Complexes of thiophene-2,3-dicarboxaldehyde bis(oxime) (2,3BTCOH 2) with nickel(II) and copper(II): Synthesis, characterization, crystal structure of 2,3BTCOH2. Rearrangement reaction with nickel(II) bromide

Article abstract of DOI:10.1016/j.ica.2012.05.029

Reacting with nickel(II) chloride, copper(II) chloride and bromide, thiophene-2,3-dicarboxaldehyde bis(oxime) (2,3BTCOH₂) leads to metal complexes formulated as [NiCl₂(2,3BTCOH₂)], [CuCl ₂(2,3BTCOH₂)]

Full text of DOI:10.1016/j.ica.2012.05.029

Inorganica Chimica Acta 392 (2012) 433–439
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Inorganica Chimica Acta
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Complexes of thiophene-2,3-dicarboxaldehyde bis(oxime) (2,3BTCOH2)
with nickel(II) and copper(II): Synthesis, characterization, crystal structure
of 2,3BTCOH2. Rearrangement reaction with nickel(II) bromide
Kusaï Alomar a, Vincent Gaumet b, Magali Allain c, Pascal Richomme a, Gilles Bouet a,
⇑
a Laboratoire SONAS, EA 921, Université d’Angers, IFR QUASAV 149, UFR Sciences Pharmaceutiques et Ingénierie de la Santé, 16 Boulevard Daviers, F-49045 Angers cedex 01, France
b UMR 990 Inserm, Imagerie Moléculaire et Thérapie Vectorisée, Université d’Auvergne, Faculté de Pharmacie, 28 place Henri Dunant, 63001 Clermont-Ferrand cedex 01, France
c Laboratoire de Chimie, Ingénierie Moléculaire d’Angers (MOLTECH-Anjou), UMR CNRS 6200, Université d’Angers, 2, Boulevard Lavoisier, 49045 Angers cedex 01, France
a r t i c l e i n f o
a b s t r a c t
Article history:
Reacting with nickel(II) chloride, copper(II) chloride and bromide, thiophene-2,3-dicarboxaldehyde
bis(oxime) (2,3BTCOH2) leads to metal complexes formulated as [NiCl2(2,3BTCOH2)], [CuCl2(2,3BTCOH2)]
and [CuBr(2,3BTCOH)]2 respectively. In the case of nickel(II) bromide, we have observed the rearrange-
ment of 2,3BTCOH2 into 2-acetamido-3-thiophene carboxaldoxime (ACTOH) instead of the expected
complex. The crystal structures of 2,3BTCOH2 and ACTOH have been determined by X-ray diffraction
methods and all other structures are proposed using usual spectroscopic techniques.
Ó 2012 Elsevier B.V. All rights reserved.
Received 15 December 2011
Received in revised form 24 May 2012
Accepted 31 May 2012
Available online 9 June 2012
Keywords:
Bis(oxime)
Oxime rearrangement
Metal complexes
Crystal structure
1. Introduction
rangement in the presence of metal catalysts (Fig. 1) to give the
primary amide via another pathway in which nickel(II) derivatives
The development of new ligands with less commonly used
functional groups contributes to expand our understanding of
coordination chemistry and allows the discovery of new transi-
tion-metal catalysts [1]. The chemistry of aldoxime ligands and
aldoxime containing metal complexes is impressively rich and is
far from being exhausted. In all cases, the ligand could act as neu-
tral oxime or as an oximato anion.
Mono-aldoximes with heterocycles and their metal complexes
were often described. Among them, pyridyl oximes and their metal
complexes were recently reviewed [2]. Review papers have also
pointed out some unconventional syntheses and reactivities of
oxime and/or oximato metal complexes [3,4]. In our laboratory,
various furan mono-aldoximes were described [5–8]. The dim-
ethylglyoxime, one of the simplest bis(oximes), was used to obtain
insoluble complex nickel(II) compound for gravimetric determina-
are often used as catalysts [15,16].
The isomerisation of oximes in the presence of various catalysts
has been described in the literature. In 1961, Field et al. published
an article about the isomerisation of oximes (e.g. benzaldoxime) to
give the corresponding amide in the presence of nickel(II) acetate
tetrahydrate, nickel(II) carbonate and other metal derivatives (var-
ious salts, oxides. . .). They suggest that the benzaldoxime can form
a complex ion with the catalyst, as intermediate, and in this case, of
the oxime reacts as an acid. They also found the catalytic effect to
appear with only some metals, their oxides or their salts with weak
acids while their salts deriving from strong acids (i.e. chlorides)
have no catalytic effect [17].
In 1973, Bourguignon et al. have synthesized the bis(oxime) thi-
ophene-2,3-dicarboxaldehyde and described the isomerisation of
the two oxime groups into amide groups simultaneously, in the
presence of a slight excess of sodium carbonate [18].
tion [9], even in presence of other metal like iron [10].
a-Furyl
dioxime was also used as a reagent for qualitative and quantitative
determination of nickel [11].
The oxime group can undergo a rearrangement, especially in
the presence of protons or of a Lewis acid to give the corresponding
secondary amide, and this rearrangement is known as Beckmann’s
rearrangement [12–14]. It can also undergo another type of rear-
As far as we know, there is no paper dealing with metal com-
plexes deriving from thiophene-2,3-dicarboxaldehyde bis(oxime)
(Fig. 2). In this article, we report the synthesis and the character-
ization of nickel(II) chloride and copper(II) chloride and bromide
complexes with this ligand. In addition, we have observed, that
when reacting with anhydrous nickel(II) bromide, thiophene-2,3-
dicarboxaldehyde bis(oxime) undergoes the isomerisation of the
oxime group in position 2 only to give 2-acetamido-3-thiophene
carboxaldoxime instead of the expected metal complex.
⇑
Corresponding author. Tel.: +33 2 41 22 66 00.
E-mail address: gilles.bouet@univ-angers.fr (G. Bouet).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.05.029

434
K. Alomar et al. / Inorganica Chimica Acta 392 (2012) 433–439
Table 1
R
H
H
Crystallographic data for 2,3BTCOH2 and ACTOH.
Beckmann
NH
O
N
R
Name
2,3BTCOH2
ACTOH
OH
Formula
C6H6N2O2S
170.19
monoclinic
C 2/c
C6H6N2O2S
170.19
triclinic
Pꢀ1
O
Formula weight
Crystal system
Space group
Unit cell dimensions
a (Å)
R
Metal catalyst
N
24.1796(7)
4.2236(10)
15.7219(4)
90
4.9593(3)
5.8203(5)
12.9937(7)
84.979(4)
86.753(5)
84.647(6)
371.54(4)
2
OH
R
NH2
H
b (Å)
c (Å)
Fig. 1. Rearrangement of oximes.
a
(°)
b (°)
114.109(2)
90
1465.54(7)
8
white
1.543
c
(°)
OH
N
V (Å3)
Z
Color
white
1.521
Dcalc (g cmꢀ3
)
Crystal size (mm)
0.83 ꢁ 0.13 ꢁ 0.10
0.44 ꢁ 0.12 ꢁ 0.07
l
(mmꢀ1
)
0.387
0.382
hkl limits
ꢀ34 6 h 6 34
ꢀ5 6 k 6 5
–22 6 l 6 22
1.85, 31.09
102
ꢀ6 6 h 6 6
ꢀ8 6 k 6 8
–18 6 l 6 18
3.53, 30.00
124
N
S
OH
hmin, hmax (°)
Number of variables
Fig. 2. Chemical structure of bis(oxime) thiophene-2,3-dicarboxaldehyde
(2,3BTCOH2).
R1 for I > 2
wR2 for I > 2
r
(I)
0.0765
0.2130
0.0534
0.1181
r(I)
2. Experimental
reduction were performed using SAINT [20]. Scaling and a numer-
ical absorption correction, based upon crystal size and faces index-
ing, were done using SADABS [20]. The structure was determined
by direct methods with the successful location of all non-hydrogen
atoms of the unique molecule within the asymmetric unit using
the program SHELXS [21]. The structure was refined with SHELXL
[22]. All non-hydrogen atoms were refined anisotropically.
Crystals of ACTOH obtained from low evaporation of EtOH solu-
tion are triclinic, with space group Pꢀ1. X-ray single-crystal
diffraction data were collected at 293 K on a STOE-IPDS diffractom-
2.1. Reactants
All reactants and solvents were analytical grade. Thiophene-2,3-
dicarboxaldehyde was purchased from Sigma–Aldrich (France).
Hydroxylammonium chloride (Alfa Aesar, France), nickel(II) chlo-
ride hexahydrate, anhydrous nickel(II) bromide, copper(II) chloride
dihydrate and anhydrous copper(II) bromide (Prolabo, France)
were used as received.
eter, equipped with a graphite monochromator using Mo Ka radi-
2.2. Measurements
ation (k = 0.71073 Å) at 293(2) K (MOLTECH-Anjou, UMR CNRS
6200, Université d’Angers). The structures were solved by a direct
method and refined by a full-matrix least-squares method in
anisotropic approximation for all non-hydrogen atoms with
SHELX-97 program [22].
Elemental analyses were carried out by the service central of
analyses (C.N.R.S. Vernaison, France). DSC diagrams were recorded
in the 25–400 °C range with a Mettler DSC 822e unit, with the help
of Mettler Toledo STARe SW 8.10 System software (Laboratoire de
Physique, Faculté de Pharmacie, Angers); the heating rate was
10 °C/min. All measurements were made in 40 mm3 closed Al cru-
cibles. The IR spectra were recorded with a Bruker FTIR Vector 22
spectrometer between 4400 and 400 cmꢀ1 (KBr disks). The far IR
spectra were recorded with a Bruker Vertex FTIR spectrophotome-
ter in the 650–50 cmꢀ1 range using polyethylene disks (Institut des
Matériaux Jean Rouxel, Université de Nantes (France).
2.4. Synthesis
2.4.1. Synthesis of 2,3BTCOH2
This bis(oxime) was prepared by reacting thiophene-2,3-dicar-
boxaldehyde and hydroxylamine in a 1:2 M ratio. The hydroxyl-
amine was obtained as follows: hydroxylammonium chloride
(0.93 g, 14 mmol, 10 mL, MeOH) reacted with potassium hydroxide
(0.77 g, 14 mmol, 10 mL, MeOH) for 10 min; potassium chloride
precipitated and was removed by filtration. Thiophene-2,3-dicar-
boxaldehyde (1 g, 7 mmol, 15 mL, EtOH) was added to MeOH solu-
tion of hydroxylamine, the mixture is heated up to 30 °C for 24 h.
After cooling to room temperature, the solution was concentrated
under reduced pressure and small polycrystals were obtained.
Monocrystals were produced by slow evaporation from ethanol.
The DSC pattern shows the melting point of this compound at
196 °C. NMR spectra (DMSO-D6, TMS as internal reference):
unequivalent hydroxyl protons at 11.34 (s) and 12.16 (s) ppm;
unequivalent CH@N at 8.24 (s) and 8.55 (s) ppm, thiophenic pro-
tons at 7.71 (d) and 7.34 (d) ppm.
2.3. Crystal data collection and processing
The crystal and instrumental parameters used in the unit-cell
determination and data collection are summarized in Table 1.
The compound 2,3BTCOH2 was crystallized from EtOH at room
temperature. The monocrystals are monoclinic wit C 2/c space
group. The crystal was placed and optically centered on a Bruker
KAPPA APEX II diffractometer equipped with a Mo K
a radiation
(k = 0.71073 Å) at 293(2) K. The initial unit cell was indexed using
the difference vectors method of a random set of reflections col-
lected from three series of 0.5° wide omega-scans, 20 s per frame,
and 12 frames per series that were well distributed in reciprocal
space. The crystal to detector distance was 50 mm. A total of
1064 frames were collected to hmax = 31.09° with 0.5° wide scans
and an exposure time of 10 s per frame using the APEX2 software
[19]. Unit cell refinement on all observed reflections and data
2.4.2. Reaction with NiBr2: synthesis of ACTOH
The 2-acetamido-3-thiophene carboxaldoxime was obtained by
the reaction of bis(oxime) thiophene-2,3-dicarboxaldehyde

K. Alomar et al. / Inorganica Chimica Acta 392 (2012) 433–439
435
(2,3BTCOH2) (0.43 g, 2.5 mmol, 15 mL, EtOH) with anhydrous nick-
el bromide NiBr2 (0.59 g, 2.5 mmol, 15 mL, water) under reflux for
6 h, the solution was concentrated under reduced pressure, the
product precipitates and was then filtered and recrystallized from
ethanol. Pale yellow monocrystals were obtained. In its DCS dia-
gram, this compound shows a fine exothermic crystallization peak
at 161 °C, immediately followed by an endothermic peak at 163 °C
attributable to its melting. NMR spectra (DMSO-D6, TMS as internal
reference): hydroxyl protons at 11.30 (s), NH2 (amide) 7.60 (s)
ppm; CH@N 8.51 (s) ppm, thiophenic protons at 7.91 (d) and
7.32 (d) ppm.
complexation easily occurs via a substitution reaction. In the case
of the anhydrous bromide, the nickel ion needs to change its sur-
rounding before bonding to 2,3BTCOH2. That is why the coordina-
tion is not possible at room temperature. At higher temperature,
Ni2+ could act as a catalyst [15] and the rearrangement is then
observed.
3.2. Crystal structure of 2,3BTCOH2
The main crystal parameters are reported in Table 1. The mono-
clinic unit cell (space group C 2/c) contains eight molecules. The
molecule of 2,3BTCOH2 with numbering scheme is given in
Fig. 3. The molecule is quite planar with a feeble mean deviation
to the plane. The most important deviation is observed for N1
and O1 (0.25 and 0.21 Å) respectively. In this oxime, the geometry
of functional group in position 2 is cis around the C6–N2 carbon–
nitrogen double bond while geometry is trans around the C5-N1
double bond for the oxime group in position 3.
Representative bond distances and angles for 2,3BTCOH2 are
shown in Table 2. The bond lengths C5–N1 and C6–N2 are equal
to 1.279 and 1.290 Å, respectively, and they correspond to car-
bon–nitrogen double bond [26,27].
2.4.3. Synthesis of [NiCl2(2,3BTCOH2)]
The complex [NiCl2(2,3BTCOH2)] was prepared by adding 20 mL
of 2,3BTCOH2 (0.85 g, 5 mmol, EtOH) into a solution of nickel(II)
chloride NiCl2,6H2O (1.3 g, 5 mmol, 15 mL, EtOH) in an equimolar
ratio. The mixture was maintained at room temperature and a
green precipitate appeared after 6 h. It was filtered and washed
with ethanol.
2.4.4. Synthesis of [CuCl2(2,3BTCOH2)]
The synthesis of the complex [CuCl2(2,3BTCOH2)] was achieved
by addition of 15 mL of 2,3BTCOH2 (0.85 g, 5 mmol, EtOH) to a
solution of CuCl2,2H2O (0.91 g, 5 mmol, 15 mL, EtOH). The complex
precipitated after one hour, the mixture was kept at room temper-
ature for 3 h and then the complex was filtered and washed with
ethanol.
The cohesion of the crystal is ensured by the presence of inter-
molecular hydrogen bonds (Table 4). The packing arrangement
with hydrogen bonds in the unit cell is given in Fig. 4. The stability
of a group of eight molecules is governed by intermolecular
2.4.5. Synthesis of [CuBr(2,3BTCOH)]2
This complex was obtained by adding 15 mL of a solution of
2,3BTCOH2(0.85 g, 5 mmol, EtOH) to a solution of CuBr2 (1.2 g,
5 mmol, 15 mL, EtOH), the complex precipitated after 5 h at room
temperature, the complex was obtained with the above described
procedure.
3. Results and discussion
As far as we know, the crystal structures of mono thiophene
carboxaldoxime (in 2- or 3-position) or bis(oxime) thiophene-
2,3-dicarboxaldehyde were not yet described. It is also the first re-
port of a rearrangement occurring with one oxime group only in
the case of bifunctional thiophene derivatives [18].
3.1. Rearrangement with nickel(II) bromide
Fig. 3. Crystal structure and atoms numbering for 2,3BTCOH2.
All complexes were easily obtained at room temperature. In the
case of nickel(II) bromide, were have not observed any complexa-
tion at room temperature. So, we have chosen to proceed under
ethanol refluxing condition. After removing ethanol, we have ob-
tained a solid which was not characterized as the expected com-
plex but as 2-acetamido-3-thiophene carboxaldoxime. We have
previously described the reaction of cobalt(II), nickel(II), copper(II)
halides with thiophene-3-carboxaldoxime (3TCOH) and we have
obtained a series of complexes: [CoX2(3TCOH)4] and [NiX2(3T-
COH)4] (X = Cl or Br) and [CuCl2(3TCOH)4], [CuBr2(3TCOH)2] with-
out pointing out any rearrangement [23]. A rearrangement is
observed in the case of mono-oximes in presence of nickel
chloride, but the reaction took place at 155 °C and not at room
temperature [15]. Many Ni(II) and Cu(II) chlorides complexes with
vic-dioximes are obtained at room temperature without conver-
sion of the ligand [24].
Table 2
Selected bond lengths (Å) and angles (°) for 2,3BTCOH2.
Bond lengths (Å)
Bond angles (°)
C5–N1
C6–N2
N1–O1
N2–O2
C1–S1
1.279
1.290
1.404
1.378
1.688
N1–C5–C3
N2–C6–C4
C5–N1–O1
C6–N2–O2
C1–S1–C4
120.44
129.10
111.09
112.41
92.10
Table 3
Selected bond lengths (Å) and angles (°) for ACTOH.
Bond lengths (Å)
Bond angles (°)
C5–N1
C6–O2
C6–N2
N1–O1
1.273
1.240
1.335
1.398
N1–C5–C3
O2–C6–N2
O2–C6–C4
N2–C6–C4
C5–N1–O1
119.40
122.03
120.98
116.99
111.70
The ionic radii for Clꢀ and Brꢀ are 1.81 and 1.96 Å respectively
[25] and this difference is not sufficient to explain the behavior
of nickel bromide. The hexahydrated nickel(II) chloride is an aquo
complex in which Ni2+ exhibits an octahedral geometry and the

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K. Alomar et al. / Inorganica Chimica Acta 392 (2012) 433–439
Table 4
Bond lengths (Å), angles (°) and positions of intermolecular hydrogen bonds for
2,3BTCOH2 and ACTOH.
Compound
2,3BTCOH2
Hydrogen bonds
Distance (Å)
Angle (°)
O1ꢂ ꢂ ꢂH2O
N1ꢂ ꢂ ꢂH2 O
O2ꢂ ꢂ ꢂH1O
N2ꢂ ꢂ ꢂH1O
N2ꢂ ꢂ ꢂH1O0
O1ꢂ ꢂ ꢂH1A
O2ꢂ ꢂ ꢂH2A
O2ꢂ ꢂ ꢂH2B
2.86
1.97
2.83
2.00
3.16
2.82
2.18
2.22
145.08
169.54
142.05
164.42
112.23
126.51
155.16
169.34
ACTOH
Fig. 5. Crystal structure and atoms numbering for 2-acetamido-3-thiophene
carboxaldoxime (ACTOH).
The molecule is quite planar with a feeble mean deviation to the
plane. The most important deviation are observed for N2 and O2
(0.63 and 0.43 Å) respectively. In the oxime functional group, the
geometry around the carbon–nitrogen double bond C5–N1 is a
trans geometry. There are not any intermolecular hydrogen bonds
in this molecule.
Cohesion of the crystal is ensured by the presence of intermo-
lecular hydrogen bonds whose characteristics are given in Table 4.
They are established between identical functional groups.
Each oxime group shared two hydrogen bonds (Oꢂ ꢂ ꢂH) with the
same group of a second molecule (Fig. 6a) and these two bonds are
identical. In some cases these bonds occurred through N (oxime)
atoms [29] but in our structure these atoms are too far from hydro-
gen (quite 4 Å) to create a hydrogen bond.
The acetamide group of a molecule is linked with two neigh-
boring molecules: O2ꢂ ꢂ ꢂH2A (2.18 Å) and O2ꢂ ꢂ ꢂH2B (2.22 Å). There
are slightly longer than in the case of 2-thiophene carboxamide
[29].
The packing arrangement in the unit cell is given in Fig. 6b. The
stacking shows that the molecules lie in a family of parallel planes.
These planes are associated together through O2ꢂ ꢂ ꢂH2A hydrogen
bonds along the plane.
Fig. 4. Hydrogen bonding (a) and cell packing (b) for 2,3BTCOH2.
hydrogen bonds (Table 4, Fig. 4a). The stacking of the molecules in
the crystal lattice is made of symmetrical parallel double zigzag
chains along c axis (Fig. 4b). Inside a series of molecules, the hydro-
gen bonds occur between N1 and H2O, O1 and H2O and, in the
same way, between N2 and H1O and O2 and H1O. In both cases,
the bonds through oxygen atoms are weaker than those obtained
with N atoms.
Two symmetrical chains lead to a series of identical hydrogen
bonds: N2ꢂ ꢂ ꢂH1O0 where N2 is located on a chain and H1O0 is lo-
cated on the symmetrical chain (Fig. 4b). Though this bond is weak,
it can stabilize the crystal, because it is present in each molecule in
the lattice [28].
3.4. Proposed structures
The main analytical data is given in Table 5. In all cases, the re-
sults of elemental analysis correspond to the proposed formulae.
The DSC diagrams of these complexes do not show endotherms
corresponding to their melting. In the case of [NiCl2(2,3BTCOH2)],
the exothermic peak 275 °C with a shoulder at 268° C is due to a
first crystallization of a low stable polymorph (268 °C) which leads
finally to a more stable crystalline form. In the [CuCl2(2,3BTCOH2)]
pattern, the crystallization peak is located at 182 and 153 °C for the
complex [CuBr(2,3BTCOH)]2. In all cases, the peaks corresponding
to their decomposition appeared for temperatures higher than
400 °C.
3.3. Crystal structure of ACTOH
The main crystal parameters are reported in Table 1. Some rep-
resentative bond lengths and angles are reported in Table 3. The
triclinic unit cell (space group Pꢀ1) contains two molecules. The
numbering scheme of a molecule is given in Fig. 5.
The bond lengths C6–O2 and C5–N1 are equal to 1.240 and
1.273 Å, respectively, and correspond to carbon–oxygen (acetam-
ide) [29] and carbon–nitrogen (oxime) double bonds [27].
All complexes were found to be paramagnetic. The main infra-
red bands for the organic molecules and the complexes are listed
in Table 6. In the IR spectrum of [NiCl2(2,3BTCOH2)], the band at

K. Alomar et al. / Inorganica Chimica Acta 392 (2012) 433–439
437
Fig. 6. Hydrogen bonding (a) and cell packing (b) for ACTOH.
Table 5
Analytical data.
Compound
Color
Yield (%)
Elemental analysis exp. (calc.)
C (%)
H (%)
N (%)
2,3BTCOH2
white
83
69
79
75
42.09
(42.34)
23.97
(24.04)
24.69
(23.66)
23.55
3.47
(3.55)
2.41
(2.02)
1.82
(1.99)
2.01
16.43
(16.46)
9.02
(9.34)
9.26
[NiCl2(2,3BTCOH2)]
[CuCl2(2,3BTCOH2)]
[CuBr(2,3BTCOH)]2
dark green
dark orange
dark orange
(9.20)
8.65
(23.05)
(1.61)
(8.96)
3330 cmꢀ1 confirms the presence of the hydroxyle. The bands
(Ni–N),
(Ni–Cl) are observed at 379 and 218 cmꢀ1 respectively.
These results are consistent with non ionized oxime and the
coordinating atoms are (Oxime). In addition, the (C@N)
m
m
N
m

438
K. Alomar et al. / Inorganica Chimica Acta 392 (2012) 433–439
Table 6
Infrared data (cmꢀ1).
Compound
m
(OH)
m(C@O)
m
(C@N)
m
(N–O)
m
(M–N)
m
(M–O)
m(M–X)
2,3BTCOH2
ACTOH
[NiCl2(2,3BTCOH2)]
[CuCl2(2,3BTCOH2)]
[CuBr(2,3BTCOH)]2
3124
3172
3330
3217
3225
–
1624
1607
1639
1640
1636
968
964
966
974
978
–
–
379
337
311
–
–
–
–
–
–
218
218
224
1646
–
–
–
494
OH
Ni
4. Conclusion
Cl
Cl
N
N
Thiophene-2,3-dicarboxaldehyde bis(oxime) (2,3BTCOH2) is
able to complex hydrated nickel(II) chloride, copper(II) chloride
and bromide. On the opposite side, the reaction with anhydrous
nickel(II) bromide induces its rearrangement into 2-acetamido-3-
thiophene carboxaldoxime (ACTOH); only the oxime functional
group in position 2 is converted. As metal complexes were ob-
tained at room temperature, they could be considered as thermo-
dynamic products of the reaction. The rearrangement of oxime
functionnal group occurs at higher temperatures (e.g. 110–
155 °C) with anhydrous nickel(II) bromide. In all complexes, the
nitrogen atoms of the two oxime groups are involved in chelation.
In addition, in the dinuclear complex [CuBr(2,3BTCOH)]2, one of
the hydroxyle is ionized and bound to copper(II) while the second
remains unchanged.
S
S
OH
OH
Cl
Cl
N
N
Cu
OH
OH
Cu
Appendix A. Supplementary material
Br
N
N
O
CCDC 857506 and 857507 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at http://
dx.doi.org/10.1016/j.ica.2012.05.029.
N
S
S
Cu
O
Br
N
HO
Fig. 7. Proposed structures for nickel(II) and copper(II) complexes.
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vibration band at 1624 cmꢀ1 (ligand) was shifted up to 1639 cmꢀ1
(complex). As it has been already observed in similar compounds
this complex is quite square-planar [30] (Fig 7).
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For the complex [CuCl2(2,3BTCOH2)], the presence of the
hydroxyle is confirmed by the presence of the band
m(OH) at
3217 cmꢀ1. The bands at 337 and 218 cmꢀ1 respectively corre-
spond to Cu–N coordination bonds and Cu–Cl bond. In addition,
we have not found any bands corresponding to copper-oxygen
coordination bond. The
m
(C@N) appeared at 1640 cmꢀ1. In this
complex, the copper(II) ion shows a geometry which is an interme-
diate between tetrahedral and square planar configurations (Fig 7)
as already observed in similar complexes [31,32].
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USA (2009).
[20] Bruker-AXS, SAINT and SADABS, Bruker Analytical X-ray Systems Inc.,
Madison, Wisconsin, USA (2009).
In this binuclear species [CuBr(2,3BTCOH)]2, the band located at
3225 cmꢀ1 is due to
m
m
(OH) vibration. The bands
m
(Cu–N),
m(Cu–O),
(Cu–Br) are present at 311, 494 and 224 cmꢀ1 respectively while
the
m
(C@N) vibration band is located at 1636 cmꢀ1 (+22 cmꢀ1
regarding the ligand). Each molecule of ligand is almost planar,
each copper ion(II) shows a distorted tetrahedral geometry with
coordination bonds as follows: (i) a coordination bond with each
nitrogen atom of the oxime groups of one of the ligands, (ii) a bond
with a bromide ion and (iii) a fourth link with the oxygen atom
(oximato) of the second ligand molecule. Thus, these fourth bond
lead to a bridge between the two symmetrical parts of the complex
molecule (Fig 7). This structure has been already described for sim-
ilar molecules [33,34].
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Germany, 1997.
SHELXS97 and SHELXL97, Universität Göttingen, Göttingen,
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