Synthesis, crystal structures and spectrothermal characterization of a heptacoordinated dimeric salicylato cadmium(II) complex with 2,2″-Azobispyridine (abpy), (μ-abpy)[Cd(Hsal)2(abpy)] 2

Article abstract of DOI:10.1002/zaac.200900333

μ-2,2′-Azobispyridinebis[2,2′-azobispyridinesalicylato(O) -salicylato(O,O′) cadmium(II)], (μ-abpy)[Cd(Hsal)₂(abpy)] ₂ (I) was synthesized and characterized by IR and UV/Vis spectroscopy, thermal, analysis, and X-ray diffraction techniques. Two abpy ligands and two salicylate ligands coordinate to the Cd²⁺ ion in a monocapped trigonal-prismatic arrangement. The capping atom is the N3 atom. One of the two abpy ligands behaves as a s-frame bridging ligand and adopts a s-cis/E/s-cis conformation, whereas the other one adopts as a s-cis/E/s-trans conformation. One of the two salicylate ligands acts as a monodentate ligand, which coordinates with the carboxylate oxygen atom, whereas the other one adopts bidentate coordination through two carboxylate oxygen atoms. The hydroxy groups of salicylate ligands, which coordinate in a monodentate fashion, are disordered over two positions, with, occupancies of 0.52 for group A and 0.48 for group B. The decomposition reaction takes place in the temperature range 20-1000 °C under nitrogen. Thermal decomposition of the title complex proceeds in two stages.

Full text of DOI:10.1002/zaac.200900333

ARTICLE
DOI: 10.1002/zaac.200900333
Synthesis, Crystal Structures and Spectrothermal Characterization of a
Heptacoordinated Dimeric Salicylato Cadmium(II) Complex with 2,2'-
Azobispyridine (abpy), (µ-abpy)[Cd(Hsal)2(abpy)]2
Figen Arslan,*[a] Halis Ölmez,[b] Mustafa Odabaşoğlu,[c] and Orhan Büyükgüngör[d]
Keywords: Cadmium; Azobispyridines; Thermal analysis; Chelates; N ligands
Abstract. µ-2,2'-Azobispyridinebis[2,2'-azobispyridinesalicylato(O)- tion. One of the two salicylato ligands acts as a monodentate ligand, which
salicylato(O,O') cadmium(II)], (µ-abpy)[Cd(Hsal)2(abpy)]2 (I) was synthe- coordinates with the carboxylate oxygen atom, whereas the other one
sized and characterized by IR and UV/Vis spectroscopy, thermal analysis, adopts bidentate coordination through two carboxylate oxygen atoms. The
and X-ray diffraction techniques. Two abpy ligands and two salicylato hydroxy groups of salicylato ligands, which coordinate in a monodentate
ligands coordinate to the Cd2+ ion in a monocapped trigonal-prismatic fashion, are disordered over two positions, with occupancies of 0.52 for
arrangement. The capping atom is the N3 atom. One of the two abpy group A and 0.48 for group B. The decomposition reaction takes place in
ligands behaves as a “s-frame” bridging ligand and adopts a s-cis/E/s-cis the temperature range 20–1000 °C under nitrogen. Thermal decomposition
conformation, whereas the other one adopts as a s-cis/E/s-trans conforma- of the title complex proceeds in two stages.
rived from the 2,2'-bipyridine ligand is now known to form a
1 Introduction
variety of complexes [5–7]. In this paper we report the synthe-
Salicylic acid (H2sal) is a diprotic acid, which forms hydro-
sis, spectral, thermal, and structural characterization of a hep-
gen salicylate (Hsal–) and salicylate (sal2–) ions in aqueous so-
tacoordinate Cd2+ complex of salicylate with abpy, (µ-
lutions. The (Hsal–) anion is able to coordinate to metal ions
abpy)[Cd(Hsal)2(abpy)]2.
in unidentate carboxylate, bidentate chelating and in bidentate
bridging carboxylate fashion. The bisdeprotonated anion (sal2–)
invariably acts as chelating ligand through the hydroxy oxygen
atom and one of the carboxylate oxygen atoms [1–3]. The abpy
ligand has several different coordination modes involving five-
membered chelate ring formation (N=N–C–N–M). When one
2-pyridyl ring remains uncoordinated due to the repulsion ef-
fects between azo nitrogen atom lone pairs and ortho-CH or
pyridyl nitrogen atom lone pairs, a single chelating complex
can form as in IIa or IIb (Scheme 1). The bridging ligands
involving the azo group –N=N– as coordinating π-acceptor
function can yield dinuclear complexes with unusual electronic
and structural features [4]. In particular, abpy as formally de-
Scheme 1.
2 Results and Discussion
* Assoc. Prof. Dr. F. Arslan
Fax: +90-370-4338204
2.1 UV/Vis Spectroscopy
E-Mail: farslan@karabuk.edu.tr
[a] Department of Chemistry
Faculty of Arts and Sciences
Karabük University
The electronic spectrum of 2,2'-azobispyridine exhibits two
absorption bands. The bands at 316 nm (ε
=
37150 L·mol–1·cm–1) and 454 nm (ε = 1150 L·mol–1·cm–1) are
assigned to π→π* and n→π* transitions, respectively. The ob-
served band at 454 nm is assigned to the azo group of abpy
and determines the color of the ligand. The electronic spectrum
of I in DMSO solution exhibits two absorption bands at
TR78050, Karabük, Turkey
[b] Department of Chemistry
Faculty of Arts and Sciences
Ondokuz Mayıs, University
TR55139 Kurupelit, Samsun, Turkey
[c] Chemistry Technology Program
Denizli Higher Vocational School
Pamukkale University
307 nm (ε
= =
40186 L·mol–1·cm–1) and 451 nm (ε
1095 L·mol–1·cm–1). The band, which is observed in the visible
region, arises from MLCT transition. Similar MLCT charge-
transfer bands were observed in various abpy complexes [8,
9]. As expected, d–d transitions are not observed.
TR20159 Kınıklı-Denizli, Turkey
[d] Department of Physics
Faculty of Arts and Sciences
Ondokuz Mayıs, University
TR55139 Kurupelit, Samsun, Turkey
Z. Anorg. Allg. Chem. 2010, 636, 1641–1644
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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F. Arslan, H. Ölmez, M. Odabaşoğlu, O. Büyükgüngör
ARTICLE
2.2 IR Spectroscopy
N5–N6. The dihedral angles between the least-squares planes
are: 41.30° between N1–O1–N6–N5 (plane1) and O4–O5–N1–
O2 (plane2); 55.67° between N5–N6–O4–O5 (plane 3) and
plane 1; 89.73° between planes 2 and 3. The dihedral angle
between two triangular planes N3–N6–O4 and N1–N5–O5 is
only 14.35°. Two salicylates coordinate to the Cd2+ ion; one
of the salicylato ligands acts as monodentate ligand coordinat-
ing with its carboxylate oxygen atom whereas the other one
acts as bidentate donor through its carboxylate oxygen atoms.
The hydroxy groups of salicylato ligands, which act as monod-
entate ligands, are disordered over two positions, with occu-
pancies of 0.52 for group A and 0.48 for group B (Figure 2).
The shortest Cd–O interaction is found between the Cd2+ and
the oxygen atom O1 of the monodentate salicylate
(2.232(2) Å). The bond lengths of Cd1–O4 and Cd1–O5 inter-
actions in bidentate salicylate amount 2.418(3) Å and
2.426(2) Å, respectively. This shows that the chelating salicyl-
ate is bonding in a significantly symmetric manner. The
amount of the angle O4–Cd1–O5 of 53.37(8)° is as expected
for a four-membered metal carboxylate ring. The amount of
the angle O5–C8–O4 of 121.0(3)° is also in the expected range
for a chelating carboxylate system. The formation of the mono-
chelating complex of abpy ligand opens structural alternatives
IIa and IIb for the remaining uncoordinated pyridyl ring. In
this complex, one of the abpy ligands acts as Cd2+(1)–Cd2+(2)
bridging ligand (µ-abpy) that adopts an s-cis/E/s-cis conforma-
tion, whereas the other abpy ligand adopts an s-cis/E/s-trans
(IIb) conformation coordinate to Cd2+ ion in trans position.
The most important characteristic vibrational modes of I are
observed at 3056 cm–1, 3014 cm–1, 1627 cm–1, 1589 cm–1,
1039 cm–1, 935 cm–1, and 863 cm–1. These bands are assigned
to aromatic ν(C–H), ν(C=O), ν(C=C), δ(C–H) and out of plane
bending. ν(Zn–N) and ν(Zn–O) vibrations appeared in the IR
spectra at 538 cm–1 and 460 cm–1, respectively.
2.3 Thermal Analysis
Thermal analysis curves (TG and DTA) of I are shown in
Figure 1. Thermal decomposition of I proceeds in two stages.
According to the DTA curve, the complex is thermally stable
up to 156 °C and it begins to decompose with melting at
185 °C. The first stage is related to the partial decomposition
of the neutral abpy ligand, and the release of CO2 from the
salicylato ligand in temperature range of 194–227 °C (exp.
8.44 %). The exothermic contribution is likely due to the re-
lease of CO2 [10]. The early reported data on thermal analysis
and mass spectrometric studies indicate that the salicylate–
metal complexes decompose with the release of CO2 [11–13].
In the second stage, abpy and salicylate decompose in several
consecutive steps in the temperature range 227–765 °C to give
metallic cadmium (exp. 82.88; calcd. 83.04).
Figure 1. TG and DTA curves of I.
2.4 X-ray Crystallography
A view of I is shown in Figure 2 together with the atom-
labeling scheme. The crystallographic data are summarized in
Table 1. The structure unit of I consists of a dinuclear neutral
molecule. The crystallographic analysis reveals that the di-
meric complex consists of two abpy ligands and two salicylato
ligands, which coordinate to each Cd2+ ion in trans position.
The arrangement around the Cd2+ ion is distorted monocapped
trigonal prismatic and selected bond lengths and angles are
Figure 2. The molecular structure of I, showing the atom-numbering
scheme. The hydroxy groups of salicylato ligands, which acts as mon-
odantate, is disordered over two position, with occupancies of 0.52 for
group A and 0.48 for group B. Displacement ellipsoids are drawn at
the 30 % probability level and hydrogen atoms are shown as small
spheres of arbitrary radii. [Symmetry code: (i) –1–x, 1–y, 1–z].
X-ray analysis data for (µ-abpy)[CdCl2(abpy)]2·0.86H2O [7],
given in Table 2. The atoms O1, N1, N5, and N6 form the [(abpy)CuCl2H2O]·H2O
[14],
(abpy)Mo(CO)4
[15],
equatorial plane of the monocapped trigonal prism, whereas (abpy)Re(CO)3Cl [16], [(abpy)Ru](PF6)2 [17] demonstrates
the atoms O4 and O5 are placed in the pseudo-axial positions that abpy coordinates like in IIb. The Cd1–Cd1i [symmetry
and the atom N3 occupies the axial position. The central Cd2+ code: (i) –1–x, 1–y, 1–z] distance amounts 6.062(2) Å, which
atom is located 0.391 Å below the least-squares plane O1–N1– is greater than that of the related dinuclear structures [6, 7, 18]
1642
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© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2010, 1641–1644

Heptacoordinated Dimeric Salicylato Cadmium(II) Complex
Table 1. Crystallographic data for I.
an s-cis/E/s-trans conformation; C21–H21···Cg(2) ring
(Cg(2) = C2/C3/C4/C5/C6/C7) [symmetry code: (ii) 1+x, y, z]
2.7315(3) Å, C21···Cg(2) = 171.98°. In addition to these π-
ring interactions, one C–H···O interaction (Figure 3), namely
C23–H23···O2 (Table 3), is formed.
Formula
C58H44Cd2N12O12
Molecular weight
Temperature
1325.87
293(2) K
0.71073 Å
triclinic
Wavelength
Crystal system
Space group
Unit cell dimensions
¯
P1
Table 3. Hydrogen-bonding geometry for I /Å, °.
a = 9.5893(6) Å
b = 11.4169(7) Å
c = 14.8791(9) Å
α = 109.573(5)°
β = 90.053(5)°
γ = 111.237(4)°
1416.67(43) Å3
1
D–H···A
D–H
H···A
D···A
D–H···A
O3A–H3A···O2 0.817(37) 1.875(42) 2.611(5)
O3B–H3B···O1 0.817(46) 1.790(57) 2.552(7)
147.24
154.49
146.14
134.52
132.21
136.78
O6–H6A···O4 0.820(4)
C26–H26···O1i 0.930(3)
C26–H26···O4i 0.930(3)
C23–H23···O2ii 0.930(4)
1.822(3)
2.422(2)
2.473(2)
2.520(2)
2.544(5)
3.144(4)
3.174(4)
3.260(4)
Volume
Z
Calculated density
m
1.55 mg·m–3
0.827 mm–1
Symmetry codes: (i) –x+1, –y+1, –z+1; (ii) –x+1, –y, –z.
F(000)
679.0
Crystal size
q Range
Index ranges
0.2 × 0.1 × 0.3 mm
2–26
–11 ≤ h ≤ 11
–14 ≤ k ≤ 14
–18 ≤ l ≤ 18
18549
Reflections collected
Independent reflections
Reflections observed (>2s)
Absorption correction
Max. and min. Transmission
Refinement method
3113
2671
Integration
0.8046–0.8629
Full-matrix least-squares on F2
3113/0/227
Data/restrains/parameters
Goodness-of-fit on F2
Final R indices [I>2s(I)]
R indices (all data)
1.033
R1 = 0.0268, wR2 = 0.0667
R1 = 0.0303, wR2 = 0.0682
0.764 and –0.289 e·Å–3
Largest diff. peak and hole
Figure 3. The π-ring interactions in I (dashed lines), with 10 % proba-
bility displacement ellipsoids. The hydroxy groups of salicylato li-
gands, which acts as monodantate, is disordered over two position,
with occupancies of 0.52 for group A and 0.48 for group B.
Table 2. Selected structural parameters for I /Å, °.
N2–N3 1.236(4)
N6–N6i 1.230(3)
N1–Cd1 2.404(2)
N3–Cd1 2.549(2)
N5–Cd1 2.368(2)
N6–Cd1i 2.682(2)
O1–Cd1 2.232(2)
O4–Cd1 2.418(3)
O5–Cd1 2.426(2)
N5–Cd1–N6 151.11(7)
N5–Cd1–O5 84.88(7)
N6–Cd1–O4 77.61(7)
N5–Cd1–O1 141.43(7)
O4–Cd1–O5 53.37(8)
O1–Cd1–N3 80.61(7)
N1–Cd1–N3 63.41(7)
O4–Cd1–N3 164.06(8)
N5–Cd1–N6 62.38(7)
O1–Cd1–O4 84.21(8)
3 Experimental Section
3.1 Preparation of I: abpy was prepared according to the method of
Riverola et al. [19]. A solution of abpy (0.09 g, 0.5 mmol) in acetoni-
trile (20 mL), was added dropwise with stirring to a solution of
[Cd(Hsal)2(H2O)4] (0.23 g, 0.5 mmol) in ethanol (50 mL). The mix-
ture was heated under reflux for 1 h and afterwards cooled to room
temperature. After a couple of weeks, well formed brown crystals were
selected for X-ray studies (yield for I 62 %). C58H44Cd2N12O12
(1325.86): calcd. C 52.75, H 3.36, N 12.92; found C 52.54, H 3.34, N
12.68.
Symmetry codes: (i) –x, 1–y, 1–z.
and a slight twist of the m-abpy ligand as illustrated by dihe-
dral angle of 27.42(12)° between the abpy and mean plane is
found. The complex has two classical intramolecular hydrogen
3.2 Materials and Measurements: Elemental analyses were per-
formed by standard methods at TUBİTAK (The Turkish Scientific Re-
search Centre). The UV/Vis. spectrum was obtained for the DMSO
bonds, which occur between the hydroxy groups and carboxyl- solution of the complex with a Unicam UV2 spectrometer in the range
of 900–190 nm. The IR spectrum was recorded with a Jasco 430 FT/IR
spectrophotometer using KBr pellets and operating at 4000–200 cm–1.
TG8110 thermal analyzer was used to record simultaneous TG, DTG
and DTA curves under nitrogen at a heating rate of 10 °C·min–1 in
the temperature range 20–1000 °C using platinum crucibles. Highly
sintered α-Al2O3 was used as a reference.
ate oxygen atoms of salicylato ligands. Intramolecular hydro-
gen bonds occur between C26–H26 with the atoms O1 and
O2. There are two intramolecular C–H···π interactions. The
first one is formed by the atom C18 of the m-abpy ligand;
C18–H18···Cg(1) ring (Cg(1) = C9/C10/C11/C12/C13/C14)
[symmetry code: (i) –1–x, 1–y, 1–z] 2.8326(3) Å,
C18···Cg(1) = 126,69° (Table 3, Figure 2). And the other one
3.3 Crystallographic Analysis: Data collection was performed with a
is formed by the atom C21 of the abpy ligand, which adopts STOE IPDSII image plate detector using Mo-Kα radiation (λ =
Z. Anorg. Allg. Chem. 2010, 1641–1644
© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
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1643

F. Arslan, H. Ölmez, M. Odabaşoğlu, O. Büyükgüngör
ARTICLE
A. Bulut, H. Ölmez, M. Odabaşoğlu, O. Büyükgüngör, Z. Anorg.
Allg. Chem. 2006, 6321606.
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methods using SHELXS-97 [21] and anisotropic displacement parame-
ters were applied to non-hydrogen atoms in a full-matrix least-squares
refinement based on F2 using SHELXL-97 [21]. Molecular drawings
were obtained using ORTEP-III [22]. All hydrogen atoms were posi-
tioned geometrically and refined with a riding model with Uiso 1.2
times that of attached carbon atoms (1.5 times for oxygen).
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3.4 Supplementary Data: Crystallographic data for the structure in
this paper has been deposited with the Cambridge Crystallographic
Data Center as the supplementary publication no. CCDC-739451. Cop-
ies of the data can be obtained, free of charge, on application to CCDC,
12 Union Road, Cambridge CB2 1EZ, UK; Fax: +44-1223-336-033;
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Received: April 14, 2010
Published Online: May 31, 2010
1644
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Z. Anorg. Allg. Chem. 2010, 1641–1644