Spectra-structure relationship: Synthesis, characterization of copper(II) complexes with ibuprofenate, o-methoxybenzoate, p-ethoxybenzoate and single crystal X-ray structure determination of [trans-Cu(en)2(H2O)2](L)2<

Article abstract of DOI:10.1016/j.molstruc.2008.08.003

To investigate the spectra-structure relationship, three new copper(II) complex salts of composition [trans-Cu(en)₂(H₂O)₂](L₁)₂ 2H₂O(1), [trans-Cu(en)₂(H₂O)₂

Full text of DOI:10.1016/j.molstruc.2008.08.003

Journal of Molecular Structure 918 (2009) 188–193
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: www.elsevier.com/locate/molstruc
Spectra–structure relationship: Synthesis, characterization of copper(II)
complexes with ibuprofenate, o-methoxybenzoate, p-ethoxybenzoate
and single crystal X-ray structure determination of [trans-Cu(en)2(H2O)2](L)2
where en = ethylenediammine, L = o-methoxybenzoate/p-ethoxybenzoate
a
a
b,
Raj Pal Sharma a, , Simardeep Singh , Ajnesh Singh , Valeria Ferretti
*
*
a Department of Chemistry, Panjab University, Chandigarh 160014, India
b Centro di Strutturistica Diffrattometrica and Dipartimento di Chimica, University of Ferrara via L. Borsari 46, I-44100, Ferrara, Italy
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 June 2008
Received in revised form 28 July 2008
Accepted 1 August 2008
Available online 14 August 2008
To investigate the spectra–structure relationship, three new copper(II) complex salts of composition
[trans-Cu(en)2(H2O)2](L1)2 2H2O(1), [trans-Cu(en)2(H2O)2](L2)2(2) and [trans-Cu(en)2(H2O)2](L3)2 (3)
(where L1 = ibuprofenate, L2 = o-methoxybenzoate and L3 = p-ethoxybenzoate) were obtained when eth-
ylenediamine was added to ‘Cu(L)2’ (L = L1/L2/L3) in methanol–water solution. The intermediate ‘Cu(L)2’
salts were prepared by reaction of copper sulphate with sodium salt of ibuprofen, o-methoxybenzoic acid
or p-ethoxybenzoic acid, respectively, in aqueous medium in 1:2 molar ratio. The newly synthesized
complex salts have been characterized by elemental analyses, spectroscopic techniques (UV/visible
and IR), magnetic moment determinations and conductance measurements. X-ray structure determina-
tion revealed an ionic structure consisting of one [trans-Cu(en)2(H2O)2]2+, two [C8H7O3]- ions in 2 and one
[trans-Cu(en)2(H2O)2]2+, two (C9H8O3)- ions in 3. In these complex salts central metal ion copper(II) is
coordinated by four nitrogen atoms, originating from two chelating ethylenediamine ligands and two
oxygen atoms of two coordinated water molecules, showing distorted octahedral geometry around cop-
per metal ion. Both of these structurally correlated octahedral [trans-Co(en)2(H2O)2]2+ species have
shown absorption at kmax ꢀ 540 nm in the UV/visible spectrum.
Keywords:
Copper(II)
Ibuprofen
o-Methoxybenzoate
p-Ethoxybenzoate
X-ray crystallography
UV/visible spectroscopy
Ó 2008 Elsevier B.V. All rights reserved.
1. Introduction
A thematic issue on biomimetic inorganic chemistry [2] has recently
appeared in literature, which contains extensive study of copper
Copper is one of the trace elements essential to the healthy life of
many plants and animals usually occurring as the part of prosthetic
group of oxidizing enzymes (e.g. ascorbic acid oxidase, tyrosinase,
laccase, monoamine oxidase, cytochrome oxidase and galactose oxi-
dase). These oxidases, high molecular weight proteins containing
0.03–0.05% of copper, play a vital role in biological oxidation and
reduction processes [1]. Copper containing proteins/enzymes (cyto-
chrome c and superoxide dismutase) are involved in important bio-
chemical functions like reduction of oxygen and destruction of
harmful superoxide anion, and the disease associated with copper
deficiency is anaemia and copper accumulation is Wilson’s disease.
Antiseptic properties of copper(II) salts and bis-copper(II)-3,5-diiso-
propyl salicylate as a promising radiation recovery agent [1b] for
application in nuclear warfare and cancer patients are also notewor-
thy for providing impetus to the chemistry of copper(II) complexes.
complexes. Besides this, a large number of papers on copper com-
plexes continue to appear in almost all the top journals of inorganic
chemistry. Cu(hfac)2 (hfac = hexafluoroacetylacetonate) is widely
used in the synthesis of molecular magnets [3–4]. Replacement of
the native mononuclear type I copper ion in cuperedoxins with other
metals has been utilized for decades to facilitate the investigation of
this key family of metalloproteins [5]. Furthermore, inorganic chem-
istry of copper(II) is very fascinating because of a number of reasons
such as (i)copper(II) exhibitsa variety of coordination numbersfrom
4 to 8 with associated geometries, (ii) copper(II) complexes are liable
to Jahn–Teller distortion, (iii) the anionic ligand may be non-coordi-
nated or coordinated and (iv) it is one of the constituent metal ions in
most of the superconductors. In the last decade, several reports have
focused on the construction of copper(II) complexes with cyclodex-
trin derivatives [6–9] which find applications as chiral recognition
receptors.
Complexation behaviour of carboxylate ligands becomes signif-
icant as many of the non-steroidal drugs like ibuprofen sodium (A)
and diclofenac sodium (B) contain carboxylate group (as shown in
Scheme 1). Carboxylates are versatile ligands, which can exhibit a
* Corresponding authors. Tel.: +91 0172 2534433; fax: +91 0172 2545074 (R.P.
Sharma); tel.: +39 0532 455144; fax: +39 0532 240709 (V. Ferretti).
E-mail addresses: rpsharmapu@yahoo.co.in (R.P. Sharma), frt@unife.it (V.
Ferretti).
0022-2860/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.molstruc.2008.08.003

R.P. Sharma et al. / Journal of Molecular Structure 918 (2009) 188–193
189
one week, blue coloured crystalline product was obtained. The
newly synthesized complex salt was sparingly soluble in water,
soluble in methanol and dichloromethane but insoluble in acetone.
The complex salt decomposed at 348 K. Anal. Calcd. Cu(en)2(L1)2(-
H2O)2: C 57.18%, H 8.57%, N 8.89%, O 15.25%, Cu 10.08%; Found: C
56.91%, H 8.07%, N 8.03%, O 14.87%, Cu 9.04%.
Cl
NH
O
ONa
Cl
ONa
2.3.2. Synthesis of Cu(en)2(L2)2(H2O)2
O
CuSO4ꢁ5H2O (0.5 g 0.0020 mol) was dissolved in 20 ml of water.
In another beaker 0.159 g (0.0040 mol) of sodium hydroxide and
0.664 g (0.0040 mol) of o-methoxybenzoic acid were dissolved in
minimum amount (20 ml) of water. On mixing two solutions, dark
blue coloured precipitated product was obtained. The dark blue
coloured product was dissolved in water–methanol solution and
then ethylenediamine was added to the solution drop wise till col-
our of solution changed to dark blue. The solution was allowed to
evaporate slowly at room temperature, after six days, blue col-
oured crystals were obtained. The newly synthesized complex salt
was freely soluble in water and ethanol but insoluble in chloro-
form. The complex salt decomposed at 465 K. Anal. Calcd.
Cu(en)2(L2)2(H2O)2: C 46.02%; H 5.75%, N 10.73%, O 24.54%, Cu
12.17%; Found: C 45.48%, H 6.02%, N 11.01%, O 23.13%, Cu 11.03%.
Scheme 1.
varity of coordination modes [10] and it is essential to have control
over the binding of the carboxylate groups to metal ions in a spe-
cific manner. A quick and efficient characterization is possible if
the spectral behaviour (especially the UV absorption) becomes
characteristic feature for a specific coordination mode of a com-
plexing ligand. That is, a positive correlation is attainable through
spectra–structure relationship. In this regard, it is worth mention-
ing that, all the three complex salts reported in this paper showed a
maximum UV absorption (kmax) around 540 nm. A detailed struc-
tural study is essential to establish a complete relationship be-
tween the spectral properties and the specific coordination
modes of L1 to L3. Thus, in continuation of our interest in Cu(II)
complexes [11], this paper reports the synthesis and characteriza-
tion of trans-diaquabis(ethylenediamine)copper(II) with L1, L2, and
L3, where L1 = ibuprofenate, L2 = o-methoxybenzoate, L3 = p-eth-
oxybenzoate, and single crystal X-ray structures of trans-diaqua-
bis(ethylenediamine)copper(II)o-methoxybenzoate and diaqua-
bis(ethylenediamine)copper(II)p-ethoxybenzoate.
2.3.3. Synthesis of Cu(en)2(L3)2(H2O)2
Copper sulphate pentahydrate (0.5 g, 0.0020 mol) was dissolved
in 20 ml water taken in a beaker. In another beaker 0.159 g
(0.004 mol) of sodium hydroxide and 0.664 g (0.004 mol) of p-eth-
oxybenzoic acid were dissolved in minimum amount of water.
When both the solutions were mixed, light blue coloured precipi-
tated product was obtained. The product was suspended in
water–methanol solution. Ethylenediamine was added drop wise
to the solution till colour changed to dark blue. Blue coloured crys-
tals appeared after one week from the solution when it was al-
lowed to evaporate slowly at room temperature. The newly
synthesized complex salt was freely soluble in water and methanol
but insoluble in dichloromethane. The complex salt decomposed at
483 K. Anal. Calcd. Cu(en)2(L3)2(H2O)2: C 48.04%, H 6.91%, N
10.19%, O 23.29%, Cu 11.56%; Found: C, 47.09, H 6.41%, N 11.17%,
O 22.43%, Cu 11.03%.
2. Experimental
2.1. Material
Analytical grade reagents were used throughout this work with-
out any further purification.
2.2. Instruments
Carbon, Hydrogen and Nitrogen were estimated micro-analyti-
cally by automatic Perkin-Elmer 2400 CHN elemental analyzer
and copper was determined gravimetrically by standard method
[12]. FT-IR spectra were recorded as KBr pellets on Perkin-Elmer
Spectrum RXFT-IR system. UV/visible spectra were recorded in
H2O using HITACHI 330 Spectrometer. Conductance measurements
were performed on Pico Conductivity Meter (Model CNO4091201,
Lab, India) in aqueous medium at 25 °C by using double distilled
water. The specifications of apparatus used for magnetic measure-
ments were as: pole face diameter, 10.2 cm; pole gap, 4.0 cm; cur-
rent, 7.0 A; magnetic field, 6 kG.
2.4. X-ray crystallography
Good single crystals of 2 and 3 suitable for X-ray diffraction
studies were grown from aqueous solution by slow evaporation
method. X-ray diffraction data were collected on a Nonius Kappa
CCD diffractometer using graphite-monochromated MoK
a radia-
0
tion (k = 0.71069 AÅ). Intensities were corrected for Lorentz, polari-
zation and absorption effects [13]. Crystal data, data collection and
refinement parameters are summarized in Table 1 and selected
bond length and angles are reported in Table 2. The structure
was solved by direct methods with the SIR97 program [14] and re-
fined by full-matrix least squares using the SHELXL-97 program
[15]. Non-hydrogen atoms were refined anisotropically and hydro-
gen atoms isotropically; hydrogen atoms were found in the Differ-
ence Fourier map and refined isotropically. All other calculations
were performed using the programs WinGX [16] and PARST [17].
2.3. Synthesis
2.3.1. Synthesis of Cu(en)2(L1)2(H2O)2
0.5 g (0.0020 mol) of CuSO4ꢁ5H2O was dissolved in 20 ml of
water taken in a beaker. In another beaker 0.160 g (0.0040 mol)
of sodium hydroxide and 0.826 g (0.0040 mol) of Ibuprofen were
dissolved in minimum amount (20 ml) of water. When both solu-
tions were mixed, a light ocean blue coloured precipitated product
was obtained, which was filtered through fine filter paper and
washed with cold water and alcohol. The product obtained was
dried in air. The precipitated product was suspended in water–
methanol mixture and ethylenediamine was added to this solution
drop wise till colour of the solution changed to dark blue. The solu-
tion was allowed to evaporate slowly at room temperature. After
3. Results and discussion
3.1. Synthesis
The intermediate ‘Cu[L]2’ salts were obtained when copper sul-
phate pentahydrate was reacted with sodium salt of ibuprofen,
o-methoxybenzoic acid and p-ethoxybenzoic acid, respectively, in
1:2 molar ratio in aqueous medium. In all cases light blue coloured
precipitated product was obtained.

190
R.P. Sharma et al. / Journal of Molecular Structure 918 (2009) 188–193
Table 1
Crystal data, data collection and refinement parameters of complex salts 2 and 3.
Crystal data
2
3
Chemical formula
Mr
Cell setting, space group
a, b, c (Å)
(CuC4H20N4O2).2(C8H7O3)
522.05
Triclinic, P1
8.0780(2), 11.8304(3), 12.7560(3)
81.0440(12), 81.1030(12), 82.8840(9)
1183.45(5)
2
1.465
(CuC4H20N4O2).2(C9H9O3)
550.10
Monoclinic, C2/c
34.5702(7), 7.1682(2), 10.5284(2)
94.6070(11)
2600.57 (10)
4
1.405
ꢀ
a
, b,
c
(°)
V (Å3)
Z
Dx (Mg m–3
)
Crystal form, colour
Crystal size (mm)
No. of measured, independent and observed
Needle, violet
0.35 ꢄ 0.12 ꢄ 0.09
19596, 5683, 4201
Plate, blue
0.45 ꢄ 0.40 ꢄ 0.09
15369, 3120, 2427
reflections
Criterion for observed reflections
I > 2r
(I)
I > 2r(I)
Rint
0.056
0.050
hmax (°)
28.0
28.0
R[F2 > 2
r
(F2)], wR(F2), S
0.041, 0.115, 1.04
5683/435
Calculated w = 1/[
P = (Fo2 + 2Fc2)/3
0.36, ꢃ0.56
0.048, 0.135, 1.05
3120/237
Calculated w = 1/[
P = (Fo2 + 2Fc2)/3
0.28, ꢃ0.34
No. of reflections/No. of parameters
Weighting scheme
r
2(Fo2) + (0.0646P)2 + 0.1245P] where
r
2(Fo2) + (0.0583P)2 + 4.9054P] where
D
qmax, D )
qmin (e Å–3
Table 2
Selected bond lengths and angles (Å and °)
Complex salt 2
Cation
Cu1–O1
Cu1–O2
Cu1–N2
N1–Cu1–N2
N1–Cu1–N4
2.634(2)
2.709(2)
2.009(2)
84.81(9)
95.04(9)
Cu1–N4
Cu1–N3
Cu1–N1
N2–Cu1–N3
N3–Cu1–N4
2.007(2)
2.003(2)
2.004(2)
95.09(9)
85.05(9)
Fig. 1. Probable structures of copper(II) complexes: [Cu(en)2(H2O)2](L1)2 (A) or
[Cu(en)2(L)2]ꢁ2H2O (B).
Anion
O3–C5
O6–C13
C5–C6
C11–O5
C13–C14
O8–C20
O3–C5–C6
O3–C5–O3
C19–O8–C20
O6–C13–C14
1.260(3)
1.252(4)
1.504(3)
1.375(3)
1.514(3)
1.419(3)
116.7(2)
124.8(2)
118.5(2)
118.5(2)
O4–C5
1.235(3)
1.240(3)
1.386(4)
1.421(3)
1.375(3)
O7–C13
C–Cring (av.)
C5–C12
O8–C19
The elemental analyses corresponded to the composition of the
complex salts consistent with either of the two structural formulae
[Cu(en)2(H2O)2](L1)2 or [Cu(en)2(L)2]ꢁ2H2O, they may have cis or
trans conformations depending upon the position of ligands with
respect to each other (as shown in Fig. 1).
O4–C5–C6
118.5(2)
107.8(2)
125.6(2)
113.9(2)
C11–O5–C12
O6–C13–O7
O7–C13–C14
Complex salt 3
3.2. Molar conductance
Cation
Cu1–O1
Cu1–N2
N1–Cu1–N2
O1–Cu1–N1
2.553(2)
2.021(2)
84.70(10)
90.93(9)
Cu1–N1
2.016(2)
89.34(9)
Conductance measurements were carried out at 25 °C in aque-
ous medium and plots of
K
(molar conductance) versus C1/2
O1–Cu1–N2
(square root of concentration) were drawn. When the concentra-
tion was extrapolated to zero, it gave Ko = 248, 238 and 258
Sm2 molꢃ1 for Cu(en)2(H2O)2(Ibf)2, Cu(en)2(H2O)2(o-methoxyben-
zoate)2 and Cu(en)2(H2O)2(p-ethoxybenzoate)2. These values fall
in the range for 1:2 electrolytes [18], which was confirmed by sin-
gle crystal X-ray structure in the case of 2 and 3.
Anion
O2–C9
C3–C9
O4–C10
O2–C9–O3
O3–C9–C3
1.253(4)
1.512(3)
1.434(3)
124.4(2)
117.8(2)
O3–C9
C6–O4
C–Cring (av.)
O2–C3–C9
C6–O4–C10
1.253(3)
1.373(3)
1.387(4)
117.8(2)
117.3(3)
3.3. Spectroscopy
Infrared spectra of the newly synthesized complex salts 1–3
have been recorded in the region 4000–400 cmꢃ1 and tentative
assignments have been made on the basis of earlier reports in lit-
erature [19]. The bands in the region, 443–461 cmꢃ1 are assigned
O
CuSO4 þ 2NaL H!2 Cu½Lꢂ2 þ Na2SO4
ð1Þ
where L = ibuprofenate, o-methoxybenzoate, p-ethoxybenzoate.
The precipitated products were filtered, washed with water fol-
lowed by alcohol and dried ‘Cu[L]2’ salts were separately dissolved/
suspended in water–methanol solution. To these solutions ethy-
lenediamine was added drop wise with continuous stirring until
dark blue solutions resulted, which when allowed to evaporate at
room temperature, gave the dark blue micro-crystalline solid/sin-
gle crystals, in accordance with Eq. (2).
to
1624 cmꢃ1 are assigned to
assigned to s(NH2). The IR bands due to
served in the region 1528–1555 and 1381–1394 cmꢃ1. In complex
salts 2 and 3 IR bands at 1236 and 1254 cmꢃ1are assigned to
(C–
O). The IR bands in the region 3030–3160 cmꢃ1 showed the pres-
m
(Cu–N), 535–541 cmꢃ1 are assigned to
m
(Cu–O), 1606–
(C@C), and 1570–1590 cmꢃ1 are
as(OCO), s(OCO) are ob-
m
m
m
m
m
ence of unsaturation in the complex salts due to the
m(@C–H)
stretching. The bands in the region 3267–3265 cmꢃ1 are character-
istic of antisymmetric stretching vibrations of N–H bond of
CuðLÞ2 þ 2en H
!
OꢃMeOH CuðenÞ ðLÞ ðH2OÞ
ð2Þ
2
2
2
2

R.P. Sharma et al. / Journal of Molecular Structure 918 (2009) 188–193
191
Fig. 4. ORTEPIII view and atom numbering scheme for 3. Thermal ellipsoids are
drawn at the 40% probability level. Hydrogen bonds are drawn as dashed lines.
served. Normally those copper(II) compounds having ionic or weak
covalent bonds have moments at room temperature in the range
1.9–2.2 B.M. Compared to 1.72–1.82 BM for those having strong
covalent bonds [22]. The Gouy’s method has been used for the mea-
surement of magnetic susceptibilities of the complex salts at room
temperature and the values observed are 1.96, 1.92, 1.95 BM for
complex salts 1, 2 and 3, respectively. The values observed for title
complex salts corresponded to the ionic nature of the complexes.
Fig. 2. UV/visible spectra of complex salt 1, 2 and 3. (kmax = 544, 546 and 542,
respectively).
ethylenediamine molecules attached to copper metal ion. The va-
lue of
D obtained by subtracting mas(OCO) and ms(OCO), falls in
the region of 160–170 cmꢃ1 which corresponded to ionic carboxyl-
ates [19b].
4. Crystal structure
The electronic spectra of the newly synthesized complex salts
have been recorded in H2O. The solution state UV/visible absorp-
tion spectrum of Cu(en)2(H2O)2(L)2 complex salts 1–3 showed
strong absorption around 540 nm (as shown in Fig. 2) due to the
d–d transitions typical of octahedral low spin copper(II). These val-
ues of kmax observed for title complex salts are comparable [20]
with those of complex salt containing [trans-Cu(en)2(H2O)2]2+ cat-
ion. In our earlier studies of copper(II) complexes with sulphonates
and p-nitrobenzoate, the kmax values around 540 nm were ob-
served where [trans-Cu(en)2(H2O)2](anion)2 type complex salts
were formed. Therefore, the composition of complex salts corre-
sponded to probable structural formula (A) (Fig. 1). [Cu(en)2
(H2O)2](L)2. Moreover elemental analysis also corresponded to
the same structural formulae as [trans-Cu(en)2(H2O)2](L)2.
For a particular metal ion, the magnitude of the ligand field split-
ting parameter for octahedral complexes, Do, depends on the nature
of the ligand. It is to be stressed that these complexes can only be
considered as approximately octahedral because of the Jahn–Teller
distortionexpected for a d9 ion. This distortionhas been clearly dem-
onstrated for [Cu(en)2X2] complexes in the solid state [21].
4.1. Coordination geometry and bonding
The structure of the copper(II) complex salts 2 and 3 were
unambiguously established by single crystal X-ray crystallography.
Table 3
Hydrogen bonding parameters (Å, °) of 2 and 3
Hydrogen bond
D–H
D. . .A
H..A
D–H..A
Complex salt 2
N1–H2ꢁꢁꢁO6
0.93(4)
0.83(4)
0.77(4)
0.78(5)
0.74(5)
0.78(3)
0.80(4)
0.85(3)
0.84(4)
0.83(3)
3.107(3)
2.998(3)
3.004(3)
2.794(3)
2.743(3)
3.240(3)
2.957(3)
2.954(3)
2.724(3)
2.912(3)
2.30(3)
2.26(3)
2.32(3)
2.04(5)
2.05(5)
2.54(3)
2.19(4)
2.12(3)
1.94(4)
2.16(3)
146(3)
149(3)
147(3)
162(4)
155(5)
151(3)
159(4)
164(3)
153(4)
151(3)
N3–H1ꢁꢁꢁO3
N4–H19ꢁꢁꢁO6
O1–H33ꢁꢁꢁO3
O2–H32ꢁꢁꢁO6
N1–H3ꢁꢁꢁO1i
O1–H31ꢁꢁꢁO4ii
N4–H22ꢁꢁꢁO4ii
O2–H27ꢁꢁꢁO7iii
N2–H23ꢁꢁꢁO7iii
Complex salt 3
O1–H7ꢁꢁꢁO2
0.93(4)
0.91(4)
0.95(3)
0.82(4)
0.99(4)
0.90(4)
2.781(3)
3.005(3)
3.170(3)
2.770(3)
3.021(3)
3.148(3)
1.86(4)
2.14(4)
2.36(3)
1.97(4)
2.11(4)
2.35(4)
167(4)
160(3)
143(3)
166(4)
151(3)
147(3)
3.4. Magnetic measurements
N1–H2ꢁꢁꢁO3
N1–H3ꢁꢁꢁO2iv
O1–H8ꢁꢁꢁO3v
N2–H15ꢁꢁꢁO2vi
N2–H14ꢁꢁꢁO3vii
Copper in +2 oxidation state has spin only magnetic moment of
1.73 BM but due to spin orbit coupling, higher values are often ob-
Symmetry codes: (i) ꢃx ꢃ 1, 1 ꢃ y, ꢃz; (ii) ꢃx, 1 ꢃ y, ꢃz; (iii) ꢃx ꢃ 1, ꢃy, ꢃz; (iv) x,
ꢃyꢃ1, zꢃ1/2; (v) 1/2ꢃx, ꢃyꢃ3/2, ꢃz; (vi) x, y + 1, z; (vii) x, ꢃyꢃ1, z + 1/2.
Fig. 3. ORTEPIII view and atom numbering scheme for 2. Thermal ellipsoids are
drawn at the 40% probability level. Hydrogen bonds are drawn as dashed lines.
Fig. 5. Hydrogen bonding arrangement in the crystal of 2.

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R.P. Sharma et al. / Journal of Molecular Structure 918 (2009) 188–193
Fig. 6. Unit cell packing diagram for 2(a) and 3(b) (view along b axis).
In 2, the asymmetric unit contains one p-ethoxybenzoate anion
and a half of the [trans-Cu(en)2(H2O)2]2+ cation, while in 3, the cat-
ion lies on an inversion center. ORTEPIII [23] view of the complex
salts 2 and 3 are shown in Figs. 3 and 4. In both the complex cat-
ions, two chelating ethylenediamine molecules coordinated with
copper metal ion and the slightly distorted octahedral coordination
is completed by two water O atoms in axial positions (Figs. 3 and
4). The values of T parameter [24] (indicating the degree of tetrag-
onal distortion about the Cu(II) atom) in the complex salts 2 and 3
are 0.75 and 0.79 which are within the range 0.76–0.84 reported
for such complex salts [25]. A comparison of T parameter and
structural parameters of the present complex salts with those of
other related Cu(II) complexes showed a substantial agreement
for bond lengths and angles (given in Table S1 in Supplementary
material). The C–O distances in the carboxylate anions of the two
complex salts (Table 2) are very similar and are typical of delocal-
ized bonds. Hydrogen-bonding parameters are reported in Table 3.
Thus, we have shown that the electronic spectrum may be used
to (i) predict the formation of ionic [trans-Cu(en)2(H2O)2]2+and aryl
carboxylates anions in solution which may be confirmed by the so-
lid state X-ray structure determination of the single crystals (ob-
tained after evaporation of solution at room temperature) and (ii)
complex salts are anhydrous and their formation is unaffected by
the substitution on the benzene ring. Further studies are in pro-
gress to establish this spectra–structure relationship for other cop-
per(II) aryl carboxylate complex salts in the presence of
ethylenediamine ligand.
Appendix A. Supplementary data
Crystallographic data for complex salts 2 and 3 have been
deposited with the Cambridge Crystallographic Data Center as sup-
plementary publications CCDC 691637 and CCDC 691638. Copies
of the data can be obtained free of charge on application to CCDC,
12 Union Road, Cambridge CB2 1EZ, UK [fax: +44 1223 336033,
e-mail: deposit@ccdc.cam.ac.uk. Supplementary data associated
with this article can be found, in the online version, at
doi:10.1016/j.molstruc.2008.08.003.
4.2. Packing
In both crystals, the packing architecture is mainly controlled
by the formation of O–HꢁꢁꢁO hydrogen bonds, involving O–H groups
of the coordinated water molecules as donors and the oxygen
atoms of the carboxylate anions as acceptors. The structures are
made more robust by additional N–HꢁꢁꢁO interactions. The H-bond-
ing parameters are reported in Table 3. The OꢁꢁꢁO contact distances,
on average 2.80(9) and 2.789(1) Å for 2 and 3, respectively, are
longer than expected for Charge Assisted Hydrogen Bonds, that
are usually in the range 2.45–2.65 Å [26], due to the fact that the
donor atoms are involved in the formation of the additional N–
HꢁꢁꢁO bonds. Taking into consideration only the strongest interac-
tions, the hydrogen-bond pattern can be described in terms of
graph-set approach [27]. In both cases there is the formation, by
symmetry, of the same R44(12) motif (R = ring) shown in Fig. 5,
which, in turn, leads to two C22(8) chains running, in both structures,
along the b axis. The hydrogen bond links in the crystal lattice re-
sulted the separate columns formation by the cations and the anions
(Fig. 6), the only difference between the two structures being the
mutual orientation of the benzoate derivatives, i.e. the carboxylate
anions are arranged in the herringbone pattern in 2 while in 3 they
are disposed in a parallel way.
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