Helical superstructures of a C2-symmetric molecule exhibiting strong second harmonic generation in the solid-state

Article abstract of DOI:10.1002/1521-3773(20010702)40:13<2451::AID-ANIE2451>3.0.CO;2-M

The crystallization solvent exerts a critical control of the nonlinear optical properties of helical superstructures in molecular crystals based on N,N′-bis(4-nitrophenyl)- (1R,2R)-diaminocyclohexane. While crystallization from ethyl acetate resulted in mutually orthogonal helices with different handedness, crystallization from ethyl acetate/hexane or acetyl acetone/hexane resulted in the formation of helical motifs (see picture) of a single-handedness oriented in one direction. The latter showed a strong solid-state second harmonic generation capability.

Full text of DOI:10.1002/1521-3773(20010702)40:13<2451::AID-ANIE2451>3.0.CO;2-M

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[12] For recent examples of supramolecular systems deposited on surfaces,
see a) P. Laitenberger, C. G. Claissens, L. Kuipers, F. M. Raymo, R. E.
Palmer, J. F. Stoddart, Chem. Phys. Lett. 1997, 279, 209 ± 214; b) G.
Ashkenasy, G. Kalyuzhny, J. Libman, I. Rubenstein, A. Shanzer,
Angew. Chem. 1999, 111, 1333 ± 1336; Angew. Chem. Int. Ed. 1999, 38,
1257 ± 1261; c) M. Lahav, L. Leiserowitz, Angew. Chem. 1999, 111,
2691 ± 2694; Angew. Chem. Int. Ed. 1999, 38, 2533 ± 2536; d) A.
Semenov, J. P. Spatz, M. Müller, J.-M. Lehn, B. Sell, D. Schubert, C. H.
Weidl, U. S. Schubert, Angew. Chem. 1999, 111, 2701 ± 2705; Angew.
Chem. Int. Ed. 1999, 38, 2547 ± 2550; e) N. Bampos, C. N. Woodburn,
M. E. Welland, J. K. M. Sanders, Angew. Chem. 1999, 111, 2949 ± 2953;
Angew. Chem. Int. Ed. 1999, 38, 2780 ± 2783; f) H. Imahori, H.
Yamada, S. Ozawa, K. Ushida, Y. Sakata, Chem. Commun. 1999,
1165 ± 1166; g) D. Ryan, S. N. Rao, H. Rensmo, D. Fitzmaurice, J. A.
Preece, S. Wenger, J. F. Stoddart, N. Zaccheroni, J. Am. Chem. Soc.
2000, 122, 6252 ± 6257; h) M. Lahav, A. N. Shipway, I. Willner, M. B.
Nielsen, J. F. Stoddart, J. Electroanal. Chem. 2000, 482, 217 ± 221; i) G.
Cooke, F. M. A. Duclairoir, V. M. Rotello, J. F. Stoddart, Tetrahedron
Lett. 2000, 41, 8163 ± 8166.
[21] P.-L. Anelli, P. R. Ashton, R. Ballardini, V. Balzani, M. Delgado, M. T.
Gandolfi, T. T. Goodnow, A. E. Kaifer, D. Philp, M. Pietraszkiewicz,
L. Prodi, M. V. Reddington, A. M. Z. Slawin, N. Spencer, J. F.
Stoddart, C. Vicent, D. J. Williams, J. Am. Chem. Soc. 1992, 114,
193 ± 218.
Â
[22] D. B. Amabilino, P.-L. Anelli, P. R. Ashton, G. R. Brown, E. Cordova,
L. A. Godinez, W. Hayes, A. E. Kaifer, D. Philp, A. M. Z. Slawin, N.
Spencer, J. F. Stoddart, M. S. Tolley, D. J. Williams, J. Am. Chem. Soc.
1995, 117, 11142 ± 11170.
[23] P. R. Ashton, J. Huff, S. Menzer, I. W. Parsons, J. A. Preece, J. F.
Stoddart, M. S. Tolley, A. J. P. White, D. J. Williams, Chem. Eur. J.
1996, 2, 31 ± 44.
Helical Superstructures of a C2-Symmetric
Molecule Exhibiting Strong Second Harmonic
Generation in the Solid-State**
[13] C. J. Brinker, G. W. Scherer, Sol ± Gel Science, Academic Press, San
Diego, 1990.
[14] A silica sol ± gel provides a stable transparent matrix for encapsulating
molecules physically in a macroscopic solid; see a) B. Dunn, J. I. Zink,
Chem. Mater. 1997, 9, 2280 ± 2291; b) D. Avnir, Acc. Chem. Res. 1995,
28, 328 ± 334; c) B. Dunn, J. I. Zink, J. Mater. Chem. 1991, 1, 903 ± 913.
The sol ± gel process is a synthetic technique for preparing oxide gels,
glasses, and inorganic compounds at far lower temperatures than is
possible by conventional synthesis. The approach is based on the
hydrolysis and condensation of molecular precursors such as metal
alkoxides. It has received considerable attention because it possesses a
number of desirable characteristics in terms of producing materials of
high purity and excellent homegeneity. Moreover, since the sol ± gel
approach is a solution-based method, it is readily adaptable to
producing thin films and fibres as well as bulk materials. The flexible
solution chemistry associated with the synthesis of sol ± gels makes it
possible to incorporate a large variety of organic molecules in the
inorganic oxide matrix. The optical properties of the molecular
dopants are then imparted upon the solid derived from the sol ± gel.
Hence this process gives rise to a large number of materials with
interesting and unique properties. The interconnected nanopores
in sol ± gels are filled with liquid which can provide supramolec-
ular machines with a local solution environment in which large
molecular movements (co-conformational changes) can be per-
formed, with the silicate framework providing the macroscopic
support. The silicate matrix is also transparent to visible light and
this transparency makes it possible to study a photoactivated system
inside its pores.
P. Gangopadhyay and T. P. Radhakrishnan*
The design of molecular materials for quadratic nonlinear
optical (NLO) applications involves optimization of the
structure at both the molecular and the materials level.[1]
Molecular design aims at the maximization of the hyper-
polarizability (b) as well as the incorporation of structural
features that facilitate suitable assembly in the bulk phase.
The latter features include hydrogen-bonding functionali-
ties,[2] ionic groups,[3] optimally long alkyl chains,[4] and
chirality.[5, 6] Of these, only chirality ensures noncentrosym-
metric organization, an essential prerequisite for the obser-
vation of quadratic NLO effects. However, even though the
basic symmetry requirement is satisfied, efficient exploitation
of the inherently strong molecular nonlinear response is rarely
achieved at the bulk level. An exceptionally successful case is
that of N-4-nitrophenyl-(S)-prolinol (NPP).[6] We previously
investigated the strategic placement of stereogenic centers in
push-pull quinonoid molecules to achieve enhanced second
harmonic generation (SHG).[7] A logical extension of this
study is that an axial chiral system having a strong b compo-
nent coincident with the symmetry axis would be a promising
candidate. We also envisaged that C2-symmetric molecules
could potentially form helical assemblies, the chirality of
which extends over the whole molecular superstructure.
Recent studies have demonstrated enhanced NLO effects
arising from supramolecular chirality in polymers,[8] meso-
scopic systems,[9] and Langmuir± Blodgett films.[10] Helical
[15] This particular BHEEEN derivative with four oxygen atoms present
in each of its polyether chains is well suited to maximizing the C H ´´´
O interactions with CBPQT4‡; see M. Asakawa, W. Dehaen, G.
Â
Lꢁabbe, S. Menzer, J. Nouwen, F. M. Raymo, J. F. Stoddart, D. J.
Williams, J. Org. Chem. 1996, 61, 9591 ± 9595.
[16] a) M. H. Huang, H. M. Soyez, B. Dunn, J. I. Zink, Chem. Mater. 2000,
12, 231 ± 235; b) F. Nishida, J. McKiernan, B. Dunn, J. I. Zink, C. J.
Brinker, A. J. Hurd, J. Am. Ceram. Soc. 1995, 78, 1640 ± 1648.
[17] I. Haller, J. Am. Chem. Soc. 1978, 100, 8050 ± 8055.
[18] The derivatization of the silica surface by using monomeric ICPES is
important as the first step in the anchoring of the monobenzylated
BHEEEN derivative. If this derivative is treated first of all with
ICPES prior to silanization, then undesired oligomers are formed on
the silica surface.
[19] The derivatized films were immersed in an aqueous solution
of CBPQT´ 4Cl for two days. The residual percentage (ca. 3.4%)
of unthreaded BHEEEN is shown by T1 in Figure 3b. Dethreading,
was effected by immersing the film in an aqueous solution
(ca. 4 mL) of NaBH4 (ca. 2 nm) for 2 ± 3 h. The resulting luminescent
intensity is shown in D1 in Figure 3b. Threading and dethreading
was demonstrated over three redox cycles, namely, T1/D1 ± T2/D2 ±
T3/D3.
[*] Dr. T. P. Radhakrishnan, P. Gangopadhyay
School of Chemistry
University of Hyderabad
HyderabadÐ500046 (India)
Fax : (‡91)40-3012460
E-mail: tprsc@uohyd.ernet.in
[**] Financial support from the DST (Swarnajayanti Fellowship) and the
use of the National Single Crystal Diffractometer Facility (funded by
the DST at the School of Chemistry, University of Hyderabad) are
gratefully acknowledged. P.G. thanks the University Grants Commis-
sion for a senior research fellowship. We thank du Pont Deutschland
for a generous gift of 1,2-diaminocyclohexane.
[20] Ordered arrays of molecular motors are essential to the life of a cell;
see a) R. A. Cross, Nature 2000, 406, 839 ± 840; b) T. Hasson, R. E.
Cheney, Curr. Opin. Cell Biol. 2001, 13, 29 ± 35.
Supporting information for this article is available on the WWW under
http://www.angewandte.com or from the author.
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molecules with large hyperpolarizability have been studied
computationally and experimentally.[11] There has been con-
tinued interest in the design of helical assemblies of metal
complexes[12] and organic molecules.[13] However, to the best
of our knowledge, there has been no
solvent and growth conditions; extensive polymorphism
occurs. Crystals grown from ethyl acetate, methanol, and
acetone had different platelike morphologies and unit cells.
Different batches of crystals from ethyl acetate alone showed
two distinct, though very similar, unit cells. Microcrystalline
powders of the various crystals showed SHG in the range 5 ±
20 U. We have investigated the crystal structure of thin, long
plates of BNDC grown from ethyl acetate (Table 1). They
belong to the P212121 space group, with one molecule in the
asymmetric unit. Two types of intermolecular N H ´´´ O
interactions lead to the formation of helical assemblies
with different pitches that extend along the three crystallo-
graphic axes (Figure 2). The helices oriented along the
a and b axes are M (left-handed), whereas the one along
the c axis is P (right-handed). Since the orthogonally oriented
helices with different handedness do not lead to strong
SHG, we explored other solvent systems for crystalliza-
tion in an effort to produce a lattice structure with helical
motifs of a single handedness that are oriented in one
direction.
Crystals with a distinct prismatic morphology different
from the earlier cases could be grown from mixtures of ethyl
acetate (ea)/hexane and pentan-3-one (diethyl ketone, dek)/
hexane. Spectroscopic characterizations indicated the inclu-
sion of solvent molecules, and hence these crystals were
labeled as BNDC.ea and BNDC.dek, respectively. Freshly
grown crystals show strong SHG (Table 1). However, loss of
solvent is observed over a period of a few days leading to
opaque crystals or powders with diminished SHG capabilities
which melt at 200 ± 2048C. X-ray investigations showed that
both crystals belong to the C2221 space group and have similar
cell dimensions (Table 1) and identical lattice structures. The
asymmetric unit consists of a half molecule each of BNDC
and the solvent; a C2 operation generates the other halves.
The BNDC molecules form M-helices that extend solely along
the c axis, with disordered solvent molecules in the helical
channels. Both the nitro and amino groups are involved in
noncovalent interactions between the BNDC molecules, thus
ruling out any strong interactions with the solvent molecules.
Since no weak interactions are found either, we carried out
crystallizations from pentan-2,4-dione (acetyl acetone, acac)
to take advantage of the possible weak interactions between
the solvent molecules and BNDC.
demonstration of strong SHG in the solid
state in structurally characterized organic
molecular crystals built up of helical supra-
molecular assemblies. We have now real-
ized this using the C2-symmetric N,N'-
bis(4-nitrophenyl)-(1R,2R)-diaminocyclo-
hexane (BNDC).
There is a brief report of weak SHG
observed in the related compound having
only one 4-nitrophenyl group,[14] although
no structural information is available. We
have prepared the bis-substituted product
by the reaction of 1,2-diaminocyclohexane with 4-fluoroni-
trobenzene in the presence of K2CO3 in DMSO. Initially we
investigated the racemic material, rac-BNDC; interestingly it
has a noncentrosymmetric crystal structure (Table 1)[15] with
molecular tapes generated through intermolecular H-bonds
(Figure 1), and exhibits weak SHG in a Kurtz ± Perry experi-
ment.[16] The 1R,2R enantiomer was prepared from carefully
isolated, enantiomerically pure (1R,2R)-diaminocyclohexane.
Crystallization of BNDC is found to be very sensitive to the
Figure 1. H-bonded tape structure in rac-BNDC obtained from a single-
crystal X-ray analysis. The alternating molecules are enantiomers. The
H-bonds are shown by broken lines.
Table 1. Significant crystallographic data and powder SHG capability of the various crystals.[a]
rac-BNDC
BNDC
BNDC ´ ea
BNDC ´ dek
BNDC ´ acac
formula of asymmetric unit
space group
a [Š]
b [Š]
c [Š]
b [8]
V [Š3]
Z
C36H40N8O8
P21
C18H20N4O4
P212121
10.2375(19)
12.827(2)
13.662(9)
90
C11H14N2O3
C2221
11.793(2)
15.737(3)
12.750(4)
90
C11.5H15N2O2.5
C2221
12.084(2)
15.847(3)
12.935(3)
90
C11.5H14N2O3
C2221
12.3650(11)
15.8963(10)
12.5817(9)
90
10.210(4)
15.34(2)
11.933(3)
109.43(3)
1762(3)
2
1794.0(13)
4
2366.1(10)
8
2477.0(9)
8
2473.0(3)
8
no. of refl. with
total no. of param.
R(Iꢀ 2sI)
SHG
I ꢀ sI 3104
I ꢀ sI 1813
I ꢀ sI 1190
I ꢀ 2sI 1287
I ꢀ sI 1221
469
235
156
150
159
0.0453
6 U
0.0454
20 U
0.0514
0.93 NPP
0.0689
1.01 NPP
0.0446
1.15 NPP
[a] 1 U ˆ SHG of urea with an average particle size ꢀ150 mm, 1 NPP ˆ SHG of NPP with an average particle size ꢀ175 mm (our calibration measurements
gave 1 NPP ˆ 115 U; reported values for NPP are in the range 50 ± 150 U.[5, 6, 14]
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cules assemble into a beautiful M-helix extending along
the c axis (Figure 3a, b) and with a dipolar interaction
between the nitro groups of neighboring molecules. N O
bonds of adjacent molecules are oriented in an antiparallel
Figure 2. Helical superstructures in BNDC obtained from single-crystal
X-ray analysis: view along the helical axis parallel to the a (a), b (b), and
c axes (c). The H-bonds are shown by broken lines.
Prismatic crystals were grown by diffusion of hexane into a
solution of BNDC in acetyl acetone. The BNDC.acac crystals
are found to be considerably more stable than the earlier two
toward solvent loss at room temperature; when heated the
crystals show a shrinkage at 130 ± 1358C as a consequence of
solvent expulsion, and then melt at 2028C. Strong SHG, which
is stable over several weeks, is observed in the crystals, and a
powder study showed a phase-matchable SHG 1.15 times
that of NPP (Table 1). An X-ray study once again showed
a C2221 space group with cell dimensions and molecular
structure similar to BNDC.ea and BNDC.dek, and with an
identical lattice structure. The C2-symmetric BNDC mole-
Figure 3. The helical superstructure in BNDC.acac obtained from a single-
crystal X-ray analysis: a) view along the helical axis (c axis), and b) stereo-
view perpendicular to the helical axis (space-filling representation). Solvent
molecules are omitted for clarity. c) View of the packing of helical channels
(projection onto the ab plane) including the solvent molecules. The
H-bonds and interactions of the nitro groups are shown by broken lines.
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manner to form a gently twisted parallelogram with sides of
length 1.230 Š (N O) and 3.175 Š (nonbonded N ´´´ O), and
angles of 105.18 (N-O ´´´ N) and 73.68 (O-N ´´´ O). The helical
superstructures assemble to form the lattice shown in Fig-
ure 3c through formation of intermolecular H-bonds between
the amino and nitro groups, with an N ´´´ O distance of 3.003 Š
and an N-H ´´´ O angle of 143.98. The two oxygen atoms of the
nitro group participate in the dipolar and H-bonding inter-
actions, respectively. The acetyl acetone solvent molecules
exist in the helical channels; unlike the earlier two cases, there
is no sign of disorder. The central carbon atom lies on the
C2 axis and the bond lengths clearly indicate an enol structure.
Several weak H-bonding interactions are observed between
the central sp2 carbon atom of acetyl acetone and the amino
nitrogen and the phenyl ring carbon atoms on the BNDC
molecule in its vicinity (the shortest C ´´´ N and C ´´´ C
distances are 3.733 and 3.623 Š, respectively). The oxygen
atoms of acetyl acetone also show weak interactions with
some of the phenyl ring carbon atoms of BNDC (the shortest
C ´´´ O distances are 3.612 and 3.855 Š). The cooperative
effect of these interactions appears to stabilize the solvent
molecules in the helical channels.
probable cause of the enhanced SHG in BNDC ´ acac. A
complete resolution of this question has to await single-crystal
SHG measurements for which large enough crystals are not as
yet available.
The BNDC crystals illustrate the facile formation of helical
supramolecular assemblies from simple building blocks. An
examination of the relation between the solvent of crystal-
lization and the superstructures formed is instructive. Crys-
tallization from ethyl acetate resulted in the mutually
orthogonal helical motifs assembled solely through the
formation of H-bonds. The addition of nonpolar hexane to
ethyl acetate led to the realization of dipolar interactions of
the nitro group and the single helical motif. Retention of the
solvent molecules is critically dependent on their capability to
enter into weak noncovalent interactions with the channel
walls. These observations provide a basis for further explora-
tion of these helical architectures. The robust channel
structure, which accommodates different solvent molecules,
suggests the possibility of incorporating a variety of active
species in a chiral environment. The strong SHG together
with the thermal stability and versatility of the structural
framework points to the potential of helical superstructures in
the design of efficient molecular NLO materials.
The asymmetric unit in BNDC ´ acac (as well as the other
two solvated ones) is the half molecule N-alkyl-4-nitroaniline.
Taking into account its orientation with respect to the crystal
axes we have used the oriented gas model[17] to estimate the
effective susceptibility coefficient bXYZ (notation of ref. [17])
as 0.151. This value is smaller than the theoretical limit of
0.192 for the 222 point group, but is higher than the value in
the well-known NLO crystal 3-methyl-4-nitropyridine-1-ox-
ide (POM)[18] and may be contrasted with the bYXX value of
0.380 in NPP.[6] We have estimated the hyperpolarizability of
the half unit of the BNDC molecule at 1.17 eV to be 23.7 Â
10 30 esu by using semiempirical AM1/TDHF[19] computation
on the full molecule and by assuming a vectorial addition of
the contributions of the half units (calculated b tensor
components show that the usual 1D model is appropriate
for BNDC as well as the half unit). The b1.17 value of NPP
from AM1/TDHF calculations is 29.2 Â 10 30 esu; the exper-
imental value[20] is 42 Æ 9 Â 10 30 esu. In the absence of any
information at the moment on the local field factors and
phase-matching conditions in BNDC ´ acac, we assume these
factors to be similar to those in NPP. The approximate ratio of
the effective susceptibilities of BNDC ´ acac:NPP then works
out to be 0.32:1, which implies a ratio of 0.1:1 between the
SHGs of the powders (for details see the Supporting
Information). Even if allowance is made for error margins
on this estimate, the observed powder SHG of BNDC ´ acac
which is comparable to that of NPP and is very much larger
than is suggested by the ratio above. The discrepancy may be
traced to one of the following effects in BNDC ´ acac: the
modification of local field factors leading to enhanced bulk
susceptibility; an optimal combination of the phase-matching
conditions;[16] or the extended helical superstructure giving
rise to an enhancement of the b value over that calculated for
a single molecule. In view of the basic NLO chromophore
being the traditional 4-nitroaniline moiety and the recent
demonstrations of enhanced nonlinearity in aggregate struc-
tures,[8±10] the helical superstructure appears to be the most
Received: January 15, 2001
Revised: April 5, 2001 [Z16422]
[1] a) J. Zyss, D. S. Chemla in Nonlinear Optical Properties of Organic
Molecules and Crystals, Vol. 1 (Eds.: D. S. Chemla, J. Zyss), Academic
Press, New York, 1989, p. 23; b) N. J. Long, Angew. Chem. 1995, 107,
37; Angew. Chem. Int. Ed. Engl. 1995, 34, 21; c) J. Zyss, J. F. Nicoud,
Curr. Opin. Solid State Mater. Sci. 1996, 1, 533.
[2] a) C. Serbutoviez, J. F. Nicoud, J. Fischer, I. Ledoux, J. Zyss, Chem.
Mater. 1994, 6, 1358; b) K. Huang, D. Britton, M. C. Etter, S. R. Byrn,
J. Mater. Chem. 1995, 5, 379.
[3] S. R. Marder, J. W. Perry, W. P. Schaefer, Science 1989, 245, 626.
[4] a) P. Gangopadhyay, S. Sharma, A. J. Rao, D. N. Rao, S. Cohen, I.
Agranat, T. P. Radhakrishnan, Chem. Mater. 1999, 11, 466; b) P.
Gangopadhyay, T. P. Radhakrishnan, Chem. Mater. 2000, 12, 3362.
[5] D. F. Eaton, Science 1991, 253, 281.
[6] J. Zyss, J. F. Nicoud, M. Coquillay, J. Chem. Phys. 1984, 81, 4160.
[7] M. Ravi, D. N. Rao, S. Cohen, I. Agranat, T. P. Radhakrishnan, Chem.
Mater. 1997, 9, 830.
[8] M. Kauranen, T. Verbiest, C. Boutton, M. N. Teerenstra, K. Clays,
A. J. Schouten, R. J. M. Nolte, A. Persoons, Science 1995, 270, 966.
[9] K. Clays, E. Hendrickx, T. Verbiest, A. Persoons, Adv. Mater. 1998, 10,
643.
[10] a) T. Verbiest, S. V. Elshocht, M. Kauranen, L. Hellemans, J.
Snauwaert, C. Nuckolls, T. J. Katz, A. Persoons, Science 1998, 282,
913; b) S. V. Elshocht, T. Verbiest, M. Kauranen, L. Ma, H. Cheng,
K. Y. Musick, L. Pu, A. Persoons, Chem. Phys. Lett. 1999, 309, 315.
[11] a) M. Panda, J. Chandrasekhar, J. Am. Chem. Soc. 1998, 120, 13517;
b) H.-J. Deussen, E. Hendrickx, C. Boutton, D. Krog, K. Clays, K.
Bechgaard, A. Persoons, T. Bjùrnholm, J. Am. Chem. Soc. 1996, 118,
6841.
[12] a) B. F. Abrahams, S. R. Batten, H. Hamit, B. F. Hoskins, R. Robson,
Chem. Commun. 1996, 1313; b) C. Piguet, G. Bernardinelli, G.
Hopfgartner, Chem. Rev. 1997, 97, 2005; c) H. C. Aspinall, J. F.
Bickley, J. L. M. Dwyer, N. Greeves, A. Steiner, Angew. Chem. 2000,
112, 2980; Angew. Chem. Int. Ed. 2000, 39, 2858.
[13] a) T. B. Norsten, R. McDonald, N. R. Branda, Chem. Commun. 1999,
719; b) J. R. Koe, M. Fujiki, M. Motonaga, H. Nakashima, Chem.
Commun. 2000, 389; c) J. H. K. K. Hirschberg, L. Brunsveld, A.
Ramzi, J. A. J. M. Vekemans, R. P. Sijbesma, E. W. Meijer, Nature
2000, 407, 167.
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characterized [P4Mo6O25(OH)3]3 ion.[5] We describe here the
synthesis, structure, and magnetic properties of the new two-
dimensional cobaltomolybdenum phosphate 1, which is con-
structed from unprecedented large structural groups contain-
ing sixteen CoII and sixteen MoV ions. These groups are linked
by four dicobalto bridges. The related compound 2 has been
also isolated and characterized by X-ray diffraction. The
structure of 2 contains the same basal units connected by four
tetrahedral CoII centers.
[14] J. F. Nicoud, R. J. Twieg in Nonlinear Optical Properties of Organic
Molecules and Crystals, Vol. 2 (Eds.: D. S. Chemla, J. Zyss), Academic
Press, New York, 1989, p. 221.
[15] Crystallographic data (excluding structure factors) for the structures
reported in this paper have been deposited with the Cambridge
Crystallographic Data Centre as supplementary publication nos.
CCDC-155121 ± 155125. Copies of the data can be obtained free of
charge on application to CCDC, 12 Union Road, Cambridge
CB21EZ, UK (fax: (‡44)1223-336-033; e-mail: deposit@ccdc.cam.
ac.uk).
[16] S. K. Kurtz, T. T. Perry, J. Appl. Phys. 1968, 39, 3798. All the BNDC
crystals are transparent yellow; powder SHG measurements were
carried out using a nanosecond-pulsed Nd:YAG laser operating at
1064 nm.
[17] J. Zyss, J. L. Oudar, Phys. Rev. A 1982, 26, 2028.
[18] a) J. Zyss, D. S. Chemla, J. F. Nicoud, J. Chem. Phys. 1981, 74, 4800;
b) M. Sigelle, R. Hierle, J. Appl. Phys. 1981, 52, 4199.
[19] a) M. J. S. Dewar, E. G. Zoebisch, E. F. Healy, J. J. P. Stewart, J. Am.
Chem. Soc. 1985, 107, 3902; b) M. Dupuis, S. Karna, J. Comput. Chem.
1991, 12, 487; c) MOPAC93, Fujitsu Inc.
[(Mo2O4)8(HPO4)14(PO4)10{Co22Cl2(H2O)42}] ´ 28H2O
[(Mo2O4)8(HPO4)14(PO4)10{Co19Na4(H2O)34}] ´ 14H2O
1
2
Reaction of sodium molybdate with Mo metal as reducing
agent, phosphoric acid, and CoII chloride under hydrothermal
conditions gave, for a starting pH of 2.0, red parallelepiped
crystals of 1 in good yield and, for an initial pH of 3.9 and a
smaller amount of CoII, dark purple crystals of the related
compound 2. A single-crystal structure determination of 1[6]
revealed a two-dimensional network. The structure can be
described as building groups containing sixteen molybdenum
centers and four tetramers of cobalt that form a wheel with a
diameter of 19 Š with overall C4v symmetry (Figure 1a).
Valence bond summations have been applied on all atoms to
confirm the valence of the metal atoms and to locate water
molecules and fourteen terminal hydroxo groups of the
[20] M. Barzoukas, D. Josse, P. Fremaux, J. Zyss, J. F. Nicoud, J. O. Morley,
J. Opt. Soc. Am. B 1987, 4, 977.
A New Family of Layered Molybdenum(v)
Cobalto-Phosphates Built up of
[H14(Mo16O32)Co16(PO4)24(H2O)20]10 Wheels
Charlotte du Peloux, Anne Dolbecq, Pierre Mialane,
 Ã
Á
Â
Jerome Marrot, Eric Riviere, and Francis Secheresse*
Metal ± oxo cluster compounds exhibit unusual topological
properties, and are attractive in view of their use in various
fields ranging from catalysis to medicine.[1] Self-assembly
processes involving MoV lead to a structurally diverse family
of well-defined ring-shaped nanoparticles or clusters,[2] and it
has been shown recently that such compounds can be
connected in several different ways to design extended
solids.[3] An alternative way to this step-by-step aggregation
process for the design of oxomolybdenum frameworks is the
one-pot hydrothermal method. Hydrothermal synthesis of
fully reduced molybdenum phosphates has thus been exten-
sively used to prepare solid-state materials. The octahedral
coordination of the metal centers combined with the tetrahe-
dral geometry of the phosphate groups is at the origin of a
large variety of structures, ranging from one-dimensional
polymers to three-dimensional open frameworks.[4] Among
these materials, to our knowledge, the only examples of
molybdenum phosphates that incorporate first-row transition
metals are based on the same building unit, namely the well-
Â
[*] Prof. F. Secheresse, C. du Peloux, Dr. A. Dolbecq, Dr. P. Mialane,
Dr. J. Marrot
Institut Lavoisier, IREM, UMR 8637
Â
Universite de Versailles Saint-Quentin
45 Avenue des Etats-Unis, 78035 Versailles (France)
Fax : (‡33)1-39-25-43-81
E-mail: secheres@chimie.uvsq.fr
Á
Dr. E. Riviere
Laboratoire de Chimie Inorganique, URA CNRS 420
Â
Institut de Chimie Moleculaire dꢁOrsay
Figure 1. a) Polyhedral representation of the building unit in 1 and 2;
b) ball-and-stick side view of one quarter of the building unit showing the
tetramers of CoII and MoV.
Â
Universite Paris-Sud
91405 Orsay (France)
Angew. Chem. Int. Ed. 2001, 40, No. 13
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