Rolling Up the sheet: Constructing metal-organic lamellae and nanotubes from a [{mn3(propanediolato)2}(dicyanamide) 2]n honeycomb skeleton

Article abstract of DOI:10.1021/ja409569q

Target synthesis of metal-organic nanotubes (MONTs) through a classic "rolling-up" mechanism remains a big challenge for coordination chemists. In this work, we report three 2D lamellar compounds and one (4,0) zigzag MONT based on a common honeycomb coord

Full text of DOI:10.1021/ja409569q

Communication
pubs.acs.org/JACS
Rolling Up the Sheet: Constructing Metal−Organic Lamellae and
Nanotubes from a [{Mn3(propanediolato)2}(dicyanamide)2]n
Honeycomb Skeleton
Gang Wu,*,† Jiaquan Bai,† Yuan Jiang,† Guanghua Li,† Jian Huang,† Yi Li,† Christopher E. Anson,‡
Annie K. Powell,*,‡,§ and Shilun Qiu*,†
†State Key Laboratory of Inorganic Synthesis & Preparative Chemistry, Jilin University, 2699 Qianjin Street, Changchun 130012, P. R.
China
‡Institut fur Anorganische Chemie, Karlsruhe Institute of Technology, Engesserstrasse 15, 76131 Karlsruhe, Germany
̈
§Institute of Nanotechnology, Karlsruhe Institute of Technology, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen,
Germany
S
* Supporting Information
coupled sheet compounds because the strong inter-layer
interaction prohibits the peeling off of a sheet.5
ABSTRACT: Target synthesis of metal−organic nano-
tubes (MONTs) through a classic “rolling-up” mechanism
remains a big challenge for coordination chemists. In this
work, we report three 2D lamellar compounds and one
(4,0) zigzag MONT based on a common honeycomb
coordination skeleton. Our synthetic strategy toward
sheet/tube superstructure transformation is to asymmetri-
cally modify the inter-layer interactions by gradually
increasing the size of the amine templates. Eventually, to
relieve the surface tension of individual layers and to
enhance surface areas and optimize host−guest inter-
actions to accommodate bigger guests, spontaneous rolling
up to form a tubular structure was achieved.
Recently, there has been considerable interest in the
assembly of metal−organic nanotubes (MONTs), stimulated
by the well-defined crystal structures of the bulk material and
potential applications in gas storage, catalysis, and molecular
magnetism.6 Although the “rolling-up” concept has been
proposed for the formation of MONTs,6h,k this has so far not
been experimentally observed either through rolling-up a
lamellar bulk compound into a MONT or by unzipping a
given MONT into its corresponding sheet structure. Indeed,
sheet-to-tube conversion for coordination compounds is
extremely difficult to achieve through a single-crystal-to-
single-crystal transformation using lamellar compounds as
precursors, because this procedure requires the deconstruction
and reconstruction of a very large number of chemical bonds. It
remains a big challenge for coordination chemists to synthesize
coordination sheets and tubes based on a common
coordination skeleton.
Inspired by the formation mechanisms of asbestos, perov-
skite, and related tubular structures, we thus hypothesize that,
for a bilayered coordination compound with an ABAB structure
and weak inter-layer interactions, the corresponding tubular
structure could be achieved by introducing anisotropic chemical
stresses between the layers. Herein, we report a series of
coordination networks based on [Mn3(propandiolato)2]
building blocks and dicyanamide (dca) linkers, which exhibit
identical (6,3) honeycomb connectivity. As the size of the
amine templates is gradually increased, the inter-layer distance
also increases, and the inter-layer contacts become more and
more anisotropic for individual layers. Eventually, in order to
relieve the different surface tension on the top and bottom
surfaces of an individual layer, spontaneous rolling up and
formation of a tubular structure could be achieved. To the best
of our knowledge, this is the first time that a classic rolling-up
strategy is accomplished in the synthesis of MONTs and also
the first observation of a guest-induced sheet/tube supra-
he discovery of carbon nanotubes (CNTs), especially
Tsingle-walled carbon nanotubes (SWNTs), in conjunction
with their outstanding physical and chemical properties,1 has
stimulated extensive investigation into nanotubes of other
compositions, such as metal oxides, metal chalcogenides, and
organic compounds.2 In general, the formation of these tubular
structures can be regarded as the rolling-up conversion of their
corresponding layered materials. For example, asbestos can
form cylindrical or tubular structures at high temperature, and a
rolling-up process is proposed to explain this.3 The rationale is
that a hybrid layered compound, in which the unit cell of one
layer differs from that of the second layer, is likely to bend upon
heating because of the anisotropic thermal strain on either side
of the individual layers. Similar curling processes have also been
observed in layered perovskites through the “foliation and
rolling” mechanism: partial exchange of the K+ and H+ inter-
layer counterions by bulkier tetra(n-butyl)ammonium (TBA+)
molecules enhances the inter-layer spacing and eventually
causes the foliation of multilayer structures; such an unstable
unilamellar phase spontaneously rolls up and forms a tubular
structure.4 Weak inter-layer contacts and strong intra-layer
coupling are usually suggested to be necessary for constructing
the corresponding single-walled nanotubes. Such a curling-up
process is much more challenging to achieve for strongly
Received: September 19, 2013
Published: November 21, 2013
© 2013 American Chemical Society
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Communication
molecular isomerism in metal−organic framework (MOF)
chemistry.7
and (b) the dicyanamide bridges between the units. If we
represent these by orange and blue lines, respectively, then it is
clear that the layers have a topology consisting of fused six-
membered rings (see Table of Content, TOC). The plane of
the {Mn3(μ2-OR)4} moiety within the Mn3 unit is in fact
rotated about its Mn3 axis by 29.7° out of the plane of the 2D
sheet. As a consequence, the two sulfamide groups are not
equivalent within the structure; the one containing S(2) is
rather embedded within the hybrid 2D layer, whereas that
containing S(1) is oriented with its tolyl group lying above one
surface of the layer, and closely parallel to it. Consequently, the
layers are thus anisotropic, and the inter-layer contacts are of
two types (Figure 1c). However, neither of these sets of inter-
layer interactions involves hydrogen-bonding or π−π inter-
actions. The layers are therefore primarily held stacked together
by weak dipolar interactions between C−H groups (aromatic,
or aliphatic adjacent to O) and either the bromide ligands or
sulfamide oxygens, in addition to simple van der Waals
interactions. Given the lack of stronger supramolecular
interactions (hydrogen-bonding or π−π stacking) between
adjacent layers, the slightly puckered lamellar structure appears
to be the stable form for this complex.
Compound 1, (Me3NH)[MnII2MnIII(L)2(dca)2Br2-
(CH3OH)4], was isolated by the reaction of MnBr2, H2L, and
Na(dca) in a mixture of methanol and ethyl acetate, in the
presence of trimethylamine (Me3N). The asymmetric unit of
the crystal structure of 1 is shown in Figure 1a. Both H2L
The size of the amine templates was then systematically
increased. Using N,N-dimethylethylamine (EtMe2N) or N,N-
diethylmethylamine (Et2MeN), we obtained (EtMe2NH)-
[MnII MnIII(L)2(dca)2Br2(CH3OH)4] (2) and (Et2MeN)-
2
[MnII MnIII(L1)2(dca)2Br2(CH3OH)4] (3), respectively, under
2
the same reaction condition as for 1. The asymmetric units and
extended 2D networks of both compounds are closely
isostructural, with slight (but systematic) differences in unit
cell dimensions (see Supporting Information (SI)). If one
considers the two distinct inter-layer separations and defines
the plane of a sheet as the mean plane of the metal atoms
contained, then the inter-sheet separations for 1 are 10.52 and
7.10 Å, with the larger value corresponding to adjacent sheets
with (Me3NH)+ cations intercalated between them, and the
lower value to pairs of sheets not separated by these cations.
For 2 and 3, the corresponding values are 10.95 and 6.90 Å, and
10.96 and 6.96 Å, respectively. Increasing the size of the cation
from (Me3NH)+ to (EtMe2NH)+ has, as might be expected,
increased the corresponding inter-layer separation. However,
additing the second CH2 group to the cation in 3 did not result
in a further increase in this separation. In 3, the larger cation is
accommodated by a swing of the tolylsulfamide pendants on
the surface of the layer (Figures S1−S3). Such a rotation
enhances the surface area to accommodate the bigger guest, but
also dramatically weakens the host−guest H-bonding strength
between the amine cations and the sulfamide, with the NH···O
distance changing from 2.84 to 3.15 Å for 2 and 3, respectively.
Increasing the size of the amine templates also results in a
slipping of the adjacent sheets. This shearing of the structure
results in an increase in both the unit cell length a and the
monoclinic angle β (see SI).
Figure 1. (a) The (Me3NH)[MnII MnIII(L)2(dca)2Br2(CH3OH)4]
2
unit (1), highlighting the intra-trimer and host−guest H-bonds
(dashed lines). (b) The honeycomb sheet of 1. (c) ABAB stacking
of the sheets, highlighting the amine counterions (C, dark gray; MnII,
pink; MnIII, purple; O, red; S, yellow; Br, brown; N, blue; H, light
gray).
ligands have been doubly deprotonated, with the alkoxy
oxygens bridging between MnIII and MnII centers to form an
almost linear trinuclear MnII MnIII unit. Similar bridging has
2
been previously observed in related Mn-1,3-diol systems.8 It
should be noted that the two tolylsulfamide groups are to the
same side of the Mn3(μ2-O)4 mean plane; their N−H groups
both form hydrogen-bonds to the same bromide ligand, Br(2).
The {MnII MnIII(L)2Br2(CH3OH)4} is thus not centrosym-
2
metric, but instead has an idealized mirror plane defined by the
Mn, Br, and methanol O atoms. Each dca ligand bridges two
MnII ions from different MnII MnIII units via its two terminal
2
nitrogen atoms, such that each unit is connected to four others
via MnII-dca-MnII linkages, forming a 2D layered architecture
(Figure 1b). Each of the four methanol O−H groups forms a
hydrogen-bond to Br(1) or Br(2); the O−H···Br and N−H···
Br hydrogen-bonds are thus all between atoms in the same
asymmetric unit. One of the sulfamide oxygens also accepts a
hydrogen-bond from the N−H group of the slightly disordered
Me3NH+ cation (Figure 1a).
Using Et3N as the template, (Et3NH)[MnII MnIII(L)2-
2
(dca)2Br2(CH3OH)3.25(OH2)0.75]·3/4MeOH·1/4H2O (4) was
isolated under the same reaction conditions as 1−3. It
crystallizes in the tetragonal space group P4/n with Z = 16
(see SI). The asymmetric unit of 4 (Figure S4) contains two
(Et3N)+ cations and two trinuclear complex units, which are
both closely isostructural to those in 1−3. Although the
If we consider MnII ions as nodes in the lamellar structure,
then these can be regarded as being linked by two types of
linkers: (a) the alkoxo bridges and the MnIII within the unit,
trinuclear MnII MnIII complex units in 4 are also linked via
2
dicyanamide linkers, the two independent units have Mn3(μ2-
OR)4 mean planes that are mutually perpendicular, so that, in
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Communication
contrast to 1−3, these linkages results in 1D tubular structures
(Figure 2). According to the classification of CNTs,1 this
noted that there are multiple inter-tube supramolecular
interactions in 4, involving CH−O hydrogen-bonds and
CH−π interactions (Figure S6). The cooperation of these
weak interactions can then stabilize the “nanotube” structure, in
preference to the less-puckered 2D structure found in 1−3.
In conclusion, three 2D lamellar compounds and one (4,0)
zigzag MONT from [MnII MnIII] building blocks and dca
2
linkers are successfully prepared. For the first time, a classic
rolling-up strategy is accomplished in the synthesis of MONTs,
and the key factor is to asymmetrically verify the inter-layer
interactions by increasing the size of the amine templates. Our
results demonstrate that the spontaneous rolling-up process for
bulk tubular compounds could be utilized in MOF chemistry,
and we believe that our results could further the understanding
of guest/template-induced supramolecular isomerism in
dynamic supramolecular systems. In this system, it is quite
plausible that armchair or chiral MONTs with tunable
diameters could be obtained through further increasing the
size of amine templates. This work is currently in progress in
our laboratory.
ASSOCIATED CONTENT
■
S
* Supporting Information
Additional synthetic and structural details and crystallographic
data (CIF). This material is available free of charge via the
Internet at http://pubs.acs.org.
Figure 2. (Top) The 1D tubular structure resulting from linking the
MnIIIMnII units through dicyanamide bridges in 4. (Bottom) The
2
“(4,0) zigzag nanotube” topology resulting from linkage of the MnII
nodes via dicyanamide (blue) and trinuclear complex (orange) linkers.
AUTHOR INFORMATION
■
Corresponding Authors
wug@jlu.edu.cn
annie.powell@kit.edu
sqiu@jlu.edu.cn
topology can be viewed as equivalent to a (4,0) zigzag
nanotube, resulting from “rolling up” the 2D network in 1−3.
All the sulfamide groups are now directed toward the outside of
the tubes. Of the two (Et3NH)+ cations in the asymmetric unit,
one hydrogen-bonds to the sulfamide oxygen, and one is
disordered across an inversion center and hydrogen-bonds to
Br; the remaining half cation is inside the tube, extensively
disordered by the four-fold symmetry axis. The mean outer
diameter of the tube is given by a/√2 = 20.4 Å. Using a space-
filling model, the accessible inner diameter is variable along the
tube: “pinching in” to 3.5 Å between the bromide ligands, but
expanding to 6.5 Å between the dicyanamide linkers.
At this point, it must be asked why the relatively minor
variations of the organic amine counterions have such dramatic
effects on 3 and 4. Throughout compounds 1−3, varying the
size of the amine countercations is counteracted by both
increasing the inter-layer distance and subtle swinging of the
tolylsulfamide pendants. If we sequentially increase the size of
the amine templates, the hypothetical sheet aggregate would
have to slip and further increase the inter-layer spacing to
accommodate bigger guests. However, such an imaginary
bilayer structure is thermodynamically unfavorable because of
the increased inter-layer distance and the increased surface
tension for the individual layers. As the result, the third CH2
group added onto the template becomes the last straw that
breaks the bilayer-stacking aggregates, and the honeycomb
sheets are forced to roll up into tubes to enhance the surface
areas and optimize host−guest interactions. The H-bonding
strength between the amine cation and the sulfamide confirms
this tendency, with the N−O distances 2.84, 2.84, 3.15, and
2.79 Å for 1, 2, 3, and 4, respectively. Theoretical calculations
reveal the tendency toward increased surface areas from 1 to 4,
with the calculated values 190.6, 221.5, 261.5, and 373.2 Å2 per
unit cell for 1, 2, 3, and 4, respectively (see SI). It should be
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Dedicated to the memory of Ian J. Hewitt. This work was
supported by the National Basic Research Program of China
(2011CB808703, 2012CB821700), National Natural Science
Foundation of China (Grant nos. 20901027, 91022030,
21261130584), “111” project (B07016), and Award Project
of KAUST (CRG-1-2012-LAI-009).
REFERENCES
■
(1) (a) Iijima, S. Nature 1991, 354, 56. (b) Dresselhaus, M. S.;
Dresselhaus, G.; Eklund, P. C. Science of Fullerenes and Carbon
Nanotubes; Academic Press: San Diego, 1996.
(2) (a) Tenne, R.; Margulis, L.; Genut, M.; Hodes, G. Nature 1992,
360, 3. (b) Remskar, M.; Mrzel, A.; Skraba, Z.; Jesih, A.; Ceh, M.;
Demsar, J.; Stadelmann, P.; Levy, F.; Mihailovic, D. Science 2001, 292,
479. (c) Horner, M. J.; K. Holman, T.; Ward, M. D. Angew. Chem., Int.
Ed. 2001, 40, 4045. (d) Bong, D. T.; Clark, T. D.; Granja, J. R.;
Ghadiri, M. R. Angew. Chem., Int. Ed. 2001, 40, 988. (e) Ye, C. H.;
Meng, G. W.; Jiang, Z.; Wang, Y. H.; Wang, G. Z.; Zhang, L. D. J. Am.
Chem. Soc. 2002, 124, 15180. (f) Li, Y. D.; Li, X. L.; He, R. G.; Zhu, J.;
Deng, Z. X. J. Am. Chem. Soc. 2002, 124, 1411. (g) Bouchmella, K.;
Dutremez, S. G.; Guerin, C.; Longato, J.-C.; Dahan, F. Chem.Eur. J.
2010, 16, 2528.
(3) (a) Pauling, L. Proc. Natl. Acad. Sci. U.S.A. 1930, 16, 578.
(b) Bates, T. F; Sand, L. B.; Mink, J. F. Science. 1950, 111, 512.
(4) Saupe, G. B.; Waraksa, C. C.; Kim, H.-N.; Han, Y. J.; Kaschak, D.
M.; Skinner, D. M.; Mallouk, T. E. Chem. Mater. 2000, 12, 1561.
(5) Clearfield, A. Chem. Rev. 1988, 88, 125.
18278
dx.doi.org/10.1021/ja409569q | J. Am. Chem. Soc. 2013, 135, 18276−18279

Journal of the American Chemical Society
Communication
(6) (a) Orr, J. W.; Barbour, L. J.; Atwood, J. T. Science 1999, 285,
1049. (b) Cui, Y.; Lee, S. J.; Lin, W. J. Am. Chem. Soc. 2003, 125, 6014.
(c) Yamaguchi, T.; Tashiro, S.; Tominaga, M.; Kawano, M.; Ozeki, T.;
Fujita, M. J. Am. Chem. Soc. 2004, 126, 10818. (d) Zhao, B.; Cheng, P.;
Chen, X.; Cheng, C.; Shi, W.; Liao, D.; Yan, S.; Jiang, Z. J. Am. Chem.
Soc. 2004, 126, 3012. (e) Pickering, A. L.; Seeber, G.; Long, D.-L.;
Cronin, L. Chem. Commun. 2004, 136. (f) Fei, Z.; Zhao, D.; Geldbach,
T. J.; Scopelliti, R.; Dyson, P. J.; Antonijevic, S.; Bodenhausen, G.
Angew. Chem., Int. Ed. 2005, 44, 5720. (g) Dai, F.; He, H.; Sun, D. J.
Am. Chem. Soc. 2008, 130, 14064. (h) Huang, X.-C.; Luo, W.; Shen,
Y.-F.; Lin, X.-J.; Li, D. Chem. Commun. 2008, 3995. (i) Luo, T.-T.; Wu,
H.-C.; Jao, Y.-C.; Huang, S.-M.; Tseng, T.-W.; Wen, Y.-S.; Lee, G.-H.;
Peng, S.-M.; Lu, K.-L. Angew. Chem., Int. Ed. 2009, 48, 9461.
(j) Kennedy, S.; Karotsis, G.; Beavers, C. M.; Teat, S. J.; Brechin, E. K.;
Dalgarno, S. J. Angew. Chem., Int. Ed. 2010, 49, 4205. (k) Thanasekar-
an, P.; Luo, T.-T.; Lee, C.-H.; Lu, K.-L. J. Mater. Chem. 2011, 21,
13140. (l) Otsubo, K.; Wakabayashi, Y.; Ohara, J.; Yamamoto, S.;
Matsuzaki, H.; Okamoto, H.; Nitta, K.; Uruga, T.; Kitagawa, H. Nat.
Mater. 2011, 10, 291. (m) Lin, Q.; Wu, T.; Zheng, S.-T.; Bu, X.; Feng,
P. Chem. Commun. 2011, 47, 11852. (n) Panda, T.; Kundu, T.;
Banerjee, R. Chem. Commun. 2012, 48, 5464. (o) Kong, G.-Q.; Ou, S.;
Zou, C.; Wu, C.-D. J. Am. Chem. Soc. 2012, 50, 1743. (p) Ju, P.; Jiang,
L.; Lu, T. Chem. Commun. 2013, 49, 1820.
(7) (a) Moulton, B.; Zaworotko, M. J. Chem. Rev. 2001, 101.
(b) Schroeder, M.; Champness, N. R. In Encyclopedia of Supra-
molecular Chemistry; Atwood, J. L., Steed, P., Eds.; Marcel Dekker, Inc.:
New York, 2004; p 1420. (c) Zhang, J. P.; Huang, X. C.; Chen, X. M.
Chem. Soc. Rev. 2009, 38, 2385. (d) Makal, A.; Yakovenko, A.; Zhou,
H. C. J. Phys. Chem. Lett. 2011, 2, 1682.
(8) (a) Stamatatos, T. C.; Abboud, K. A.; Wernsdorfer, W.; Christou,
G. Angew. Chem., Int. Ed. 2006, 45, 4134. (b) Manoli, M.; Johnstone,
R. D. L.; Parsons, S.; Murrie, M.; Affronte, M.; Evangelisti, M.;
Brechin, E. K. Angew. Chem., Int. Ed. 2007, 46, 4456. (c) Ako, A. M.;
Hewitt, I. J.; Mereacre, V.; Cler
Powell, A. K. Angew. Chem., Int. Ed. 2006, 45, 4926. (d) Nayak, S.;
Beltran, L. M. C.; Lan, Y.; Clerac, R.; Hearns, N. G. R.; Wernsdorfer,
́
ac, R.; Wernsdorfer, W.; Anson, C. E.;
́
W.; Anson, C. E.; Powell, A. K. Dalton Trans. 2009, 1901. (e) Wu, G.;
Huang, J.; Sun, L.-L.; Bai, J.-Q.; Li, G.-H.; Cremades, E.; Ruiz, E.;
Cler
Bai, J.-Q.; Jiang, Y.; Li, G.-H.; Qiu, S.-H.; Cler
11051.
́
ac, R.; Qiu, S.-H. Inorg. Chem. 2011, 8580. (f) Huang, J.; Wu, G.;
́
ac, R. Inorg. Chem. 2013,
18279
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