of the packing of [CuACHTUNGTREN(NNUG bpgx)ACHTUNTRGEG(NNUN HCO2)ACHTNUGTREN(GUNN bipy)] sheets
within the crystal structure of 3 along the (a+c) axis. Four different
sheets are represented. The sheets are folded along (a+c) owing to the
conformation of bpgx2À ligands. The benzene rings of bpgx2À ligands con-
stitute the folding zone of the sheet (circled). b) View of the packing in
3, showing the voids detected by PLATON (spheres), located between ar-
omatic rings of bpgx2À ligands belonging to two neighboring sheets.
TGA shows a weight loss of 8.2% centered around 1258C
(attributed to interstitial solvent and coordinated water situ-
ated outside of the tubes, 8.4% expected) and a smooth de-
crease of 3.3% between 1258C and 3408C (attributed to
guest and coordinated water molecules inside the tubes,
2.94% expected) while the weight loss observed in the tem-
perature range from 3608C corresponds to the decomposi-
tion of 1 to La2O3 (observed 60.2%, calculated 62%) (Fig-
ure S2 in the Supporting Information). 1 is thus a robust
framework stable to 3608C. After removal of the solvent at
1008C overnight, the crystalline features of the powder pat-
tern of 1 disappear and are replaced by a main broad peak
centered around 2q=20.38 (d spacing of 5.05 ꢁ) and some
smaller broad peaks, suggesting a loss of crystallinity while
retaining some local order. After soaking the evacuated
sample in water at room temperature for one day, the crys-
talline peaks characteristic for 1 reappear (Figure S3 in the
Supporting Information).
3 is obtained as a pure phase by reaction of copper nitrate
with bgxH4 and 4,4’-bipyridine in the ratio Cu/bgxH4/bipy
1:1:2 in Water/EtOH/DMF v/v/v 3:3:2 at 1008 for 18 h. 3 is
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M. J. Rosseinsky et al.
FULL PAPERS
late ligand. The bpgxH2 ligand displays a flexible backbone.
Those two aspects are probably the driving forces that favor
the ꢂstapleꢃ conformation of bpgx2À in 1 and 2.
À
À
N
In particular, rotations about the CAr CCH2 and the CCH2
bonds are responsible for the different relative orientations
of the two carboxylate functions observed in 1, 2, and 3
(Scheme 1). A wide range of conformations are thus accessi-
ble, among which a pseudo ꢂcisꢃ conformation, where the
carboxylate functions are oriented along a similar mean di-
rection, giving the ligand a ꢂstapleꢃ shape.
In the case of 3, the ligand adopts a conformation where
the carboxylates project away from each other and their ori-
entations form an angle of 1298. This corresponds to the
general situation depicted in Scheme 4a. In 3, the metallic
node is a formate-bridged dimeric copper unit and the sub-
structure generated by coordination of bpgx2À to these
nodes is a chain (Figure 5b). Along (a+c), the axes of the
carboxylates form a high angle of 1298. They project away
from each other (Figure 5b), preventing the structure from
coiling on itself as in 1 and 2 (Scheme 4). This situation is
probably the result of the lower coordination number of
copper compared to lanthanides, as well as the presence in
the reaction medium of ligands such as 4,4’-bipyridine that
compete with the bridging mode of the carboxylate. The
flexibility of bpgx2À allows conformations in which the
ligand can act either as a coil-generator (Scheme 4b, 4c) or
as a spacer (Scheme 4a). The ꢂstaple-conformationꢃ of
bpgx2À observed in 1 and 2 generates the formation of a
loop that brings metallic nodes in the vicinity of other car-
boxylates (Scheme 4b) and allows them to become bridging
Coordination of bpgx2À to metal centers can lead to ex-
tended linear 1D chain substructures as would be formed by
any dicarboxylate ligand (Scheme 4a). However, the ꢂcisꢃ
À
and extend the number of M O bonds (Scheme 4c). It thus
requires oxophilic metals that can access a high coordination
number, typically lanthanides. The conformation of bpgx2À
observed in 3, with a high angle between the directions of
the two carboxylates, prevents this phenomenon and sees
carboxylates acting as simple non-bridging ligands, with the
presence of the bipy ligands organizing the carboxylate-
bridged chains into higher order structures. It is thus adapt-
ed to transition metals with a lower coordination number,
and a better affinity for nitrogen ligands. In those reaction
conditions, lanthanides would thus tend to generate low di-
mensional structures, as the structure coils, to keep metal
centers close to each other through bridging carboxylates. In
the copper case, bpgx2À carboxylates are bidentate non-
bridging and keep metal centers away from each other in a
1D arrangement, leaving free sites in the coordination
sphere to allow the framework to extend to other dimen-
sions by means of a second linker. The use of bipy leads to
the 2D structure of 3. In all structures, the amide bond of
bpgx2À is not involved in coordination, but plays a crucial
role in the way the 1D and 2D substructures are arranged
within the crystal. In 1, it organizes the tubular structures by
an interstitial water molecule hydrogen-bonded to two
amide oxygen atoms belonging to different tubes. In 3, the
presence of those functions in the vicinity of the ꢂsolvent
voidsꢃ suggests a similar organization. This ligand illustrates
the fact that H-bonding interactions play a key role in the
crystal generation.[41,42] The carboxylate functions of bpgx2À
generate metal–organic structures that are organized by a
second functionality, the amide groups.
Scheme 4. a) Reaction of bpgx2À with a metal generates a chain when the
carboxylates act as monodentate ligands; b) This chain can coil on itself
if bpgx2À adopts the ꢂcisꢃ conformation; c) This arrangement allows the
formation of extra coordination bonds as the carboxylates become bridg-
ing which is impossible in the linear chain arrangement depicted in (a). b
and c views: Top: The metal centers at the front are represented as large,
dark spheres, those at the back are light grey; the bridging carboxylate
2À
À
M O bonds are represented as dotted lines. Bottom: Case of 1. bpgx is
highlighted in dark grey (front) and light grey (back). La is medium grey.
À
The bridging M O bonds are represented as thick dotted lines.
conformation in particular tends to favor the coiling of this
1D chain (Scheme 4b): Unlike the linear 1D arrangement,
this coil arrangement allows every carboxylate function to
become bridging, which is entropy favored (Scheme 4c).
Indeed, if the 1D chain coils on itself and its carboxylates
become bridging, coordinated solvent molecules will be sub-
stituted and released, leading to an increase in entropy. Fur-
thermore, the encapsulated water molecules can act as tem-
plates for the formation of the coils, as they fit perfectly in
the generated pockets and are held inside by H-bonding.
Nevertheless, the use of bpgx2À allows us to constrain the
distances between metal centers. Indeed, the 1D chain sub-
structures of lanthanide ions in 1 and 2 or copper and bipyr-
idine in 3, are separated by the bpgx2À ligand by 9.80 ꢁ in 1,
10.04 ꢁ in 2, and 9.55 ꢁ in 3. This validates our approach,
900
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Chem. Asian J. 2009, 4, 892 – 903

1D Tubular and 2D Metal–Organic Frameworks
as this distance is, as expected, considerably increased with
respect to the one induced by a single amino acid ligand
(typically 5.5 ꢁ).
metal Cu in comparison with the lanthanides. The role of
formate in all cases is to rigidify the inorganic structure by
bridging metal centers and by locking specific coordination
sites. In this manner, the flexibility of the framework is thus
confined to the organic backbone of bpgx2À (by rotation
Flexibility is a useful tool to generate various types of
framework topologies. Nevertheless, it can decrease the
crystallinity of materials. In the examples reported here, this
is avoided by the presence of a secondary bidentate ligand,
formate, which rigidifies the structure. Formates are not in-
troduced directly in the reaction mixture. They are generat-
ed in situ from the hydrolysis of DMF. Indeed, the solvent
mixture contains water and DMF, heated at 1008C, condi-
tions harsh enough to hydrolyze DMF to formic acid and di-
ethylamine. This has the advantage of slowly generating a
base (HNEt2) and a secondary ligand (formate) during the
course of the reaction. Attempts to generate 3 from the
copper formate salt in water/methanol mixtures at the same
temperature (1008C) led to a reported phase incorporating
bipy but not bpgx2À. Formate is a small ligand, with versatile
coordination (mono or bidentate), that is relatively rigid
owing to its limited organic backbone. It can thus easily
complete the coordination sphere of metal without steric
hindrance, bridge metal centers, and rigidify the inorganic
part of the system. In 1 and 2, formate ligands display (1,3)
(h1 h1 m2) syn-syn bridging modes on the outside of the
tubes, improving the linkage between metals within the two
lanthanide chains constituting each tube. They also act as bi-
dentate non-bridging ligands inside the tubes, and thus only
leave specific coordination sites accessible to bpgx2À carbox-
ylates in the coordination sphere. When 1 and 2 are evacuat-
ed, the crystal structure peaks disappear, as solvent mole-
cules organize the tubes with respect to one another by hy-
drogen bonding. Nevertheless, a broad peak replaces them
(centered around a d spacing of 5.05 ꢁ), which indicates
that local ordering remains despite desolvation. The crystal
structure peaks reappear when the evacuated solid is soaked
in water, suggesting that the tube substructure is retained
upon desolvation, and that rehydration restores the hydro-
gen bonding network responsible for their organization
within the structure. This d spacing of 5.05 ꢁ might be relat-
ed to the distance between two metal centers bridged by the
carboxylate groups of a bpgx2À ligand which in the solvated
structures are between 4.608 ꢁ and 4.945 ꢁ in 1 and be-
tween 4.612 ꢁ and 5.032 ꢁ for 2 (Figure S12 in the Support-
ing Information).
À
À
about CAr
CCH2 and the CCH2 N bonds).
The reaction conditions used here, that gather the use of
a flexible ligand and a formate-generating mixture of sol-
vents, also allows us to incorporate up to three different or-
ganic linkers in the materials. Indeed, in all cases, two link-
ers, bpgx2À and formate, bridge ions and balance their
charge. In the case of 3, another neutral ligand is incorporat-
ed to further extend the dimensionality. This situation is not
common. Most frameworks display a maximum of two or-
ganic linkers; either two charged linkers both balancing the
charge of the metal[43,44] or one balancing the charge of the
metal and the other neutral.[45–48] In some cases, an extra
linker is present to enhance rigidity, in the form of an inor-
ganic oxo or hydroxo bridge for instance, generating cluster
nodes or more extended substructures.[11,49,50] Formate is an
organic linker that plays a similar role, arising from its small
size, its bridging ability, and its in situ formation during the
synthesis of the framework.
Conclusions
Three extended frameworks have been synthesized using a
chiral spacer ligand derived from glutamic acid. The flexibil-
ity of the ligand backbone gives access to several topologies
and dimensionalities depending on the type of metal center
used in the synthesis. The reaction conditions produced in
situ generation of formate ions, leading to 1D and 2D
frameworks incorporating up to three different organic link-
ers. Formate ions also rigidify the inorganic architectures,
giving access to coordination polymers where flexibility is
mainly confined to the organic part of the framework. This
synthetic strategy could be generalized to obtain open
metal–organic frameworks from flexible ligands that are
rigid enough to remain crystalline but that also display a cer-
tain degree of flexibility than could lead to properties such
as guest-responsive behavior, gating processes, or kinetic
trapping.[51]
In 3, formates form the diamond-shaped Cu2O2 core of
the structure by a (1,1) h2 bridging mode. This motif locks
two cis coordination sites on each Cu of the dimer and si-
multaneously locks the relative orientation of the coordina-
tion spheres of the two edge-sharing octahedral Cu centers.
4,4’-bipyridine tends to generate chain substructures and for
this purpose locks two trans coordination sites on the axis
perpendicular to the diamond-shaped Cu2O2 core, leaving
the bpgx2À carboxylates only the last two sites that sit trans
to the formate oxygen atoms. The extended bridging rather
than coil-forming cis conformation adopted by the bpgx
ligand in 3 reflects the smaller and better-defined, more reg-
ular coordination sphere typically adopted by the transition
Experimental Section
Single Crystal X-ray Diffraction
The single-crystal diffraction data were collected on station 9.8 of the
Synchrotron Radiation Source at Daresbury Laboratory. Station 9.8 is a
high flux single crystal facility which utilizes a Bruker-Nonius APEXII
CCD area detector and D8 diffractometer at an X-ray wavelength of
0.6710 ꢁ (1) and 0.6884 ꢁ (2, 3). Data were recorded at 150 K. The re-
flection data were integrated using APEX II software.[52] The data were
corrected for absorption, decay and other systematic errors using
SADABS V2008-1.[53] The structure was solved (by direct methods) and
refined using SHELX-97.[54]
Chem. Asian J. 2009, 4, 892 – 903
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901

M. J. Rosseinsky et al.
FULL PAPERS
Thermal Analysis
Acknowledgements
TGA data were recorded using a Seiko S-II instrument.
X-ray Powder Diffraction
We thank the EPSRC for funding under EPSRC/C511794 and for access
to the SRS, and the Leverhulme Trust for support of J.N.R. We thank the
Royal Society for a Wolfson Research Merit Award to MJR.
X-ray powder diffraction data were collected with CoKa1 radiation with a
Panalytical X’pert Pro Multi-Purpose diffractometer in reflection geome-
try and CuKa1 radiation with a Stoe Stadi-P diffractometer using a linear
position sensitive detector.
[1] B. F. Hoskins, R. Robson, J. Am. Chem. Soc. 1990, 112, 1546.
[2] S. R. Batten, R. Robson, Angew. Chem. 1998, 110, 1558–1595;
Angew. Chem. Int. Ed. 1998, 37, 1460–1494.
[3] M. Eddaoudi, D. B. Moler, H. Li, B. Chen, T. M. Reineke, M.
OꢃKeeffe, O. M. Yaghi, Acc. Chem. Res. 2001, 34, 319–330.
[4] O. R. Evans, W. Lin, Acc. Chem. Res. 2002, 35, 511–522.
[5] M. Verdaguer, M. Julve, A. Michalowicz, O. Kahn, Inorg. Chem.
1983, 22, 2624–2629.
[6] E. Pardo, D. Cangussu, M.-C. Dul, R. Lescouꢅzec, P. Herson, Y.
Journaux, E. F. Pedroso, C. L. M. Pereira, M. C. MuÇoz, R. Ruiz-
Garcꢆa, J. Cano, P. Amorꢇs, M. Julve, F. Lloret, Angew. Chem. 2008,
120, 4279–4284; Angew. Chem. Int. Ed. 2008, 47, 4211–4216.
[7] G. F. De Sꢈ, O. L. Malta, C. De Mello Donega, A. M. Simas, R. L.
Longo, P. A. Santa-Cruz, E. F. Da Silva Jr, Coord. Chem. Rev. 2000,
196, 165–195.
[8] W. Lin, J. Solid State Chem. 2005, 178, 2486–2490.
[9] D. Bradshaw, T. J. Prior, E. J. Cussen, J. B. Claridge, M. J. Rossein-
sky, J. Am. Chem. Soc. 2004, 126, 6106–6114.
[10] J. S. Seo, D. Whang, H. Lee, S. I. Jun, J. Oh, Y. J. Jeon, K. Kim,
Nature 2000, 404, 982–986.
[11] M. Eddaoudi, J. Kim, N. Rosi, D. Vodak, J. Wachter, M. OꢃKeeffe,
O. M. Yaghi, Science 2002, 295, 469–472.
[12] X. Zhao, B. Xiao, A. J. Fletcher, K. M. Thomas, D. Bradshaw, M. J.
Rosseinsky, Science 2004, 306, 1012–1015.
[13] O. M. Yaghi, M. OꢃKeeffe, N. W. Ockwig, H. K. Chae, M. Eddaoudi,
J. Kim, Nature 2003, 423, 705–714.
Synthesis
All reagents used in the ligand synthesis as well as (CF3SO3)3La·xH2O
and Pr
ACHTUNGTRENNUNG(NO3)3·6H2O were purchased from Sigma–Aldrich. Cu-
ACHTUNGTRENNUNG(NO3)2·3H2O and solvents were purchased from VWR.
a,a’-bis(N-glutamyl)-p-xylene (bgxH4): Glutamic acid (4 g, 27.2 mmol)
was dissolved in an aqueous solution of sodium hydroxide (2m, 20.4 mL).
A solution of terephthalaldehyde (1.52 g, 11.34 mmol) in 60 mL of etha-
nol was added and the mixture was stirred at room temperature for
30 min, then cooled to 08C. Sodium borohydride (0.604 g, 15.9 mmol)
was added in small portions and stirring was continued at room tempera-
ture for 90 min.
A second portion of terephthalaldehyde (0.334 g,
2.5 mmol) was added, and the mixture was stirred for 20 min. Finally, a
second portion of sodium borohydride (0.121 g, 2.9 mmol) was added and
the suspension stirred for 45 min. The mixture was extracted with diethyl
ether (2ꢄ50 mL) to remove excess terephthalaladehyde and the aqueous
layer, diluted with 10 mL of water, was acidified at 08C to pH 2 by drop-
wise addition of concentrated HCl, at which point the compound precipi-
tated as a white powder. The suspension was filtered, and washed with
cold water. The white powder was then refluxed in ethanol for one hour,
filtered again, and dried in air. Yield: 45%; 1H NMR (bgxH4. 4 LiOH in
D2O): d=1.85 (m, 4H); 2.20 (t, 4H); 3.13 (t, 2H); 4.64 (d, 2H); 4.78 (d,
2H); 7.36 ppm (s, 4H); [bgxH4](H2O)0.33: M=402.2; elemental analysis:
calcd (%) for C18H24.66N2O8.33: C 53.73, H 6.18, N 6.96; found: C 53.78,
H 6.17, N 6.69.
[LaACHTUNGTRENNUNG(bpgx)ACHTUNGTRENNUNG(HCO2)ACHTUNGTRENNUNG(H2O)2]ACHTNUGTERN(UNGN H2O)1.5 1: Lanthanum triflate (0.03 g,
[14] C. D. Wu, A. Hu, L. Zhang, W. Lin, J. Am. Chem. Soc. 2005, 127,
8940–8941.
[15] U. Mueller, M. Schubert, F. Teich, H. Puetter, K. Schierle-Arndt, J.
Pastre, J. Mater. Chem. 2006, 16, 626–636.
[16] L. Alaerts, C. E. A. Kirschhock, M. Maes, M. A. Van der Veen, V.
Finsy, A. Depla, J. A. Martens, G. V. Baron, P. A. Jacobs, J. F. M. De-
nayer, D. E. De Vos, Angew. Chem. 2007, 119, 4371–4375; Angew.
Chem. Int. Ed. 2007, 46, 4293–4297.
[17] L. Alaerts, E. Seguin, H. Poelman, F. Thibault-Starzyk, P. A. Jacobs,
D. E. De Vos, Chem. Eur. J. 2006, 12, 7353–7363.
0.05 mmol) and bgxH4 (0.020 g, 0.05 mmol) were mixed with 2 mL of
water/EtOH/DMF (v/v/v 3:3:2) in a 12 mL scintillation vial and reacted
at 1008 for 18 h. The product crystallized as white needles that were fil-
tered, washed thoroughly with water and ethanol and dried in air. Yield:
81%; [La
(bpgx)
E
E
(H2O)
N
: M=611.6; elemental
analysis: calcd (%) for C19.66H27LaN2O11.33
:
La 22.71; found: C 38.79, H 4.24, N 4.46, La 22.91. Single crystals suitable
for X-ray diffraction were obtained from the reaction of lanthanum tri-
flate (0.03 g, 0.05 mmol) and bgxH4 (0.015 g, 0.037 mmol) in 2 mL of
water/EtOH/DMF (v/v/v 2:3:3) in a 12 mL scintillation vial and reacted
at 1008 for 18 h.
[18] J. M. Newsam, M. M. J. Treacy, W. T. Koetsier, C. B. De Gruyter,
Proc. R. Soc. London Ser. A 1988, 420, 375–405.
[19] M. W. Anderson, O. Terasaki, T. Ohsuna, A. Phllippou, S. P.
MacKay, A. Ferreira, J. Rocha, S. Lidin, Nature 1994, 367, 347–351.
[20] T. Ezuhara, K. Endo, Y. Aoyama, J. Am. Chem. Soc. 1999, 121,
3279–3283.
[21] C. J. Kepert, T. J. Prior, M. J. Rosseinsky, J. Am. Chem. Soc. 2000,
122, 5158–5168.
[PrACHTUNGTRENNUNG(bpgx)ACHTUNGTRENNUNG(HCO2)0.75ACHTUNGTRENNUNG(NO3)0.25ACUHTGNTERN(NUNG H2O)2]CAHTNUTGRENUG(N H2O)1.5 2: Praseodymium nitrate
hexahydrate (0.022 g, 0.05 mmol) and bgxH4 (0.020 g, 0.05 mmol) were
mixed with 2 mL of water/EtOH/DMF (v/v/v 3:3:2) in a 12 mL scintilla-
tion vial and reacted at 1008 for 18 h. The product crystallized as white-
greenish needles that were filtered, washed thoroughly with water and
ethanol, and dried in air. Yield: 82%; [PrACHTUNGRTENN(NUG bpgx)ACHTNUTREGG(NNUN HCO2)]ACHTUNGRTEN(NUGN H2O)3.5: M=
[22] D. N. Dybtsev, A. L. Nuzhdin, H. Chun, K. P. Bryliakov, E. P. Talsi,
V. P. Fedin, K. Kim, Angew. Chem. 2006, 118, 930.
607.3; elemental analysis: calcd (%) for C19H26PrN2O11.5: C 37.57, H 4.31,
N 4.61, Pr 23.20; found: C 37.86, H 4.12, N 4.88, Pr 22.88.
[23] S. Thushari, J. A. K. Cha, H. H. Y. Sung, S. S. Y. Chui, A. L. F.
Leung, Y. F. Yen, I. D. Williams, Chem. Commun. 2005, 5515–5517.
[24] E. V. Anokhina, A. J. Jacobson, J. Am. Chem. Soc. 2004, 126, 3044–
3045.
[25] E. V. Anokhina, Y. B. Go, Y. Lee, T. Vogt, A. J. Jacobson, J. Am.
Chem. Soc. 2006, 128, 9957–9962.
[CuACHTUNGTRENNUNG(bpgx)0.5ACHTUNGTRENNUNG(HCO2)ACHTUNGTRENNUNG(bipy)]ACHTUNGTREN(NGUN H2O) 3: Copper nitrate trihydrate (0.018 g,
0.075 mmol), bgxH4 (0.030 g, 0.075 mmol) and 4,4’-bipyridine (0.024 g,
0.15 mmol) were mixed with 2 mL of water/EtOH/DMF (v/v/v 3:3:2) in a
12 mL scintillation vial and reacted at 1008 for 18 h. The product crystal-
lized as blue needles that were filtered, washed thoroughly with water
and ethanol, and dried in air. Yield: 90%; [Cu
ACHTUGNNERTU(NGN bpgx)0.5ACHTUNREGTG(NNNU HCO2)ACTHUNGTREN(NUGN bipy)]-
[26] M. J. Ingleson, J. Bacsa, M. J. Rosseinsky, Chem. Commun. 2007,
3036–3038.
ACHTUNGTRENNUNG
C 52.00, H 4.36, N 9.10, Cu 13.76; found: C 52.16, H 4.29, N 9.15,
Cu 13.69. Single crystals suitable for X-ray diffraction were obtained
from the reaction of copper nitrate trihydrate (0.048 g, 0.20 mmol),
bgxH4 (0.040 g, 0.10 mmol), and 4,4’-bipyridine (0.032 g, 0.20 mmol) in
6 mL of water/EtOH/DMF (v/v/v 3:3:2) carried out in a 23 mL Teflon
liner (Parr vessels) at 1008 for 18 h.
[27] R. Vaidhyanathan, D. Bradshaw, J. N. Rebilly, J. P. Barrio, J. A.
Gould, N. G. Berry, M. J. Rosseinsky, Angew. Chem. 2006, 118,
6645–6649; Angew. Chem. Int. Ed. 2006, 45, 6495–6499.
[28] M. J. Ingleson, J. Perez Barrio, J. Bacsa, C. Dickinson, H. Park, M. J.
Rosseinsky, Chem. Commun. 2008, 1287–1289.
[29] L. Antolini, L. Menabue, G. C. Pellacani, G. Marcotrigiano, Dalton
Trans. 1982, 2541.
902
www.chemasianj.org
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Asian J. 2009, 4, 892 – 903

1D Tubular and 2D Metal–Organic Frameworks
[30] H. Schmidbaur, I. Bach, J. Riede, G. Muller, J. Helbig, G. Hopf,
Chem. Ber. 1988, 121.
[44] W. Chen, J.-Y. Wang, C. Chen, Q. Yue, H.-M. Yuan, J.-S. Chen, S.-N.
Wang, Inorg. Chem. 2003, 42, 944–946.
[45] T. K. Maji, K. Uemura, H. C. Chang, R. Matsuda, S. Kitagawa,
Angew. Chem. 2004, 116, 3331–3334; Angew. Chem. Int. Ed. 2004,
43, 3269–3272.
[46] C. Ruiz-Pꢉrez, P. Lorenzo-Luis, M. Hernandez-Molina, M. Milagros
Laz, F. S. Delgado, P. Gili, M. Julve, Eur. J. Inorg. Chem. 2004,
3873–3879.
[47] E.-Y. Choi, K. Park, C.-M. Yang, H. Kim, J.-H. Son, S. W. Lee, Y. H.
Lee, D. Min, Y.-U. Kwon, Chem. Eur. J. 2004, 10, 5535–5540.
[48] R. Matsuda, R. Kitaura, S. Kitagawa, Y. Kubota, T. C. Kobayashi, S.
Horike, M. Takata, J. Am. Chem. Soc. 2004, 126, 14063–14070.
[49] J. Jia, X. Lin, C. Wilson, A. J. Blake, N. R. Champness, P. Hubber-
stey, G. Walker, E. J. Cussen, M. Schrçder, Chem. Commun. 2007,
840–842.
[50] M. Latroche, S. Surble, C. Serre, C. Mellot-Draznieks, P. L. Llewel-
lyn, J. H. Lee, J. S. Chang, H. J. Sung, G. Ferey, Angew. Chem. 2006,
118, 8407–8411; Angew. Chem. Int. Ed. 2006, 45, 8227–8231.
[51] A. J. Fletcher, K. M. Thomas, M. J. Rosseinsky, J. Solid State Chem.
2005, 178, 2491–2510.
[31] T. H. Doyne, R. Pepinsky, T. Watanabe, Acta Crystallogr. 1957, 10,
438.
[32] Y. Zhang, M. K. Saha, I. Bernal, CrystEngComm 2003, 5, 34.
[33] M. Mizutani, N. Maejima, K. Jitsukawa, H. Masuda, H. Einaga,
Inorg. Chim. Acta 1998, 283, 105.
[34] R. J. Flook, H. C. Freeman, M. L. Scudder, Acta Crystallogr. Sect. B
1977, 33, 801.
[35] C. M. Gramaccioli, Acta Crystallogr. 1966, 21, 600.
[36] Y. Yukawa, Y. Inomata, T. Takeuchi, Bull. Chem. Soc. Jpn. 1983, 56,
2125.
[37] Y. Xie, H.-H. Wu, G.-P. Yong, Z.-Y. Wang, R. Fan, R.-P. Li, G.-Q.
Pan, Y.-C. Tian, L.-S. Sheng, L. Pan, J. Li, J. Mol. Struct. 2007, 833,
88.
[38] J. Perez Barrio, J.-N. Rebilly, B. Carter, D. Bradshaw, J. Bacsa, A. Y.
Ganin, H. Park, A. Trewin, R. Vaidhyanathan, A. I. Cooper, J. E.
Warren, M. J. Rosseinsky, Chem. Eur. J. 2008, 14, 4521–4532.
[39] B. Wisser, A.-C. Chamayou, R. Miller, W. Scherer, C. Janiak, Crys-
tEngComm 2008, 10, 461.
[40] G. N. Abraham, D. M. Podell, Mol. Cell. Biochem. 1981, 38, 181–
190.
[41] C. J. Kepert, T. J. Prior, M. J. Rosseinsky, J. Solid State Chem. 2000,
152.
[52] Bruker, APEX II, Bruker AXS Inc., Madison, Wisconsin, USA,
2005.
[53] Bruker, SADABS Version 2008-2, Bruker AXS Inc., Madison, Wis-
consin, USA, 2007.
[54] G. M. Sheldrick, SHELX97, University of Gçttingen, Germany,
1997.
[42] T. J. Prior, M. J. Rosseinsky, Chem. Commun. 2001, 1222–1223.
[43] K. Koh, A. G. Wong-Foy, A. J. Matzger, Angew. Chem. 2008, 120,
689–692; Angew. Chem. Int. Ed. 2008, 47, 677–680.
Received: February 22, 2009
Published online: May 4, 2009
Chem. Asian J. 2009, 4, 892 – 903
ꢀ 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemasianj.org
903