A novel supramolecular tetrahedron assembled from tetranuclear copper(l) cluster molecules via aryl embrace interactions

Article abstract of DOI:10.1021/ic801972e

An intriguing supramolecular tetrahedral aggregate [Cu₄l(ptt) ₃(Hptt)₃]₄ (1; Hptt = 1-phenyl-1H-tetrazole-5- thiol) based on novel copper(l) iodide thiolate clusters in the solid state has been synthesized and c

Full text of DOI:10.1021/ic801972e

Inorg. Chem. 2009, 48, 420-422
A Novel Supramolecular Tetrahedron Assembled from Tetranuclear
Copper(I) Cluster Molecules via Aryl Embrace Interactions
Wei Wei,†,‡ Mingyan Wu,† Qiang Gao,†,‡ Qingfu Zhang,†,‡ Yougui Huang,† Feilong Jiang,†
and Maochun Hong*,†
The State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of
Matter, The Chinese Academy of Sciences, Fuzhou, Fujian 350002, People’s Republic of China, and
Graduate School of the Chinese Academy of Sciences, Bejing 100039, People’s Republic of China
Received October 19, 2008
An
intriguing
supramolecular
tetrahedral
aggregate
collective contribution to the formation of a reliable su-
pramolecular synthon, which would be used to interlink
ambient individual molecules into a regular aggregation like
a supramolecular polyhedron, as is found to be prevalent in
many biological molecules. One of the supramolecular
synthons has been described as a multiple aryl embrace by
Dance and co-workers,4,5 which is a concerted set of
interactions between aryl groups through a combination of
offset face-to-face π-π stacking (OFF) and edge-to-face
C-H · · · π (EF) interactions.3a Actually, these multiarmed,
concerted, and attractive motifs are frequently observed in
crystals of molecules with multiple aryl groups on the
surfaces.5,6 In this respect, we chose 1-phenyl-1H-tetrazole-
5-thiol (Hptt) as the ligand, which obviously could be divided
into two parts: thiotetrazole and phenyl groups. The former
is expected to be bridging groups in the construction of
copper(I) clusters like other N-heterocyclic thiolate ligands,7
while the latter can offer additional noncovalent aromatic
interactions to modulate and influence the assembly and
packing of copper(I) cluster molecules. Also, we fortunately
obtained a delicate supramolecular tetrahedron [Cu4I(ptt)3-
(Hptt)3]4 (1) in the solid state, which is assembled from four
novel copper(I) iodide thiolate cluster molecules via many
cooperative aromatic-aromtic interactions. In this Com-
munication, we will report its synthesis and crystal structure,
together with temperature-dependent green photolumines-
cence and its considerable thermal stability.
[Cu4I(ptt)3(Hptt)3]4 (1; Hptt ) 1-phenyl-1H-tetrazole-5-thiol) based
on novel copper(I) iodide thiolate clusters in the solid state has
been synthesized and characterized. Four tetra-copper(I) cluster
molecules join together with the cooperation of multiple offset face-
to-face π-π stacking (OFF) and edge-to-face C-H· · ·π (EF)
interactions in the form of aryl embrace of a (EF)3(OFF)3 motif,
which leads to the formation of this tetrahedral aggregate.
Furthermore, this complex exhibits a temperature-dependent green
photoluminescence.
Supramolecular chemistry describes the spontaneous as-
sembly of noncovalently linked molecular polyhedra of
unique shape and composition. In the past decade, the
coordination-driven1 and conventional hydrogen-bonding-
directed2 self-assembly of a high-symmetry conglomerate
has been developed rapidly based on the edge- or face-
directed strategies.1a,e However, it is still a great challenging
subject to construct supramolecular polyhedra merely via
weaker affinities such as aromatic-aromatic interaction
because of the weak attraction of an individual interaction.3
To overcome this difficulty, multiple concerted aromatic-
aromatic interactions will be required, thus resulting in a
*
To whom correspondence should be addressed. E-mail:
hmc@fjirsm.ac.cn.
†
The Chinese Academy of Sciences.
Graduate School of the Chinese Academy of Sciences.
‡
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420 Inorganic Chemistry, Vol. 48, No. 2, 2009
10.1021/ic801972e CCC: $40.75  2009 American Chemical Society
Published on Web 12/15/2008

COMMUNICATION
Reaction and evaporation at ambient temperature of the
Hptt ligand and CuI at a ratio of 1:1 in CH3CN afford
colorless prismatic crystals.8 Single-crystal X-ray diffraction
reveals that 1 crystallizes in the noncentrosymmetric cubic
9
j
group P43n. The structure of 1 features a discrete tetra-
copper(I) cluster linked by ptt anion and neutral Hptt
ligands.10 As shown in Figure 1, there are only two
crystallographically independent Cu atoms in the asymmetric
unit. Cu1 is located on the crystallographic C3 axis and is
ligated by three S2 atoms from three ptt ligands in a triangle
geometry with a bond length of 2.287 Å (Cu1-S2). In
contrast to Cu1, Cu2 shows a distorted tetrahedron geometry:
two S atoms and one N atom from the ptt and Hptt ligands
create its tapered bottom, and I- occupies its apex to
complete the configuration. Here, similar to Cu1, I- also
locates on the C3 axis and has an occupancy of one-third.
The distance of Cu2-I1 is measured to be 2.8034(7) Å,
which is slightly longer than those found in other copper(I)
complexes containing Cu-I bonds.11 The separation between
Cu1 and Cu2 is 2.8234(9) Å, which is close to the sum of
the van der Waals radii (2.80 Å) of CuI centers, implying
the existence of weak Cu-Cu interactions. Thus, the
connectivity of four Cu ions and one I anion gives rise to a
novel tetrametal core of [Cu4I] with C3V symmetry. Addition-
ally, there are relatively few examples known of the
simultaneous incorporation of competitive iodide and thiolate
anions bridging adjacent coinage metal ions.12
Figure 1. View of the metal-cluster molecule with C3 symmetry in 1. All H
atoms have been omitted for clarity. Two types of ligands are marked with
Hptt and ptt. Symmetry code: #1, 1 - y, z, 1 - x; #2, 1 - z, 1 - x, y.
Because the copper(I) cluster molecule is electrically
neutral and hydrophobic, it lacks charge-compensating
interactions like ion-dipole interaction and conventional
hydrogen bonding. Consequently, the self-assembly force for
the construction of supramolecular conglomerates mainly
comes from the concerted aromatic-aromatic interactions,
which are originated from the tetrazole ring and protruding
phenyl group of the ligands. As shown in Figure 2a, a trimer
generated from C3 symmetry operation can be extracted from
packing topology to expound the complicated aromatic-
aromaticinteractions.Itisobviousthatthreetypesofaromatic-
aromatic interactions exist among the trimer: (I) edge-to-
face CH · · · π interactions (red dashed lines) between two
neighboring phenyl rings, ab. EF; (II) offset face-to-face
phenyl-tetrazole stacking (dark dashed lines), ab. OFF; (III)
tetrazole-tetrazole stacking interctions (yellow dashed lines).
All of these interaction separations and angles are listed in
Table 1. Primarily, three phenyl rings from different copper(I)
cluster molecules interact with each other through three EF
(dCH· · · centroid ) 2.82 Å) in a concerted manner, which gives
rise to a concerted (EF)3 motif. At the same time, tetrazole
moieties from adjacent molecules also affect the phenyl ring
by the formation of OFF interaction (dcentroid· · · centroid ) 3.78
Å). In this manner, each phenyl ring, acting as both a proton
acceptor and a donor, is sandwiched with interactions of two
EF and one OFF motifs from three other aromatic rings.
Thus, for the whole trimer, it includes an extended array of
aryl embrace of (EF)3(OFF)3. In addition, tetrazole moieties
from ptt ligands of neighboring molecules are involved in
another type of energetically favorable π deficient-π
deficient stacking,13 and the close contact (3.14 Å) between
N atoms of two tetrazole rings indicates considerable
tetrazole-tetrazole interaction. As a result, by means of the
aryl embrace of the (EF)3(OFF)3 motif and the tetrazole-
(8) Synthesis of the compound: The ligand Hptt (89 mg, 0.50 mmol) and
CuI (90 mg, 0.50 mmol) were mixed with 10 mL of CH3CN and stirred
for 2 h. After 48 h, slow evaporation of the solution in air afforded a
large number of fine colorless crystals. Yield: 68% (with respect to
Hptt supplied). Anal. Calcd for [C42H33N24S6ICu4]: C, 34.85; H, 2.30;
N, 23.23. Found: C, 35.27; H, 2.32, N, 23.15. IR (KBr, cm-1):
3073(m), 2920(m), 2771(m), 1594(m) 1497(s), 1376(s), 1313(s),
761(s), 687(m), 566(m).
j
(9) Crystal data for 1: C42H33N24S6ICu4, MW ) 1447.3, cubic, P43n (No.
218), a ) 22.4646 (3) Å, V ) 11336.9 (3) Å3, Z ) 8, Dc ) 1.692
g/cm3, F000 ) 5744, µ ) 2.30 mm-1, S ) 1.068, R1 ) 0.0374, wR2
) 0.1053. Considering the long distance of Cu1 and I1, ca. 3.12 Å,
we infer that there is no interaction between them.
(10) It is distinct that there are two different coordination modes of the
ligand in 1. As judged by the distance of C1 · · ·S1 atoms [1.668 (4)
Å, distinctly shorter in comparison to the C8-S2 single bond length
1.717(4) Å] and the conservation of electroneutrality of the component
molecule, the C1-S1 bond is a double covalent bond and proton
transfer from S1 to N1 has occurred. Thus, the monodentate ligand
possessing a S1 atom is electrically neutral, which is marked with
Hptt, and the ptt anion ligand containing µ-S (S2) is represented as
ptt.
(11) (a) Ohi, H.; Tachi, Y.; Kunimoto, T.; Itoh, S. Dalton Trans. 2005,
3146. (b) Li, M.; Li, Z.; Li, D. Chem. Commun. 2008, 3390.
(12) (a) Wang, J.; Zheng, S.-L.; Hu, S.; Zhang, Y. H.; Tong, M.-L. Inorg.
Chem. 2007, 46, 795. (b) Verhagen, J. A. W.; Tock, C.; Lutz, M.;
Spek, A. L.; Bouwman, E. Eur. J. Inorg. Chem. 2006, 4800. (c) Wang,
J.; Zhang, Y.-H.; Li, H.-X.; Lin, Z.-J.; Tong, M.-L. Cryst. Growth
Des. 2007, 7, 2352. (d) Mentzafos, D.; Terzis, A.; Karagiannidis, P.;
Aslanidis, P. Acta Crystallogr., Sect. C 1989, 45, 54.
(13) (a) Hunter, C. A.; Sanders, J. K. M. J. Am. Chem. Soc. 1990, 120,
5525. (b) Cozzi, F.; Cinquini, M.; Annuziata, R.; Siegel, J. S. J. Am.
Chem. Soc. 1993, 115, 5330.
Inorganic Chemistry, Vol. 48, No. 2, 2009 421

COMMUNICATION
Figure3.Formationofasupramoleculartetrahedronvia30aromatic-aromatic
interactions. The interactions are represented as red dashed lines.
The other attractive characteristic of this complex is its
temperature-dependent green photoluminescent property. At
ambient temperature, 1 does not display any obvious
emission. However, at the low temperature of 10 K,
excitation of solid samples at λ ) 380 nm produces a broad
green emission with a peak maximum at 528 nm (Figure S3
in the Supporting Information). More detailed theoretical and
spectroscopic studies are being pursued.
Figure 2. (a) View of the formation of a trimer along the C3 axis via the
CH· · ·π (red dashed lines), phenyl-tetrazole stacking (dark dashed lines),
and additional tetrazole-tetrazole stacking interactions (yellow dashed lines).
(b) Cartoon representation of the hypothetical formation of the trimer
depicted as an open cone with C3 symmetry and finally a supramolecular
tetrahedron.
In summary, an interesting supramolecular tetrahedron
complex based on novel tetracopper(I) clusters has been
synthesized and characterized. These tetrametal cluster
molecules join together with the cooperation of C-H · · ·π
and π-π stacking interactions in the form of an aryl embrace
of the (EF)3(OFF)3 motif, which leads to the formation of
a supramolecular tetrahedron in the solid state. This crystal
structure serves as a useful example of these weak
aromatic-aromatic interactions for organization into highly
symmetric architectures with considerable stabilization,
which affords a significant approach to the biological
simulation. Furthermore, this complex exhibits a temperature-
dependent green photoluminescence deserving further in-
vestigations of the emissive mechanism.
Table 1. Aromatic-Aromatic Interactions Existing in the Crystal
Structure of 1
central
shortest
interaction
group
interaction
type
separation/ contact/
angle/
deg
Å
Å
phenyl-phenyl
C-H· · ·π
2.82a
3.78
3.92
θ ) 141
ꢀ ) 17.31
ꢀ ) 22.23
phenyl-tetrazole
π-π stacking
3.52
3.14
tetrazole-tetrazole π-π stacking
a Separation of an H atom and π ring centroid; θ ) angle of C-H· · ·ring
centroid in C-H· · ·π interactions; ꢀ ) angle between the ring normal and
centroid-centroid vector in π-π stacking.
tetrazole interactions, the assembly of the trimer can be
depicted as the formation of an open cone with C3 symmetry
(Figure 2b). On the other hand, the copper(I) cluster molecule
itself also has a C3 symmetry. Accordingly, simultaneous
satisfaction of the two 3-fold symmetry axes can only be
achieved by the formation of a supramolecular tetrahedron
via 30 aromatic-aromatic interactions (Figure 3). Interest-
ingly, we cannot find any appreciable interactions among
these tetrahedra, implying an independence of the supramo-
lecular conglomerates in crystal packing. Thermogravimetric
analysis indicates that the highly symmetric structure with a
void of ca. 160 Å3 can survive until 180 °C. This tetramer
structure is reminiscent of the hemoglobin molecule, which
is also a tetramer of four globular protein subunits composed
of heme groups containing metal ions and protein chains.
Additionally, it is also assembled via weak hydrogen bonds,
π-π stacking, and van der Waals contacts.
Acknowledgment. We thank the 973 Program (2006CB-
932900), the National Natural Foundation of China and the
Natural Science Foundation of Fujian Province for funding
this research.
Supporting Information Available: Crystallographic data in
CIF format, table of selected bond lengths and angles, XRPD
patterns, TG-MS analyses, solid-state emission spectrum, space-
filling representation, and packing diagram. This material is
available free of charge via the Internet at http://pubs.acs.org.
IC801972E
422 Inorganic Chemistry, Vol. 48, No. 2, 2009