Confined metallophilicity within a coordination prism

Article abstract of DOI:10.1002/chem.201100081

Similarities attract: The designed coordination prism (see graphic; Cu orange, N blue, C gray), based on the renowned Cu^I-pyrazolate trimer, features an unprecedented stacking mode and an unusual, luminescent Stokes shift of 23470 cm^-1

Full text of DOI:10.1002/chem.201100081

COMMUNICATION
DOI: 10.1002/chem.201100081
Confined Metallophilicity within a Coordination Prism
[a]
Guo-Fen Gao, Mian Li, Shun-Ze Zhan, Zhi Lv, Guang-hui Chen, and Dan Li*
Metallophilicity (also called metal–metal bonding) is a
structural chemical concept that describes unusual chemical
bonding between closed-shell metal centers, despite the
10
[1,2]
formal nd electronic configurations.
During the past de-
cades, the occurrence of metal–metal interactions have been
[
2,3]
testified by compelling experimental evidence,
origin remains controversial.
but the
[4–6]
Hoffmann and co-worker
postulated that the hybridization of nd orbitals with (n+1)s
and (n+1)p orbitals is responsible for the metal–metal
[4]
bonding; this was strongly supported by the direct obser-
[3]
vation of d orbital holes in Cu O. However, higher-level
2
calculations performed by Pyykkç et al. concluded that met-
allophilic attraction does not involve electronic transition,
but is just another van der Waals force based on correlation
[5]
F
i
g
u
r
e
1
.
M
o
l
e
c
u
l
a
r
d
i
a
g
r
a
m
o
f
t
h
e
C
u
t
r
i
m
e
r
a
n
d
t
h
e
p
o
s
s
i
b
l
e
C
u
and relativistic effects. Cotton and co-workers also claimed
that their DFT calculations did not reveal any evidence for
3
6
dimer of trimers. There are three related stacking modes of Cu
by a set of geometrical parameters (d, l, and a). Assuming each Cu
6
defined
tri-
3
I
I
possible metal–metal bonding, despite very short Cu –Cu
distances; hence contradicting the above-mentioned hybridi-
angle defines a plane and a centroid, the perpendicular separation of the
two Cu3 planes is set as the first parameter, d. If the centroid distance,
which is the smallest value, equals the value of d, and the orthogonal pro-
[6]
zation hypothesis.
The phenomenon of metallophilicity is usually encoun-
jections of the two Cu
rangement is called a frontal mode. The eclipsed mode refers to the sit-
uation when the two parallel Cu triangles show horizontal displacement,
3
triangles coincide with each other, the stacking ar-
I
I
I
[2]
tered in coinage metal (Cu , Ag , and Au ) compounds,
3
I
which include a classic family of cyclic, trinuclear, Cu -pyra-
(henceforth referred to as Cu , see
3
Figure 1) assembled through Cu –Cu interactions. Recently,
where the horizontal distance of the two centroids is set as the second pa-
rameter, l. The introduction of the third parameter, a, which describes
the rotational angle when the orthogonal projections of the two Cu3 tri-
angles do not coincide, generates the staggered mode when a=608.
[7–10]
zolate complexes
I
I
I
I
such coinage-metal (Cu and Ag )-pyrazolate trimers were
[11]
[12]
used by us and others as building blocks to assemble in-
triguing, supramolecular architectures. Note, in both oligo-
[7–10]
[11,12]
meric
and polymeric
Cu -based aggregates, the in-
grand orbital hybridization at the excited state of the coordi-
nation prism is unveiled.
3
I
I
tertrimeric Cu –Cu contact, rather than the intratrimeric
one, functions as bright phosphor and features interesting
Interestingly, all reported Cu cases, including theoretical
6
[7–9]
[10]
[7–9,11]
luminescent behaviors
triggered by the unassisted dimer
optimization
and experimental observation,
are
of trimers (henceforth referred to as Cu , see Figure 1).
Herein, we describe the design and synthesis of a new coor-
found in the staggered mode (Figure 1) or in a combination
of the eclipsed and staggered modes (usually called chair
6
dination prism, namely, [Cu L ] (L=p-xylylene-bis(3,5-di-
conformation)—no Cu frontal mode has been documented
6
3
6
methyl)pyrazol-4-yl), exhibiting an unprecedented Cu6
stacking mode, with which we are able to capture structural
and spectroscopic evidence of enhanced metallophilicity.
Furthermore, upon DFT analysis, an unusual situation of
so far, due to energetic and steric effects. Our presynthetic
consideration for targeting the frontal mode involved the
designer ligand L with bispyrazolate components for con-
struction of Cu units, two of which that were supposed to
3
be fixed in a parallel fashion by three semirigid xylylene
linkers with appropriate binding angles to yield a cage-
shaped Cu -pyrazolate molecule with a prism conformation.
+
+
I
[
a] G.-F. Gao, M. Li, S.-Z. Zhan, Z. Lv, Prof. G.-h. Chen, Prof. D. Li
Department of Chemistry, Shantou University
Guangdong 515063 (P.R. China)
As shown in Figure 2, the crystal structure of the [Cu L ]
6
3
coordination prism clearly shows the frontal mode for Cu6
bound by three semirigid ligands. The two triangle facets of
Fax : (+86)754-2902767
E-mail: dli@stu.edu.cn
+
the prism are composed of two Cu trimers featuring essen-
3
[
] These authors contributed equally to this work.
tially planar nine-membered Cu N rings with two-coordi-
nate Cu sites, whereas the three edges perpendicular to
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201100081.
3
6
I
Chem. Eur. J. 2011, 17, 4113 – 4117
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
4113

stricted due to the flexibility of methylene in the linker, war-
ranting the unprecedented presence of the frontal mode of
Cu6.
Usually the emissive bands of Cu -based compounds
3
range from 540 to 660 nm (see Section 3 of the Supporting
[
7–11]
Information) with microsecond lifetimes.
the extensive spectroscopic investigations by Che and co-
workers,
According to
[14,15]
these low-energy and long-lived emissions are
attributed to phosphorescent, triplet, metal–metal-bonded,
3
excited states ( MM), whereas the excitations are singlet
1
ligand-to-metal–metal charge transfers ( LMMCT), which
I
involve Cu 3ds*!4ps transitions, implying a bonding
I
I
nature of the Cu –Cu interactions. In this [Cu L ] coordina-
6
3
I
I
tion prism, albeit the intertrimeric Cu –Cu distances are too
long for ground-state bonding according to the crystal struc-
ture data, some interesting luminescent behaviors with simi-
lar unstructured, but also unique, profiles, are observed
6 3
Figure 2. The crystal structure of the [Cu L ] coordination prism along
with the temperature-dependent excitation and emission spectra. The
crystal structure was measured at room temperature (298 K). Color
codes: orange Cu, blue N, and gray C. The 3,5-dimethyl substituents of
the pyrazolate rings as well as all H atoms of the ligands are omitted for
(
Figure 2). The excitation spectra at a very short wavelength
I
(l =290 nm) is required to generate the very long-wave-
clarity. The golden dashed lines depict the intra- and intertrimeric Cu –
ex
I
Cu interactions that form a prism configuration. Intratrimeric distances:
length emission spectra (lem =716 nm), showing very intense
red emission with an obvious redshift compared with previ-
ously reported results.
Cu1ꢁCu2 3.174, Cu1ꢁCu3 3.217, Cu2ꢁCu3 3.203, Cu4ꢁCu5 3.195, Cu4ꢁ
Cu6 3.212, and Cu5ꢁCu6 3.199 ꢁ; intertrimeric distances: Cu1ꢁCu4
3
.868, Cu2ꢁCu5 3.946, and Cu3ꢁCu6 3.696 ꢁ. The crystalline sample of
This lowest-energy excited state (lem =716 nm, compared
[
Cu
picture below the emission spectra) with an emission band at lem
16 nm at room temperature, and an excitation band at lex =290 nm.
6 3
L ] shows intense red photoluminescence (as shown in the inserted
with 542 nm for the unassisted oligomeric Cu dimer and
598 nm for the polymeric Cu -based frameworks)
=
3
[
11]
7
would
3
Upon lowering the temperature, both the intensity of the excitation and
emission increased significantly, but no luminescent thermochromism was
recorded.
not be possible without the existence of the geometrical
confinement and the presence of the frontal mode. Given
that the excitation wavelengths are similar (l =290 nm,
ex
compared with 305 nm for the Cu -based oligomer and poly-
3
[11]
these triangle facets consist of xylylene groups. The structure
is slightly distorted from the ideal equilateral triangular
prism configuration and hence crystallizes in the monoclinic
P2 /c space group with an entire [Cu L ] molecule as the
mer), we speculate that this lower-energy T state is sup-
1
ported by the unprecedented three Cu –Cu interactions
confined in the coordination prism, compared with one or
I
I
two for other Cu compounds. This geometrical confinement
1
6
3
3
asymmetric unit (see Section 2 of the Supporting Informa-
tion for additional structural illustrations). The intertrimeric
also enables the high activation energy needed for the inter-
nal conversion to a higher-energy T state, and thus, there is
1
I
I
Cu –Cu distances of 3.696, 3.868, and 3.946 ꢁ (298 K), re-
spectively, are generally longer than those measured in Cu6,
which exhibits eclipsed and staggered modes or a combina-
tion of the two (see Section 3 of the Supporting Informa-
only one possible emissive T1 state for the coordination
prism; this explains why the emission spectra only vary in
intensity with different temperatures, whereas in other Cu3-
based compounds the phenomenon of luminescence thermo-
I
I
[7–9]
tion). Note that there are three Cu –Cu contacts herein,
chromism is usually observed.
Also, the temperature-de-
I
I
whereas only one or two Cu –Cu contacts exist in previous
pendent lifetimes of the [Cu L ] emission, ranging from
6 3
[7–12]
documentation.
18.84ꢂ0.04 to 24.66ꢂ0.03 ms (see Section 4 of the Support-
ing Information), are consistent with the microsecond scale
of phosphorescence. The colossal Stokesꢂ shift (about
Three aspects of structural uniqueness of this coordination
prism should be highlighted: 1) Compared with other heavi-
I
I
ꢁ1
er coinage metals (Ag and Au ), the selection of the smaller
23470 cm !) indicates that the excited states may experi-
I
and lighter Cu , with which relativistic effects are expected
ence huge distortion; this will be discussed below.
Other than the spectroscopic evidence mentioned above,
[13]
to be much less important,
lessens the complications
when discussing the origin of the metallophilicity. 2) The
length of the xylylene linker of ꢀ4.0 ꢁ is much longer than
the CuꢁCu van der Waals radii sum of 2.8 ꢁ, significantly
from the structural point of view, the two Cu triangles show
a slight deviation from the planarity defined by the three
edges, that is, the xylylene linkers of the prism with a length
3
I
I
weakening intertrimeric Cu –Cu interactions at the ground
state (S ), but it is reasonable to speculate that the Cu cen-
of ꢀ4.0 ꢁ. Clearly the two Cu triangles are attracted to
3
each other, resulting in concave triangle facets compared
with the planar triangle facets of an ideal prism. To assess
the existence of such a metallophilic attraction, the crystal
structure of [Cu L ] was measured at a cryogenic tempera-
0
6
ters may interact strongly at the triplet excited state (T1)
and cause low-energy visible emissions. 3) The prism config-
uration allows geometrical confinement (even at T ), where
1
6
3
I
I
the above-mentioned parameters of l and a (Figure 1) are
completely restricted and the variation of d is partially re-
ture. Accordingly, the three intertrimeric Cu –Cu separa-
tions are shorten by 0.1 ꢁ, from 3.696, 3.868, and 3.946 ꢁ
4114
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ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2011, 17, 4113 – 4117

Cu–Cu Interactions in a Coordination Prism
COMMUNICATION
(
average 3.837 ꢁ, 298 K) to 3.556, 3.804, and 3.848 ꢁ (aver-
age 3.736 ꢁ, 143 K), respectively, implying enhancement of
such an attraction at lower temperatures. But this trend is
not reflected in the temperature-dependent luminescent
spectra (Figure 2), and some previous works also showed
that genuine ligand-unassisted cuprophilic attraction is not
I
I
[16,17]
relevant to very short Cu –Cu distances.
In fact, it is
I
I
questionable whether the compression of the Cu –Cu dis-
tances is due to the constraints of the bridging ligands or to
genuine metal–metal interactions. A literature survey (see
Section 3 of the Supporting Information) shows that the
face value of Cu –Cu distances (related to the radii sum of
.8 ꢁ) is an unreliable criterion for assessing metallophilicity
I
I
2
in the Cu family.
3
Figure 3. Frontier-orbital contours of the TDDFT-optimized S0 and T1
states of [Cu L ], showing the HOMO–LUMO band gap of S and the
Instead, energetic considerations by calculating the over-
all stabilization can provide more convincing evidence of
metallophilicity. Theoretical treatments by Schwerdtfeger
6
3
0
lower–upper SOMOs band gap of T
1
, assigned as excitation and emission
bands, respectively. The geometrical optimization is based on the crystal-
lographic data of [Cu ]. To simplify the calculation, the 3,5-dimethyl
6
L
3
[18]
et al. estimated that the pure cuprophilic bonding is in the
substituents of the pyrazolate rings were replaced by hydrogen atoms.
The atomic labels and positions are consistent with the crystal structure
shown in Figure 2. Color codes: orange Cu, blue N, gray C and H; the
ꢁ
1
range of 3.5–4 kcalmol for the ligand-unassisted dimeric
model that contains only one Cu –Cu contact, and for the
I
I
I
I
electron density is shown in red and green. The optimized Cu –Cu sepa-
unassisted Cu dimer, with chair conformation and in which
3
0
rations are given below. For S , intratrimeric distances: Cu1
ꢁ
Cu2 3.227,
I
I
multiple Cu –Cu contacts exist, the intertrimeric cuprophilic
Cu1ꢁCu3 3.208, Cu2ꢁCu3 3.247, Cu4ꢁCu5 3.227, Cu4ꢁCu6 3.217, and
stabilization at the S state is calculated to be up to 18.1 kcal
0
Cu5ꢁCu6 3.239 ꢁ; intertrimeric distances: Cu1ꢁCu4 4.165, Cu2ꢁCu5
ꢁ
1 [10]
mol . Herein, we calculate the overall metallophilic sta-
bilization for [Cu L ] (see Figure S6 in Section 5 of the Sup-
4.183, and Cu3ꢁCu6 3.982 ꢁ. For T , intratrimeric distances: Cu1ꢁCu2
1
3
.219, Cu1ꢁCu3 3.230, Cu2ꢁCu3 3.231, Cu4ꢁCu5 2.594, Cu4ꢁCu6 2.554,
6
3
and Cu5ꢁCu6 3.047 ꢁ; intertrimeric distances: Cu1ꢁCu4 3.407, Cu2ꢁCu5
porting Information for calculation details), resulting in a
3
.584, and Cu3ꢁCu6 3.555 ꢁ.
ꢁ
1
value of 19.74 kcalmol , which is larger than in the above-
mentioned reports. Despite the much longer intertrimeric
I
I
I
Cu –Cu separation (3.837 ꢁ on average) of [Cu L ] than
Cu centers. This HOMO–LUMO band-gap energy is as-
6
3
1
those of the analogous Cu -based oligomer (2.954 ꢁ) and
polymer (3.331 ꢁ),
signed as the excitation band of LMMCT and calculated to
3
[
11]
the larger stabilization energy indi-
appear at l =272 nm, which is close to the experimental
ex
cates enhanced cuprophilicity within the coordination prism.
value of 290 nm. For the phosphorescent T state, the upper
1
I
I
The three Cu –Cu contacts, which exist only in the frontal
mode of the coordination prism, entail this enhanced metal–
metal bonding, also manifested by the above-discussed
structural and spectroscopic uniqueness.
The theoretical origin of the metallophilicity was inter-
preted as hybridization of nd orbitals with (n+1)s and (n+
singly occupied molecular orbital (SOMO) shows increased
intertrimeric bonding compared with the singlet LUMO,
whereas the lower SOMO populated with intratrimeric den-
I
I
sity indicates the disconnection of the intertrimeric Cu ꢁCu
3
bonding. The emission band of the MM state is attributed
to the upper-to-lower SOMOs band-gap energy of T , with a
1
[
4]
1
)p orbitals or as correlation effects strengthened by rela-
calculated emission band at lem =565 nm (experimental
lem =716 nm). Compared with previous modeling of the
[5]
tivistic effects, as introduced above. The key point of this
contention is whether electronic transitions that form
metal–metal bonds are involved. Early DFT calculations
disaffirmed this hypothesis, but recent time-dependent DFT
photophysics of Cu systems (see Table S6 in Section 5 of
3
[6]
the Supporting Information), this result is acceptable. The
theoretical assignments of the luminescent spectra are con-
sistent with the above-discussed experimental data.
[10]
(
TDDFT) analysis performed by Cundari and co-workers,
who considered both the S and T states of cyclic, trinu-
Further structural clues are carefully examined to ration-
alize the unprecedented geometry of the coordination prism
and the unique photophysical behaviors. The above-men-
tioned geometrical optimization (Figure 3) gives rise to the
0
1
clear, coinage metal pyrazolates, clearly showed HOMO–
LUMO, intertrimeric, electron density transitions between
the frontier orbitals of S and T . The intriguing luminescent
0
1
I
I
behaviors presented herein and for other members of the
intertrimeric Cu –Cu distances (3.982, 4.165, 4.183; average
[7–9]
Cu family
also imply a metal–metal bonding character.
4.110 ꢁ) at S ; these are slightly longer than the experimen-
3
0
Herein, we utilize TDDFT calculations to analyze the
frontier orbitals of the optimized S and T states of [Cu L ].
tal values (3.696, 3.868, 3.946; average 3.837 ꢁ), whereas at
T1 the calculated values (3.555, 3.407, 3.584; average
3.515 ꢁ) are shorten by 0.595 ꢁ on average (see Figure S5
and Table S5 in Section 5 of the Supporting Information for
details). This result is experimentally supported by a recent
0
1
6
3
As shown in Figure 3, at the HOMO of S , the electron den-
0
sity is highly distributed on the ligands and metal–ligand co-
ordinative bonds, whereas at the LUMO of S , the electron
0
[19]
density is primarily located around the Cu atoms, showing
study by Coppens and co-workers,
who developed the
I
I
delocalized, intertrimeric, Cu ꢁCu bonding across multiple
technique of time-resolved single-crystal X-ray diffraction
Chem. Eur. J. 2011, 17, 4113 – 4117
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4115

D. Li et al.
and determined the excited-state structure of an unassisted
ordinative bonds. This grand orbital mixing is responsible
for the decrease of the SOMOs band gap in the phosphores-
cent state, thus leading to the redshift of the low-energy and
long-lived emission of the coordination prism.
I
I
Cu dimer to show that one of the Cu –Cu distances therein
3
was reduced by 0.56 ꢁ from 4.018 ꢁ at S to 3.461 ꢁ at T .
0
1
The drastic distortion in the geometry of the emissive excit-
ed state of [Cu L ] corresponds to the above-mentioned co-
Taken together, we have reached three conclusions in this
research: 1) In this [Cu L ] coordination prism, the occur-
6
3
ꢁ
1
lossal Stokesꢂ shift of ꢀ23470 cm .
6
3
With such a significant geometrical adjustment, the
pseudo-D3h symmetry (equilateral triangle) at S0 of the
rence of enhanced cuprophilicity is unambiguously evi-
denced by structural, spectroscopic, and computational in-
vestigations. 2) The phosphorescent emission assignment
and frontier-orbital analysis suggest that the intertrimeric
[
Cu L ] coordination prism is reduced to pseudo-C symme-
6
3
2
v
I
try (isosceles triangle) at T . Notably, one site of the six Cu
1
I
I
atoms in [Cu L ], namely Cu4, is mainly responsible for this
Cu –Cu contacts within this coordination prism involve nat-
ural electronic transitions. 3) It is reasonable to speculate
6
3
drastic distortion; the distance between Cu4 and Cu1 is re-
duced by 0.758 ꢁ from 4.165 ꢁ at S to 3.407 ꢁ at T (both
I
I
that the reason for this Cu ꢁCu bonding is orbital hybridiza-
tion (3d, 4s and 4p), which is supported by examining the
composition of the frontier orbitals of [Cu L ], especially for
0
1
calculated). Such intense contraction operated by the en-
I
I
hanced Cu ꢁCu bonding at the excited state even over-
whelms the CuꢁN coordinative bonds. As shown in
6
3
the Cu4 site with significant photoinduced Jahn–Teller dis-
tortion. This newly designed coordination prism that exhib-
its an unprecedented stacking mode represents a unique
case for assessing the existence and the nature of metallo-
I
Figure 4, the linear geometry of two-coordinate Cu is des-
[23,26]
philicity within a confined space.
Further, this research
suggests that there should be no generalization for the
nature of metallophilicity—in this case evident metallophi-
licity accompanied by electron transitions seems warranted,
but in other cases the effects of bridging ligands and electro-
static interactions may obscure any genuine metallophilicity.
Since metallophilicity is widely considered by theoretical
chemists as a type of van der Waals force, it is highly recom-
mended that further computational assessment is performed
by taking advantage of the recently developed model of
Figure 4. Partial structural views of the optimized bonding environment
of Cu4 in [Cu
6 3
L ], illustrating the drastic geometrical distortion from the
S
0
to the T state. Only Cu4 and Cu1 along with the corresponding coor-
1
I
I
dinated pyrazolate components are depicted here. The Cu1 ꢁCu4 bonds
are shown in dashed lines and the N5-Cu4-N1 bond lengths and angles
[24]
DFT with long-range corrections.
I
I
are marked. From the S
0
to the T
1
state, the Cu1 ꢁCu4 separation is dra-
matically shorten by 0.758 ꢁ from 4.165 to 3.407 ꢁ, whereas the CuꢁN
bonds are elongated by 0.19 ꢁ from ꢀ1.86 to 2.05 ꢁ, and the N5-Cu4-N1
angle is reduced by up to 49.98 from 176.4 to 126.58.
Experimental Section
Synthesis of [Cu
6 3 2
L ]: A mixture of Cu O (0.0288 g, 2.0 mmol), HL
tructed and the CuꢁN distances are significantly elongated
by ꢀ0.2 ꢁ. Such an unusual phenomenon is referred to as
(
0.0147 g, 1.0 mmol), n-hexane (4.0 mL), and acetonitrile (4.0 mL) was
stirred for 15 min in air. It was then transferred and sealed in a 12 mL
Teflon-lined reactor, which was heated in an oven at 1408C for 72 h and
[10,20–22]
photoinduced Jahn–Teller distortion,
which describes
ꢁ
1
then cooled to room temperature at a rate of 38C0.5 h . Yellowish block
crystals of [Cu ] were obtained as the major product (see Section 1 of
the Supporting Information for additional synthetic details)
Crystallographic study of [Cu ]: Data collection was performed on a
the drastic geometrical adjustment in the T1 states of d
blocks and the corresponding spectroscopic uniqueness, such
as huge Stokesꢂ shifts and phosphorescent emissions.
6
L
3
6
L
3
A logical explanation for such a huge distortion is that
the lowest-energy excited state of [Cu L ] involves electron-
Bruker Smart Apex CCD diffractometer (MoKa, l=0.71073 ꢁ) by using
SMART (Bruker AXS, Madison, WI, USA, 1997) at 298 and 143 K. Re-
flection intensities were integrated with the SAINT software and absorp-
tion correction was applied semiempirically (Bruker AXS, Madison, WI,
USA, 1997). The structures were solved by direct methods and refined
6
3
ic transitions from filled 3d antibonding orbitals to vacant
bonding orbitals arising from 4s and 4p subshells. This hy-
pothesis is testified herein by examining the composition of
2
by full-matrix least-squares refinements based on F . Anisotropic thermal
parameters were applied to all non-hydrogen atoms. The hydrogen atoms
the frontier orbitals of [Cu L ] deduced from the above
6
3
TDDFT calculations. As shown in Table S7 in the Support-
ing Information, at the site of Cu4, the located electron den-
sity accounts for up to 42.8% (of which 31.2% arise from
the s subshell and 10.6% from the p subshell) of the overall
were generated geometrically (CꢁH=0.960 ꢁ). The crystallographic cal-
culations were conducted with the SHELXL-97 programs. Crystal data
for [Cu
P2 /c; a=20.0870(16), b=29.696(2), c=9.2062(7) ꢁ; b=94.919(2)8; V=
471.2(7) ꢁ ; Z=4; 1calcd =1.528 gcm ; m=2.338 mm ; F
31535 reflections collected; 9579 unique reflections (Rint =0.0461); R =
6 3 6 54 60 r
L ]: 298 K; Cu C H N12; M =1258.38; monoclinic; space group
1
3
ꢁ3
ꢁ1
5
ACHTUNGTRENNUNG( 000)=2568;
population in the HOMO of T . In this case, it is reasonable
1
1
that at the triplet excited state of [Cu L ], the existence of
0.0932 and wR
data with I> 2s(I): 143 K; Cu
space group P2 /c; a=20.0147(12), b=29.5576(18), c=9.0406(6) ꢁ; b=
2
=0.1371 for all data; R
1
=0.0461 and wR
2
=0.1026 for
6
3
6
C H N12; M =1258.38; monoclinic;
54 60 r
metallophilicity significantly weakens the coordinating abili-
ty of Cu4, because the 4s and 4p subshells of Cu4 are par-
tially occupied by the promoted 3d electrons. This means
1
3
ꢁ3
9
5.3590(10)8;
V=5324.9(6) ꢁ ;
(000)=2568; 37561 reflections collected; 9351 unique re-
1
=0.0566 and wR =0.1135 for all data, R =
Z=4;
1
calcd =1.570 gcm
;
m=
ꢁ1
2
.402 mm ; F
A
H
U
G
E
N
N
I
I
that one Cu ꢁCu bond can overwhelm the related CuꢁN co-
flections (Rint =0.0379); R
1
2
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Cu–Cu Interactions in a Coordination Prism
COMMUNICATION
0
.0409 and wR
2
=0.0963 for data with I> 2s(I). CCDC-784867 (298 K)
[11] J. He, Y.-G. Yin, T. Wu, D. Li, X.-C. Huang, Chem. Commun. 2006,
2845–2847.
[12] J.-P. Zhang, S. Kitagawa, J. Am. Chem. Soc. 2008, 130, 907–917.
[13] M. A. Carvajal, S. Alvarez, J. J. Novoa, Chem. Eur. J. 2004, 10,
2117–2132.
and 784868 (143 K) contain the supplementary crystallographic data for
this paper. These data can be obtained free of charge from The Cam-
bridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif. See Section 1 of in the Supporting Information for additional
crystallographic details.
[14] C.-M. Che, Z. Mao, V. M. Miskowski, M.-C. Tse, C.-K. Chan, K.-K.
Cheung, D. L. Phillips, K.-H. Leung, Angew. Chem. 2000, 112, 4250–
6 3
Spectroscopic study of [Cu L ]: Solid-state luminescence spectra were ac-
4
254; Angew. Chem. Int. Ed. 2000, 39, 4084–4088.
quired with an Edinburg FLS920 fluorescence spectrometer equipped
with a continuous Xe900 Xenon lamp. Lifetime data were acquired with
a single-photon-counting spectrometer with a hydrogen-filled pulse lamp
as the excitation source. For low-temperature measurements, the samples
were mounted on a closed-cycle cryostat (10–350 K, DE202, Advanced
Research Systems), interfaced with a liquid helium tank. See Section 4 of
in the Supporting Information for additional luminescent measurement
details.
[
[
15] C.-M. Che, S.-W. Lai, Coord. Chem. Rev. 2005, 249, 1296–1309.
16] R. D. Kçhn, G. Seifert, Z. Pan, M. F. Mahon, G. Kociok-Kçhn,
Angew. Chem. 2003, 115, 818–820; Angew. Chem. Int. Ed. 2003, 42,
7
93–796.
17] K. Singh, J. R. Long, P. Stavropoulos, J. Am. Chem. Soc. 1997, 119,
942–2943; Inorg. Chem. 1998, 37, 1073–1079.
18] H. L. Hermann, G. Boche, P. Schwerdtfeger, Chem. Eur. J. 2001, 7,
333–5342.
[
[
2
5
Computational study of [Cu
with the Gaussian03 program package.
the local minima were obtained at the DFT/B3LYP level of theory. The
–31G(d) basis set was used for C, N and H elements, whereas the
6 3
L ]: Theoretical calculations were performed
[25]
[19] I. I. Vorontsov, A. Yu. Kovalevsky, Y.-S. Chen, T. Graber, M. Gemb-
The optimized geometries of
icky, I. V. Novozhilova, M. A. Omary, P. Coppens, Phys. Rev. Lett.
2
005, 94, 193003.
20] K. A. Barakat, T. R. Cundari, M. A. Omary, J. Am. Chem. Soc.
003, 125, 14228–14229.
6
[
[
Lanl2dz effective core potential (ECP) basis set was used for Cu ele-
ments. The counterpoise method was used to eliminate basis-set superpo-
sition errors (BSSEs). See Section 5 of in the Supporting Information for
additional theoretical calculation details.
2
21] V. R. Bojan, Fernꢃndez, E. J. A. Laguna, J. M. Lꢄpez-de-Luzuriaga,
M. Monge, M. E. Olmos, C. Silvestru, J. Am. Chem. Soc. 2005, 127,
1
1564–11565.
22] M. Iwamura, S. Takeuchi, T. Tahara, J. Am. Chem. Soc. 2007, 129,
248–5256.
23] T. Osuga, T. Murase, K. Ono, Y. Yamauchi, M. Fujita, J. Am. Chem.
Soc. 2010, 132, 15553–15555. This most recent paper published
during the submission of this work shows a gold(I)-pyrazolate-
trimer array with a frontal mode, which is confined in a host coordi-
nation cage, showing the importance of such an unprecedented
stacking mode in this system of complexes.
[
[
5
Acknowledgements
This work is financially supported by the National Natural Science Foun-
dation for Distinguished Young Scholars of China (20825102) and the
National Natural Science Foundation of China (20571050 and 20771072).
[
24] J. A. Alonso, A. MaÇanes, Theor. Chem. Acc. 2006, 117, 467–472.
25] Gaussian 03, Revision C.02, M. J. Frisch, G. W. Trucks, H. B. Schle-
gel, G. E. Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgom-
ery, Jr., T. Vreven, K. N. Kudin, J. C. Burant, J. M. Millam, S. S.
Iyengar, J. Tomasi, V. Barone, B. Mennucci, M. Cossi, G. Scalmani,
N. Rega, G. A. Petersson, H. Nakatsuji, M. Hada, M. Ehara, K.
Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P. Hratchian,
J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts, R. E.
Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W.
Ochterski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J.
Dannenberg, V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C.
Strain, O. Farkas, D. K. Malick, A. D. Rabuck, K. Raghavachari,
J. B. Foresman, J. V. Ortiz, Q. Cui, A. G. Baboul, S. Clifford, J. Cio-
slowski, B. B. Stefanov, G. Liu, A. Liashenko, P. Piskorz, I. Komaro-
mi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham, C. Y. Peng,
A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W.
Chen, M. W. Wong, C. Gonzalez, J. A. Pople, Gaussian, Inc., Wall-
ingford CT, 2004.
[
Keywords: cage compounds · Cu–Cu interactions · density
functional calculations · luminescence · metallophilicity
[
1] M. Jansen, Angew. Chem. 1987, 99, 1136–1149; Angew. Chem. Int.
Ed. Engl. 1987, 26, 1098–1110.
[
[
2] H. Schmidbaur, A. Schier, Chem. Soc. Rev. 2008, 37, 1931–1951.
3] J. M. Zuo, M. Kim, M. OꢂKeeffe, J. C. H. Spence, Nature 1999, 401,
4
9–52.
[
[
[
4] K. M. Merz, Jr., R. Hoffmann, Inorg. Chem. 1988, 27, 2120–2127.
5] P. Pyykkç, Chem. Rev. 1997, 97, 597–636.
6] F. A. Cotton, X. Feng, D. J. Timmons, Inorg. Chem. 1998, 37, 4066–
4
069.
[
[
[
7] H. V. R. Dias, H. V. K. Diyabalanage, M. A. Rawashdeh-Omary,
M. A. Franzman, M. A. Omary, J. Am. Chem. Soc. 2003, 125,
1
2072–12073.
8] H. V. R. Dias, H. V. K. Diyabalanage, M. G. Eldabaja, O. Elbjeirami,
M. A. Rawashdeh-Omary, M. A. Omary, J. Am. Chem. Soc. 2005,
[26] Note added in proof (7.3.2011): During the proof of the this work a
paper was published that described the synthesis, structure, and lu-
minescence of a Cu6 coordination cage with a staggered mode (T.
Jozak, Y. Sun, Y. Schmitt, S. Lebedkin, M. Kappes, W. R. Thiel,
Chem. Eur. J. 2011, 17, 3384–3389).
1
27, 7489–7501.
9] M. A. Omary, M. A. Rawashdeh-Omary, M. W. A. Gonser, O. Elb-
jeirami, T. Grimes, T. R. Cundari, Inorg. Chem. 2005, 44, 8200–
8
210.
[
10] T. Grimes, M. A. Omary, H. V. R. Dias, T. R. Cundari, J. Phys.
Chem. A 2006, 110, 5823–5830.
Received: January 9, 2011
Published online: March 11, 2011
Chem. Eur. J. 2011, 17, 4113 – 4117
ꢀ 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
4117