A spectral and structural study of the new cadmium salt [(H 2L)2][Cd2I6][(NO3) 2]

Article abstract of DOI:10.5560/znb.2013-2295

The reaction between 2-(piperazin-1-yl)ethanol and cyclohexene oxide under microwave irradiation gave 2-(4-(2-hydroxyethyl)piperazin-1-yl)cyclohexanol (L). The new cadmium salt [(H₂L)₂][Cd₂I ₆][(NO₃)₂] (1) was prepared from the reaction of cadmium iodide with L and identified by elemental analysis, FT-IR and Raman spectroscopy, and single-crystal X-ray diffraction. In the crystal structure of 1, there is a [Cd₂I₆]² dianion with distorted tetrahedral geometry for each cadmium atom. The piperazine and cyclohexane rings in 1 have a chair conformation. In the crystal there are several intermolecular hydrogen bonds including N-H O, O-H O, O-H I, C-H O, and C-H I interactions.

Full text of DOI:10.5560/znb.2013-2295

A Spectral and Structural Study of the New Cadmium Salt
[(H2L)2][Cd2I6][(NO3)2]
Mohammad Hakimia, Zahra Mardania, Keyvan Moeinia, Esther Schuhb, and
Fabian Mohrb
a
Chemistry Department, Payame Noor University, 19395-4697 Tehran, I. R. Iran
Fachbereich C – Anorganische Chemie, Bergische Universita¨t Wuppertal, 42119 Wuppertal,
b
Germany
Reprint requests to Mohammad Hakimi. Fax: +98 511 8683001. E-mail: mohakimi@yahoo.com
Z. Naturforsch. 2013, 68b, 272 – 276 / DOI: 10.5560/ZNB.2013-2295
Received November 1, 2012
The reaction between 2-(piperazin-1-yl)ethanol and cyclohexene oxide under microwave ir-
radiation gave 2-(4-(2-hydroxyethyl)piperazin-1-yl)cyclohexanol (L). The new cadmium salt
[(H2L)2][Cd2I6][(NO3)2] (1) was prepared from the reaction of cadmium iodide with L and iden-
tified by elemental analysis, FT-IR and Raman spectroscopy, and single-crystal X-ray diffraction. In
the crystal structure of 1, there is a [Cd2I6]2− dianion with distorted tetrahedral geometry for each
cadmium atom. The piperazine and cyclohexane rings in 1 have a chair conformation. In the crystal
there are several intermolecular hydrogen bonds including N–H···O, O–H···O, O–H···I, C–H···O, and
C–H···I interactions.
Key words: Cadmium Complex, Iodide Bridge, Piperazine Moiety, Amino Alcohol, X-Ray Crystal
Structure
Introduction
2-Amino alcohols are characteristic structural fea-
tures of many natural products [1]. They are used in the
synthesis of biologically active natural products, phar-
maceuticals and pesticides [2 – 4]. Moreover, they play
an important role as auxiliaries to control a range of
asymmetric transformations by forming a 5-membered
chelate in the presence of a metal ion [2].
Fig. 1. Structure of 2-(4-(2-hydroxyethyl)piperazin-1-yl)-
cyclohexanol, L.
In this work, the new potentially tetradentate ligand,
2-(4-(2-hydroxyethyl)piperazin-1-yl)cyclohexanol (L,
Fig. 1) as well as the cadmium salt [(H2L)2]
[Cd2I6][(NO3)2] (1) were prepared, and their spectral
and structural properties were investigated.
an ethanolic solution of cadmium(II) iodide and neu-
tralization with HNO3 in a molar ratio of 1 : 1 gave
[(H2L)2][Cd2I6][(NO3)2], 1, which was characterized
by elemental analysis, IR and Raman spectroscopy and
single-crystal X-ray diffraction. This compound is air-
stable and soluble in ethanol, water, DMF, and DMSO.
In the IR spectrum of 1, the ν(NH) band at
Results and Discussion
The reaction of 2-(piperazin-1-yl)ethanol and cy- 3016 cm−1 appears at lower frequency than that of
clohexene oxide under microwave irradiation afforded an amine group typically of alkylammonium ions [5].
L which is a potentially tetradentate asymmetric lig- Four bands in the IR spectrum at 1381, 1280, 1072, and
and with two different types of donor centers: two ni- 910 cm−1 can be assigned to vibrations of the nitrate
trogen atoms of the piperazine ring and two oxygen groups (ν4, ν1, ν2 and ν6) [6]. The lines in the Raman
atoms of the two hydroxyl groups. Reaction of L with spectrum were observed in similar regions. The free
© 2013 Verlag der Zeitschrift fu¨r Naturforschung, Tu¨bingen · http://znaturforsch.com

M. Hakimi et al. · The Cadmium Salt [(H2L)2][Cd2I6][(NO3)2]
273
˚
Table 1. Crystal data and structure refinement for Table 2. Selected bond lengths (A) and angles (deg) for
[(H2L)2][Cd2I6][(NO3)2] (1).
[(H2L)2][Cd2I6][(NO3)2] (1) with estimated standard devi-
ations in parenthesesa.
Empirical formula
C12H26CdI3N3O5
Formula weight, g mol−1
Crystal size, mm3
Temperature, K
Crystal system
Space group
785.46
Bond lengths
Angles
Cd1-I1
Cd1-I2
Cd1-I3
Cd1-I3i
N1-H1
N1-C2
N1-C3
N1-C4
N3-O3
N3-O4
N3-O5
2.7124(5)
2.7369(6)
2.8682(6)
2.8491(6)
0.9100
1.508(7)
1.500(7)
1.500(6)
1.246(6)
1.259(6)
1.223(6)
I1-Cd1-I2
I1-Cd1-I3
I1-Cd1-I3i
I3-Cd1-I3i
Cd1-I3-Cd1i
C3-N1-H1
C3-N1-C4
C3-N1-C2
O3-N3-O4
O3-N3-O5
O4-N3-O5
116.448(19)
105.808(18)
116.788(19)
97.192(16)
82.808(16)
107.7
108.6(4)
113.3(4)
118.9(5)
120.1(5)
0.18 × 0.13 × 0.07
150
monoclinic
P21/c
Unit cell dimensions
˚
a, A
12.2894(6)
14.2810(6)
12.7047(6)
97.850(5)
2208.83(18)
4
2.36
5.2
1464
˚
b, A
˚
c, A
β, deg
3
˚
Volume, A
120.9(5)
Z
Calculated density, g cm−3
Absorption coefficient, mm−1
F(000), e
a
Symmetry code: i −x, 1−y, 2−z.
θ range for data collection, deg
h, k, l ranges
2.9 – 29.3
drawn with the use of the programs ORTEP-III [9] and
DIAMOND [10]. Selected bond lengths and angles are
collected in Table 2 and hydrogen bond geometries in
Table 3.
−8 ≤ h ≤ 16, −17 ≤ k ≤ 18,
−17 ≤ l ≤ 13
11 861 /
5156 / 0.025
5156 / 218
1.059
0.0358 / 0.0858
0.0479 / 0.0928
2.17 / −1.50
Reflections collected /
independent / Rint
Data / ref. parameters
Goodness-of-fit on F2
R1 / wR2 (I > 2σ(I))
R1 / wR2 (all data)
In the crystal structure of 1 (Fig. 2), the cadmium
atoms with a coordination number four have dis-
torted tetrahedral geometry with average Cd–I bond
−3
˚
Largest diff. peak / hole, e A
˚
lengths of 2.7916 A which is similar to an average
˚
Cd–I bond length of 2.792 A based on CSD data.
nitrate ion has D3h symmetry and three infrared active The dihedral angle between the Cd1/I3/I3i/Cd1i and
vibrations, but this symmetry is lowered to C2v and Cs I1/I2/Cd1/Cd1i/I2i/I1i planes is 86.81◦. The [Cd2I6]2−
in metal complexes [7] to give up to six infrared-active unit has a center of inversion which lies in the center
vibrations. In 1, the nitrate groups are involved in hy- of the Cd1/I3/I3i/Cd1i plane (Ci symmetry).
drogen bonds lowering their symmetry. In the Raman
In the cation of 1, the piperazine moiety has a chair
spectrum of 1, the terminal Cd–I stretching vibration conformation, and its two nitrogen atoms are proto-
has been assigned to the strong band at 125 cm−1 con- nated and have a distorted tetrahedral geometry. The
sistent with values reported in the literature [8].
conformation of the cyclohexane ring is similar to that
The crystal structure of [(H2L)2][Cd2I6][(NO3)2] of the piperazine ring. As an indicator of their rela-
(1) was determined by single-crystal X-ray diffrac- tive orientation, the dihedral angle between their mean
tion analysis (Table 1 and Experimental Section). Di- planes is 83.94◦. The cyclohexane ring has two chiral
agrams of the molecular structure and unit cell were centers at C6 and C5 with the same absolute configu-
Table 3. Hydrogen bond
geometries (A, deg) for
[(H2L)2][Cd2I6][(NO3)2] (1).
D–H···A
d(D–H)
d(H···A) < (DHA)
d(D···A)
Symmetry code
˚
N(1)–H(1)···O(4)
0.910
0.910
0.910
0.819
0.820
0.969
0.980
0.97
0.970
0.970
0.970
0.970
1.851
2.006
2.384
2.128
2.8319
2.665
3.1728
2.698
2.648
2.606
2.522
2.620
176.7
166.8
129.3
175.2
149.3
110.1
169.9
129.6
112.4
125.8
143.9
114.6
2.760(6)
2.900(6)
3.044(6)
2.945(8)
3.562(5)
3.133(6)
4.141(6)
3.40(1)
1−x, 1−y, 1−z
1−x, 0.5+y, 0.5−z
1−x, 0.5+y, 0.5−z
1−x, 1−y, 1−z
−x, 1−y, 1−z
1−x, 1−y, 1−z
1−x, 0.5+y, 1.5−z
x, 1.5−y, −0.5+z
1−x, 0.5+y, 0.5−z
1−x, 1−y, 1−z
x, y, z
N(2)–H(2)···O(3)
N(2)–H(2)···O(5)
O(2)–H(2C)···O(1)
O(1)–H(1C)···I(2)
C(4)–H(4A)···O(3)
C(5)–H(5)···I(1)
C(10)–H(10A)···O(2)
C(11)–H(11A)···O(5)
C(10)–H(11B)···O(3)
C(12)–H(12A)···O(4)
C(12)–H(12B)···O(5)
3.148(7)
3.270(7)
3.355(7)
3.151(7)
x, y, z

274
M. Hakimi et al. · The Cadmium Salt [(H2L)2][Cd2I6][(NO3)2]
Fig. 2 (color online). ORTEP-
III diagram of the crys-
tal structure of [(H2L)2]
[Cd2I6][(NO3)2] (1). The
displacement ellipsoids are
drawn at the 30% probabil-
ity level.
Fig. 3 (color online). Packing
of [(H2L)2][Cd2I6][(NO3)2],
showing the hydrogen bonds
and R22 (22), R21 (4) motifs.
Only the hydrogen atoms of
the hydroxyl and ammonium
groups are shown. Each CdI4
moiety is drawn as tetrahedron.
ration. Each unit cell of 1 contains four [H2L]2+ units [H2L]2+ units via two O–H···I and two C–H···I hydro-
consisting of a racemic mixture of the R,R and S,S iso- gen bonds, while each [H2L]2+ unit is surrounded by
mers. The bond lengths and angles of the nitrate anions two [Cd2I6]2− units via O–H···I and C–H···I hydrogen
◦
˚
in 1 (1.224(7) – 1.258(6) A, 119.0(5)–121.0(5) ) show bonds.
only small deviations from ideal values.
Extension of the hydrogen bonds in three direc-
In the crystal structure of 1 there are strong N– tions creates a 3D supramolecular network in the crys-
H···O, O–H···O, O–H···I, as well as weak C–H···O tal structure of 1. The twoO(2)–H(2C)···O(1) hydro-
and C–H···I hydrogen bonds. The iodide ligands act gen bonds participate in the formation of a R22(22)
as proton acceptors, and carbon atoms participate in motif [11] between two adjacent [H2L]2+ moieties
hydrogen bonding as proton donors, whereas the oxy- (Fig. 3) and the N(2)–H(2)···O(3)nitrate and N(2)–
gen and nitrogen atoms act as both proton donors and H(2)···O(5)nitrate hydrogen bonds form a R21(4) motif
acceptors. Each [Cd2I6]2− unit is surrounded by four between nitrate anions and [H2L]2+ cations (Fig. 3).

M. Hakimi et al. · The Cadmium Salt [(H2L)2][Cd2I6][(NO3)2]
275
Conclusion
(H2O): λmax (nm): 290. – 1H NMR (300 MHz, CDCl3):
δ = 1.2 (m, 4 H, C9H2, C8H2); 1.6 – 1.8 (m, 2 H, C10H2);
2.0 (m, 2 H, C7H2); 2.5 (m, 9 H, C5H, C11H2, C4H2, C12H2,
C3H2); 2.7 (m, 3 H, C6H, C2H2); 3.3 (s, 1 H, C1OH); 3.6
(t, 2 H, C1H2); 3.9 (s, 1 H, C6OH). – 13C NMR (dept 135,
100 MHz, CDCl3): δ = 22.3 (C9, C8); 24.0 (C10); 25.5 (C7);
33.1 (C4, C3); 57.7 (C11, C12); 59.3 (C2); 60.1 (C1); 68.8
(C5); 70.1 (C6).
In this work 2-(4-(2-hydroxyethyl)piperazin-1-
yl)cyclohexanol (L) and [(H2L)2][Cd2I6][(NO3)2] (1)
were prepared, and their spectral and structural prop-
erties were investigated. Crystal structure analysis re-
vealed that the piperazine moiety in 1 has a chair con-
formation, and its two nitrogen atoms have a distorted
tetrahedral geometry. The cadmium atoms with coordi-
nation number four have distorted tetrahedral geome-
tries in a [Cd2I6]2− moiety with a center of inversion
(Ci symmetry). Vibrations of the nitrate group were
studied by IR spectroscopy. Hydrogen bonding influ-
ences the nitrate geometry and lowers its symmetry
from D3h to C2v or Cs. These hydrogen bonds give rise
to a 3D supramolecular network.
[(H2L)2][Cd2I6][(NO3)2] (1)
A solution of 0.23 g (1 mmol) of L dissolved in ethanol
(15 mL) was added with stirring to a solution of 0.36 g
(1 mmol) of CdI2 in ethanol (30 mL). The reaction mix-
ture was stirred at 60 ◦C for 3 h, and a colorless pre-
cipitate was formed. It was filtered, and the filtrate was
cloudy after 2 h. The pH of the cloudy filtrate was ad-
justed to around 5 by dropwise addition of aqueous 0.1 M
HNO3 until clarity. The mixture was vigorously stirred for
30 min and filtered. The solution was left at room tempera-
ture for several days, and colorless crystals suitable for X-
ray diffraction were collected. Yield: 0.31 g, 39%; m. p.:
211 ◦C. – C12H26CdI3N3O5 (785.48): calcd. C 18.35, H
3.34, N 5.35; found C 18.12, H 3.29, N 5.14. – IR (KBr
disk): ν = 3448 (OH), 3016 (NH), 2939 (CH), 2862 (CH2),
Experimental Section
Materials and instrumentation
All chemicals and solvents were reagent or analytical
grade and used as received. The microwave-assisted reac-
tion for the synthesis of the ligand (L) was carried out us-
ing a Microwave Laboratory Systems MicroSYNTH reac-
tor from Milestone s. r. l. The infrared spectra of KBr pel-
lets in the range of 400 – 4000 cm−1 were recorded with
a FT-IR 8400 Shimadzu spectrometer. The Raman spectrum
was obtained using a Nicolet Model 910 Fourier-transform
spectrometer. The electronic spectrum of L was recorded in
H2O using a Shimadzu model 2550 UV/Vis spectrophotome-
ter (190 – 900 nm). 1H NMR and 13C NMR spectra were
recorded on a Bruker Advance DPX300 instrument operating
at 300 and 100 MHz, respectively; chemical shifts are given
in parts per million, with values relative to TMS as internal
standard. The carbon, hydrogen and nitrogen contents were
determined using a Thermo Finnigan Flash Elemental Ana-
lyzer 1112 EA. Melting points were determined with a Barn-
sted Electrothermal 9200 electrically heated apparatus.
δ
as = 1442 (CH−2), ν4 = 1381 (NO3−), δs = 1344 (CH2),
ν1 = 1280 (NO3 and/or ν CO), ν = 1133 (CN), ν2 = 1072
(NO3−), ν6 = 910 cm−1 (NO3−). – Raman: ν = 2901 (CH),
ν4 = 1408 (NO3−), ν1 = 1281 (NO3 and/or ν CO), 1156
−
(CN), ν2 = 1033 (NO3−), ν6 = 893 (NO3−), ν = 125 cm−1
(Cd-I).
X-Ray structure determination
A suitable single crystal of [(H2L)2][Cd2I6][(NO3)2] was
placed on a Xcalibur Eos Gemini Ultra diffractometer and
kept at 150 K during data collection. Using the program
package OLEX-II [12], the structure was solved with the
program SHELXS [13 – 15] using Direct Methods and re-
fined with SHELXL [13 – 15] using least-squares minimiza-
tion. Crystallographic data and details of the data collec-
tion and structure refinement are listed in Table 1. Selected
bond lengths and angles are reported in Table 2, and hydro-
gen bond geometries are presented in Table 3.
CCDC 899816 for [(H2L)2][Cd2I6][(NO3)2] contains the
supplementary crystallographic 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.
R,S-2-(4-(2-Hydroxyethyl)piperazin-1-yl)cyclohexanol, L
A
mixture of 1.30 g (10 mmol) of 2-(piperazin-1-
yl)ethanol and 0.98 g (10 mmol) cyclohexene oxide was ir-
radiated inside a microwave oven for 15 min with a power up
to 1 kW. After microwave irradiation, an oily liquid was ob-
tained. Excess precursors were removed using a rotary evap-
orator. A viscous brown oil was obtained. Several attempts
to crystallize the compound were unsuccessful. C12H24N2O2
(228.33): calcd. C 63.12, H 10.59, N 12.27; found C 62.65, H
10.37, N 11.86. – IR (KBr disk): ν = 3447 (OH), 2934 (CH),
2815 (CH2), δas = 1454 (CH2), δs = 1354 (CH2), ν = 1294
Acknowledgement
We are grateful to Payame Noor University of I. R. Iran
(CO), 1157 (C5N), 1123 (C11N, C12N) cm−1. – UV/Vis for financial support.

276
M. Hakimi et al. · The Cadmium Salt [(H2L)2][Cd2I6][(NO3)2]
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