X-ray structure and photoluminescence of copper(I) 2,6-bis(trifluoromethyl)benzoate

Article abstract of DOI:10.1016/j.ica.2007.02.023

This report describes synthesis, X-ray crystallographic characterization, and photoluminescence of copper(I) 2,6-bis(trifluoromethyl)benzoate, [Cu(O₂C(2,6-CF₃)₂C₆H₃)] (1). Complex 1 has a polymeric structure comprised of axially bound dinuclear [Cu₂(O₂C(2,6-CF₃)₂C₆H₃)₂] units that is reminiscent of the well-known structure of copper(I) acetate, [Cu₂(O₂CMe)₂] (2). However, a close comparison of two analogues revealed a non-planarity of 1D chains and their orthogonal disposition in the crystal structure of 1 versus parallel alignment of planar chains in 2. Complex 1 exhibits green photoluminescence at ca. 560 nm upon UV-radiation (λ_ex = 350 nm) in the solid state.

Full text of DOI:10.1016/j.ica.2007.02.023

Inorganica Chimica Acta 360 (2007) 3103–3107
www.elsevier.com/locate/ica
Note
X-ray structure and photoluminescence of copper(I)
2,6-bis(trifluoromethyl)benzoate
*
Yulia Sevryugina, Dimitri D. Vaughn II, Marina A. Petrukhina
Department of Chemistry, University at Albany, State University of New York, 1400 Washington Avenue, Albany, NY 12222, USA
Received 15 December 2006; received in revised form 1 February 2007; accepted 13 February 2007
Available online 21 February 2007
Abstract
This report describes synthesis, X-ray crystallographic characterization, and photoluminescence of copper(I) 2,6-bis(trifluoro-
methyl)benzoate, [Cu(O2C(2,6-CF3)2C6H3)] (1). Complex 1 has a polymeric structure comprised of axially bound dinuclear
[Cu2(O2C(2,6-CF3)2C6H3)2] units that is reminiscent of the well-known structure of copper(I) acetate, [Cu2(O2CMe)2] (2). However, a
close comparison of two analogues revealed a non-planarity of 1D chains and their orthogonal disposition in the crystal structure of
1 versus parallel alignment of planar chains in 2. Complex 1 exhibits green photoluminescence at ca. 560 nm upon UV-radiation
(kex = 350 nm) in the solid state.
ꢀ 2007 Elsevier B.V. All rights reserved.
Keywords: Copper(I) 2,6-bis(trifluoromethyl)benzoate; Single crystal structure analysis; X-ray diffraction; Photoluminescence
1. Introduction
zag chains (Scheme 1c). The recently reported copper(I)
pivalate shows a new and unique structural arrangement
of cylindrical right- and left-handed infinite chains com-
posed of copper(I) ions bridged by carboxylate groups
(Scheme 1d).
Copper(I) carboxylates have had a long-standing inter-
est due to their significant role in catalytic processes [1],
separation science [2], and medicine [3]. In spite of the
well-known synthetic routes to access various copper(I)
carboxylate complexes [4], only four compounds of the
general formula [Cu(O2CR)], R = Me [5], Ph [6], CF3 [7],
The Cuꢀ ꢀ ꢀCu distances in the abovementioned copper(I)
complexes are close to the sum of the van der Waals radii
˚
(rvdW(Cu) = 1.40 A [9]) and can be speculated to fall into
t
and Bu [8], have been structurally characterized to date.
the category of metallophilic interactions similar to those
in Au(I) compounds [10].
Interestingly, each complex exhibits a unique structural
type with specific architectural and functional features.
Thus, copper(I) acetate consists of dinuclear molecules,
which are linked through weak axial Cuꢀ ꢀ ꢀO interactions
into planar polymeric chains (Scheme 1a). In contrast, both
copper(I) benzoate and copper(I) trifluoroacetate have a
tetranuclear core structure. However, while in the former
compound copper tetramers display no intermolecular
interactions (Scheme 1b), those in the latter are further
bound through axial Cuꢀ ꢀ ꢀO contacts to form infinite zig-
It is known that copper(I)-based complexes commonly
display photoluminescence in the solid state, and therefore
they are broadly studied as potential optoelectronic mate-
rials [11]. The arrangement of copper centers and, in partic-
ular, the number of those in a close proximity is suggested
to influence the photophysical behavior of polynuclear
copper(I) systems [12]. In a view of rich luminescence prop-
erties of copper(I) carboxylates [13] and their potential
applications as optoelectronic materials, their structural
characterization should be one of the key requirements
for elucidation of the structure–property relationships. A
very limited number and unique characteristic features of
*
Corresponding author. Tel.: +1 518 442 4406; fax: +1 518 442 3462.
E-mail address: marina@albany.edu (M.A. Petrukhina).
0020-1693/$ - see front matter ꢀ 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2007.02.023

3104
Y. Sevryugina et al. / Inorganica Chimica Acta 360 (2007) 3103–3107
mull. The photoluminescence spectra were collected on a
Me
Ph
Varian Cary Eclipse spectrophotometer, in which the
PMT detector was positioned at 90ꢁ to the incident beam.
Default settings (slits widths 5 nm and integration time
0.5 s) were applied. The bulk single crystalline sample
was placed in a Varian Cary Sub-micro Fluorometer cell,
which was mounted on a standard single cell holder with
base. Elemental analysis was performed by Guelph Chem-
ical Laboratories Ltd., Canada.
Me
Ph
O
O
Cu
O
O
O
Cu
O
O
Cu
O
O
Cu
O
O
Cu
O
O
Cu
Cu
Cu
O
O
O
Me
Ph
Ph
Me
CF3
2.2. Synthesis of [Cu(O2C(2,6-CF3)2C6H3)] (1)
CF3
A mixture of [Cu4(O2CCF3)4] (0.500 g, 0.71 mmol) and
(2,6-CF3)2C6H3COOH (0.911 g, 3.53 mmol) was loaded
into a 100 mL Schlenk flask and 50 mL of anhydrous
benzene was added under anaerobic conditions. The
resulting mixture was refluxed overnight and the solvent
was then removed under vacuum to afford a very pale
blue powder. It was washed with benzene (3 · 10 mL)
and then heated at 80–90 ꢁC under reduced pressure for
two days to remove traces of unreacted acid. Yield:
0.562 g (62%). Colorless needles of 1 were obtained by
sublimation of the crude powder at 240 ꢁC for 1–3 days.
Anal. Calc.: C, 33.70; H, 0.94. Found: C, 33.72; H,
0.80%. IR (KBr, cmꢁ1): 3121(w), 1606(m), 1588(m),
1558(s), 1480(w), 1402(s), 1343(m), 1303(s), 1215(s),
1185(s), 1155(sh), 1128(s), 1076(m), 1067(m), 990(w),
850(w), 822(m), 780(w), 754(m), 697(w), 677(s). IR (nujol,
cmꢁ1): 1586(w), 1557(m), 1482(w), 1402(m), 1342(m),
1303(m), 1214(m), 1185(m), 1158(sh), 1121(m), 1074(w),
1065(w), 988(w), 853(w), 819(w), 784(w), 755(w), 697(w),
680(m). PL (250–750 nm, kex = 350 nm, solid, kmax, nm)
558.
CF3
CF3
O
O
O
O
O
Cu
O
Cu
O
Cu
O
Cu
O
Cu
O
Cu
O
O
Cu
O
Cu
O
CF3
CF3
O
O
CF3
CF3
tBu
O
tBu
O
tBu
O
tBu
O
O
O
O
Cu
Cu
Cu
Cu
O
O
O
O
O
Cu
Cu
Cu
Cu
tBu
tBu
Cu
Cu
O
tBu
tBu
O
O
O
O
O
O
O
tBu
tBu
Scheme 1. Four structural types of copper(I) carboxylates: acetate (a),
benzoate (b), trifluoroacetate (c), and pivalate (d).
2.3. Crystal structure determination of
[Cu2(O2C(2,6-CF3)2C6H3)2] (1)
1
four structurally confirmed copper(I) carboxylates
prompted us to initiate a broad study toward the synthesis
and characterization of new members of this family. Herein
we report the synthesis, photoluminescence, and the X-ray
structural characterization of copper(I) 2,6-bis(trifluoro-
methyl)benzoate (1).
The X-ray data were collected with a Bruker SMART
APEX CCD-based X-ray diffractometer system using Mo
Ka radiation (k = 0.71073 A). A colorless single crystal
˚
with dimensions 0.12 · 0.02 · 0.01 mm was mounted on
the tip of a glass fiber with silicone grease. A total of
1850 frames were collected with a scan width of 0.3ꢁ in x
and an exposure time of 30 s/frame. Data reduction was
carried out with the Bruker SAINT program [14] using a nar-
row-frame integration algorithm. The structure was solved
by direct methods and refined with the Bruker SHELXTL
(Version 6.10) software package [15]. Refinement was made
by full-matrix least-squares on F2 with anisotropic dis-
placement parameters for all non-hydrogen atoms, except
one disordered CF3-group for which disorder was modeled
over three rotational orientations. All hydrogen atoms
were included at idealized positions for structure factor cal-
culations. Absorption correction was performed using the
empirical method (SADABS) [16]. The crystallographic
parameters and details of data collection and refinement
are given in Table 1.
2. Experimental
2.1. General
All synthetic procedures were carried out under a dry
atmosphere of dinitrogen using standard Schlenk and
glove-box techniques. Copper(I) trifluoroacetate was syn-
thesized according to the literature method [7]. 2,6-Bis(tri-
fluoromethyl)benzoic acid, (2,6-CF3)2C6H3COOH, was
purchased from SynQuest Fluorochemicals and used as
received. Anhydrous benzene was obtained from Aldrich.
The infrared spectra were measured on a Nicolet Magna
550 FTIR spectrometer using a KBr pellet and a nujol

Y. Sevryugina et al. / Inorganica Chimica Acta 360 (2007) 3103–3107
3105
Table 1
Crystallographic data for [Cu2(O2C(2,6-CF3)2C6H3)2]1 (1)
X
Empirical formula
Formula weight
T (K)
C18H6Cu2F12O4
641.31
173(2)
monoclinic
P21/n
14.941(2)
13.833(2)
15.009(2)
94.558(3)
3092.3(9)
6
0.71073
2.066
2.196
O
Cu
O
O
Cu
O
X = (2,6-CF3)2C6H3 (1)
CH3 (2)
Crystal system
Space group
˚
a (A)
˚
b (A)
˚
c (A)
X
b (ꢁ)
3
˚
V (A )
Scheme 2. A building block of copper(I) 2,6-bis(trifluoromethyl)benzoate
(1) and acetate (2).
Z
˚
k (A)
Dcalc (g cmꢁ3
)
l (mmꢁ1
)
Transmission factors
Unique data
0.7785–0.9784
5440
Observed data [I>2r(I)]
Parameters refined
Quality-of-fita on F2
2776
496
0.977
c
R1b, wR2 [I > 2r(I)]
0.0729, 0.1592
0.1564, 0.2051
1.169, ꢁ1.163
1=2
c
R1b, wR2 (all ꢁd3ata)
˚
Dqmax,min (e A
)
P
2
a
Quality-of-fit ¼ ½ ½wðF 2o ꢁ F c2Þ ꢂ=ðNobs ꢁ NparamsÞꢂ
.
P
P
b
c
R1 ¼ kF oj ꢁ jF ck= jF oj.
P
P
2
2 1=2
wR2 ¼ ½ ½wðF 2o ꢁ F c2Þ ꢂ= ½wðF 2oÞ ꢂꢂ
.
3. Results and discussion
The synthesis of copper(I) 2,6-bis(trifluoromethyl)ben-
zoate, [Cu(O2C(2,6-CF3)2C6H3)], is based on a ligand
exchange reaction between copper(I) trifluoroacetate and
2,6-bis(trifluoromethyl)benzoic acid. A similar procedure
using copper(I) n-butyrate was first reported in 1973 by
Edwards and Richards [4a]. The crude light blue solid pro-
duced in quantitative yield contains traces of unreacted
acid, which are removed by multiple benzene washings fol-
lowed by mild heating under reduced pressure. Pure crys-
talline product in the form of colorless, very thin needles
is easily accessible by the gas-phase sublimation-deposition
procedures in the 220–260 ꢁC range in a tube sealed under
vacuum. Single crystals subjected to X-ray structural deter-
mination were obtained in one day at 260 ꢁC. Crystals of 1
are slightly moisture sensitive. They are readily soluble in
coordinating solvents, such as tetrahydrofuran and aceto-
nitrile, while being only sparingly soluble in toluene,
dichloromethane, and hexane.
Fig. 1. ORTEP diagram of 1 at the 45% probability level.
Cu-atoms and two O2C-bridges is nearly planar with the
O–Cu–O angles averaged to 169.7(3)ꢁ.
The dinuclear units of 1 held together by intermolecular
Cuꢀ ꢀ ꢀO contacts form one-dimensional chains running
along the crystallographic c-axis. This is similar to the
known structure of copper(I) acetate (2) [5]. A close com-
parison of the two structural analogues reveals similarity
in their Cuꢀ ꢀ ꢀCu and Cu–O distances, as well as in O–
Cu–O angles (Table 2). However, there are noticeable dis-
crepancies in intermolecular Cuꢀ ꢀ ꢀO contacts as well as in
Compound 1 crystallizes in the monoclinic space group,
P21/n (Z = 6). In contrast to copper(I) benzoate [6], the
main structural building block in 1 is a dinuclear unit in
which two copper atoms are bridged by two carboxylate
ligands (Scheme 2). As the asymmetric unit contains three
crystallographically independent Cu(I) centers, there are
two distinct Cuꢀ ꢀ ꢀCu distances of 2.556(2) and
˚
Cu–Cuꢀ ꢀ ꢀO angles. The former averaged to 2.229(6) A in
˚
1 are shorter than those in 2 (2.310(7) A).
Each copper(I) center in 1 is four-coordinate having
three oxygen atoms and one copper atom in its coordina-
tion environment (Fig. 2). However, the square planar
environment of the copper center in 1 is distorted com-
pared to that in 2. For example, the Cu–Cuꢀ ꢀ ꢀO bond
angles vary from 152.66(18)ꢁ to 155.81(17)ꢁ in 1, while
being 164.0(2)ꢁ and 163.1(2)ꢁ in copper(I) acetate (2). The
deviation from the ideal square planar geometry is also
˚
2.570(2) A. By means of two inversion centers, one at the
midpoint of Cu(3)ꢀ ꢀ ꢀCu(3A) and the other at the center
of the Cu(1)–O(1)–Cu(1A)–O(1A) tetragon, the crystallo-
graphically unique fragment translates in the crystal lattice
(Fig. 1). The eight-membered ring system formed by two

3106
Y. Sevryugina et al. / Inorganica Chimica Acta 360 (2007) 3103–3107
Table 2
direction so that the [Cu2(O2C(2,6-CF3)2C6H3)2]1 chains
are oriented perpendicularly (Fig. 4).
˚
Selected bond lengths (A) and angles (ꢁ) in copper(I) 2,6-bis(trifluorom-
ethyl)benzoate (1) and acetate (2) [5c]
Crystalline sample of 1 displays green photolumines-
cence. The emission spectrum of 1 collected at room tem-
perature upon exposure to UV-radiation (kex = 350 nm)
shows a broad peak centered at ca. 560 nm (Fig. 5). It
should be mentioned here that 2,6-bis(trifluoromethyl)ben-
R
(2,6-CF3)2C6H3 (1)
CH3 (2)
2.556(2)
Cuꢀ ꢀ ꢀCu
2.556(2)
2.570(2)
1.893(6)
1.924(6)
1.883(6)
1.923(6)
1.926(6)
1.888(6)
2.229(6)
2.244(6)
2.213(6)
168.2(3)
171.1(3)
169.8(3)
153.01(19)
152.66(18)
155.81(17)
Cu–O
1.933(6)
1.917(6)
1.888(7)
1.920(7)
zoic acid emits at 412 nm upon UV-radiation at kex
300 nm, while it shows no emission upon excitation at
ex = 350 nm. It is noteworthy that the reported value of
=
k
emission maximum of 2 is 560 nm at 300 K [13]. This
shows that structural changes imposed both in carboxylate
ligands and difference in crystal structures of 1 and 2 show
no effect on the emission properties of the copper(I)
complexes.
Cuꢀ ꢀ ꢀO
2.313(6)
2.306(7)
O–Cu–O
Cu–Cuꢀ ꢀ ꢀO
169.8(3)
171.4(3)
164.0(2)
163.1(2)
Fig. 2. A coordination environment of the Cu(1) center in (1).
Fig. 4. A fragment of the ab layer in copper(I) 2,6-bis(trifluoro-
methyl)benzoate (1) and the bc layer in copper(I) acetate (2).
seen in non-planarity of polymeric chains in 1: dicopper
units are oriented at either 0ꢁ or 139.47(9)ꢁ with respect
to each other. In contrast, in copper(I) acetate eight-mem-
bered rings assembled in infinite chains are coplanar
(Fig. 3).
In addition, the packing arrangement of the copper(I)
2,6-bis(trifluoromethyl)benzoate chains differs from that
of copper(I) acetate. The [Cu2(O2CCH3)2] subunits of 2
stack together in polymeric chains that run parallel to each
other along the a-axis, while those of 1 disperse in the [001]
Fig. 3. View of polymeric chains in copper(I) 2,6-bis(trifluoromethyl)ben-
Fig. 5. The photoluminescence spectrum of solid copper(I) 2,6-bis(triflu-
zoate (1) and acetate (2).
oromethyl)benzoate (1).

Y. Sevryugina et al. / Inorganica Chimica Acta 360 (2007) 3103–3107
3107
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4. Conclusions
This work provides structural characterization of cop-
per(I) 2,6-bis(trifluoromethyl)benzoate, thus contributing
to scarce crystallographic data available for copper(I) carb-
oxylates. The X-ray diffraction study revealed the resem-
blance of the [Cu2(O2C(2,6-CF3)2C6H3)2]1 structure to
that of copper(I) acetate. Both structures comprise dinu-
clear copper units that form polymeric chains through
additional axial Cuꢀ ꢀ ꢀO interactions. However, the new
member of the copper(I) carboxylate family exhibits some
unique structural features such as the non-planarity of
polymeric chains and their non-parallel alignment in the
crystal lattice. This type of arrangement has not been pre-
viously seen for copper(I) carboxylates. Further studies are
aimed at adding new members of this family in order to
examine the effect of the nature of bridging carboxylate
groups on the overall structural type.
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Acknowledgements
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This work was supported by the National Science Foun-
dation Career Award, NSF-0546945, and by the Donors of
the American Chemical Society Petroleum Research Fund
(ACS PRF 42910-AC3). The authors also thank NSF-
01300985 for the provision of the CCD X-ray
diffractometer.
[6] M.G.B. Drew, D.A. Edwards, R. Richards, J. Chem. Soc., Dalton
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(b) A.L. Balch, Gold Bull. 37 (2004) 45;
(c) D.B. Leznoff, J. Lefebvre, Gold Bull. 38 (2005) 47.
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CCDC 629535 contains the supplementary crystallo-
graphic data for 1. These data can be obtained free of charge
via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or
from the Cambridge Crystallographic Data Centre, 12
Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-
336-033; or e-mail: deposit@ccdc.cam.ac.uk. Supplemen-
tary data associated with this article can be found, in the
online version, at doi:10.1016/j.ica.2007.02.023.
(c) H.V.R. Dias, H.V.K. Diyabalanage, M.G. Eldabaja, O. Elbjei-
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refinement of crystal structures, Bruker AXS, 2001.
[16] Bruker, SADABS, Program for Empirical Absorption Correction of
Area Detector Data, Bruker AXS, 2001.
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