Spectroscopic, magnetic and crystal structure analysis of diammine-bis(2,6-dibromo-4-chlorophenolato-O)copper(II)

Article abstract of DOI:10.1515/znb-2005-0511

The [Cu(C₆H₂Br₂ClO)₂(NH ₃)₂] complex was synthesized and characterized by XRD, UV/vis, FTIR, DSC, elemental analysis and magnetic susceptibility measurements. The structural analysis of the title complex indicated that it is a monomeric centrosymmetric compound which crystallizes in the monoclinic system, P2 ₁/c, and has a trans-planar CuO₂N₂ coordination [Cu-O 1.940(5) and Cu-N 1.978(7) ?]. In the coordination sphere of the Cu atom, there are long range interactions with Br2 and the centrosymetrically related Br2i (i: -x, -y, -z) atoms [Cu-Br2: 3.079(2) ?], resulting in a tetragonally elongated octahedral structure for the CuO₂N ₂Br₂ coordination. The molecules form one-dimensional chains along the x-axis of the unit cell held together by intermolecular hydrogen bonds.

Full text of DOI:10.1515/znb-2005-0511

Spectroscopic, Magnetic and Crystal Structure Analysis of
Diammine-bis(2,6-dibromo-4-chlorophenolato-O)copper(II)
Gu¨lsu¨n Go¨kag˘ac¸a, Leyla Tatar Yildirimb, Muammer Sonsuza, and Fatih S¸ena
a Middle East Technical University, Department of Chemistry, 06531 Ankara, Turkey
b Hacettepe University, Department of Engineering Physics, Beytepe 06800, Ankara, Turkey
Reprint requests to Assoc. Prof. Dr. G. Go¨kag˘ac¸. E-mail: ggulsun@metu.edu.tr
Z. Naturforsch. 60b, 543 – 547 (2005); received August 11, 2004
The [Cu(C6H2Br2ClO)2(NH3)2] complex was synthesized and characterized by XRD, UV/vis,
FTIR, DSC, elemental analysis and magnetic susceptibility measurements. The structural analysis
of the title complex indicated that it is a monomeric centrosymmetric compound which crystallizes
in the monoclinic system, P21/c, and has a trans-planar CuO2N2 coordination [Cu-O 1.940(5) and
˚
Cu-N 1.978(7) A]. In the coordination sphere of the Cu atom, there are long range interactions with
˚
Br2 and the centrosymetrically related Br2i (i: −x,−y,−z) atoms [Cu-Br2: 3.079(2) A], resulting in
a tetragonally elongated octahedral structure for the CuO2N2Br2 coordination. The molecules form
one-dimensional chains along the x-axis of the unit cell held together by intermolecular hydrogen
bonds.
Key words: UV/vis, FTIR, DSC, Crystal Structure, Cu(II) Complex, Magnetic Susceptibility
Introduction
The solution with a white precipitate was cooled in an ice
bath for 20 minutes, filtered and then dried in a vacuum oven.
The structure and the purity of the product were established
by the 1H NMR spectrum [6].
Preparation of polymers from inorganic complexes
is a very interesting subject in inorganic and poly-
mer chemistry. For instance, flame-retarding poly-
mers, poly(dihalophenolates), can be prepared with
CuL2(THP)2 complexes, where L is pyridine, eth-
ylenediamine, 2,2ꢀ-dipyridyl, or ammonia, and THP
is 2,4,6-trichloro-phenolato, 2,4,6-tribromo-phenol-
ato, 4-chloro-2,6-dibromo-phenolato or 4-fluoro-2,6-
dibromo-phenolato. There are several criteria which
affect the molecular weight and the structure of the
polymers. These are the structure of the complexes and
the kind of the ligands [1 – 5]. Therefore, in this study,
the Cu(II) complex [Cu(C6H2ClBr2O)2(NH3)2] has
Preparation of the diammine-bis(2,6-dibromo-4-chloro-
phenolato-O)copper(II) complex
An aqueous solution (15 ml) of potassium 2,6-dibromo-
4-chloro-phenolate was prepared by adding an excess of
KOH (0.12 g, 3 mmol) dissolved in water (10 ml) to 2,6-
dibromo-4-chloro-phenol (0.43 g, 1.5 mmol) solution dis-
solved in water (5 ml). This solution was added dropwise
to a concentrated aqueous solution (5 ml) of CuSO4 (0.12 g,
0.75 mmol) with stirring. Initially, the formation of a dark
brown precipitate was observed. Upon addition of all 2,6-
been prepared and characterized by structural, spec- dibromo-4-chloro-phenolate solution, the dark brown pre-
cipitate turned to a light blue color. Concentrated ammonia
(13 ml, 0.695 mol) and water (60 ml) were added to this mix-
ture until the light blue precipitate dissolved to give a clear
dark blue solution. Upon leaving this solution in a dark place
for several days, dark brown crystals were formed. These
crystals were collected, washed with cold water and dried
in a vacuum overnight [2, 3].
troscopic, thermal, and elemental analysis, and mag-
netic susceptibility measurements. The polymerization
study with the title complex is currently under investi-
gation.
Experimental Section
Preparation of potassium 2,6-dibromo-4-chloro-phenolate
Structure determination
4-Chlorophenol was brominated by adding a solution con-
taining 0.1 M bromine and 0.15 M KBr in 150 ml of distilled
To determine the crystal structure of the title compound
water to another solution containing stochiometric amounts X-ray diffraction data were collected at room temperature
of the phenol in the minimum amount of ethanol very slowly. with graphite-monochromated Mo-Kα radiation on an Enraf-
c
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544
G. Go¨kag˘ac¸ et al. · Diammine-bis(2,6-dibromo-4-chlorophenolato-O)copper(II)
Table 1. Summary of crystallographic data.
Table 2. Atomic coordinates and equivalent isotropic dis-
placement parameters for non-hydrogen atoms.
Formula
Fw
Wavelength [A]
Temperature [◦C]
Crystal shape
[Cu(C6H2Br2ClO)2(NH3)2]
668.27
0.71073
25
needle
2
˚
Atom
Cu
O
x
y
z
Ueq [A ]
0.0294(4)
0.0364(15)
0.0395(18)
0.0563(4)
0.0448(3)
˚
0
0
0
0.1796(11) −0.0134(5)
−0.1102(3)
N
0.2881(14) −0.0902(6)
0.0558(5)
Crystal color
dark-brown
0.40×0.20×0.15
monoclinic
P21/n (no. 14)
4.887(3)
12.760(8)
15.243(4)
92.77(3)
949.4(9)
2
Br1
Br2
Cl
C1
C2
C3
C4
C5
C6
H1A
H1B
H1C
H3
H5
0.3415(2)
−0.2272(2)
−0.3637(8)
0.12859(9) −0.25975(7)
Crystal size [mm3]
Crystal system
Space group
−0.19807(7) −0.09304(6)
−0.1304(3)
−0.44875(18) 0.0850(11)
0.0509(17) −0.0378(7)
−0.1852(5)
−0.2643(5)
−0.3440(6)
−0.3472(6)
−0.2731(6)
−0.1952(5)
0.1123
0.033(2)
0.037(2)
0.048(3)
0.052(3)
0.044(2)
0.034(2)
0.059
˚
a [A]
0.0994(18)
−0.021(2)
−0.207(2)
0.0119(7)
−0.0134(8)
−0.0939(8)
˚
b [A]
˚
c [A]
β
−0.2723(19) −0.1471(8)
−0.1431(18) −0.1203(7)
3
˚
V [A ]
Z
0.2562
0.4509
0.2868
0.022
−0.0988
−0.06
Dcalc [g/cm3]
Absorption coefficent [mm−1
F(000)
2.338
9.856
630
0.0509
0.0292
0.059
0.059
0.057
0.053
]
−0.1523
0.0227
−0.3945
Scan method
ω/2θ
−0.402
−0.2005
−0.276
2θmax [◦]
52.6
◦
˚
Index range
0 ≤ h ≤ 6,
0 ≤ k ≤ 15,
−18 ≤ l ≤ 18
2135
1909
106
Table 3. Selected bond lengths (A) and bond angles ( ).
Cu – O
1.940(5)
3.079(2)
1.908(8)
1.315(9)
Cu – N
Br1 – C2
Cl – C4
1.978(7)
1.901(9)
1.757(9)
Cu – Br2
Br2 – C6
O – C1
No. of reflections collected
No. of reflections unique
No. of variables
Max shift/esd
Phasing method
R/Rw(%)
0.992
direct methods
0.0543/0.1305
O – Cu – N
88.8(3)
72.4(2)
123.8(5)
117.2(7)
117.9(6)
119.4(8)
O – Cu – N
91.2(3)
87.4(2)
117.3(7)
118.2(7)
119.1(8)
Br2 – Cu – O
C1 – O – Cu
C1 – C2 – Br1
Br2 – Cu – N
C3 – C2 – Br1
C5 – C6 – Br2
C5 – C4 – Cl
Nonius CAD4 diffractometer [7]. The cell parameters were C1 – C6 – Br2
determined from a least-squares refinement of 25 centred re-
C3 – C4 – Cl
flections in the range of 8.45 ≤ θ ≤ 18.84◦. Cell refinement
was carried out using CAD-4 EXPRESS. During data collec-
tion, three standard reflections were periodically measured
every 120 minutes, showing no significant intensity variation.
Data reduction was carried out using SHELXL97 [8].
The structure was solved by direct methods using the pro-
gram SHELXS97 [8] in the WinGX package [9]. ψ-Scan
absorption correction was applied (Tmin = 0.108, Tmax
=
0.228). A full-matrix least-squares refinement on F2 was
done. For all non-hydrogen atoms anisotropic displacement
parameters were refined. All hydrogen atoms were placed ge-
ometrically and a riding model was used with Uiso(H) = 1.2
Ueq(C) and Uiso(H) = 1.5 Ueq(N). Electron density syn-
Fig. 1. ORTEP [10] drawing of the title molecule with the
atom numbering scheme.
A differential scanning calorimeter, DSC, was used in or-
der to investigate the thermal behaviour of the complex. The
thermogram was taken with a heating of 1 ◦C/min under at-
mospheric conditions by a Dupont thermal analyst 2000 DSC
910S model differential scanning calorimeter. At 170.02 ◦C,
a sharp exothermic peak was observed.
thesis with coefficients Fo-Fc: A positive residual electron
3
˚
˚
density of 1.21 e/A was observed at a distance of 0.95 A
from the Cu atom and negative residual electron density of
3
˚
˚
−1.29 e/A at a distance of 1.01 A from the Br1 atom.
The data collection details, crystal data and refinement pa-
rameters are summarised in Table 1. The atomic coordinates
and isotropic displacement parameters are listed in Table 2,
selected bond lengths and angles are given in Table 3 and
the ORTEP drawing is given in Fig. 1. Displacements ellip-
soids are drawn at the 50% probability level and H atoms are
shown as small circles with arbitrary radii.
Results and Discussion
Crystal structure
We previously reported the structures of the iso-
structural complexes [Cu(C6H2Br3O)2(NH3)2] [3] and
[Cu(C6H2Cl3O)2(NH3)2] [2]. In these complexes, the
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G. Go¨kag˘ac¸ et al. · Diammine-bis(2,6-dibromo-4-chlorophenolato-O)copper(II)
545
◦
˚
Table 4. Coordination bond lengths (A) and angles ( ) for
three isostructural copper complexes.
with PLATON [11]. There is an intermolecular
N–H1B...Oii hydrogen bond with D...A and H...A
˚
distances of 2.999(9) and 2.19 A, respectively and
[Cu(C6H2-
[Cu(C6H2-
[Cu(C6H2-
a D–H...A angle of 150.8(5)◦ [symmetry code
ii: 1 − x,−y,−x]. As shown in Fig. 2, the com-
plexes form hydrogen bonded polymeric bands
of [Cu(C6H2Br2ClO)2(NH3)2] molecules which
are lined up along the [100] direction like as the
isostructural complexes [2, 3]. There is a differ-
ence in the hydrogen bonding geometry between
the title molecule and the isostructural molecules
reported previously [Cu(C6H2Br3O)2(NH3)2] [3]
and [Cu(C6H2Cl3O)2(NH3)2] [2]. These molecules
have two intermolecular hydrogen bonds, but
[Cu(C6H2Br2ClO)2(NH3)2] has only one. However,
all these molecules show a similar molecular packing
geometry. The shortest intermolecular contact less
than the sum of the van der Waals Radii was observed
Cl3O)2(NH3)2] Br3O)2(NH3)2] Br2ClO)2(NH3)2]
Cu – Br
–
3.129(1)
–
3.079(2)
–
Cu – Cl
Cu – O
Cu – N
O – Cu – N
Br – Cu – O
Br – Cu – N
Cl – Cu – O
Cl – Cu – N
2.982(1)
1.946(2)
1.984(2)
90.66(9)
–
1.943(5)
1.977(6)
89.1(2)
70.9(2)
87.1(2)
–
1.940(5)
1.978(7)
88.8(3)
72.4(2)
87.4(2)
–
–
71.20(7)
86.99(8)
–
–
ii
˚
between Cu and H1B [2.9311 ꢁ 3.52 A].
UV/vis
The UV/vis electronic spectra of the title complex
and of the ligand, 2,6-dibromo-4-chlorophenolate, and
detailed data are given in Figs 3, 4 and Table 5, re-
spectively. The complex has intense peaks at 208, 290
and 296 nm, shoulders at 222 and 318 nm, and a broad
peak at 410 nm. The ligand has intense peaks at 208,
290, 296 nm and a shoulder at 222 nm. It is well known
that π electrons of a phenol give characteristic ultravi-
olet absorption bands between 200 and 300 nm [12].
The ligand displays four absorption bands which might
originate from π → π∗ transitions. Their peak intensi-
ties are about half as large as the corresponding peaks
of the complex. The shoulder at 318 nm and a broad
peak at 410 nm for the title complex might be due to
Fig. 2. Hydrogen bonding geometry and the molecular pack-
ing.
copper atom is located at the inversion centre. The co-
ordination around the Cu atom is a tetragonally elon-
gated octahedron involving centrocymetrically related
O and N atoms from THP molecules in the equatorial
plane, and Br and Cl atoms with secondary interaction
in the axial positions, respectively. In the present study,
[Cu(C6H2Br2ClO)2(NH3)2] is reported. The coordina-
tion sphere of the Cu atom is similar to that of the
isostructural complexes (Table 3). A comparison of the
bond lengths and angles is given in Table 4 for the three
isostructural complexes. The remarkable similarity of
the three structures is obvious.
The dihedral angle between the O/Cu/N plane and
the least-squares plane defined by the six-membered
ring (C1...C6) is 80.8(2)◦ (Fig. 1). This is slightly
smaller than the corresponding values of 81.7(1)◦ and
82.6(2)◦ observed in the Cu-tribromophenolate [3]
and Cu-trichlorophenolate [2] complexes, respectively.
The O/Cu/Br2 and N/Cu/Br2 planes are almost perpen-
dicular to each other. The dihedral angle between these
two planes is 89.5(2)◦. The Br2/Cu/O/C1/C6 ring has
an envelope conformation.
Fig. 3. UV/vis spectrum of the complex in an acetonitrile
solvent. Curve 1: 3.5 × 10−4 M; curve 2: 2.02 × 10−5 M in
The hydrogen bonding and molecular pack-
ing geometry of the title molecule was calculated
[Cu(C6H2ClBr2O)2(NH3)2].
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546
G. Go¨kag˘ac¸ et al. · Diammine-bis(2,6-dibromo-4-chlorophenolato-O)copper(II)
Table 5. UV/vis data λmax[nm] (ε[l/mol−1cm−1]) of the title
complex and the ligand.
[Cu(C6H2ClBr2O)2(NH3)2]
208 (89100)
[C6H2ClBr2O]− K+
208 (44500)
222 (25150) (sh)
290 (5810)
222 (12500) (sh)
290 (2900)
296 (6050)
296 (3000)
318 (2990) (sh)
410 (980) (broad)
Fig. 5. FTIR spectrum of [Cu(C6H2ClBr2O)2(NH3)2].
the title complex was found to be 1.85 µB. The calcu-
lated spin-only magnetic moment (µ/µB) for a single
unpaired electron complexes is 1,73 µB. The differ-
ence might be due to spin-orbit coupling [15] which
was also observed for the [Cu(C6H2I3O)2(NH3)2]
complex [13].
Fig. 4. UV/vis spectrum of the ligand in an acetonitrile
solvent. Curve 1: 3.6 × 10−5 M K[C6H2ClBr2O]; curve 2:
4.14×10−4 M in K[C6H2ClBr2O].
Conclusions
The crystal structure of [Cu(C6H2Br2ClO)2(NH3)2]
has been determined by X-ray diffraction. It crystal-
lizes in the monoclinic system and shows a trans-
planar CuO2N2 coordination sphere, with the fifth and
sixth coordination sites occupied by Br atoms of the
phenoxide ions to form a tetragonally elongated octa-
hedral structure. Intermolecular hydrogen bonds hold
the complex molecules together in a one-dimensional
chain.
d-d transitions and/or ligand to metal charge transfer
transitions in the complex. The color of the complex
in an acetonitrile solution is yellow and one of the d-d
transitions is observed in the violet region of the spec-
trum as it is expected.
IR data
The complex [Cu(C6H2Br2ClO)2(NH3)2] has in-
tense UV/vis absorption peaks at 208, 290 and 296 nm,
and a shoulder at 222 nm tentitavely assigned to π →
π∗ transitions of the 2,6-dibromo-4-chloro-phenolate
ligand, and a shoulder at 318 nm and a broad peak
at 410 nm probably due to d-d transitions and/or lig-
and to metal charge transfer transitions. The magnetic
susceptibility data indicate that the title complex has a
d9 electron configuration with one unpaired electron as
expected.
The FTIR spectrum of the Cu(II) complex is given
in Fig. 5 and the characteristic bands are:
γ(N−H) and γ(C−H aromatic) = 3500 − 3000 cm−1
,
γ(aromatic rings) = 1602 cm−1, γ(C=C ring stretchings)
=
,
,
1460 − 1260 cm−1
,
γ(C−O) = 1225 cm−1
γ
(C−H bending) = 855 cm−1, γ(C−Cl) = 800−650 cm−1
γ(C−Br) = 750 − 600 cm−1 and γ(C=C bending)
=
438 cm−1 [13, 14].
Acknowledgements
Magnetic susceptibility
This work was financially supported by the Scientific Re-
search Project (Bilimsel Aras¸tırma Projesi) of Middle East
Technical University, Turkey, Grant No: BAP–2003–07–02–
00–95.
Magnetic susceptibility measurement was per-
formed at room temperature using a Sherwood mag-
netic susceptibility balance. The magnetic moment of
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G. Go¨kag˘ac¸ et al. · Diammine-bis(2,6-dibromo-4-chlorophenolato-O)copper(II)
547
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