Breaking infinite CuI carboxylate helix held by cuprophilicity into discrete Cun fragments (n = 6, 4, 2)

Article abstract of DOI:10.1002/ejic.200701035

A new copper(I) carboxylate complex with 3,5-bis(trifluoromethyl)benzoate ligands, [Cu(O₂C(3,5-CF₃)₂C₆H ₃)] (1), has been prepared in high yield and fully characterized. An X-ray diffraction study rev

Full text of DOI:10.1002/ejic.200701035

FULL PAPER
DOI: 10.1002/ejic.200701035
Breaking Infinite CuI Carboxylate Helix Held by Cuprophilicity into Discrete
Cun Fragments (n = 6, 4, 2)
Yulia Sevryugina[a] and Marina A. Petrukhina*[a]
Keywords: Copper(I) carboxylate / Gas-phase reactions / Polyaromatic hydrocarbons
A new copper(I) carboxylate complex with 3,5-bis(trifluoro- fluoranthene (C16H10), pyrene (C16H10), and coronene
methyl)benzoate ligands, [Cu(O2C(3,5-CF3)2C6H3)] (1), has
been prepared in high yield and fully characterized. An X-
ray diffraction study revealed a remarkable infinite double-
helical chain motif held together by cuprophilic interactions
ranging from 2.69 to 3.14 Å. Both left- and right-handed heli-
ces are present in the unit cell of the centrosymmetric struc-
ture of 1 thus making the crystalline compound racemic.
Complex 1 shows bright emission at ca. 594 nm upon UV/Vis
radiation in the solid state (λex = 350 nm). The Cu···Cu con-
tacts in 1 are easily broken in the gas phase to afford copper
clusters of ascertained nuclearity upon sublimation with vari-
ous polyaromatic hydrocarbons. Several polyarenes such as
(C24H12) were selected to cover a broad temperature range
from 130 to 220 °C for the gas-phase co-deposition reactions.
As a result of the successive temperature increase, cleavage
of the infinite copper(I) chain into [Cun(O2C(3,5-CF3)2-
C6H3)n] fragments of decreasing nuclearity, n = 6, 4, and 2,
has been achieved. The isolation of these units represents
the first instance where various polynuclear copper(I) com-
plexes are prepared and structurally characterized for the
same carboxylate ligand.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
for crystal growth, we have recently accomplished the prep-
aration and structural characterization of [Cu2(O2C(2,6-
Introduction
[9]
Copper(I) carboxylates attract special attention due to
numerous catalytic applications[1] and rich photolumines-
cence properties.[2] They are known to exhibit a remarkable
structural diversity for only a few structurally confirmed
complexes. The synthetic routes toward copper(I) carboxyl-
ate complexes have been well developed,[3] but the ease of
disproportionation, hydrolysis, and oxidation of these com-
pounds in solutions[4] thwarted the isolation of single crys-
talline products and the study of their physical and chemi-
cal properties. Thus, crystallographic characterization of
copper(I) carboxylates has been so far limited to [Cu2-
(O2CCH3)2]ϱ[5] (Scheme 1, a), [Cu4(O2CC6H5)4][6] (b), [Cu4-
CF3)2C6H3)2]ϱ (Scheme 1, a), [Cu4(O2C(3-F)C6H4)4] and
[Cu4(O2C(2,3,4-F)3C6H2)4][10] (b), [Cu4(O2CCF3)2(O2CC6-
F5)2]ϱ[10] (c), and [Cu6(O2C(3,5-F)2C6H3)6][11] (d). Thus, the
known structural types of copper(I) carboxylates range from
discrete[6,10,11] to infinite motifs,[5,7–9] based on mono-,[8]
di-,[5,9] tetra-,[6,7,10] or hexanuclear[11] copper(I) units.
Such structural diversity is fascinating but not well ra-
tionalized so far. Only a few general observations can be
made at this point. For example, we noticed that very elec-
tron-withdrawing carboxylate ligands such as trifluoroacet-
ate and pentafluorobenzoate enhance intermolecular
Cu···O interactions between the tetracopper units to afford
extended motifs in contrast to discrete tetracopper(I) com-
plexes formed by mono- and trifluorobenzoates.[10] Surpris-
ingly, in contrast to the above-mentioned benzoate ligands
that resulted in the tetracopper(I) clusters, 3,5-difluoroben-
zoate afforded a remarkable hexanuclear copper(I) com-
plex, the first such example in the series.[11] At the same
time, copper(I) pivalate was found to exhibit a unique
double helical polymeric structure (Scheme 1, e). Its forma-
tion was explained by a delicate balance between the cupro-
philicity and the steric effect of the bulky tBu groups.[8]
Then, one might speculate that the cuprophilicity could be
enhanced when bulky but more electrophilic carboxylates
than pivalates are employed. However, the use of 2,6-bis(tri-
fluoromethyl)benzoate has afforded an extended polymeric
product structurally similar to that of copper(I) acetate.[9]
[7]
[8]
(O2CCF3)4]ϱ (c), and [Cu(O2CC(CH3)3)]ϱ (e). We have
recently expanded the copper(I) carboxylate family with the
goal of examining the influence of bridging carboxylate li-
gands on the solid-state structure of the resulting com-
plexes. Specifically, we focus on fluorinated carboxylate li-
gands to yield volatile copper(I) products, because that al-
lowed us to avoid the above-mentioned solution problems
and to perform crystallization by sublimation-deposition
procedures in the gas phase. Using solvent-free conditions
[a] Department of Chemistry, University at Albany, State Univer-
sity of New York,
1400 Washington Avenue, Albany, New York 12222, USA
Fax: +1-518-442-3462
E-mail: marina@albany.edu
Supporting information for this article is available on the
WWW under http://www.eurjic.org or from the author.
Eur. J. Inorg. Chem. 2008, 219–229
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219

Yu. Sevryugina, M. A. Petrukhina
FULL PAPER
Scheme 1. Schematic representation of structural types for copper(I) carboxylates.
These results show that our ability to control the formation der of 1 obtained by the above procedures is readily soluble
of a specific polynuclear copper(I) core based on the nature in coordinating solvents such as acetonitrile or tetrahydro-
of the bridging carboxylate ligands is still very limited. Fur- furan. However, the dissolution process is accompanied by
ther expansion of this family to incorporate new members the formation of a yellow precipitate and change of the
should provide better rationalization of the observed struc- solution color to blue within a few minutes, which is indica-
tural variety which is a key to understanding of their prop- tive of a rapid disproportionation.[4]
erties and reactivity. In this work, we report the synthesis,
X-ray structural characterization, and photoluminescence
of a new copper(I) carboxylate, namely 3,5-bis(trifluoro-
methyl)benzoate. In addition, its gas phase fragmentation
studies have been performed using various polyaromatic
hydrocarbons as weak complexing ligands and temperature
controlling agents.
Because the title complex is volatile, the sublimation-de-
position approach can be used for crystal growth and reac-
tivity studies. It was proven to be effective for the isolation
of single crystalline products of electrophilic complexes
without any exogenous ligands and interfering solvent ef-
fects.[7,9–11] Thus, crystals of 1 in the form of colorless thin
needles are readily accessible by the gas-phase sublimation
of the crude powder in the temperature range of 140–190 °C
in a sealed evacuated Pyrex tube.
The compositions of the crude powder and the single
crystalline product both correspond to the general formula,
[Cu(O2C(CF3)2C6H3)]. However, our attempts to correlate
the X-ray powder diffraction spectrum of the purified poly-
Results and Discussion
Synthesis of Copper(I) 3,5-Bis(trifluoromethyl)benzoate (1)
The preparation of the title copper(I) carboxylate, crystalline material, prior to its sublimation, with the calcu-
[Cu(O2C(3,5-CF3)2C6H3)] (1), was accomplished by a lated pattern for the single crystalline sample, revealed their
modification of the common ligand-exchange procedure de- unambiguous difference (see Supporting Information, Fig-
veloped earlier by Edwards and Richards.[3a] In contrast, ure S1). This result indicates that the structures of single
we have started with the [Cu4(O2CCF3)4] complex and sub- crystals of 1 obtained by sublimation-deposition and of the
stituted the trifluoroacetate groups by 3,5-bis(trifluoro- crude powder isolated initially from the carboxylate-ex-
methyl)benzoate ligands. The resulting product was con- change reaction are not identical. It is important to men-
taminated with excess carboxylic acid, which was removed tion, however, that the crystals of 1 were produced in high
by several benzene washings and repetitive re-sublimations yield, and only those have been further used for characteri-
under dynamic vacuum and mild heating. The crude pow- zation and all reactivity tests.
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Eur. J. Inorg. Chem. 2008, 219–229

Copper(I) Carboxylate Helix
X-ray Structure of Copper(I) 3,5-Bis(trifluoromethyl)-
benzoate (1)
Table 1. Selected bond lengths (Å) and angles (°) for 1 and 2.
[Cu(O2CR)]ϱ, R = (3,5-CF3)C6H3
C(CH3)3
1
2[8]
The X-ray crystallographic study of new copper(I) 3,5-
bis(trifluoromethyl)benzoate, [Cu(O2C(3,5-CF3)2C6H3)] (1),
has revealed a remarkable structural motif. Compound 1,
crystallizing in the monoclinic space group P21/n (Z = 28
for the empirical formula), contains seven Cu atoms in an
asymmetric unit (Z = 4 for the heptanuclear unit) which are
bridged by the carboxylate groups in consecutive fashion
(Figure 1).
Cu···Cucarb–bridged
Cu···Cuno[an]–bridged
Cu–Ocarb
2.693(2)–3.143(2)
2.818(2)–3.008(2)
1.858(8)
2.850(2)–2.897(2)
2.891(2)–3.125(2)
1.850(7)
Cu–Cu–Cu[a]
60.77(5)
62.64(5)
[a] Averaged.
3.008(2) Å] falls within that for the µ2-bridged Cu(n)···
Cu(nϮ1) contacts [2.693(2)–3.143(2) Å], which essentially
eliminates any difference between the bridged- and non-
bridged copper–copper separations. In copper(I) pivalate
(2), however, the µ2-bridged Cu(n)···Cu(nϮ1) contacts are
distinguishable from the unsupported Cu(n)···Cu(nϮ2) dis-
tances.
In the crystal structure of 1, the crystallographically
unique seven Cu atoms represent a repetitive fragment of a
polymer that is formed by further bridging of the Cu(7)
and Cu(1) atoms with the symmetry equivalent Cu(1A) and
Cu(7A) centers, respectively (Figure 2). Due to a similarity
between the supported and unsupported copper–copper
distances in 1, we suggest to view the polymer as if it con-
sisted of two infinite chains of Cu(nϮ2) atoms, in which the
Cu(n–2)–Cu(n)–Cu(n+2) angles are averaged to 157.57(7)°
(Scheme 2). The two parallel Cu(nϮ2) chains running along
the [100] direction are paired up by the carboxylate ligands,
which bridge the Cu(nϮ1) atoms belonging to different
chains. In addition, these parallel and bridged copper(I)
strings twist around the [100] axis to form a helix
(Scheme 2) with a period of 9.11 Å.
Figure 1. Thermal ellipsoid representation of an asymmetric unit
of 1 drawn at the 30% probability level. This ORTEP scheme is
used in all figures. The (3,5-CF3)2C6H3 groups are omitted for clar-
ity.
The Cu···Cu distances between the µ2-bridged copper
atoms in 1 vary in the wide range of 2.693(2)–3.143(2) Å (∆
= 0.45 Å). Specifically, four of the unique seven copper–
copper distances, Cu(1)···Cu(2), Cu(2)···Cu(3), Cu(3)···
Cu(4), and Cu(7)···Cu(1), are very close, averaging to
2.803(2) Å. The longest intermetallic separation, Cu(5)···
Cu(6), of 3.143(2) Å is neighbored by the shorter Cu(4)···
Cu(5) and Cu(6)···Cu(7) contacts of 2.730(2) and
2.693(2) Å, respectively. This discrepancy in metal–metal
distances is also reflected in the geometry of the carboxylate
bridge between Cu(5) and Cu(6), which results in the
Cu(5)–O(10)–C and Cu(6)–O(11)–C angles being 128.1(7)
and 135.3(8)°, respectively. At the same time, the average
value for the rest of the Cu–O–C angles is 124.8(7)°.
Figure 2. A fragment of the infinite double-helical structure of 1.
Only copper atoms are shown.
The revealed structural type of 1 is close to the recently
reported helical structure of copper(I) pivalate, [Cu(O2CC-
(CH3)3)] (2). In contrast to 1, complex 2 crystallizes in the
¯
triclinic space group P1 (Z = 10 for the empirical formula)
and has five Cu atoms in an asymmetric unit (Z = 2 for the
pentanuclear unit). Selected bond lengths and angles for 1
and 2 are listed in Table 1. A close comparison of 1 and 2
shows that the range of Cu···Cu carboxylate-bridged dis-
tances is greater in 1 (∆ = 0.45 Å) than in 2 (2.850(2)–
2.897(2), ∆ ≈ 0.05 Å). At the same time, the seesaw coordi-
nation of each Cu-center in 1 results in Cu–Cu–Cu angles
of 60.77(5)° on average, which are comparable to those in
2 [62.64(5)°].
Scheme 2. Schematic representation of the double-helical structure
of 1.
In copper(I) 3,5-bis(trifluoromethyl)benzoate (1), each of
In the crystal lattice of 1, the infinite double-helical units
the seven copper atoms, Cu(n), besides being in proximity stack together in parallel columns of constant but different
with the adjacent carboxylate-bridged Cu(nϮ1) atoms, has helicity. The presence of both left- and right-handed helices
close contacts to the non-bridged Cu(nϮ2) atoms. The in the centrosymmetric structure of 1 makes the crystalline
range of these Cu(n)···Cu(nϮ2) distances in 1 [2.818(2)– compound racemic (Figure 3).
Eur. J. Inorg. Chem. 2008, 219–229
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Yu. Sevryugina, M. A. Petrukhina
FULL PAPER
(O2CR)4] (R = (2,3,4-F)3C6H2 and (3-F)C6H4) and hexanu-
clear [Cu6(O2C(3,5-F)2C6H3)6] complexes. An analysis of
the H···F interactions in 1 has shown them to fall in the
2.29–2.84 Å range with the C–H···F angles varying from
131 to 168°. However, one should keep in mind that the
trifluoromethyl groups in the crystal structure of 1 are dis-
ordered over two or three rotational orientations. Note-
worthy, copper(I) 2,6-bis(trifluoromethyl)benzoate reported
earlier,[9] having the same molecular formula [Cu(O2C-
(CF3)2C6H3)] but differently positioned trifluoromethyl
substituents (2,6- instead of 3,5-) on the benzene rings,
forms a different solid state assembly (Scheme 1, a).
Figure 3. The left- and right-handed helices in the centrosymmetric
structure of 1 (two helices out of four are shown). Only copper
atoms are shown.
The structure of the previously reported copper(I) pival-
ate (2) can also be regarded as a double helix. The Cu(n–
2)–Cu(n)–Cu(n+2) angles in 2 of 143.66(6)° imply that the
helical twist in 2 is greater than that in 1. A projection array
Fragmentation Studies of Copper(I) 3,5-Bis(trifluoromethyl)-
benzoate (1)
Crystals of copper(I) 3,5-bis(trifluoromethyl)benzoate,
perpendicular to the a axis in 2 exhibits a perfect pentagon [Cu(O2C(3,5-CF3)2C6H3)] (1), can be quantitatively resub-
of copper atoms. In contrast, a similar projection in 1 does limed in the 140–190 °C range. At these temperatures, the
not indicate any symmetry elements (Scheme 3).
deposited product has been confirmed to have the same in-
finite double-helical polymeric structure, [Cu(O2C(3,5-
CF3)2C6H3)]ϱ. We hypothesized that in the gas phase this
compound exists in the form of some discrete molecular
species, the isolation and characterization of which turned
out to be a synthetic challenge. We reasoned that polycyclic
aromatic hydrocarbons (PAHs) may be appropriate π-donor
agents for crystallization of the copper(I) carboxylate frag-
ments from the vapor phase. We have recently observed that
co-deposition of the hexanuclear copper(I) carboxylate
complex with coronene from the gas phase did not change
the nuclearity of the copper(I) core in its crystalline ad-
duct.[11] The choice of ligands, fluoranthene (L1 = C16H10),
pyrene (L2 = C16H10), and coronene (L3 = C24H12)
(Scheme 4), was based on their different volatility that co-
vers a broad temperature range for co-deposition reactions
(melting points are 105 °C for fluoranthene, 146 °C for py-
rene, and 428 °C for coronene). In addition, the copper(I)
binding toward π-donor substrates has been long consid-
ered important in molecular recognition processes for many
biological and artificial systems,[17] as well as in catalysis
of aromatic cross-coupling reactions.[18] However, only two
copper(I) carboxylate–arene adducts have been structurally
characterized to date,[11,19] with only the recent work at-
tempting to interpret the bonding in such systems.
Scheme 3. Schematic representation of projections perpendicular to
the a axis for the structures of 1 and 2. Cu shaded spheres, O black,
C white. The C(CH3)3 and (3,5-CF3)2C6H3 groups are omitted for
clarity.
The helical shape is a common natural motif. The simi-
larity between the double helices of 1 and 2 and those of
nucleic acids is particularly attractive. Materials of such
type are expected to exhibit a wide range of potential appli-
cations in the fields of supramolecular chemistry,[12] asym-
metric catalysis,[13] and nonlinear optics.[14] Although dis-
crete copper(I) double-helices supported by oligopyridine
and oligophenanthroline ligands are known,[15] complex 2
reported by Awaga[8] and complex 1 prepared in our labora-
tory are the only copper(I) carboxylates with the infinite
helical architectures. A few other extended copper(I) chains
and infinite arrays held by cuprophilicity should be men-
tioned here.[16]
It has been previously observed that π-stacking interac-
tions between aromatic rings play an important role in sta-
bilizing the double-helical geometry.[15] However, a thor-
ough analysis of the solid state packing of [Cu(O2C(3,5-
CF3)2C6H3)]ϱ (1) revealed only very weak intramolecular π-
π stacking interactions of 4.33–4.74 Å between the adjacent
benzene rings of carboxylate moieties (dihedral angles in
the range of 11.1–35.1°). Such weak intramolecular con-
tacts could not be a major driving force in the formation of
Scheme 4. Schematic representation of polycyclic hydrocarbons L1–
L3.
Using the gas-phase deposition approach that we found
a helix. For comparison, the analogous contacts are in the to be very effective for utilizing intermolecular metal–π-
range of 3.71–4.16 Å for the discrete tetranuclear [Cu4- arene interactions for the controlled preparation of discrete
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Copper(I) Carboxylate Helix
Table 2. Selected bond lengths (Å) and angles (°) for complexes 3–6.
L (name):
L (formula):
[Cun(O2CR)n]Lm:
fluoranthene
C16H10
3, n = 6, m = 2
fluoranthene
C16H10
4, n = 4, m = 1
pyrene
C16H10
5, n = 4, m = 1
coronene
C24H12
6, n = 2, m = 1
Cu···Cucarb-bridged
Cu···Cuno[an]-bridged
Cu–Ocarb
2.6973(13)–2.8280(13)
2.8547(18)–2.9407(13)
1.858(5)
2.82(2)–3.26(3)
115.73(4), 175.37(4), 65.58(3)
172.1(2)
2.7203(15)–2.7475(16)
2.8410(14)
1.856(5)
2.895(10)–3.234(8)
117.47(5)[a], 62.53(4)[a]
175.8(3)
2.7028(6), 2.7344(6)
2.8315(8)
1.862(2)
2.862(3), 3.044(3)
117.210(16), 62.763(16)
175.99(11)
2.5678(15)
1.876(4)
2.783(9)–3.230(11)
Cu···C
Cu–Cu–Cu
O–Cu–O[a]
169.73(16)
[a] Averaged.
Table 3. Data collection and structure refinement parameters for 1, 3–6.
1
3
4
5
6
Formula
Fw
C9H3CuF6O2
320.65
C86H38Cu6F36O12
2328.40
C52H22Cu4F24O8
1484.86
C52H22Cu4F24O8
1484.86
C42H18Cu2F12O4
941.64
Color
Crystal size [mm]
T [K]
colorless
0.28ϫ0.03ϫ0.02
173(2)
yellow
0.09ϫ0.07ϫ0.02
173(2)
yellow
0.09ϫ0.07ϫ0.07
173(2)
yellow
0.20ϫ0.06ϫ0.05
173(2)
yellow
0.17ϫ0.13ϫ0.02
173(2)
Crystal system
Space group
monoclinic
P21/n
triclinic
P1
monoclinic
P21/c
monoclinic
C2/c
monoclinic
P21/c
¯
a [Å]
b [Å]
c [Å]
α [°]
9.1145(8)
23.718(2)
35.093(3)
9.9582(8)
12.9219(10)
17.7942(14)
71.889(1)
73.817(1)
89.921(1)
2080.9(3)
1
17.7712(10)
20.9291(12)
15.1217(9)
15.7991(10)
17.8081(11)
18.6724(12)
17.204(3)
8.1182(15)
12.557(2)
β [°]
90.614(2)
114.099(1)
96.366(1)
101.025(3)
γ [°]
V [Å3]
7585.9(12)
28
5134.1(5)
4
5221.1(6)
4
1721.4(6)
2
Z
λ [Å]
0.71073
1.965
2.089
0.71073
1.858
1.650
0.71073
1.921
1.779
0.71073
1.889
1.749
0.71073
1.817
1.348
ρcalcd. [gcm–3]
µ [mm–1]
Min./max. transmission
2θmax
Unique data
0.5924/0.9594
50.20
13468
0.8657/0.9677
50.32
7329
0.8563/0.8856
49.98
9001
0.7212/0.9176
56.50
6161
0.8032/0.9735
50.14
3047
Observed data [IϾ2σ(I)] 8975
4592
615
1.046
0.0761, 0.1813
0.1222, 0.2106
1.124, –0.611
5652
856
1.106
0.0863, 0.1636
0.1390, 0.1850
0.704, –0.563
5261
468
1.026
0.0487, 0.1220
0.0563, 0.1278
1.005, –0.725
1945
277
1.055
0.0683, 0.1589
0.1143, 0.1876
1.515, –0.539
Parameters refined
1212
1.122
Goodness-of-fit[a] on F2
R1,[b] wR2[c] [IϾ2σ(I)]
R1,[b] wR2[c] [all data]
0.0988, 0.2071
0.1443, 0.2261
Residual ρmax, min [eÅ–3] 0.839, –0.773
2
2 2
2
2 2
[a] Quality-of-fit = {Σ[w(Fo – Fc ) ]/(Nobsd. – Nparams)}1/2. [b] R1 = Σ||Fo| – |Fc||/Σ|Fo|. [c] wR2 = {Σ[w(Fo – Fc ) ]/Σ[w(Fo2)2]}1/2
.
complexes and extended organometallic networks in a sol-
Reaction with Fluoranthene: The reaction of copper(I)
vent-free environment,[20] we have isolated several new 3,5-bis(trifluoromethyl)benzoate (1) with fluoranthene (L1)
products, each incorporating a certain molecular fragment, afforded a mixture of two new products of stoichiometries
[Cun(O2C(3,5-CF3)2C6H3)n].
Cu/L1 = 6:2 (3) and 4:1 (4) that were deposited in different
These compounds, namely [Cu6(O2C(3,5-CF3)2C6H3)6]- parts of the same ampule. The big yellow blocks of the lat-
(C16H10)2 (3), [Cu4(O2C(3,5-CF3)2C6H3)4](C16H10) (4), ter compound were mainly found in the “hot” end, where
[Cu4(O2C(3,5-CF3)2C6H3)4](C16H10) (5), and [Cu2(O2C(3,5- the sublimation temperature was set at 137 °C, while thin
CF3)2C6H3)2](C24H12) (6), were isolated in the form of air- yellow plates of the former adduct were located in the
stable but slightly moisture sensitive crystals of pale yellow “cold” end having a ca. 5 °C lower temperature. In the mid-
color. Their IR spectra are very similar in the 2000– dle part of the ampule, co-deposition of both types of crys-
500 cm–1 range and indicate the presence of aromatic and tals was observed but their different visual appearance al-
carboxylate functions. Additionally, the composition of the lowed for their manual separation.
newly prepared compounds 4–6 was confirmed by elemen-
Compound [Cu6(O2C(3,5-CF3)2C6H3)6](C16H10)2 (3)
¯
tal analysis. The molecular structures of 3–6 have been de- crystallizes in the triclinic space group P1 (Z = 1). The
termined by X-ray diffraction analysis. The X-ray crystal building blocks in the structure are a planar hexagon of
data for 1, 3–6 as well as selected bond lengths and angles six copper atoms bridged by carboxylate ligands and two
for 3–6 are listed in Tables 2 and 3, respectively.
fluoranthene molecules (Figure 4). The hexagon resides on
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Yu. Sevryugina, M. A. Petrukhina
FULL PAPER
an inversion center with only three copper atoms and the
In our recent work we have demonstrated that the nature
halves of two fluoranthene molecules being crystallographi- of communication between the hexanuclear copper(I) car-
cally independent. The 3,5-bis(trifluoromethyl)benzoate li- boxylate complex and the polyaromatic system of coronene
gands support the [Cu6]-core in an alternate manner by po- is described by strong electrostatic ion-induced dipole inter-
sitioning above and below the hexacopper plane.
actions.[11] DFT calculations confirmed an absence of any
bonding interactions and suggested that the [Cu6(O2C(3,5-
F)2C6H3)6](C24H12) adduct be treated as a product of
cocrystallization rather than a coordination compound. In
contrast, in the recent theoretical work[23] the η6 complex
between the naked Cu(+)-cation and benzene was charac-
terized by strong 3d-π*(C6H6) back-bonding. However, the
η6-binding was not experimentally observed in the solid
state and all crystallographically confirmed examples of π-
arene complexes of CuI are based on η1 or η2-type of inter-
actions. In line with our findings for the latter, we will con-
sider compounds 3–6 as products of cocrystallization, dis-
cussing the short copper-to-carbon distances as non-bond-
ing contacts.
The second product with fluoranthene, [Cu4(O2C(3,5-
CF3)2C6H3)4](C16H10) (4), crystallizes in the monoclinic
space group P21/c (Z = 4). The structural block is a planar
tetragon of four crystallographically unique copper atoms
bridged by 3,5-bis(trifluoromethyl)benzoate groups and one
fluoranthene molecule (Figure 5).
Figure 4. Building blocks of 3. The (3,5-CF3)2C6H3 groups and the
H atoms are omitted for clarity.
Importantly, the [Cu6] unit present in the structure of 3
is only the second example of a hexanuclear core for the
whole copper(I) carboxylate series; the first one was
discovered recently for copper(I) 3,5-difluorobenzoate,
[Cu6(O2C(3,5-F)2C6H3)6].[11] Herein, this hexanuclear frag-
ment was isolated from the sublimation-deposition of the
polymeric compound 1 and fluoranthene at the lowest tem-
perature for the series of experiments, namely at 130 °C.
This may be indicative of the existence of the [Cu6] frag-
ment in the vapor phase at the above temperature.
The geometry of the [Cu6] core in 3 is very similar to
that in copper(I) 3,5-difluorobenzoate. The copper–copper Figure 5. Building block in the structure of 4. The (3,5-CF3)2C6H3
groups and the H atoms are omitted for clarity.
distances for the µ2-bridged Cu atoms range from
2.6973(13) to 2.8280(13) Å (2.7064(8)–2.8259(8) Å in cop-
per(I) 3,5-difluorobenzoate) and the interior Cu–Cu–Cu
angles are 115.73(4), 175.37(4), and 65.58(3)° [123.48(3),
170.27(3), and 66.15(2)° for copper(I) 3,5-difluorobenzo- turally similar to those of the several previously reported
ate].
[Cu4(O2CR)4] complexes [R = CF3,[7] C6H5,[6] (3-F)-
The tetracopper core of the molecular complex 4 is struc-
The solid-state structure of 3 can be viewed as a 2D net- C6H4,[10] (2,3,4-F)3C6H2,[10] and CF3/C6F5[10]]. The average
work running in the ab plane. In the layer, fluoranthene copper–copper distances [2.7372(16) Å] and angles
molecules adopt different orientations around the hexanu- [117.47(5) and 62.53(4)°] fall in the same range as for the
clear copper complex. The details of the solid state packing other [Cu4]-core carboxylates. The fluoranthene molecule
are described in the Supporting Information (Figures S8, exhibits a shortest Cu(2)···C(37) distance of 2.895(10) Å,
S9). The shortest contact of 2.82(2) Å is found between while the adjacent Cu(2)···C(38) and Cu(2)···C(51) separa-
Cu(1) and C(44) (Figure 4). Several Cu···C contacts in the tions are noticeably longer [3.173(10) and 3.182(11) Å,
range of 3.014(18)–3.26(3) Å exceed the sum of the van der respectively].
Waals radii rvdW for Cu and C [ΣrvdW(Cu,C) = 3.10 Å].[21]
For comparison, the range of Cu···C distances in [Cu4(O2- ribbon (Figure 6) built on intermolecular copper–carbon
It is convenient to consider 4 as a polymeric zigzag-type
[19]
CCF3)4](C6H6)2
is 2.7–3.0 Å, while the bonding Cu···C interactions, namely the Cu(2)···C(37) and Cu(4)···C(44A)
distances in copper(I) cation–arene π complexes with li- contacts (Figure 5). The latter of 3.234(8) is, however, con-
gands other than carboxylates range from 2.09 to 2.92 Å.[22] siderably longer than the former [2.895(10) Å].
224
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Copper(I) Carboxylate Helix
Reaction with Coronene: Complex [Cu2(O2C(3,5-CF3)2-
C6H3)2](C24H12) (6) of the stoichiometry Cu/L3 = 2:1 was
obtained at sublimation temperature 220 °C by reacting
[Cu(O2C(3,5-CF3)2C6H3)]ϱ (1) with coronene (L3). Com-
pound 6 crystallizes in the monoclinic space group P21/c (Z
= 2) and has an inversion center at the midpoint of the
Cu(1)···Cu(1A) separation. The main structural block is the
dicopper(I,I) carboxylate unit with one coronene molecule
(L3) (Figure 9).
Figure 6. A fragment of a polymeric zigzag chain in 4. The (3,5-
CF3)2C6H3 groups and the H atoms are omitted for clarity.
Reaction with Pyrene: The reaction of 1 with pyrene (L2)
at 160 °C produced the new copper(I) 3,5-bis(trifluoro-
methyl)benzoate complex with a Cu/L2 = 4:1 composition.
Compound [Cu4(O2C(3,5-CF3)2C6H3)4](C16H10) (5), crys-
tallizing in the monoclinic space group C2/c (Z = 4), has a
twofold rotation axis at the center of the [Cu4]-core. The
main structural unit contains four copper atoms, two of
which are crystallographically independent, and one pyrene
molecule (Figure 7).
Figure 9. Building block in the structure of 6. The (3,5-CF3)2C6H3
groups and the H atoms are omitted for clarity.
The Cu(1)···Cu(1A) bond length of 2.5678(15) Å within
a dimetal unit is significantly shorter than copper–copper
distances for polynuclear compounds 1 and 3–5 but
comparable to those for analogous dicopper(I)-based ace-
tate[5] [2.556(2) Å] and 2,6-bis(trifluoromethyl)benzoate[9]
[2.563(2) Å].
Each Cu atom in 6 is directed toward the C–C π bonds
of two different coronene molecules. In the [001] direction
the Cu···C distances range from 2.783(9) to 2.950(11) Å and
are within the sum of the van der Waals radii for copper
and carbon [ΣrvdW (Cu, C) = 3.10 Å].[21] In the [010] direc-
tion, the Cu···C contacts of 3.100(10)–3.230(11) Å are
longer. It is convenient to consider 6 as a 2D layer running
in the bc plane, that consists of alternating dicopper units
and coronene molecules (Figure 10).
Figure 7. Building block in the structure of 5. The (3,5-CF3)2C6H3
groups and the H atoms are omitted for clarity.
Although the tetranuclear motif is common among cop-
per(I) carboxylates, the structure of 5 is the first example
having almost equal and parallel Cu···Cu sides of 2.7028(6)
and 2.7344(6) Å, which make a parallelogram core. The in-
terior Cu–Cu–Cu angles of 117.210(16) and 62.763(16)° are
the same as in the tetragonal core of compound 4. Only
one of the two crystallographically independent Cu atoms
has contacts of 2.862(3) and 3.044(3) Å with two carbon
atoms of pyrene, C(19A) and C(24A), respectively.
Compound 5 can be viewed as an infinite 1D linear net-
work propagating along the [010] direction (Figure 8). Re-
petitive units are related by an inversion center at the mid-
point of the C(21A)···C(21B) bond of pyrene.
Figure 8. A fragment of a polymeric 1D chain in 5. The (3,5-CF3)2-
C6H3 groups and the H atoms are omitted for clarity.
Figure 10. A fragment of the 2D infinite layer in 6. The (3,5-CF3)2-
C6H3 groups and the H atoms are omitted for clarity.
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225

Yu. Sevryugina, M. A. Petrukhina
FULL PAPER
It should be mentioned here that in the polymeric com- color emission. The PL spectrum for compound 5,
plex [Ag4(C24H12)3(ClO4)4]ϱ, the interaction between AgI [Cu4(O2C(3,5-CF3)2C6H3)4](C16H10), has, therefore, been
and coronene is so strong that it results in a bent conforma- recorded in the IR range at room temperature, and the posi-
tion of the latter [Ag···C contacts range from 2.402(4) to tion of an emission maximum was determined at 1363 nm
2.517(4) Å].[24] In complex 6, however, the geometrical pa- (λex = 515 nm). The fact that the emission band for the
rameters of coronene are unchanged as compared to the adduct 5 is significantly red-shifted to the IR region com-
uncoordinated molecule.[25]
pared to both copper(I) 3,5-bis(trifluoromethyl)benzoate
The isolation and structural characterization of adducts (1) and pyrene (that emits radiation at 482 and 515 nm, λex
3–6 revealed an interesting trend: an increase in the reaction = 350 nm) suggests that the copper(I) unit and polyarene
temperature is accompanied by a controlled fragmentation are both affected by cocrystallization. The photolumines-
of the infinite helical chain of 1 to form [Cu6]-, [Cu4]- and, cence spectra of 5 and free pyrene (L2) are given in Fig-
finally [Cu2]-based units, cocrystallized with the corre- ure 11 (see also Supporting Information).
sponding polyarene. This clearly illustrates the effect of re-
action conditions on the outcome of the co-deposition reac-
tions and gives a tool for controlling the nuclearity of cop-
per(I) clusters.
Photoluminescence
Considerable attention has been paid to understanding
the photophysical behavior of polynuclear copper(I) ha-
lides, chalcogenides, acetylides, and pyrazolates.[26] How-
ever, the only reference to photoluminescent properties of
copper(I) carboxylates is dated back to 1981.[2] The emis-
sion maxima for a series of aliphatic copper(I) carboxylates
were reported in the range of 535–660 nm at room tempera-
ture (λex = 305–325 nm), but these data were not supported
Figure 11. Solid state photoluminescence spectra for 5 and L2.
by structural characterization of the complexes.
Our recent findings showed that copper(I) clusters dis-
We have recently reported[11] that the copper(I) 3,5-di-
play strikingly different emissive behavior.[9–11] Similar to
fluorobenzoate complex with coronene, [Cu6(O2C(3,5-F)2-
other copper(I) carboxylates,[9–11,2] complex 1 exhibits pho-
C6H3)6](C24H12), is also nonluminescent in the visible re-
toluminescence (PL) upon exposure to UV radiation (λex
=
gion at room temperature. In contrast, the photolumines-
cence for [Cu2(CF3SO3)2](C6H6) was detected at 518 nm
(λex = 320 nm) and was suggested to originate from the CuI
Ǟ π* C6H6 MLCT transitions.[27] Besides these, there are
no systematic studies discussing the origin of photolumines-
cence and its dependence on the structural type and π-arene
complexation for copper(I) carboxylates, thus thwarting the
rationalization of the above-mentioned effects. A full inves-
tigation of the luminescent properties of a series of cop-
per(I) carboxylates having different nuclearities and dif-
ferent structural arrangements is currently underway, and
that should shed some light on their photophysical behav-
ior.
350 nm). The PL spectrum of 1 in the solid state at room
temperature displays an emission maximum centered at ca.
594 nm (yellow color). It should be noted that 3,5-bis(tri-
fluoromethyl)benzoic acid is also luminescent in the solid
state with an emission peak at ca. 493 nm (λex = 350 nm)
(see Supporting Information, Figure S10). In contrast, cop-
per(I) 2,6-bis(trifluoromethyl)benzoate having a [Cu2]-
based polymeric structure held by Cu···O intermolecular in-
teractions (Scheme 1, a) showed green photoluminescence
centered at ca. 560 nm under the same conditions. Interest-
ingly, the structurally similar to 1 copper(I) pivalate was
reported as nonluminescent.[8] The infinite helical structure
of the latter held together by cuprophilicity was suggested
as a possible explanation for the nonradiative decay. How-
ever, now that does not provide a rationale for the different
luminescent behavior of 1 and 2. The overall subtle struc-
tural differences as well as the nature of the bridging car-
Conclusions
The isolation and structural characterization of cop-
boxylate ligands both seem to affect the emission properties per(I) 3,5-bis(trifluoromethyl)benzoate, [Cu(O2C(3,5-CF3)2-
of the copper(I) carboxylate complexes. C6H3)]ϱ (1), has added to the copper(I) carboxylate family
None of the copper(I) carboxylate adducts with polyar- the second member having a remarkable double-helical
ene ligands (3–6) exhibit detectable emission in the solid structure. In contrast to copper(I) pivalate having a 6.35 Å
state. The PL spectra recorded for 3–6 in the range of 400– periodicity and being reported as nonluminescent, the title
700 nm at room temperature are featureless. Under a stream complex has a period of 9.11 Å and shows bright lumines-
of liquid nitrogen, however, weak and feeble photolumines- cence in the solid state. The gas phase reactions of the infi-
cence can be hardly observed with the naked eye as a red- nite double-helical complex, [Cu(O2C(3,5-CF3)2C6H3)]ϱ,
226
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Copper(I) Carboxylate Helix
(3,5-CF3)2C6H3COOH (1.709 g, 6.62 mmol) in benzene (50 mL).
The volume of a homogeneous solution was then reduced to 2 mL
to initiate a precipitation of a light blue powder. The solution above
a precipitate was then decanted. The solid was washed with ben-
zene (3ϫ10 mL) and then heated at 90–100 °C overnight under
the dynamic vacuum to remove the traces of unreacted acid. This
afforded a very pale blue microcrystalline powder of 1. Yield:
1.147 g (70%). C9H3CuF6O2 (320.7): calcd. C 34.73, H 0.96, O
10.29, F 33.44, Cu 20.58; found C 35.06, H 1.09, O 10.49, F 32.91,
Cu 21.01. Crystals of 1 as white thin needles were obtained by
with fluoranthene, pyrene, and coronene at the tempera-
tures of 137, 162, and 220 °C, afforded hexa- (3), tetra- (4
and 5), and dinuclear (6) copper(I)-core fragments crys-
tallized as adducts with the above polyarenes. Thus, using
π-donor aromatic ligands of different volatility, we were
able to break the copper(I) 3,5-bis(trifluoromethyl)benzoate
helix and isolate several discrete [Cun]-clusters, n = 6, 4, and
2. In accord with our expectations, the molecular unit of
the highest nuclearity is formed at the lowest reaction tem-
perature, while temperature increase results in a further sublimation of the crude powder at 140–200 °C for 1–3 d. IR
(KBr): ν = 3095 (w), 2966 (w), 2931 (w), 2857 (w), 1631 (m), 1571
˜
cleavage of the extended motif into smaller copper(I) frag-
ments. This shows that tuning the temperature of gas-phase
reactions offers control over the formation of copper(I)
clusters of a specific nuclearity. Importantly, the reported
system provides the first example where polynuclear [Cun]-
core complexes have been isolated and structurally charac-
(m), 1549 (m), 1468 (m), 1456 (m), 1438 (m), 1347 (s), 1278 (s),
1180 (s), 1131 (s), 939 (w), 917 (m), 846 (m), 791 (w), 773 (m), 765
(m), 700 (m), 707 (m), 682 (s), 668 (w), 576 (w), 548 (w) cm–1. PL
(250–750 nm, λex = 350 nm, solid): λmax = 594 nm. C9H3CuF6O2
(320.7): calcd. C 34.73, H 0.96; found C 34.55, H 0.86.
terized for the same carboxylate ligand. All prior structur- [Cu6(O2C(3,5-CF3)2C6H3)6](C16H10)2 (3) and [Cu4(O2C(3,5-CF3)2-
C6H3)4](C16H10) (4): A mixture of crystals of [Cu(O2C(3,5-CF3)2-
C6H3)] (1) (0.054 g, 0.174 mmol) with fluoranthene (L1 = C16H10)
(0.005 g, 0.025 mmol) was sealed under vacuum in a small glass
ampule, which was placed in an electric oven at 137 °C. Over four
days, two types of crystals appeared in the tube. Thin pale yellow
plates of 3 were found mostly in the “cold” end of the ampule,
where the temperature was set at ca. 130 °C. Yield: 0.010 g (15%).
ally confirmed copper(I) carboxylate complexes created an
illusion that a specific structure is related to a particular
carboxylate ligand. Although crystallized as adducts with
polyarenes, compounds 3–6 show a more complicated pic-
ture and confirm the existence of various structural pos-
sibilities for a given carboxylate group. Thus, structures of
the known copper(I) carboxylates may depend additionally
on the preparation or crystallization conditions, and varia-
tion of those would result in the structural changes.
IR (KBr): ν = 3068 (w), 3033 (w), 2924 (w), 2854 (w), 1631 (m),
˜
1572 (m), 1456 (m), 1436 (m), 1348 (s), 1278 (s), 1266 (sh), 1177
(m), 1131 (s), 1106 (sh), 914 (m), 845 (m), 806 (w), 773 (m), 761
(sh), 735 (w), 724 (w), 702 (m), 682 (m), 655 (w), 610 (w), 574 (w),
540 (w) cm–1.
Experimental Section
The yellow blocks of 4 were found at the “hot” end of the ampule.
Yield: 0.025 g (40%). IR (KBr): ν = 3088 (w), 3069 (w), 1631 (m),
˜
General: All synthetic reactions and manipulations were carried out
under dry dinitrogen or vacuum using standard Schlenk and glove-
box techniques. Sublimation-deposition procedures were per-
formed in evacuated (less than 10–2 Torr) sealed glass ampules (ca.
7 cm long with an o.d. of 1.1 cm), which were placed in electric
furnaces having a small temperature gradient along the length of
the tube.
1574 (m), 1465 (w), 1454 (m), 1436 (m), 1346 (s), 1275 (s), 1264
(sh), 1175 (s), 1135 (s), 1105 (sh), 937 (w), 914 (m), 846 (m), 825
(w), 781 (m), 775 (m), 766 (m), 752 (w), 708 (m), 699 (m), 681 (m),
619 (w), 579 (w) cm–1. C52H22Cu4F24O8 (1484.9): calcd. C 42.05,
H 1.48, O 8.63; found C 42.30, H 1.56, O 9.01.
[Cu4(O2C(3,5-CF3)2C6H3)4](C16H10) (5): A mixture of crystals of
[Cu(O2C(3,5-CF3)2C6H3)] (1) (0.127 g, 0.408 mmol) with pyrene
(L2 = C16H10) (0.020 g, 0.099 mmol) was sealed under vacuum in
a small glass ampule, which was placed in an electric oven at
162 °C. Over two days, pale yellow blocks of 5 had grown at the
“cold” end of the tube. In 10 d the yield of 5 reached 0.040 g (27%).
The [Cu4(O2CCF3)4] complex was synthesized according to the lit-
erature method.[7] Anhydrous benzene, fluoranthene (L1 = C16H10),
and coronene (L3 = C24H12) were purchased from Aldrich, while
pyrene (L2 = C16H10) was obtained from Acros. The 3,5-bis(trifluo-
romethyl)benzoic acid, (3,5-CF3)2C6H3COOH, was purchased
from SynQuest Fluorochemicals and used as received.
IR (KBr): ν = 3090 (w), 3046 (w), 1628 (m), 1583 (m), 1466 (m),
˜
1457 (m), 1437 (m), 1347 (s), 1278 (s), 1178 (m), 1170 (m), 1139
(s), 1130 (s), 1105 (sh), 940 (w), 934 (w), 912 (m), 847 (m), 777 (m),
771 (sh), 766 (m), 754 (w), 714 (m), 708 (m), 699 (m), 682 (s), 553
(w) cm–1. PL (250–1700 nm, λex = 515 nm, solid): λmax = 1363 nm.
C52H22Cu4F24O8 (1484.9): calcd. C 42.05, H 1.48; found C 42.12,
H 1.41.
The infrared spectra were recorded using KBr pellets with a Nicolet
Magna 550 FTIR spectrometer. Elemental analyses were per-
formed by Guelph Chemical Laboratories Ltd., Canada. The pho-
toluminescence spectrum of 1 was collected with a Varian Cary
Eclipse spectrophotometer, in which the PMT detector was posi-
tioned 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. The photolu-
minescence spectrum of 5 was collected at the College of Nanoscale
Science and Engineering, University at Albany, using the following
setup. The Ar+ laser was used as an excitation source. Light emitted
from the sample was focused by a lens on the input slit of a mono-
chromator (1 mm). The Ge p-i-n photodiode attached to the output
slit of a monochromator (1 mm) was used as a detector.
[Cu2(O2C(3,5-CF3)2C6H3)2](C24H12) (6): A mixture of crystals of
[Cu(O2C(3,5-CF3)2C6H3)] (1) (0.051 g, 0.164 mmol) with coronene
(L3 = C24H12) (0.024 g, 0.080 mmol) was sealed under vacuum in
a small glass ampule, which was placed in an electric oven at
220 °C. Over the next six days, yellow plates of 6 had grown in the
middle part of the tube. Yield: 0.037 g (50%). IR (KBr): ν = 2921
˜
(w), 2829 (w), 1628 (m), 1565 (m), 1453 (w), 1429 (w), 1348 (s),
1313 (w), 1279 (s), 1262 (m), 1197 (m), 1131 (s), 1105 (sh), 912 (m),
862 (m), 844 (w), 775 (m), 708 (m), 700 (m), 681 (m), 554 (w) cm–1.
C42H18Cu2F12O4 (941.6): calcd. C 53.56, H 1.91; found C 53.69, H
1.81.
[Cu(O2C(3,5-CF3)2C6H3)] (1): The title compound was prepared by
an overnight reflux of [Cu4(O2CCF3)4] (0.902 g, 1.27 mmol) and
Eur. J. Inorg. Chem. 2008, 219–229
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227

Yu. Sevryugina, M. A. Petrukhina
FULL PAPER
5, 1143–1148; h) T. Cohen, R. J. Ruffner, D. W. Shull, E. R.
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X-ray Crystallography: The X-ray diffraction data for single crys-
tals were collected on a Bruker SMART APEX CCD-based dif-
fractometer by using a Mo-target X-ray tube (λ = 0.71073 Å) oper-
ated at 1800 W power. Crystal data and data collection parameters
for 1, 3–6 are listed in Table 3. A total of 1850 frames were collected
with a scan width of 0.3° in ω and an exposure time of 30 s/frame
for each experiment. The frames were integrated with the Bruker
SAINT software package[28] using a narrow-frame integration algo-
rithm. Analysis of the data showed negligible decay during data
collection. The structures were solved by the direct methods and
refined with the Bruker SHELXTL (Version 6.1) software pack-
age.[29] Data were corrected for absorption effects using the empiri-
cal methods SADABS.[30]
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[5]
All non-hydrogen atoms were refined anisotropically, except for dis-
ordered carbon and fluorine atoms. The fluorine atoms of the CF3
groups in 1, 3–6 were disordered over two or three rotational orien-
tations, and this disorder was modeled individually in each case. In
compounds 1 and 3, in addition to the CF3 rotational disorder,
some benzene rings of the bridging carboxylate groups were disor-
dered over two orientations. Moreover, in complex 3, both fluoran-
thene molecules exhibited crystallographically imposed disorder
due to internal symmetry elements, and that was modeled individu-
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the difference Fourier map and refined independently, while in the
structures 1, 3, 4, and 6 all hydrogen atoms were included at ideal-
ized positions for structure-factor calculations.
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Research Fund (PRF 42910-AC3) and the National Science Foun-
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work. We also acknowledge the National Science Foundation
(NSF) funding of the X-ray powder diffractometer (CHE-0619422)
at the University at Albany. We thank Dr. Roman V. Shpanchenko
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