The first hexanuclear copper(I) carboxylate: X-ray crystal structure and reactivity in solution and gas-phase reactions

Article abstract of DOI:10.1021/ic7005327

The carboxylate ligand-exchange reaction of copper(I) trifluoroacetate by 3,5-difluorobenzoate yielded a new product, [Cu(O₂C(3,5-F) ₂C₆H₃)] (1). Single crystals of 1 suitable for X-ray structural characterization were obtained by sublimation-deposition procedures at 230°C. An X-ray diffraction study revealed a remarkable planar hexanuclear copper(l) core supported by bridging carboxylates, the first such structural type among other known copper(I) carboxylates. The Cu-Cu distances within the core range from 2.7064(8) to 2.8259(8) A and fall into the category of cuprophillic interactions. The hexacopper unit remains intact upon gas-phase deposition with a planar polyarene, coronene (C₂₄H ₁₂), to give [Cu₆(O₂C(3,5-F)₂C ₆H₃)₆](C₂₄H₁₂) (2). Density functional theory calculations suggest the latter compound to be a cocrystallization product having electrostatic interactions between the hexacopper complex and coronene. However, cocrystallization affects the photophysical properties of 2. While copper(I) 3,5-difluorobenzoate (1) exhibits photoluminescence at ca. 554 nm (λ_ex = 350 nm) in the solid state, compound 2 is nonluminescent at room temperature in the visible region. Gas-phase and solution reactions of 1 with alkyne ligands, diphenylacetylene (C₁₄H₁₀) and 1,4-bis(p-tolylethynyl)benzene (C ₂₄H₁₈), result in the rupture of the [Cu₆] core to afford dinuclear organometallic copper(I) complexes. The latter have a dimetal core cis-bridged by two carboxylate groups with acetylene ligands η²-coordinated to each copper(I) center.

Full text of DOI:10.1021/ic7005327

Inorg. Chem. 2007, 46, 7870−7879
The First Hexanuclear Copper(I) Carboxylate: X-ray Crystal Structure
and Reactivity in Solution and Gas-Phase Reactions
Yulia Sevryugina, Andrey Yu. Rogachev, and Marina A. Petrukhina*
Department of Chemistry, UniVersity at Albany, 1400 Washington AVenue,
Albany, New York 12222
Received March 20, 2007
The carboxylate ligand-exchange reaction of copper(I) trifluoroacetate by 3,5-difluorobenzoate yielded a new product,
[Cu(O2C(3,5-F)2C6H3)] (1). Single crystals of 1 suitable for X-ray structural characterization were obtained by
sublimation-deposition procedures at 230 °C. An X-ray diffraction study revealed a remarkable planar hexanuclear
copper(I) core supported by bridging carboxylates, the first such structural type among other known copper(I)
carboxylates. The Cu‚‚‚Cu distances within the core range from 2.7064(8) to 2.8259(8) Å and fall into the category
of cuprophillic interactions. The hexacopper unit remains intact upon gas-phase deposition with a planar polyarene,
coronene (C24H12), to give [Cu6(O2C(3,5-F)2C6H3)6](C24H12) (2). Density functional theory calculations suggest the
latter compound to be a cocrystallization product having electrostatic interactions between the hexacopper complex
and coronene. However, cocrystallization affects the photophysical properties of 2. While copper(I) 3,5-difluorobenzoate
(1) exhibits photoluminescence at ca. 554 nm (λex
) 350 nm) in the solid state, compound 2 is nonluminescent
at room temperature in the visible region. Gas-phase and solution reactions of 1 with alkyne ligands, diphenylacetylene
(C14H10) and 1,4-bis(p-tolylethynyl)benzene (C24H18), result in the rupture of the [Cu6] core to afford dinuclear
organometallic copper(I) complexes. The latter have a dimetal core cis-bridged by two carboxylate groups with
acetylene ligands
η
2-coordinated to each copper(I) center.
Introduction
carboxylate complexes have been crystallographically
characterized to date, all showing unique polynuclear core
structures in the solid state. Copper(I) acetate7 and 2,6-bis-
(trifluoromethyl)benzoate8 exhibit one-dimensional poly-
meric structures based on dicopper units that are further
linked by intermolecular copper-oxygen interactions
(Scheme 1a). Copper(I) pivalate is an infinite double-helical
chain held together by cuprophilicity (Scheme 1d).9 In
contrast, copper(I) benzoate10 and trifluoroacetate11 are
composed of tetrameric molecules, in which four copper(I)
centers are bridged by carboxylate groups alternately above
The controlled formation of small clusters and polynuclear
copper(I) complexes is of great importance for supramo-
lecular assembly,1 optoelectronics,2 catalysis,3 and structural
and chemical mimicking of active sites in metallo-
enzymes.4 In particular, copper(I) carboxylate complexes
attract special attention due to their rich catalytic5 and
photoluminescence properties.6 Only a handful of copper(I)
* To whom correspondence should be addressed. E-mail: marina@
albany.edu.
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7870 Inorganic Chemistry, Vol. 46, No. 19, 2007
10.1021/ic7005327 CCC: $37.00
© 2007 American Chemical Society
Published on Web 08/15/2007

Hexacopper(I) 3,5-Difluorobenzoate
developed earlier by Edwards and Richards.12 In contrast,
we have started with the [Cu4(O2CCF3)4] complex11 and
substituted the trifluoroacetate groups by 3,5-difluoroben-
zoate ligands. This resulted in the isolation of a new product,
1, in quantitative yield. The crude powder was washed with
several portions of benzene to remove traces of unreacted
acid and then re-sublimed at 90-110 °C to provide a high-
purity crystalline product, which is volatile in the temperature
range from 210 to 250 °C. At higher temperatures, decom-
position was observed with the appearance of a red powder
in the “hot” part of the sublimation tube. Single crystals of
1 suitable for X-ray structure determination were obtained
by sublimation-deposition procedures carried out at 230 °C.
The colorless dichroic block-shaped crystals of 1 are stable
in air at room temperature. They have very limited solubility
in benzene and dichloromethane, but in coordinating solvents,
such as acetonitrile or tetrahydrofuran (THF), they readily
dissolve. However, this process is accompanied by the
formation of a yellow precipitate and change of the solution
color to blue within a few minutes. While we have not
attempted to analyze the yellow precipitate, crystals of the
bis-adduct of copper(II) 3,5-difluorobenzoate, [Cu2(O2C(3,5-
F)2C6H3)4(THF)2], have been obtained from the above THF
solution in good yield and crystallographically character-
ized.13 When these crystals of copper(II) complex were
dissolved in acetonitrile, the UV-vis spectrum showed peaks
at the same positions (ca. 227 and 279 nm) as those obtained
by dissolving the title copper(I) complex 1 in acetonitrile.
This shows spectroscopically that the blue color of the
solution may be associated with the formation of Cu(II)
(Supporting Information, Figure S1). The disproportionation
of copper(I) complexes to metallic copper and copper(II)
derivatives both in solution and in the solid state is a
commonly reported main decomposition pathway.14 Although
the observed disproportionation limited the solution studies
of the title complex, crystals of 1 have been characterized
by X-ray diffraction, elemental analysis, and IR and UV-
vis spectroscopy.
Scheme 1
and below the [Cu4] plane. However, while the former has
discrete tetracopper clusters in the solid state (Scheme 1b),
in the latter, the tetranuclear units form a polymeric zigzag
ribbon (Scheme 1c). Within this series of copper(I) carboxy-
lates, the intermetallic Cu‚‚‚Cu separations are the shortest
in copper(I) acetate and 2,6-bis(trifluoromethyl)benzoate, in
which the neighboring copper(I) centers are doubly bridged
by carboxylate ligands. In the rest of the copper(I) carboxy-
lates, the adjacent copper atoms are linked by a single bridge.
The composition of the crude powder as well as that of
the single-crystalline material 1 was confirmed by elemental
analysis to correspond to the general formula [Cu(O2-
CF2C6H3)]. In an attempt to correlate the X-ray powder
diffraction (XRPD) spectrum of a purified crude powder,
prior to its sublimation, with the calculated pattern for the
single-crystalline sample, we discovered their essential
difference (Supporting Information, Figure S2). The XRPD
data indicate that the structure of the single-crystalline
product obtained by sublimation-deposition may differ from
that of the crude powder isolated initially from the carboxy-
late-exchange reaction. However, sublimation-deposition
This structural diversity for the few copper(I) carboxy-
late complexes has prompted us to expand this family and
pursue the crystallographic characterization of the newly
prepared copper(I) 3,5-difluorobenzoate, [Cu(O2C(3,5-
F)2C6H3)]. In addition to the crystal structure, we report the
synthesis, photophysical properties, and gas-phase and
solution reactivity of this complex toward π-donor arene and
alkyne ligands. To get some insights on bonding in a complex
polynuclear copper(I)-polyaromatic system, we also look
into the nature of copper(I) binding to an aromatic
hydrocarbon using density functional theory (DFT) calcula-
tions.
(12) Edwards, D. A.; Richards, R. J. Chem. Soc., Dalton Trans. 1973,
2463-2468.
(13) Crystal data for [Cu2(O2C(3,5-F)2C6H3)4(O(CH2)4)2]: formula C36H28-
Cu2F8O10; fw ) 899.66; P21/n; a ) 10.6295(6) Å; b ) 10.6884(6)
Å; c ) 16.2486(8) Å; â ) 94.3240(10)°; V ) 1840.79(17) Å3; Z )
2; T ) 173(2) K; Dcalc ) 1.623 g‚cm-3; µ ) 1.253 mm-1; 15 677
reflections were collected; final R1 and wR2 values are 0.0410 and
0.1013 for 3481 independent reflections [I > 2σ(I)].
(14) Klaui, W.; Lenders, B.; Hessner, B.; Evertz, K. Organometallics 1988,
7, 1357-1363.
Results and Discussion
Synthesis of [Cu(O2C(3,5-F)2C6H3)] (1). The preparation
of the title copper(I) carboxylate was performed by a
modification of the common ligand-exchange procedure
Inorganic Chemistry, Vol. 46, No. 19, 2007 7871

Sevryugina et al.
Table 1. Selected Bond Lengths (Å) and Angles (deg) in the Structures
of Complexes [Cun(O2CR)n] (n ) 4, R ) CF3, C6H5; n ) 6, R )
(3,5-F)2C6H3 (1); n ) ∞ , R ) C(CH3)3)
b
R
(3,5-F)2C6H3
1 (this work)
CF3
(11)
C6H5
(10)
C(CH3)3
(9)
(ref no.)
n
6
4
4
∞
Cu‚‚‚Cucarb-bridged 2.7064(8)
2.719(1)- 2.709(6)- 2.850(2)-
2.7215(8)
2.833(1)
2.975(1)
2.770(5)
2.897(2)
2.8259(8)
Cu‚‚‚Cunon-bridged
2.9621(8)
3.1889(11)
1.851(3)
2.968(6)
3.180(6)
2.891(2)-
3.1254(18)
a
Cu-Ocarb
1.870(5)
2.621(6)
1.840(15) 1.850(7)
Cu‚‚‚O
Cu-Cu-Cu
66.15(2)
123.48(3)
170.27(3)
64.62(4)a
115.37(4)
68.4(2)
59.14(5)-
111.7(2)
65.84(5)
O-Cu-Oa
173.72(13) 172.9(6)
173.6(9)
a Averaged. b Averaged for two crystallographically independent units.
of 2.9621(8) Å. An averaged Cu-Ocarb distance of 1.851(3)
Å is similar to those in the previously reported copper(I)
carboxylates.
Figure 1. Molecular structure of 1 showing the Cu and O atoms numbering
scheme. Color key: Cu, blue; O, red; F, green; C, gray; H, light gray. This
color scheme is used in all figures.
The structure of 1 is particularly interesting and merits
further discussion. To the best of our knowledge, this is the
first instance of a hexanuclear core copper(I) carboxylate.
Among other copper(I) compounds, examples are limited to
[{MeC(CH2PPh2)3}CoP3]2(CuBr)6‚CH2Cl2, which has six
copper atoms bridged by bromide ligands,18 and the phos-
phido-bridged [Cu12(PPh)6(PPh3)6] compound. The latter is
built of three interpenetrated planar [Cu6] units that form a
Cu12 cuboctahedron.19 For other coinage metals, the [M6]
moiety (M ) AgI, AuI) is present in [Au6Ag{µ-C6H2-
(CHMe2)3}6]CF3SO3,20 [Au6(o-CH3C6H4CS2)6],21 and anionic
cluster carbonyls [Au6(CO)n]- (n ) 0-3).22
reactions yield crystals of 1 in high (ca. 80%) yield, and
only these crystals have been further used in all reactivity
tests.
Solid-State Structure of 1. The molecular structure of 1
has been determined by single-crystal X-ray diffraction.
Copper(I) 3,5-difluorobenzoate (1) crystallizes in the triclinic
space group P1h with Z ) 1, which requires the molecule to
reside on an inversion center. As shown in Figure 1, the
molecule has a planar hexanuclear core comprised of six
copper atoms bridged by six fluorinated benzoate ligands
alternating above and below the plane. This structural type
is unique in the copper(I) carboxylate series.
Intermetallic Cu‚‚‚Cu distances within the [Cu6] plane
range from 2.7064(8) Å for Cu(1)‚‚‚Cu(3) to 2.8259(8) Å
for Cu(3)‚‚‚Cu(2A) and are comparable to those in other
monocarboxylato-bridged copper(I) complexes with trifluo-
roacetate and benzoate groups, but not with pivalate ligands
(Table 1). The noticeably longer Cu‚‚‚Cu contacts in the latter
may stem from its essential structural difference from others.
While three former complexes (Table 1) have discrete
polynuclear Cun (n ) 6 and 4) cores, copper(I) pivalate is
an infinite Cu∞-helical chain (Scheme 1d). The Cu‚‚‚Cu
distances in 1 are close to the sum of the van der Waals
radii (rvdW(Cu) ) 1.40 Å)15 and can be assigned to the
category of metallophilic interactions similar to those in
gold(I)16 or mercury(II)17 compounds. The interior angles
within the [Cu6] core range from 170.27(3)° for Cu(1)-
Cu(3)-Cu(2A) to 123.48(3)° for Cu(1)-Cu(2)-Cu(3A) and
to 66.15(2)° for Cu(2)-Cu(1)-Cu(3). This results in ad-
ditional short Cu‚‚‚Cu contacts between the nonbridged metal
centers, Cu(3)‚‚‚Cu(3A) of 3.1889(11) Å and Cu(2)‚‚‚Cu(3)
Due to the absence of an actual bond between the d10 metal
centers, each copper center of the polynuclear [Cun(O2CR)n]
complex is nominally linearly coordinated by two carboxylate
oxygen atoms. The proximity of other metal ions, however,
reflects the tendency of copper(I) to expand its coordination
sphere, especially in the presence of electron-withdrawing
ligands. This has been noticed earlier for copper(I) trifluo-
roacetate,11 in which copper atoms demonstrate highly
distorted trigonal-bipyramidal, tetragonally elongated octa-
hedral, and seesaw-coordination geometries with coordination
numbers ranging from four to six. Considering only the
adjacent copper atoms in 1, the Cu(1) and Cu(2) centers
display a seesaw coordination, while the geometry around
Cu(3) can be viewed as square-planar (Figure 1). However,
an inclusion of the additional contacts between nonbridged
copper atoms mentioned earlier would make the Cu(2) and
Cu(3) atoms become five- and six-coordinate, respectively.
Gas-Phase Reactivity of 1. The title hexanuclear copper(I)
complex 1 is readily accessible by deposition from the vapor
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7872 Inorganic Chemistry, Vol. 46, No. 19, 2007

Hexacopper(I) 3,5-Difluorobenzoate
structurally characterized copper(I) carboxylate complex with
an aromatic ligand is the benzene adduct, [Cu4(O2CCF3)4]-
(C6H6)2.25 It shows the range of Cu‚‚‚C distances within 2.7-
3.0 Å. However, due to large thermal motion of the aromatic
rings, the discussion of benzene coordination in the latter
compound was not possible. Several copper(I) cation-π-
arene complexes such as (C6H6)CuAlCl4,26 (CuOSO2CF3)2‚
(C6H6),27 Cu(GaCl4)‚((p-C6H4(CH2)3)2),28 ((C6H6)CuCl3)2Zr,29
and ((C6H6)2Cu)2Zr2Cl10‚(C6H6)30 have been structurally
characterized to show Cu‚‚‚C contacts in the 2.09-2.92 Å
range and suggest an η2 binding. Regarding other group 11
metals, bonding Au‚‚‚C interactions generally are 2.96-3.25
Å31 (ΣrvdW (Au, C) ) 3.36 Å), while bonding Ag‚‚‚C contacts
are 2.47-2.76 Å32 (ΣrvdW (Ag, C) ) 3.42 Å).15 In the
polymeric silver(I) complex with coronene, [Ag4(C24H12)3-
(ClO4)4],33 the Ag‚‚‚C contacts are short and range from
2.402(4) to 2.517(4) Å. In addition, coronene adopts a bent
conformation, which indicates strong interactions between
Ag+ cations and the coordinated coronene ligand.
An analysis of the copper-carbon distances in 2 shows
them lying barely around the sum of the van der Waals radii
for Cu and C (ΣrvdW (Cu, C) ) 3.10 Å),15 which raises the
question of whether 2 should be considered as a coordination
compound.
DFT Description of Bonding in 2. We attempted to
address the question of interaction between the hydrocarbon
and metal complex by using the DFT computational method.34
Our study is the first example of the theoretical modeling of
a polynuclear copper(I)-polycyclic arene system. Moreover,
modeling of the hexanuclear copper(I) complex was also
Figure 2. Molecular structure of 2 showing the Cu, O, and selected C
atoms numbering scheme.
phase at 210-250 °C. Its very low solubility and instability
in solvents limited solution studies, but its volatility allowed
us to test the reactivity toward a planar polyaromatic
hydrocarbon, coronene, using the gas-phase sublimation-
deposition conditions. Deposition of 1 with coronene (C24H12)
at 248 °C has resulted in the formation of a new product of
the [Cu6]/C24H12 ) 1:1 stoichiometry in the single-crystalline
form. Its crystal structure was determined to confirm that
the hexanuclear units remain intact in the gas phase and can
be co-deposited with a polyarene in the solid state to afford
[Cu6(O2C(3,5-F)2C6H3)6](C24H12) (2) (Figure 2).
A comparison of the [Cu6] cores in 2 and the parent
complex 1 shows a close similarity with small variations in
copper-copper distances and angles (Figure 3). Likewise,
a comparison of the geometrical parameters of the coronene
ligand in 2 with the corresponding bond lengths and angles
in the uncoordinated molecule23 shows that the two are
essentially similar (Table 2).
(24) (a) Moser, W. R. J. Am. Chem. Soc. 1969, 91, 1135-1140, 1141-
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The significant difference between 1 and 2 is found in
their solid-state structures. In contrast to 1 having isolated
hexacopper complexes, the [Cu6(O2C(3,5-F)2C6H3)6] units in
2 exhibit intermolecular Cu‚‚‚O interactions with neighboring
units (Figure 4). The latter contacts of 2.5805(16) Å for
Cu(1)‚‚‚O(2A) in 2 are significantly longer than those in
copper(I) acetate (2.310(7) Å)7 but shorter than those in
copper(I) trifluoroacetate (2.621(6) Å).11 For comparison, the
closest intermolecular Cu‚‚‚O contacts in 1 exceed 4 Å.
The coronene ligand approaches the copper hexamer at
the Cu(2)-Cu(3A) side with Cu‚‚‚C contacts of 2.919(3),
3.211(3), 3.127(3), and 3.259(3) Å to the C(22), C(23),
C(24), and C(25) atoms, respectively (Figure 2). The Cu‚‚‚C
separations exceed 3.3 Å for the rest of the carbon atoms.
Although π complexes of copper(I) are common inter-
mediates in catalytic transformations,24 the only other
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Chem., Int. Ed. Engl. 1986, 25, 1089-1090.
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Y. L.; Zhang, Z.-Z. Organometallics 2003, 22, 633-640.
(32) (a) Munakata, M.; Wu, L. P.; Ning, G. L. Coord. Chem. ReV. 2000,
198, 171-203. (b) Lindeman, S. V.; Rathore, R.; Kochi, J. K. Inorg.
Chem. 2000, 39, 5707-5716.
(33) Munakata, M.; Wu, L. P.; Kuroda-Sowa, T.; Maekawa, M.; Suenaga,
Y.; Ning, G. L.; Kojima, T. J. Am. Chem. Soc. 1998, 120, 8610-
8618.
(34) Molecular geometry optimizations were performed at the DFT level
by using the hybrid Perdew-Burke-Ernzerhof parameters free
exchange-correlation functional (PBE0) as implemented in the PC
GAMESS version of the GAMESS-US program package. The Hay and
Wadt effective core potential (ECP) and the LANL2DZ basis set were
used for Cu atoms, and the 3-21G(d) basis sets were employed for all
other atoms. When optimizations were achieved, single-point calcula-
tions along with NBO analysis were performed using the same ECP
and the same basis set for Cu atoms and the extended 6-311G(d,p)
basis sets for all other atoms (see the Supporting Information for
details).
(23) Krygowski, T. M.; Cyranski, M.; Ciesielski, A.; Swirska, B.; Leszc-
zynski, P. J. Chem. Inf. Comput. Sci. 1996, 36, 1135-1141.
Inorganic Chemistry, Vol. 46, No. 19, 2007 7873

Sevryugina et al.
Figure 3. [Cu6] core structures in 1 and 2.
Table 2. Selected Bond Lengths (Å) and Angles (deg) in the Structures
of C24H12 and Complexes 1 and 2
Full geometry optimizations of the molecular structures
of 2 and the parent complex 1 were performed at the DFT
level of theory using the hybrid Perdew-Burke-Ernzerhof
parameters free exchange-correlation functional (PBE0),38
which is known to better describe coordination compounds
of transition metals with weak bonding39 and polyaromatic
systems.40 Recently, the PBE0 functional was successfully
applied for the modeling of a tetranuclear copper cluster.36b
We also found that the optimized geometries obtained with
the use of PBE0 for 1 and 2 reproduce the experimental
X-ray structures very closely (Supporting Information, Tables
S3 and S4).
23
1
2
C24H12
Cu‚‚‚Cucarb-bridged
Cu‚‚‚Cunon-bridged
2.7064(8)
2.7215(8)
2.8259(8)
2.9621(8)
3.1889(11)
4.8863(10)
1.851(3)
2.7131(4)
2.7437(4)
2.7530(4)
2.9407(5)
3.3205(7)
4.6179(7)
1.8571(15)
2.5805(16)
2.919(3)
a
Cu-Ocarb
Cu‚‚‚O
Cu‚‚‚C
A high value of bonding energy for the [Cu6(O2C(3,5-
F)2C6H3)6](C24H12) unit, namely, 33.89 kcal/mol, has been
calculated. It is comparable to the value of 48.7 kcal/mol
calculated for the system comprised of the naked Cu+ cation
and benzene.41 In contrast, the bonding energies of electro-
philic diruthenium(I,I) complexes with a polyarene were
found to be only 9.0-11.5 kcal/mol.42 A detailed analysis
of electronic structures in terms of natural bond orbitals
(NBO) shows that the bonding between the hexanuclear
copper(I) core and coronene in 2 has a strong electrostatic
nature. The donor-acceptor interactions in 2 do not exceed
1.00 kcal/mol, indicating a lack of any significant covalent
contribution. However, in contrast to the parent [Cu6(O2C-
(3,5-F)2C6H3)6] molecule, which does not display any dipole
moment due to symmetry reasons, a noticeable polarization
of both the [Cu6] core and coronene has been found upon
their interaction. This fact is clearly illustrated by the charge
distribution in the [Cu6(O2C(3,5-F)2C6H3)6]/(C24H12) ) 1:1
unit (Supporting Information, Table S5). The positive charges
of copper(I) centers in the [Cu6] core as well as negative
charges of carbon atoms in coronene are larger in [Cu6(O2C-
(3,5-F)2C6H3)6](C24H12), as compared to free hexacopper
molecule and free coronene, generating a dipole moment of
4.36 D in the coronene adduct (Figure 5). Thus, the bonding
between the hexanuclear copper(I) cluster and coronene can
be best ascribed to an ion-induced dipole interaction.
3.211(3)
3.127(3)
3.259(3)
65.088(12)
166.630(16)
128.167(15)
173.47(8)
1.373(5)
1.404(4)
1.425(4)
1.414(4)
121.5(3)
Cu-Cu-Cu
O-Cu-Oa
66.15(2)
170.27(3)
123.48(3)
173.72(13)
a
C-Ccoronene(a)
1.357(3)
1.421(3)
1.416(2)
1.424(2)
121.5(2)
118.5(2)
120.0(2)
122.9(2)
120.0(2)
a
C-Ccoronene(b)
a
C-Ccoronene(c)
a
C-Ccoronene(d)
a
a
a
a
C-C-Ccoronene(a-b)
C-C-Ccoronene(b-c)
C-C-Ccoronene(c-d)
118.5(3)
120.0(2)
123.0(3)
120.0(2)
C-C-Ccoronene(b-b)
C-C-Ccoronene(d-d)
a
a Averaged.
carried out for the first time. Prior theoretical works were
devoted to tri-35 and tetranuclear copper(I) clusters36 only,
and the previously found trends37 may not be applicable to
larger systems.
(35) (a) Bera, J. K.; Nethaji, M.; Samuelson, A. G. Inorg. Chem. 1999,
38, 218-228. (b) Lo, W.-Y.; Lam, C.-H.; Yam, V. W.-W.; Zhu, N.;
Cheung, K.-K.; Fathallah, S.; Messaoudi, S.; Le Guennic, B.; Kahlal,
S.; Halet, J.-F. J. Am. Chem. Soc. 2004, 126, 7300-7310.
(36) (a) Vega, A.; Saillard, J.-Y. Inorg. Chem. 2004, 43, 4012-4018. (b)
Lam, W. H.; Cheng, E. C.-C.; Yam, V. W.-W. Inorg. Chem. 2006,
45, 9434-9441. (c) De Angelis, F.; Fantacci, S.; Sgamellotti, A.;
Cariati, E.; Ugo, R.; Ford, P. C. Inorg. Chem. 2006, 45, 10576-10584.
(37) Hubig, S. M.; Lindeman, S. V.; Kochi, J. K. Coord. Chem. ReV. 2000,
200-202, 831-873.
This bonding description in 2 is in good agreement with
recent works,41,43 where interactions between the Cu+ cation
and benzene were shown to have a similar nature. In accord
(38) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. ReV. Lett. 1997, 78,
1396-1396.
(39) Adamo, C.; Barone, V. J. Chem. Phys. 1999, 110, 6158-6170.
(40) (a) Avramov, P. V.; Kudin, K. N.; Scuseria, G. E. Chem. Phys. Lett.
2003, 370, 597-601. (b) Johansson, M. P.; Sundholm, D.; Vaara, J.
Angew. Chem., Int. Ed. 2004, 43, 2678-2681. (c) Barone, V.; Peralta,
J. E.; Scuseria, G. E. Nano Lett. 2005, 5, 1830-1833. (d) Bettinger,
H. F. J. Phys. Chem. B 2005, 109, 6922-6924. (e) An, W.; Gao, Y.;
Bulusu, S.; Zeng, X. C. J. Chem. Phys. 2005, 122, 204109-1-204109-
8.
(41) Zhang, S.-L.; Liu, L.; Fu, Y.; Guo, Q.-X. J. Mol. Struct. THEOCHEM
2005, 757, 37-46.
(42) Petrukhina, M. A.; Sevryugina, Y.; Rogachev, A. Yu.; Jackson, E.
A.; Scott, L. T. Angew. Chem., Int. Ed. 2006, 45, 7208-7210.
(43) Dargel, T. K.; Hertwig, R. H.; Koch, W. Mol. Phys. 1999, 96, 583-
591.
7874 Inorganic Chemistry, Vol. 46, No. 19, 2007

Hexacopper(I) 3,5-Difluorobenzoate
Figure 6. Photoluminescence spectra (λex ) 350 nm) of solid samples of
1 (O) and C24H12 (9). Compound 2 is nonluminescent.
Figure 4. Fragment of the ab layer in 2. The carboxylate groups and H
atoms are omitted for clarity. Only the O atoms involved in axial interactions
are shown (red).
λex ) 290 nm, while showing no emission upon excitation
at λex ) 350 nm. For comparison, the emission maxima
were found in the broad range of 535-660 nm at room
temperature for copper(I) formate, acetate, propionate, bu-
tyrate, valerate, hexanoate, and heptanoate,6 but those were
not correlated with the structures of the complexes. The
emission maxima for the structurally similar copper(I) 2,6-
bis(trifluoromethyl)benzoate8 and acetate (Scheme 1a) were
measured at 558 and 560 nm at room temperature, respec-
tively.
In contrast to the parent copper(I) 3,5-difluorobenzoate
complex 1 and coronene itself, compound 2 is nonlumines-
cent at room temperature in the visible region. Thus, the
incorporation of coronene into the copper(I) carboxylate
lattice showed a dramatic influence on the photophysical
properties of the resultant system.
To our knowledge, no systematic studies discussing the
origin of photoluminescence and its dependence on the
structural type for copper(I) carboxylate complexes have been
done, thus thwarting the rationalization of the above effect
for the coronene adduct. A full investigation of the lumi-
nescent properties of a series of copper(I) carboxylates is
currently underway, and that should shed some light on their
photophysical behavior.
Reactivity of 1 Toward Alkynes. To further study the
properties of the hexanuclear core complex 1, its reactivity
toward selected alkyne ligands has been tested. To date, only
a few copper(I) carboxylate complexes with alkyne ligands
have been reported, including [Cu2(O2CC6H5)2(C14H10)2],45
[Cu4(O2CCH3)4(C8H18Si2)2],46 and [Cu4(O2CCF3)4(C6H10)2].47
As a result of refluxing [Cu6(O2C(3,5-F)2C6H3)6] in
benzene with an excess of diphenylacetylene (C14H10,
Figure 5. Direction of the dipole moment vector in the [Cu6(O2C(3,5-
F)2C6H3)6](C24H12) adduct (blue arrow) along with selected charges given
in comparison to [Cu6(O2C(3,5-F)2C6H3)6] and C24H12 (in square brackets).
with the report of Koch et al.,43 the nature of interactions
between the copper(I) cation and an aromatic system is
mainly electrostatic. Moreover, it was shown that η1, η2, η3,
and η6 coordination modes are degenerate, indicating no
specific preferences in the coordination of an arene to
Cu(I).
A detailed analysis of frontier molecular orbitals for [Cu6-
(O2C(3,5-F)2C6H3)6] and C24H12 in 2 revealed no symmetry
match between them (Supporting Information, Table S7). The
energy gap of 6.67 eV between suitable molecular orbitals
of the [Cu6] core and coronene results in the absence of any
orbital interactions in the [Cu6(O2C(3,5-F)2C6H3)6](C24H12)
adduct, which makes any consideration of bonding and
hapticity for such a system inadequate.
Photoluminescence. Copper(I) carboxylates are known to
exhibit rich photoluminescence properties and therefore are
of interest as potential optoelectronic materials.44 The new
copper(I) 3,5-difluorobenzoate complex (1) exhibits bright
green photoluminescence (PL) upon exposure to UV radia-
tion in the solid state. The PL measurements (λex ) 350 nm)
carried out at room temperature in the range of 250-750
nm using a crystalline sample of 1 determined λmax at ca.
554 nm (Figure 6). It should be mentioned here that 3,5-
difluorobenzoic acid emits at 377 nm upon UV radiation at
(44) (a) Yam, V. W.-W.; Lo, K. K.-W. Chem. Soc. ReV. 1999, 28, 323-
334. (b) Ford, P. C.; Cariati, E.; Bourassa, J. Chem. ReV. 1999, 99,
3625-3647. (c) Zhang, J.; Xiong, R.-G.; Chen, X.-T.; Che, C.-M.;
Xue, Z.; You, X.-Z. Organometallics 2001, 20, 4118-4121. (d) Rasika
Dias, H. V.; Diyabalanage, H. V. K.; Eldabaja, M. G.; Elbjeirami,
O.; Rawashdeh-Omary, M. A.; Omary, M. A. J. Am. Chem. Soc. 2005,
127, 7489-7501.
(45) Pasquali, M.; Leoni, P.; Floriani, C.; Gaetani-Manfredotti, A. Inorg.
Chem. 1982, 21, 4324-4328.
(46) Lang, H.; Ko¨hler, K.; Zsolnai, L. Chem. Ber. 1995, 128, 519-523.
(47) Reger, D. L.; Huff, M. F.; Wolfe, T. A.; Adams, R. D. Organometallics
1989, 8, 848-850.
Inorganic Chemistry, Vol. 46, No. 19, 2007 7875

Sevryugina et al.
Figure 7. Molecular structure of the [Cu2(O2C(3,5-F)2C6H3)2(C14H10)2]
unit in 3 and 4 showing the Cu atoms numbering scheme. The H atoms are
omitted for clarity.
Figure 8. Molecular structure of 5 showing the Cu atoms numbering
scheme. The H atoms are omitted for clarity.
Scheme 2
Å and distances between the central ones of 3.93 Å (see the
Supporting Information for additional details on the solid-
state packing of 3-5). The Cu-C bond distances for 3-5
are in the same range as that generally observed for other
copper(I)-π-alkyne complexes (1.95-2.01 Å).
A comparison of the geometrical parameters of complexes
3-5 reveals an elongation of the copper-copper distances,
falling in the 2.7829(8)-2.8149(6) Å range, as compared to
those in the parent compound 1 (Tables 1 and Supporting
Information, Figure S1). Notably, the presence of innocent
solvents, such as benzene or toluene, in the crystal lattices
of 3 and 4, respectively, affects the packing of otherwise
similar complexes, which is seen in slightly different
Cu‚‚‚Cu separations within the dimers (2.8033(6) Å in 3 vs
2.7829(8) Å in 4).
Scheme 2), two new crystalline compounds 3 and 4, having
a general formula [Cu2(O2C(3,5-F)2C6H3)2(C14H10)2]‚solv,
were isolated in crystalline form. Gas-phase reactions with
diphenylacetylene were not successful due to a large differ-
ence in sublimation temperatures of the reactants and,
possibly, due to the vital role of spacers, such as toluene or
benzene molecules, in the crystallization of products. Another
interesting example of the transformation of the [Cu6] core
is provided by the gas-phase sublimation-deposition reaction
of 1 with 1,4-bis(p-tolylethynyl)benzene (C24H18) (Scheme
2), which resulted in the formation of a new complex 5, [Cu2-
(O2C(3,5-F)2C6H3)2(C24H18)]2. In contrast to the hexanuclear
copper(I) adduct with coronene, in all new alkyne complexes
3-5 we observe the fragmentation of the [Cu6] core.
Complexes 3-5 have the dinuclear copper(I) core, regardless
whether they were obtained from gas-phase or solution
reactions.
The dicopper(I,I) units in 3-5 are cis-bridged by two 3,5-
difluorobenzoates. In addition, each copper(I) center is
involved in an η2 interaction with the triple bond of an alkyne
ligand (Figure 7). The structures of 3 and 4 are similar to
that of the previously reported [Cu2(O2CC6H5)2(C14H10)2]45
(Supporting Information, Table S1). All three complexes
consist of discrete neutral molecules [Cu2(O2CR)2(C14H10)2],
in which each copper(I) center coordinates one diphenyl-
acetylene molecule through two alkyne C atoms at averaged
distances 1.959(4) and 1.965(5) Å in 3 and 4, respectively.
The composition of complex 5, however, can be represented
as [Cu2(O2C(3,5-F)2C6H3)2(C24H18)]2. Since the 1,4-bis(p-
tolylethynyl)benzene ligand incorporates two CtC bonds,
each is coordinated to a metal center of two separate copper
dimers at an average distance of 1.957(3) Å (Figure 8). Two
such dicopper units align two C24H18 ligands nearly coplanar
with distances between the terminal benzene rings of 3.87
The impact of metal coordination on the length of a
carbon-carbon triple bond is worth mentioning. The Cu-C
contacts in 3-5 are short (average distance 1.960(4) Å) as
compared with those in the aforementioned copper(I)-π-
arene compounds. As a consequence, the coordinated
carbon-carbon bond in 5 is noticeably elongated (1.237(5)
Å) as compared with free 1,4-bis(p-tolylethynyl)benzene
(1.1992(15) Å),48 indicating that the triple-bond order is
reduced as a result of strong interaction with the metal
moiety. Due to a variety of bond lengths reported for the
carbon-carbon triple bond of free diphenylacetylene (1.192-
1.226 Å),49 we cannot make a similar comparison for
complexes 3 and 4. However, the evaluation of the CsCtC
angles in compounds 3-5 and uncoordinated acetylenes
supports the tenet of strong π bonding between the copper(I)
centers and the CtC groups (157.4(4)° and 158.8(5)° in 3
and 4 vs 178.0(2)° in free C14H10;49d 158.3(3)° in 5 vs 179.43-
(13)° in free C24H18).48
(48) Filatov, A. S.; Petrukhina, M. A. Acta Crystallogr. 2005, C61, o193-
o194.
(49) (a) Samarskaya, V. D.; Myasnikovam, R. M.; Kitaigorodskii, A. I.
Kristallografiya 1968, 13, 525-529. (b) Mavridis, A.; Moutakali-
Mavridis, A. Acta Crystallogr. 1977, B33, 3612-3615. (c) Espiritu,
A. A.; White, J. G. Z. Kristallogr. 1978, 147, 177-186. (d)
Abramenkov, A. V.; Almenningen, A.; Cyvin, B. N.; Cyvin, S. J.;
Jonvik, T.; Khaikin, L. S.; Rømming, C.; Vilkov, L. V. Acta Chem.
Scand. A 1988, 42, 674-684. (e) Zanin, I. E.; Antipin, M. Yu.;
Struchkov, Yu. T. Kristallografiya 1991, 36, 411-419.
7876 Inorganic Chemistry, Vol. 46, No. 19, 2007

Hexacopper(I) 3,5-Difluorobenzoate
Table 3. Crystallographic Data and Structural Refinement Parameters for 1-5
1
2
3
4
5
formula
fw
cryst syst
space group
a (Å)
C42H18Cu6F12O12
1323.80
triclinic
C66H30Cu6F12O12
1624.14
triclinic
C48H32Cu2F4O4
875.82
monoclinic
P21/n
13.6060(9)
18.9596(13)
15.3574(11)
C49H34Cu2F4O4
889.84
monoclinic
P21/c
13.4866(10)
16.5619(12)
18.4314(14)
C76H48Cu4F8O8
1495.30
monoclinic
P21/n
7.1445(4)
24.6212(12)
17.5605(9)
P1h
P1h
9.4517(8)
9.7078(9)
11.9872(10)
87.4160(10)
70.4870(10)
83.5180(10)
1030.06(16)
1
9.5577(5)
11.9244(6)
12.9601(7)
81.5120(10)
76.6640(10)
78.8140(10)
1401.72(13)
1
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
99.9570(10)
98.7990(10)
95.0310(10)
3902.0(5)
4
4068.5(5)
4
3077.1(3)
2
T (K)
173(2)
173(2)
173(2)
173(2)
173(2)
λ (Å)
0.71073
2.134
3.163
28.22
4648
0.71073
1.924
2.345
28.27
6336
0.71073
1.491
1.155
28.27
9139
0.71073
1.453
1.109
25.00
7152
0.71073
1.614
1.449
28.28
7254
d
calc (g‚cm-3
)
µ (mm-1
max (deg)
unique data
)
θ
observed data [I > 2σ(I)]
3388
325
1.027
0.0465, 0.1008
0.0701, 0.1091
0.499, -0.439
5229
493
1.033
0.0332, 0.0803
0.0432, 0.0852
0.365, -0.301
5475
517
1.015
0.0533, 0.1196
0.1066, 0.1395
0.697, -0.388
4479
522
1.013
0.0580, 0.1216
0.1059, 0.1425
0.536, -0.431
5279
507
1.047
0.0539, 0.1109
0.0817, 0.1217
0.693, -0.393
params
GOFa on F2
R1b, wR2c [I > 2σ(I)]
R1b, wR2c (all data)
∆Fmax,min (e‚A-3
)
2
2
2
2
2
a GOF ) [∑[w(Fo - Fc )2]/(Nobs - Nparams)]1/2
.
b R1 ) ∑||Fo| - |Fc||/∑|Fo|. c wR2 ) [∑[w(Fo - Fc )2]/∑[w(Fo )2]]1/2
.
The copper(I)-alkyne complexes 3-5 showed no lumi-
nescence in the visible region at room temperature upon
UV-vis radiation. To further characterize complexes 3-5,
we studied their 13C NMR spectra in chloroform solution.
The general observation was that the 13C NMR resonances
of π-coordinated ligands in 3-5 display no change in
chemical shifts with respect to those of free C14H10 and
C28H14, most probably suggesting the dissociation of ligands
even in noncoordinating chloroform. However, when record-
ing the solid-state IR spectra, we found that νCtC absorptions
for complexes 3-5 are shifted to lower wavenumbers (νCtC
) 1983 (3), 1982 (4), 1981 (5) cm-1) as compared with the
uncoordinated ligands C14H10 (νCtC ) 2100-2300 cm-1)50
and C24H18 (νCtC ) 2211 cm-1).51 This is generally observed
for copper(I) η2-coordinated alkynes52 and indicates the
weakening of the CtC bond, which is consistent with our
solid-state structural observations.
The coordination geometry at each Cu center in 3-5 is
considered to be nearly trigonal planar with the inclusion of
two carboxylate oxygens and a triple CtC bond. It is
important that despite the bifunctionality offered by two
ligands (alkyne and arene functions),53 diphenylacetylene and
1,4-bis(p-tolylethynyl)benzene coordinate to copper(I) ex-
clusively by their alkyne parts. The Cu-C interactions in
alkyne complexes are considerably stronger than those in
copper(I)-arene systems, which certainly affects the nucle-
arity of the resulting Cu-based units.
Summary. The novel copper(I) complex, [Cu6(O2C(3,5-
F)2C6H3)6] (1), having a discrete planar [Cu6] core, was
prepared in good yield and high purity. This is the first
example of the hexanuclear structure among the copper(I)
carboxylate family. Importantly, the [Cu6] unit remains intact
upon sublimation with polycyclic aromatic coronene to form
[Cu6(O2C(3,5-F)2C6H3)6](C24H12) (2). Detailed structural and
DFT analyses suggest that 2 is a product of cocrystallization.
First, this is confirmed empirically by the finding of long
intermolecular Cu‚‚‚C distances, all exceeding the sum of
the van der Waals radii for copper and carbon. Second, DFT
calculations reveal the bonding in 2 to be an ion-induced
dipole interaction without any covalent contribution. Interest-
ingly, although no significant structural changes are observed
in the hydrocarbon or metal moieties in 2, its photolumi-
nescence is found to be highly affected by cocrystallization.
In contrast to the parent copper(I) 3,5-difluorobenzoate
complex (1) which shows photoluminescence at 554 nm and
coronene, which emits at 503 nm, compound 2 is nonlumi-
nescent at room temperature in the visible region. In addition,
the reactivity of the hexacopper core in 1 toward alkyne
ligands has been tested to confirm its fragmentation to
dinuclear copper(I) complexes.
Experimental Section
Materials and Methods. All manipulations were performed
under a dinitrogen atmosphere, employing either drybox or standard
Schlenk techniques. Sublimation-deposition procedures were carried
out in small Pyrex glass ampules of 1.1 cm o.d. and of varied (5-8
cm) length. The ampules equipped with a vacuum adapter were
loaded with starting materials in a drybox. They were evacuated
to ca. 10-2 Torr and sealed under vacuum. The ampules were then
placed in electric furnaces having a ca. 5 °C temperature gradient
along the length of the tube. The starting material [Cu4(O2CCF3)4]
(50) Sorrell, T. N. Interpreting Spectra of Organic Molecules; University
Science Books: Mill Valley, CA, 1988.
(51) Nguyen, P.; Yuan, Z.; Agocs, L.; Lesley, G.; Marder, T. B. Inorg.
Chim. Acta 1994, 220, 289-296.
(52) (a) Fosch, W.; Back, S.; Rheinwald, G.; Ko¨hler, K.; Zsolnai, L.;
Huttner, G.; Lang, H. Organometallics 2000, 19, 5769-5779. (b) Lang,
H.; Ko¨hler, K.; Rheinwald, G. Organometallics 1999, 18, 598-605.
(53) Cotton, F. A.; Dikarev, E. V.; Petrukhina, M. A.; Stiriba, S.-E.
Organometallics 2000, 19, 1402-1405.
was synthesized following
a
reported procedure.11 Com-
Inorganic Chemistry, Vol. 46, No. 19, 2007 7877

Sevryugina et al.
mercially available coronene (C24H12), diphenylacetylene (C14H10),
and anhydrous benzene and toluene were used as received. 1,4-
Bis(p-tolylethynyl)benzene (C24H18) was prepared by the known
method.51
g (60%). IR (KBr, cm-1): 3082 w, 3073 w, 3055 w, 3030 w, 3000
w, 1617 m, 1607 sh, 1583 s, 1571 sh, 1489 m, 1481 w, 1469 m,
1443 m, 1435 m, 1395 s, 1324 w, 1301 m, 1179 w, 1117 s, 1071
w, 1026 w, 985 s, 953 m, 917 w, 900 w, 892 w, 881 w, 850 m,
781 s, 769 s, 763 s, 752 s, 757 s, 666 m, 632 m, 621 sh, 595 m,
Physical Measurements. Elemental analyses were performed
by Guelph Chemical Laboratories, Ltd., Canada. The electronic
spectra were measured at room temperature on a Perkin-Elmer
Lambda 35 UV-vis spectrometer equipped with an integrating
sphere for diffuse-reflectance spectroscopy. The NMR spectra were
recorded on a Varian Gemini spectrometer at 300 MHz for protons,
282 MHz for fluorine, and 75 MHz for carbon. Chemical shifts (δ,
1
530 w, 506 m, 469 m, 458 m. H NMR (CDCl3, 22 °C): δ 7.71
(m), 7.52 (br), 7.33 (br), 7.17 (s), 6.96 (br). 19F NMR (CDCl3,
22 °C): δ -109.70. 13C{1H} NMR (CDCl3, 22 °C): δ 131.56
(PhC), 130.88, 128.37 (PhC), 123.29 (PhC), 89.85 (C).
Preparation of [Cu2(O2C(3,5-F)2C6H3)2(C14H10)2]‚C6H5CH3
(4). This compound was prepared similarly to 3 but using toluene.
Yield: 55%. IR (KBr, cm-1): 3082 w, 3066 w, 3030 w, 3017 w,
2914 w, 2858 w, 1662 w, 1615 s, 1585 s, 1569 sh, 1494 w, 1489
w, 1481 w, 1468 w, 1444 m, 1436 m, 1417 sh, 1392 s, 1324 w,
1301 m, 1208 w, 1180 w, 1156 w, 1118 m, 1070 w, 1029 w, 986
m, 950 w, 916 w, 895 m, 851 m, 781 m, 770 m, 763 s, 754 s, 728
m, 684 m, 664 m, 634 m, 621 sh, 597 m, 531 w, 506 m, 465 m. 1H
NMR (CDCl3, 22 °C): δ 7.71 (m), 7.51 (br), 7.31-7.23 (m), 7.19-
7.16 (m), 6.92 (br), 2.36 (s). 19F NMR (CDCl3, 22 °C): δ -110.46.
13C{1H} NMR (CDCl3, 22 °C): δ 131.54 (PhC), 130.86, 129.02,
128.36 (PhC), 123.29 (PhC), 90.40 (C).
ppm) for 19F were referenced to CFCl3, and chemical shifts for 13
C
and 1H were referenced to SiMe4. The infrared spectra were
measured using KBr pellets or Nujol mulls on a Nicolet Magna
550 FTIR spectrometer. The photoluminescence spectra were
collected on a Varian Cary Eclipse spectrophotometer, in which
the PMT detector was positioned 90° to the incident beam. Default
settings (slit widths of 5 nm and integration time of 0.5 s) were
applied. The crystalline sample was placed in a Varian Cary Sub-
micro Fluorometer cell, which was mounted in a standard single
cell holder.
Preparation of [Cu2(O2C(3,5-F)2C6H3)2(C24H18)]2 (5). A mix-
ture of crystals of 1 (0.040 g, 0.03 mmol) with 1,4-bis(p-
tolylethynyl)benzene (0.014 g, 0.05 mmol) was sealed under
vacuum in a small glass ampule that was placed in an electric tube
furnace at 245 °C. In 11 days, yellow blocks of 5 were deposited
in the cold end of the ampule. Yield: 0.020 g (60%). IR (KBr,
cm-1): 3077 w, 3030 w, 2913 w, 1615 s, 1591 s, 1511 m, 1466
m, 1436 sh, 1390 s, 1303 m, 1261 w, 1182 w, 1120 s, 1021 w, 989
s, 952 w, 894 m, 851 m, 833 m, 809 m, 784 s, 768 m, 761 s, 664
m, 652 w, 613 w, 586 w, 514 w, 461 m. 1H NMR (CDCl3, 22 °C):
δ 7.69 (m), 7.52-7.39 (m), 7.16-7.13 (m), 2.35 (s). 19F NMR
(CDCl3, 22 °C): δ -108.02. 13C{1H} NMR (CDCl3, 22 °C): δ
138.62 (PhC), 131.52 (PhC), 129.18 (PhC), 123.13 (PhC), 120.00
(PhC), 103.55 (PhC), 91.37 (C), 88.55 (C).
X-ray Structural Determinations. The X-ray data sets were
collected for 1-5 at -100 °C (Bruker KRYO-FLEX) on a Bruker
APEX CCD X-ray diffractometer equipped with a graphite-
monochromated Mo KR radiation source (λ ) 0.71073 Å). Data
reduction and integration were performed with the software package
SAINT,54 and absorption corrections were applied using the program
SADABS.55 In all structures, the positions of the heavy atoms were
found via direct methods using the program SHELXTL.56 Subse-
quent cycles of least-squares refinement followed by difference
Fourier syntheses revealed the positions of the remaining non-
hydrogen atoms. Crystallographic data and X-ray experimental
conditions for 1-5 are listed in Table 3. All non-hydrogen atoms
in 1-5 were refined anisotropically, except for carbon and fluorine
atoms of all disordered groups in 3 and 4. One benzene ring of the
carboxylate group in 4 and interstitial benzene and toluene
molecules in 3 and 4, respectively, were found to be disordered.
Each disorder was modeled individually. All hydrogen atoms were
included at idealized positions for structure-factor calculations,
except for those in the structures of 2, which were found in the
difference Fourier map and refined independently. The refinement
of hydrogen atoms in the structure of 5 was mixed. Hydrogen atoms
of the methyl groups were included at idealized positions for
structure-factor calculations. The rest of the hydrogen atoms were
found in the difference Fourier map and refined independently.
Preparation of [Cu(O2C(3,5-F)2C6H3)] (1). [Cu4(O2CCF3)4]
(0.874 g, 1.23 mmol) and (3,5-F)2C6H3COOH (0.975 g, 6.17 mmol)
were dissolved in 50 mL of benzene. The mixture was then refluxed
overnight to yield a light green solution. The volume of the solution
was reduced under vacuum to about 2 mL to yield a precipitate.
After the remaining solution was decanted, the solid was washed
with benzene (3 × 7 mL) and then heated at 90-100 °C overnight
under reduced pressure to remove unreacted acid. These sublima-
tion-separation procedures were repeated 2-3 times to finally give
a light blue powder of the title complex. Yield: 0.708 g (65%).
Anal. Calcd for C7H3F2O2Cu (crude powder): C, 38.10; H, 1.36;
O, 14.51; F, 17.23; Cu, 28.80. Found: C, 38.43; H, 1.77; O, 14.10;
F, 16.62; Cu, 28.71. Colorless dichroic crystals of 1 were obtained
within 1-3 days by sublimation under vacuum at 210-250 °C (ca.
10-2 Torr). IR (KBr, cm-1): 3095 m, 1556 s, 1472 m, 1441 m,
1399 s, 1307 m, 1211 w, 1122 s, 988 s, 962 m, 892 m, 860 m, 770
s, 660 m. IR (Nujol, cm-1): 3093 w, 1561 s, 1474 m, 1436 sh,
1402 s, 1309 m, 1209 w, 1120 s, 987 s, 959 m, 891 m, 860 m, 769
s. PL (250-750 nm, λex ) 350 nm, solid, λmax, nm) 554. Anal.
Calcd for C42H18F12O12Cu6 (crystals): C, 38.10; H, 1.36; O, 14.51.
Found: C, 38.39; H, 1.16; O, 13.92. UV-vis (250-800 nm, solid,
λmax, nm): 314, 439.
Preparation of [Cu6(O2C(3,5-F)2C6H3)6](C24H12) (2). A mixture
of crystals of 1 (0.065 g, 0.05 mmol) with coronene (0.008 g, 0.03
mmol) was sealed under vacuum in a small glass ampule that was
placed in an electric tube furnace at 248 °C. In 1 day, yellow blocks
of 2 were deposited in the “cold” end of the ampule together with
volatile starting materials. Crystals were manually separated for
characterization. Yield: 0.022 g (50%). IR (KBr, cm-1): 3095 w,
1605 sh, 1557 s, 1535 s, 1475 m, 1439 m, 1414 s, 1399 s, 1308 m,
1124 m, 989 m, 961 w, 888 w, 871 w, 856 m, 774 m, 768 m, 666
w, 661 w, 528 w, 519 w, 491 w, 454 w. Anal. Calcd for
C66H30F12O12Cu6: C, 48.15; H, 1.69; O, 11.19. Found: C, 48.76;
H, 1.85; O, 11.62.
Preparation of [Cu2(O2C(3,5-F)2C6H3)2(C14H10)2]‚C6H6 (3). A
mixture of crystals of 1 (0.058 g, 0.04 mmol) with diphenylacety-
lene (0.070 g, 0.39 mmol) was dissolved in 4 mL of benzene in a
round-bottom flask. The heterogeneous reaction mixture was
vigorously stirred at room temperature for 1 h and then refluxed
for 3 h. The resulting solution was filtered into another Schlenk
tube and layered with hexanes. The tube was kept in a freezer at
-60 °C. Pale pink crystals formed within several days. Yield: 0.069
(54) SAINT, version 6.02; Bruker AXS, Inc.: Madison, WI, 2001.
(55) SADABS; Bruker AXS, Inc.: Madison, WI, 2001.
(56) Sheldrick, G. M. SHELXTL, version 6.10; Bruker AXS, Inc.: Madison,
WI, 2001.
7878 Inorganic Chemistry, Vol. 46, No. 19, 2007

Hexacopper(I) 3,5-Difluorobenzoate
Acknowledgment. We thank the Donors of the American
Chemical Society Petroleum Research Fund (PRF No.
42910-AC3) and the National Science Foundation Career
Award (NSF-0546945) for the support of this work. We
acknowledge the National Science Foundation funding of
the XRPD diffractometer (CHE-0619422) and NMR spec-
trometer (CHE-0342660) at the University at Albany. We
are very grateful to Dr. Roman V. Shpanchenko (Moscow
State University, Russia) for assistance with the X-ray
powder diffraction experiments and Alexander S. Filatov
(University at Albany, NY) for the synthesis of 1,4-bis(p-
tolylethynyl)benzene. The authors also thank Anne Shelton
and Eric Warnke from the University at Albany’s Research
IT group for their assistance in IT support and in parallel
large-scale cluster calculations.
Supporting Information Available: Preparative details, includ-
ing analytical and spectroscopic data, X-ray crystallographic files
in CIF format, ORTEP diagrams for structures 1-5, and compu-
tational details for 1 and 2. This material is available free of charge
via the Internet at http://pubs.acs.org.
IC7005327
Inorganic Chemistry, Vol. 46, No. 19, 2007 7879