Preparation and characterization of the first coordination compounds of tetrazol-2-ylacetic acid

Article abstract of DOI:10.1016/j.inoche.2010.05.003

Tetrazol-2-ylacetic acid (2-TzaH) was found to react with CuCl₂, PdCl₂, and K₂PtCl₄ in water giving Cu(2-Tza)₂, PdCl₂(2-TzaH)₂·2H₂O and PtCl₂(2-TzaH)₂, correspondingly. Obtained complexes, being the first reported examples of coordination compounds derived from 2-TzaH, have been characterized by IR spectroscopy, thermal and X-ray diffraction methods. 2-TzaH was found to act as a monodentate ligand coordinated to the metal ion via N4 atom of heteroring in palladium complex and as tridentate bridging ligand coordinated via N4 atom and two oxygen atoms in copper complex. Cu(2-Tza)₂ presents 2D coordination polymer, whereas PdCl₂(2-TzaH)₂·2H₂O is molecular complex.

Full text of DOI:10.1016/j.inoche.2010.05.003

Inorganic Chemistry Communications 13 (2010) 949–951
Contents lists available at ScienceDirect
Inorganic Chemistry Communications
journal homepage: www.elsevier.com/locate/inoche
Preparation and characterization of the first coordination compounds of
tetrazol-2-ylacetic acid
Sergei V. Voitekhovich ⁎, Tatiyana V. Serebryanskaya, Pavel N. Gaponik, Ludmila S. Ivashkevich,
Alexander S. Lyakhov, Oleg A. Ivashkevich
Research Institute for Physical Chemical Problems of Belarusian State University, Leningradskaya Street 14, Minsk 220030, Belarus
a r t i c l e i n f o
a b s t r a c t
Article history:
Tetrazol-2-ylacetic acid (2-TzaH) was found to react with CuCl , PdCl , and K PtCl in water giving Cu(2-Tza)2,
PdCl (2-TzaH) ·2H O and PtCl (2-TzaH) , correspondingly. Obtained complexes, being the first reported
2 2 2 2 2
examples of coordination compounds derived from 2-TzaH, have been characterized by IR spectroscopy, thermal
and X-ray diffraction methods. 2-TzaH was found to act as a monodentate ligand coordinated to the metal ion via
N4 atom of heteroring in palladium complex and as tridentate bridging ligand coordinated via N4 atom and two
2
2
2
4
Received 11 March 2010
Accepted 14 May 2010
Available online 8 June 2010
Keywords:
Tetrazoles
Copper(II) complexes
Palladium(II) complexes
Platinum(II) complexes
oxygen atoms in copper complex. Cu(2-Tza)
is molecular complex.
2
2 2 2
presents 2D coordination polymer, whereas PdCl (2-TzaH) ·2H O
©
2010 Elsevier B.V. All rights reserved.
Recently tetrazoles have been area of interest of coordination
chemistry because of various applications of their metal derivatives
3
tetrazol-1-ylacetates, (1-Tza)SnR , R=aryl, alkyl, were found to show
good antifungal activities in vitro [17]. At the same time complexes of
isomeric tetrazol-2-ylacetic acid (2-TzaH) (Scheme 1) are not reported
till now. One should note that investigations of 2-monosubstituted
tetrazoles as ligands are rather limited [1a].
Here we report on preparation and characterization of the first
coordination compounds of 2-TzaH, namely its copper(II), palladium(II)
and platinum(II) complexes. The ligand has been synthesized by
alkylation of tetrazole with ethyl bromoacetate followed by saponifica-
tion of intermediate ethyl tetrazol-2-ylacetate [18]. Complexes Cu(2-
[1]. In particular, they can be used as components of energetic
compositions [2] and pyrotechnics [3]. Some metal tetrazolates were
shown to be suitable precursors for preparation of semiconductor
nanoparticles [4] and ultralow-density nanostructured metal foams
[5]. Metal-organic frameworks based on tetrazoles have shown
promise for applications such as gas storage and heterogeneous
catalysis [6]. Platinum complexes with tetrazole ligands are perspec-
tive as anticancer agents [7].
A great variety of tetrazoles, especially functionally substituted
ones, are investigated as ligands. In particular, high emphasis was
placed on coordination chemistry of tetrazol-1-ylacetic acid (1-TzaH)
Tza)
[21] have been prepared by reaction of 2-TzaH with CuCl
PtCl in water.
Single crystal X-ray analysis was carried out for complexes 1 and 2
2
(1) [19], PdCl
2
(2-TzaH)
2
·2H
2
O (2) [20] and PtCl
2
(2-TzaH)
2
(3)
2
, PdCl , and
2
K
2
4
(
Scheme 1). The presence of several donor centers and capacity for
deprotonation lead to diversity of coordination modes of this ligand
[22]. Used atom numbering for ligands corresponds to that in the
Scheme 1. Complex 1 presents 2D coordination polymer. Cu atom lies
on inversion centre, whereas all remaining ones are in general
positions. Copper atom is surrounded by six ligand anions, two of
them are bonded via the tetrazole ring N4 atoms whereas four
remaining ligands are connected via O atoms to form elongated
octahedral coordination (Fig. 1). Each anion links three neighboring
Cu atoms, resulting in formation of coordination polymeric layers
parallel with the ab plane. The layers are connected together by non-
classic hydrogen bonds C5–H5···N1. The crystal structure of complex
1 differs drastically from that of isomeric copper(II) tetrazol-1-
and as a consequence to manifold architectures of formed complexes.
II
To date, series of M (1-Tza)
2
complexes, where 1-Tza=tetrazol-1-
II
ylacetate, M =Mn, Zn [8], Cd, Co [8,9], Cu [9–11]; Ag(1-Tza) [9,12],
X , where Ln =La, Pr, Nd; X=H O, MeOH [13,14] have
3 2 2
been reported. Also several tetrazol-1-ylacetate complexes of Cd , Co
III
III
Ln (1-Tza)
II
II
II
and Cu with 2,2′-bipyridyl and 1,10-phenanthroline as coligands
have been characterized [15]. Moreover, 1-TzaH was found to
II
III
generate heterometallic Cu –Ln (Ln=Gd, Nd) complexes with
Cu12Ln clusters [16]. Magnetic studies of manganese(II) and copper
II) complexes revealed weak exchange interactions between the metal
ions bridged by tetrazol-1-ylacetate ligand [8–11,16]. Triorganotin
6
(
2 2
ylacetate Cu(1-Tza) . Cu(1-Tza) is also 2D coordination polymer,
however in this compound the Cu atoms are four coordinated and
ligands play the role of bridges between two metal atoms (carbonyl O
atoms do not participate in coordination) [9–11]. Complex 2 is
molecular complex (Fig. 2). Pd atoms are on inversion centers
⁎
Corresponding author. Tel.: +375 17 2095198; fax: +375 17 2264696.
E-mail addresses: azole@tut.by, azole@rambler.ru (S.V. Voitekhovich).
1387-7003/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2010.05.003

950
S.V. Voitekhovich et al. / Inorganic Chemistry Communications 13 (2010) 949–951
Scheme 1. The structural formulas of isomeric tetrazolylacetic acids.
adopting square environment from two Cl atoms and two tetrazole
ring N4 atoms. The complex is a trans-isomer. No oxygen atoms are
coordinated by metal. A system of classic hydrogen bonds of water
molecules with 2-TzaH ones connect complex molecules into 3D
network.
In complexes 1 and 2, the tetrazole ring shows N4 monodentate
coordination mode, which is favoured for 2-monosubstituted tetra-
zoles, although in few complexes bridging modes were also realized
owing to additional coordination of N1 and N3 atoms [1a].
Free ligand and its complexes have been characterized by IR
Fig. 2. Molecular complex in the crystal structure of 2, with atom numbering scheme for
the asymmetric unit (ellipsoids are drawn at 50% probability level). Bond lengths (Ǻ):
Pd1–N4 2.033(2); Pd1–Cl1 2.2875(8).
spectroscopy. FT-IR spectra were recorded on a Thermo Nicolet Avatar
60 spectrometer in the range of 4000–400 cm− . The IR spectra of
1
3
complexes were found to differ significantly from that of the ligand
−
1
[
23]. Changes observed in the region of stretching (1500–1200 cm
)
−
1
and stretching-deformation (1150–800 cm ) vibrations of the
tetrazole ring [24] point out its involvement in coordination to the
metal ions. Essential shift of the tetrazole ring ν(C–H) stretching band
from 3166 cm for the 2-TzaH to the lower frequencies in the spectra
of complexes (3144 for 1, 3135 for 2 and 3153 cm−1 for 3) can be
attributed to participation of the C–H groups in hydrogen bonding.
−1
2
-TzaH is likely to be associated in solid, which is confirmed by
−1
essential shift of carbonyl ν(C=O) stretching band (1726 cm ) to
the lower frequencies in comparison with a value typical of
−1
monomeric carboxylic acids (1760 cm ), as well as by presence of
−1
a broad band at 921 cm corresponding to the out-of-plane δ(O–H)
deformations of the dimer [25]. In the spectrum of 1, bands of
asymmetric and symmetric stretching vibrations of the carboxylate
−1
group were observed at 1619 and 1364 cm [26]. In the spectra of 2
and 3, bands of carbonyl ν(C=O) stretching vibrations were found at
1
2
751 and 1725 cm−1 respectively, attributed to neutral molecules of
-TzaH [25]. Frequency of the carbonyl band in the platinum complex
corresponds to the group involved in the hydrogen bonding. In the
spectrum of 2, ν(C=O) stretching band of 1751 cm−1 is somewhat
Fig. 3. DSC and TG curves of 2-TzaH.
−1
lower compared with that of monomeric carboxylic acids (1760 cm ),
which is in agreement with X-ray analysis, showing the presence of
weak C–H···O hydrogen bonds. Bands at 1594 and 512 cm− in the
spectrum of 2 most probably correspond to deformation vibrations and
librations of water molecules, respectively.
1
Fig. 1. Coordination polymeric layer in the crystal structure of 1. Some bond lengths
(Ǻ): Cu1–N4 2.0309(15); Cu1–O1 1.9730(12); Cu1–O2 2.3989(13).
2
Fig. 4. DSC and TG curves of Cu(2-Tza) .

S.V. Voitekhovich et al. / Inorganic Chemistry Communications 13 (2010) 949–951
951
thereafter blue crystals of 1 were formed. Yield: 0.184 g, 58%. Anal. Calc. for
In this work, we also have examined the thermal stability of 2-TzaH
and its complexes. Differential scanning calorimetry (DSC) and thermo-
gravimetric analysis (TGA) [27] showed that free ligand 2-TzaH
undergoes decomposition immediately after melting (179 °C) with
one exothermal peak at 269 °C (Fig. 3). Decomposition of copper
complex 1 proceeds in one main step with exothermal peak at 230 °C
C
6
H
6
N
8
O
4
Cu (317.7): C, 22.68; H, 1.90; N, 35.27; Cu, 20.00. Found: C, 22.55; H,
1.83; N, 35.56. Cu, 19.90. IR (cm-1): 3144 (s), 3023 (m), 2949 (w), 1832 (s),
1745 (m), 1619 (s br), 1549 (w), 1520 (w), 1470 (m), 1416 (s), 1364 (s br),
1
7
307 (s), 1204 (s), 1150 (s), 1049 (s), 1030 (s), 961 (m), 922 (s), 810 (s), 756 (w),
12 (s), 684 (s), 588 (s), 401 (m).
[
20] Solution of 2-TzaH (0.128 g, 0.001 mol) in 10 ml of water was added to a solution
of palladium(II) chloride dihydrate (0.107 g, 0.0005 mol) in 15 ml of 1%
hydrochloric acid. The resulting solution was allowed to stand for few days and
thereafter yellow crystals of 2 were formed. Yield: 0.110 g, 47%. Anal. Calc. for
(
9
Fig. 4). The TGA curve of 2 revealed that weight loss (∼8%) occurred at
0–140 °C, corresponding to the removal of two molecules of water per
6 12 8 6 2
C H N O Cl Pd (469.5): C, 15.35; H, 2.58; N, 23.86; Pd, 22.66. Found: C, 15.52; H,
2.83; N, 23.58; Pd, 22.90. IR (cm-1): 3516 (s), 3375 (m), 3135 (s), 3010 (m), 2967
(m), 1792 (m), 1751 (vs), 1594 (m), 1431 (w), 1411 (m), 1390 (w), 1345 (m),
formula unit (7.7% calculated). Further weight loss is observed at
temperature higher 180 °C and it is accompanied by two endothermal
1307 (w), 1232 (vs), 1201 (m), 1174 (m), 1136 (m), 1056 (w), 1029 (m), 901
(
209 °C, 229 °C) and one exothermal (270 °C) peaks (Fig. S1). Complex 3
(m), 815 (s), 693 (m), 647 (s), 559 (m), 512 (s br), 414 (s).
shows lower thermal stability in comparison with 2-TzaH and
complexes 1, 2. It decomposes at temperature higher 150 °C (Fig. S2).
[
21] Solution of 2-TzaH (0.128 g, 0.001 mol) and potassium tetrachloroplatinate
(0.207 g, 0.0005 mol) in 15 ml of water was stirred for 24 h at room temperature.
The precipitating light yellow solid of 3 was filtered off, washed with cold water
and recrystallized from acetonitrile solution. Yield: 0.094 g, 36%. Anal. Calc. for
Appendix A. Supplementary material
C
1
2
6 8 8 4 2
H N O Cl Pt (522.2): C, 13.80; H, 1.54; N, 21.46; Pt, 37.36. Found: C, 13.66; H,
.71; N, 21.63; Pt, 37.70; IR (cm-1): 3587 (s), 3498 (m), 3153 (s), 3019 (m),
971 (m), 1725 (vs), 1469 (vw), 1431 (w), 1383 (m), 1324 (m), 1216 (m), 1201
CCDC 768299 and 768300 contain the supplementary crystallo-
graphic data for 1 and 2. These data can be obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cam-
bridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2
(m), 1171 (w), 1140 (m), 1057 (w), 1025 (m), 970 (w), 922 (m), 814 (s), 696 (w),
643 (s), 574 (w), 415 (s).
[22] Single crystal X-ray data for 1 and 2 were obtained with a Nicolet R3m four-circle
diffractometer, using graphite-monochromated Mo Kα radiation (λ=0.71073 Å)
at room temperature. The reflection data were corrected on absorption (ψ-scans).
The crystal structures of 1 and 2 were solved by direct methods SIR2004 [28] and
1
EZ, UK; fax: (+44)1223-336-033; or e-mail: deposit@ccdc.cam.ac.
2
uk. DSC and TG curves of complexes 2 and 3 (Figs. S1 and S2) are
presented in supplementary data file associated with this article.
Supplementary data associated with this article can be found in the
online version, at doi:10.1016/j.inoche.2010.05.003.
refined on F by full matrix least squares SHELXL 97 [29]. Hydrogen atom
positions in 1 were calculated geometrically and refined using riding model, with
U
iso =1.2Ueq(C). In 2, hydrogen atoms of water molecules were located from
difference map and refined with O-H distance restraint of 0.83(2)Å and H...H
restraint of 1.38(2)Å, with iso(H)=1.5Ueq(O). Remaining atoms of
were placed in calculated positions and refined using riding model, with
Uiso(H)=1.2Ueq(C) and iso(H)=1.5Ueq(O). Crystallographic data for 1:
Cu, Mr=317.73, blue (0.52×0.28×0.10 mm), triclinic, space group
P1 , a = 4.8562(10), b = 7.1008(16), c = 8.117(2) Å, α = 109.044(18),
U
H
2
U
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(0.085 g, 0.0005 mol) in 15 ml of water was allowed to stand for few days, and