Crystal structures and spectroscopic properties of copper(II)-bis(2-pyridylcarbonyl)amide-chlorobenzoate complexes

Article abstract of DOI:10.1016/j.poly.2007.07.019

The reaction of 2,4,6-tris(pyridyl)-1,3,5-triazine (ptz) and copper(II) salts in DMF-water (4:1) resulted in the hydrolysis of ptz, giving rise to the bis(2-pyridylcarbonyl)amide anion (ptO₂^-) and affording the complexes [Cu(ptO

Full text of DOI:10.1016/j.poly.2007.07.019

Polyhedron 26 (2007) 5009–5015
www.elsevier.com/locate/poly
Crystal structures and spectroscopic properties
of copper(II)–bis(2-pyridylcarbonyl)amide–chlorobenzoate complexes
a,
a
a
a
´
*
´
´
´
Joaquın Borras , Gloria Alzuet , Marta Gonzalez-Alvarez , Francisco Estevan ,
b
c
d
´
´
Benigno Macıas , Malva Liu-Gonzalez , Alfonso Castineiras
˜
a
` `
´
Departament de Quı´mica Inorganica, Universitat de Valencia, Vicent Andres Estelles s/n, 46100 Burjassot, Spain
´
Departamento de Quı´mica Inorga´nica, Facultad de Farmacia, Campus Unamuno, Universidad de Salamanca, 37007 Salamanca, Spain
b
c
`
SCSIE, Universitat de Valencia, Dr. Moliner 50, 46100 Burjassot, Spain
Departamento de Quı´mica Inorga´nica, Universidad de Santiago, E-15782 Santiago de Compostela, Spain
d
Received 12 June 2007; accepted 4 July 2007
Available online 14 September 2007
Abstract
The reaction of 2,4,6-tris(pyridyl)-1,3,5-triazine (ptz) and copper(II) salts in DMF–water (4:1) resulted in the hydrolysis of ptz, giving
rise to the bis(2-pyridylcarbonyl)amide anion (ptO2ꢀ) and affording the complexes [Cu(ptO2)(2-Clbenz)(H2O)] (1), [Cu(ptO2)(3-Clbenz)]
(2), and [Cu(ptO2)(4-Clbenz)(DMF)] (3). This report includes the chemical and spectroscopic characterization of all these compounds
along with the crystal structures of the Cu(II) complexes thus formed. The coordination spheres of Cu(II) in 1 and 3 are best described
as distorted square based pyramidal, while for 2 the coordination sphere is distorted square planar.
ꢀ 2007 Elsevier Ltd. All rights reserved.
Keywords: 2,4,6-Tris(pyridyl)-1,3,5-triazine; Hydrolytic derivatives; Copper complexes
1. Introduction
suggested that the coordination of ptz induces an angular
strain, thus permitting a nucleophilic attack at the carbon
atoms of the triazine ring by the solvent, which in turn
results in the hydrolysis of ptz [2,4]. Kinetic and thermody-
namic data indicate that such a reaction probably occurs
through a nucleophilic attack at the triazine ring by OHꢀ
or H2O [5]. However, a comparison of the structural and
NMR data of rhodium and ruthenium complexes with
ptz or a ptz-derivative led to the conclusion that a decrease
in electron density at the carbon atoms of the triazine ring
due to the electron-withdrawing effect (L ! M) of the
metal ion is a more important factor than angular strain
in the metal-assisted hydrolysis of ptz [6,7].
2,4,6-Tris(2-pyridyl)-1,3,5-triazine (ptz) (Scheme 1) is of
current interest due to its utility as a spacer for designing
multinuclear metal complexes. The compounds comprising
this family of 2,4,6-triaryltriazines are usually stable
against hydrolysis; indeed, their hydrolytic reaction gener-
ally requires the presence of a concentrated mineral acid
and temperatures above 150 ꢁC [1]. In their work with these
compounds, Lerner and Lippard [2,3] found that ptz
undergoes hydrolytic reaction in the presence of Cu(II) in
aqueous media. They also reported a crystal structure of
a copper(II) complex with a hydrolytic product of ptz.
On the basis of the Cu–N bond distances and angles of
the carbonyl carbon atoms within the chelate ring, it was
The hydrolytic process of ptz (Scheme 1) involves the
formation of several intermediates, namely two imino
nitrogen (ptNꢀ2 ) groups, one imino and one carbonyl
(ptNOꢀ) group each, and finally two carbonyl groups
(ptO2ꢀ). To date, there have only been reports of metal
*
Corresponding author. Tel.: +34 963544530; fax: +34 963544960.
complexes of the ptO2 ligand, usually described as bpcaꢀ
ꢀ
´
E-mail address: Joaquin.Borras@uv.es (J. Borras).
0277-5387/$ - see front matter ꢀ 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2007.07.019

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J. Borra´s et al. / Polyhedron 26 (2007) 5009–5015
tures and the spectroscopic properties of the copper com-
ꢀ
plexes with ptO2 has also been studied.
N
N
2. Experimental
ptz
2.1. Materials and physical measurements
N
Reagents and solvents were commercially available and
used without further purification.
N
Elemental analyses (C, N, H) were performed on a
Carlo Erba AAS instrument. IR spectra (KBr disks) were
taken on a Mattson satellite FT-IR in the range 4000–
400 cmꢀ1. Diffuse reflectance spectra (nujol mulls) of the
complexes were carried out on a Shimadzu UV-2101 PC
spectrophotometer. UV–Vis spectra of the complex solu-
tions were carried out on an HP 8453 spectrophotometer.
Electronic paramagnetic resonance (EPR) spectra were
taken at the Q-band frequency at room temperature with
a Bruker ELEXSYS spectrometer. Electrochemical mea-
surements were made with the aid of a Princeton Applied
Research Model 273A potentiostat/galvanostat. Cyclic vol-
tammograms were obtained for acetonitrile and DMF
solutions of the complexes with [TBA][ClO4] as the sup-
porting electrolyte under argon atmosphere. The electro-
chemical cell employed had a standard three-electrode
configuration: a platinum working electrode, a platinum
wire counter electrode, and an Ag–AgCl reference
electrode.
N
N
Cu(II)
NH
NH
ptzN2
N
H
N
N
N
N
Cu(II) + H2O
NH
O
ptzNO
N
H
N
Cu(II) + H2O
O
2.2. Synthesis of the complexes [Cu(ptO2)(2-
Clbenz)(H2O)] (1), [Cu(ptO2)(3-Clbenz)] (2), and
[Cu(ptO2)(4-Clbenz)(DMF)] (3)
O
ptzO2
N
H
Ten millilitres of an aqueous solution of
Cu(ClO4)2 Æ 6H2O (370 mg, 1 mmol) were added to 40 mL
of a yellow DMF solution containing 137 mg (1 mmol) of
chlorobenzoic acid (2-chloro, 3-chloro, or 4-chloro),
312 mg (1 mmol) of ptz and 2 ml of a methanolic solution
of KOH 2 N. A dark green solution was formed immedi-
ately; after 30 min it turned blue-green in color and over-
night it became blue. Slow evaporation of the solution
yielded blue, needle-like crystals. Yield: 57, 72, and 68%
respectively. Analytical data for 1: Anal. Calc. for
C19H14ClCuN3O5: C, 49.25; H, 3.04; N, 9.07. Found: C,
49.01; H, 3.12; N, 8.98%. Analytical data for 2: Anal. Calc.
for C19H12ClCuN3O4: C, 51.24; H, 2.71; N, 9.43. Found: C
50.98; H 2.69; N 9.28%. Analytical data for 3: Anal. Calc.
for C22H19ClCuN4O5: C, 50.97; H, 3.69; N, 10.81. Found:
C 51.07; H 3.75; N 10.98%.
N
Scheme 1.
anion, which is formed upon deprotonation of bis(2-pyr-
idylcarbonyl)amine Hbpca (see Scheme 1). Mononuclear,
dinuclear (homonuclear and heteronuclear), and trinuclear
complexes have been identified for various divalent and tri-
valent metal ions [M(II) = Cu(II), Fe(II), Mn(II), Co(II),
Ni(II), and Zn(II); M(III) = Fe(III), Rh(III)] [8–14].
Among these compounds, a ternary complex of copper(II)
with one bpcaꢀ and another derivative formed during the
hydrolysis process, namely 2-picolinamide, has been
ꢀ
described [9]. The ptO2 is obtained by means of a Canniz-
aro-type reaction of pyridine-2-carboxaldehyde and
NaNCO in the presence of a copper metal ion [15].
Recently, we have determined the crystal structures of dif-
ferenꢀt copper carboxylates and fluoride complexes with
ptO2 [16].
In this paper, we describe for the first time the crystal
structures of copper(II)–chlorobenzoate complexes with
ptO2ꢀ. The influence of the chlorine atom in positions 2,
3, and 4 of the chlorobenzoate anions on the crystal struc-
2.3. X-ray crystallography
Crystals were mounted on glass fibers and these samples
were used for data collection. Data for 1 was collected with
a Bruker X8Kappa APEXII diffractometer and for 2 and 3
with a Nonius Kappa CCD 2000 diffractometer. The data
for 1 was processed with APEX2 [17] and corrected for

J. Borra´s et al. / Polyhedron 26 (2007) 5009–5015
5011
Table 1
Crystal data and structure refinement for [Cu(ptO2)(2-Clbenz) (H2O)], [Cu(ptO2)(3-Clbenz)] and [Cu(ptO2)(4-Clbenz)(DMF)]
[Cu(ptO2)(2-Clbenz)(H2O)] (1)
19H14ClCuN3O5
463.32
100(2)
[Cu(ptO2)(3-Clbenz)] (2)
[Cu(ptO2)(4-Clbenz)(DMF)] (3)
Empirical formula
Formula weight
Temperature (K)
C
C19H12ClCuN3O4
445.31
293(2)
C22H19ClCuN4O5
518.40
293(2)
˚
Wavelength (A)
0.71073
0.71073
0.71073
Crystal system
Space group
monoclinic
P2(1)/n (No. 14)
orthorhombic
P212121
triclinic
ꢀ
P1
Unit cell dimensions
˚
a (A)
7.43560(10)
5.3540(2)
9.9360(2)
˚
b (A)
24.1903(3)
0.34180(10)
16.4790(7)
20.2130(8)
10.3590(2)
12.3830(3)
˚
c (A)
a (ꢁ)
b (ꢁ)
c (ꢁ)
90
90
90
90
99.2910
99.2770(10)
90
1835.84(4)
108.1690(9)
105.2670(10)
1126.26(4)
3
˚
Volume (A )
1783.36(12)
Z
4
4
2
DCalc (Mg/m3)
Crystal size
Absorption coefficient
F(000)
1.676
1.659
1.529
0.20 · 0.18 · 0.10
0.28 · 0.08 · 0.04
0.1 · 0.08 · 0.05
1.130 mmꢀ1
536
1.374 mmꢀ1
1.407 mmꢀ1
940
900
Limiting indices
ꢀ10 6 h 6 10, 0 6 k 6 34,
ꢀ6 6 h 6 6, ꢀ21 6 k 6 21,
ꢀ11 6 h 6 12, ꢀ13 6 k 6 11,
ꢀ16 6 l 6 15
8225/5125 [R(int) = 0.0286]
0 6 l 6 14
ꢀ25 6 l 6 26
Reflections collected/
unique
31,550/5362 [R(int) = 0.0308]
3930/3930 [R(int) = 0.0000]
Data/restraints/
parameters
5362/0/262
3930/0/248
5125/0/300
Final R indices [I > 2r(I)]
R indices (all data)
R1 = 0.0291, wR2 = 0.0692
R1 = 0.0365, wR2 = 0.0718
R1 = 0.0650, wR2 = 1636
R1 = 0.1386, wR2 = 0.2156
R1 = 0.0538, wR2 = 0.1575
R1 = 0.0882, wR2 = 0.2005
absorption using SADABS [18]. The data for 2 and 3 were
processed with collect and HKL DENZO and SCALEPACK
programs [19,20]. The structures were solved by direct
methods [21,22], which revealed the position of all non-
hydrogen atoms. These atoms were refined on F2 by a
full-matrix least-squares procedure using anisotropic dis-
placement parameters [23]. The hydrogen atoms were
located from difference syntheses or in their calculated
˚
positions (C–H, 0.93–0.97 A), and were refined using a rid-
ing model [24,25]. Atom scattering factors were taken from
the International Tables for Crystallography [26]. Crystal
and refinement data are listed in Table 1.
3. Results and discussion
3.1. Crystal structures
[Cu(ptO2)(2-Clbenz)(H2O)] (1): Fig. 1 shows an
ORTEP view of the molecule with the atomic numbering
scheme. Selected bond distances and angles are listed in
Table 2. The coordination sphere of copper(II) is best
described as a distorted square based pyramid, as can be
deduced from the s value of 0.16 [27]. The basal positions
Fig. 1. ORTEP drawing of [Cu(ptO2)(2-Clbenz)(H2O)] (1).
ꢀ
copper(II) complexes with ptO2 [8,16]. The Cu–O(2–chlo-
robenzoate) and the Cu–O water bond distances are
ꢀ
are occupied by the three nitrogen atoms from the ptO2
˚
ligand and one oxygen atom from the monodentate 2-chlo-
robenzoate anion. The apical site is occupied by the oxygen
atom from the coordinated water molecule. The Cu–N
1.9465(11) and 2.3180(11) A, respectively. The four basal
atoms are quasi coplanar, and the copper ion is displaced
˚
0.143 A below the plane. A distorted octahedron could
˚
bond distances, ranging from 1.9470(13) to 2.0140(13) A,
be considered due to fact that the Cu–O(42) distance is
˚
are very similar to those found in other previously reported
2.6890(12) A. In this case, the carboxylate acts as a

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J. Borra´s et al. / Polyhedron 26 (2007) 5009–5015
Table 2
˚
Selected bond lengths (A) and angles (ꢁ) for [Cu(ptO2)(2-Clbenz) (H2O)], [Cu(ptO2)(3-Clbenz)] and [Cu(ptO2)(4-Clbenz)(DMF)]
[Cu(ptO2)(2-Clbenz) (H2O)] (1)
[Cu(ptO2)(3-Clbenz)] (2)
[Cu(ptO2)(4-Clbenz)(DMF)] (3)
Cu(1)-O(41)
Cu(1)-N(21)
Cu(1)-N(11)
Cu(1)-N(31)
Cu(1)-O(1)
Cu(1)-O(42)
1.9465(11)
1.9470(13)
2.0115(13)
2.0140(13)
2.3180(11)
2.6890(12)
Cu(1)-N(21)
Cu(1)-O(41)
Cu(1)-N(11)
Cu(1)-N(31)
1.928(7)
1.939(6)
2.000(7)
2.002(7)
Cu(1)-O(41)
Cu(1)-N(21)
Cu(1)-N(11)
Cu(1)-N(31)
Cu(1)-O(1)
1.951(3)
1.950(3)
2.012(3)
2.018(3)
2.284(3)
O(41)-Cu(1)-N(21)
O(41)-Cu(1)-N(11)
N(21)-Cu(1)-N(11)
O(41)-Cu(1)-N(31)
N(21)-Cu(1)-N(31)
N(11)-Cu(1)-N(31)
O(41)-Cu(1)-O(1)
N(21)-Cu(1)-O(1)
N(11)-Cu(1)-O(1)
N(31)-Cu(1)-O(1)
171.50(5)
N(21)-Cu(1)-O(41)
N(21)-Cu(1)-N(11)
O(41)-Cu(1)-N(11)
N(21)-Cu(1)-N(31)
O(41)-Cu(1)-N(31)
N(11)-Cu(1)-N(31)
177.1(3)
O(41)-Cu(1)-N(21)
O(41)-Cu(1)-N(11)
N(21)-Cu(1)-N(11)
O(41)-Cu(1)-N(31)
N(21)-Cu(1)-N(31)
N(11)-Cu(1)-N(31)
O(41)-Cu(1)-O(1)
N(21)-Cu(1)-O(1)
N(11)-Cu(1)-O(1)
N(31)-Cu(1)-O(1)
164.24(13)
98.94(13)
81.89(13)
96.09(13)
81.65(14)
163.28(14)
91.09(11)
104.61(12)
92.72(12)
94.29(12)
97.93(5)
81.50(5)
97.67(5)
81.70(5)
161.86(5)
87.21(4)
101.29(5)
93.81(5)
96.15(5)
82.5(3)
99.6(3)
82.3(3)
95.5(3)
164.8(3)
Fig. 3. ORTEP drawing of [Cu(ptO2)(3-Clbenz)] (2).
In addition, the O1W forms two moderate hydrogen bonds
with the other carbonyl O22 [O1W ꢁ ꢁ ꢁ O22, 2.8838(14) and
˚
3.0218(16) A, O1W–H1A–O22 = 160.3ꢁ and O1W–H1B–
O22 = 142.3ꢁ] [28].
[Cu(ptO2)(3-Clbenz)] (2): Fig. 3 displays the structure
of the complex with the labeling scheme. Selected inter-
atomic distances and angles are listed in Table 2. The
geometry of the copper(II) ion can best be described as very
slightly distorted square planar. The distortion of the
square planar geometry is determined by the dihedral angle
between the CuN2 and CuNO planes. Thus, when the dihe-
dral angle is 0ꢁ, the geometry is planar while when the
angle is 90ꢁ, the stereochemistry is tetrahedral. In this com-
plex, the dihedral angle value is 1.91(0.23)ꢁ, which indicates
a very slightly distorted square planar configuration [29].
The coordination polyhedron is formed by a ptO2ꢀ, which
functions as a tridentate ligand through the nitrogen
atoms, and one carboxylate O atom from the 3-chloro-
Fig. 2. Crystal packing of [Cu(ptO2)(2-Clbenz)(H2O)] (1) showing the
hydrogen bonds.
bidentate ligand as is also the case in the [Cu(ptO2)(ben-
z)] Æ (H2O) complex [16].
The crystal packing is achieved by intermolecular hydro-
gen bonds (see Fig. 2). A moderate hydrogen bond is
formed between the O1W and the carbonyl O23
˚
[O1W ꢁ ꢁ ꢁ O23 = 2.9127(15) A, O1W–H1A–O23 = 137.3ꢁ].

J. Borra´s et al. / Polyhedron 26 (2007) 5009–5015
5013
benzoate ligand. The three Cu–N bond distances, which
˚
are all within the 1.928(7)–2.002(7) A range, are compara-
ble not only to those of the complex described above, but
also to those found for other copper(II)–ptO2 complexes
[8]. The distance between the other Ocarboxylate and the cop-
˚
per(II) is 2.6120(64) A, which is too large to be considered
coordinated, but a semicoordination might be possible.
Moreover, the bond distance between one of the Ocarbonyl
ꢀ
atoms of the ptO2 and the copper(II) of the contiguous
˚
molecule is 2.7189(65) A, thus tꢀhe crystal structure is a lin-
ear chain in which the ptO2 acts as bridging ligand
(Fig. 4). The influence of this semicoordination of one of
the Ocarbonyl atoms is confirmed by the differences found
in the two carbonyl bond distances [C(21)–O(22)
˚
1.207(11) and C(23)–O(23) 1.235(10) A, respectively]. In
contrast, the C@O bond lengths are similar in the two
other chlorobenzoate copper complexes, [(1.2299(18) and
˚
˚
1.2202(19) A for 1 and 1.214(5) and 1.219(5) A for 3]. This
Cu–Ocarbonyl semicoordinated bond probably helps stabi-
lize the structure.
[Cu(ptO2)(4-Clbenz)DMF] (3): An ORTEP view of the
complex with the atom numbering scheme is shown in
Fig. 5. Selected bond distances and angles are presented
in Table 2. The coordination sphere of copper(II) in this
complex can best be described as a very slightly distorted
square based pyramid, as can be deduced from the s value
of 0.016 [27]. The basal positionꢀs are occupied by the three
nitrogen atoms from the ptO2 ligand and one oxygen
atom from the monodentate 4-chlorobenzoate anion. The
apical site is occupied by the oxygen atom from the coordi-
nated DMF molecule. The Cu–N bond distances, ranging
Fig. 5. ORTEP drawing of [Cu(ptO2)(4-Clbenz)(DMF)] (3).
The individual pyrimidyl rings of the ptO2ꢀ ligand in the
three complexes are planar; indeed, the largest deviation
˚
from planarity is less than 0.0073 A.
The crystal packing, displayed in Fig. 6, shows p–p
ꢀ
stacking interactions between the ptO2 rings. No hydro-
˚
from 1.950(3) to 2.018(3) A, are very similar to those found
gen bonds were observed.
in other previously reported copper(II) complexes with
ꢀ
ptO2 [8,16]. The Cu–O(4–chlorobenzoate) and the Cu–
3.2. Spectroscopic properties
˚
O(DMF) bond distances are 1.951(3) and 2.284(3) A,
respectively. The four basal atoms are quasi coplanar, with
the copper ion displaced 0.1836 A above the plane. The
The most important feature in the IR spectra of the
three complexes is the presence of a high-intensity band
centered at 1712 cmꢀ1 [m(C@O) vibration], which indicates
that the hydrolysis of ptz has occurred [8]. Another
˚
second oxygen of the 4-chlorobenzoate anion is located
˚
at the long distance of 2.7410(38) A from copper(II). As
ꢀ
in the compound described above, if we consider this
distance to be a semicoordination, the geometry of the
copper(II) can be defined as a distorted octahedron.
remarkable aspect of the m(C@O) vibration of the ptO2
in complex 2 is the presence of a strong, sharp band at
1650 cmꢀ1 that can be attributed to a second m(C@O)
vibration. This is probably due to the semicoordination
of one of the oxygen atoms of the carbonyl group to the
copper(II) ion of a contiguous molecule, a hypothesis that
is corroborated by the differences observed in the C@O
bond distances (C(21)–O(22) and C(23)–O(23) 1.207(11)
and 1.235(10), respectively). All the spectra exhibit bands
at about 1600 and 1350 cmꢀ1 which correspond to the mas
(COOꢀ) and ms(COOꢀ) vibrations from the chlorobenzoate
group. The Dm = mas(COO)–ms(COO) = 250 cmꢀ1 indicates
that the carboxylate acts as a monodentate ligand [30], in
agreement with the crystal structures. The band that
appears at 1621 cmꢀ1 in the IR spectrum of 3 can be
assigned to the m(C@O) of the DMF. The high region of
the IR spectrum of 1 shows a strong, sharp band at
3523 cmꢀ1 due to the presence of coordinated water [31].
Fig. 4. Crystal packing of [Cu(ptO2)(3-Clbenz)] (2).

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J. Borra´s et al. / Polyhedron 26 (2007) 5009–5015
Fig. 6. Crystal packing of [Cu(ptO2)(4-Clbenz)(DMF)] (3).
The reflectance spectra of the three complexes show an
tively. These results point to a mainly copper(II) dx2ꢀy2
orbital ground state (gi > g^). The pattern of the EPR spec-
tra is in good agreement with the crystal structures.
unresolved d–d band at 633, 643, and 598 nm, respectively,
and a shoulder at about 432 nm. The latter can be attrib-
uted to a MLCT band.
The UV–Vis spectra of saturated aqueous solutions of
the three complexes show the same maxima at 634 nm,
indicating that in solution the three compounds have the
same chromophore as a result of the coordination of water
molecules and the dissociation of the carboxylate anions.
Moreover, a weak LMCT band at about 400 nm, similar
to that observed in the solid state spectra, is observed.
The spectrum of 5.3 mM acetonitrile solutions of 1 exhibits
a band at 609 nm (e = 115 Mꢀ1 cmꢀ1) and a shoulder at
ꢂ406 nm. The spectrum of 1 in DMF solution at 1.4 mM
shows a band at 631 nm (e = 150 Mꢀ1 cmꢀ1). The differ-
ences in the position of the d–d maximum among the spec-
tra in solution may be due to the different donor properties
of the solvents themselves. The spectrum of 3 in DMSO
3.4. Electrochemical behavior
The cyclic voltammogram of 1 in the electroactive
domain of acetonitrile/Bu4NClO4 is shown in Fig. 7. First,
a reduction peak around ꢀ1.0 mV (versus SCE) was
observed towards cathodic potentials; this can be attrib-
uted to the reduction of Cu(II) to Cu(I). On the reverse
scan, an anodic peak at about ꢀ0.034 mV was found.
The voltammogram is clearly irreversible, probably
20
10
solution at 3.8 mM shows
a
band at 635 nm
(e = 105 Mꢀ1 cmꢀ1). In any case, the spectra of the three
complexes are similar to those reported in a previous study,
in which acetate, formate and benzoate were used. These
findings allþconfirm that the main species in solution is
the CuptO2 cation [16].
0
-10
-20
-30
3.3. EPR spectroscopy
The Q-band spectra of polycrystalline samples of the
complexes were recorded at room temperature. Powder
samples of 1–3 were prepared from single crystals. The
EPR parameters were obtained from simulations made
with WINEPRSimphonia [32]. The Q-band EPR spectra
of the three compounds are axial, with gi = 2.244; 2.215;
2.24 and g^ = 2.061; 2.045; 2.049 for 1, 2 and 3, respec-
200
0
-200
-400
V (mV)
-600
-800
Fig. 7. Cyclic voltammogram of [Cu(ptO2)(2-Clbenz)(H2O)] (1) in
acetonitrile.

J. Borra´s et al. / Polyhedron 26 (2007) 5009–5015
5015
because after the reduction of Cu(II), the Cu(I) species thus
References
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to SCE corresponds to ꢀ0.78 mV relative to NHE. Irre-
versible cyclic voltammograms are also obtained from the
complex in DMF solution, which shows a reduction peak
at ꢀ0.654 mV relative to SCE. The negative values indicate
a strong stabilization of the copper(II) state through the
formation of the complex.
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4. Conclusions
In this paper, we present the crystal structures of three
copper(II) chlorobenzoate complexes with the hydrolysis
derivꢀative of 2,4,6-tris(2-pyridyl)-1,3,5-triazine (ptz), the
ptO2 ligand. An in-depth study of these crystal structures
has revealed several interesting differences. In the
[Cu(ptO2)(3-Clbenz)] (2) complex, the copper(II) ion is
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´
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´
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semicoordinated to a carbonyl oxygen atom of the ptO2
of another contiguous molecule with a Cu–O distance of
˚
2.719 A. In the other two complexes, the corresponding
˚
˚
distances are 3.929 A and 4.707 A for [Cu(ptO2)(2-
Clbenz)(H2O)] (1) and [Cu(ptO2)(4-Clbenz)(DMF)] (3),
respectively. These differences are influenced by the posi-
tion of the chlorine atom in the benzoate. When the chlo-
rine atom is in position 2 or 4, the donor effect of the
carboxylate oxygen atoms involved in the metal complexa-
tion is reinforced whereas a chlorine in position 3 reduces
this effect. In this last case, the electronic density on the
copper(II) is lower, which leads the metal ion in the
[Cu(ptO2)(3-Clbenz)] (2) complex to form a semicoordina-
tive bond with a contiguous ptO2ꢀ, which, in turn, gives
rise to a chain structure.
´
´
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Acknowledgements
J.B., G.A., and M.G.-A. acknowledge financial support
from the Spanish CICYT (CTQ2004-03735). B.M.
acknowledges financial support from the Junta de Castilla
´
y Leon (SA056A05). A.C. acknowledges financial support
from Spanish CICYT (CTQ2006-15329-C02/BQU). F.E.
gratefully thanks Generalitat Valenciana (Proyect GV06/
376) for financial support.
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Appendix A. Supplementary material
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CCDC 644942, 644943 and 644944 contain the supple-
mentary crystallographic data for 1, 2 and 3. These data
can be obtained free of charge via http://www.ccdc.cam.a-
c.uk/conts/retrieving.html, or from the Cambridge Crystal-
lographic Data Centre, 12 Union Road, Cambridge CB2
1EZ, UK; fax: (+44) 1223 336 033; or e-mail:
deposit@ccdc.cam.ac.uk.
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