Cd(II) complexes with pendant armed oxa- and azamacrocyclic ligands

Article abstract of DOI:10.1016/j.poly.2013.01.040

The coordination capability of the pendant-arm macrocyclic ligands-with different sizes, nature and number of the donor atoms-dioxotriaza 17-membered (L¹) and pentaaza 17-membered (L²) towards nitrate and perchlorate Cd(II) salts, has been investigated. The complexes were prepared in 1:1 metal/ligand molar ratio. The characterization carried out by elemental analysis, FAB mass spectrometry, IR and NMR spectroscopy, conductivity measurements, together with the crystal structure of the complexes [CdL ¹(CH₃CN)](ClO₄)₂·CH ₃CN and [CdL²](ClO₄)₂ confirms the formation of mononuclear complexes in all cases. The X-ray diffraction of [CdL¹(CH₃CN)](ClO₄)₂·CH ₃CN complex presents a mononuclear endomacrocyclic structure with the metal ion coordinated by the five donor atoms from the macrocyclic framework, the amine group from the pendant-arm and one acetonitrile molecule, in a distorted pentagonal bipyramid geometry. The complex [CdL²](ClO ₄)₂ is also mononuclear, but the cadmium ion is in a distorted trigonal prism environment coordinated by the six nitrogen donor atoms from the ligand. In both cases, the perchlorate ions do not participate in the coordination to the metal ion, but they are involved in numerous hydrogen bond interactions inter- and intramolecular with phenoxy and amino-groups.

Full text of DOI:10.1016/j.poly.2013.01.040

Polyhedron 54 (2013) 54–59
Contents lists available at SciVerse ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Cd(II) complexes with pendant armed oxa- and azamacrocyclic ligands
Montserrat López-Deber b, Anxela Aldrey b, Goretti Castro-Justo a, Ma del Carmen Fernández-Fernández b,
b
a
a,
Verónica García-González b, Rufina Bastida b, , Alejandro Macías , Paulo Pérez-Lourido , Laura Valencia
⇑
⇑
a Departamento de Química Inorgánica, Facultad de Química, Universidad de Vigo, 36310 Vigo, Pontevedra, Spain
b Departamento de Química Inorgánica, Universidad de Santiago de Compostela, Avda. de las Ciencias s/n 15782, Santiago de Compostela, la Coruña, Spain
a r t i c l e i n f o
a b s t r a c t
Article history:
The coordination capability of the pendant-arm macrocyclic ligands – with different sizes, nature and
number of the donor atoms – dioxotriaza 17-membered (L1) and pentaaza 17-membered (L2) towards
nitrate and perchlorate Cd(II) salts, has been investigated. The complexes were prepared in 1:1 metal/
ligand molar ratio. The characterization carried out by elemental analysis, FAB mass spectrometry, IR
and NMR spectroscopy, conductivity measurements, together with the crystal structure of the complexes
[CdL1(CH3CN)](ClO4)2ꢀCH3CN and [CdL2](ClO4)2 confirms the formation of mononuclear complexes in all
cases. The X-ray diffraction of [CdL1(CH3CN)](ClO4)2ꢀCH3CN complex presents a mononuclear endomac-
rocyclic structure with the metal ion coordinated by the five donor atoms from the macrocyclic frame-
work, the amine group from the pendant-arm and one acetonitrile molecule, in a distorted pentagonal
bipyramid geometry. The complex [CdL2](ClO4)2 is also mononuclear, but the cadmium ion is in a dis-
torted trigonal prism environment coordinated by the six nitrogen donor atoms from the ligand. In both
cases, the perchlorate ions do not participate in the coordination to the metal ion, but they are involved in
numerous hydrogen bond interactions inter- and intramolecular with phenoxy and amino-groups.
Ó 2013 Elsevier Ltd. All rights reserved.
Received 3 December 2012
Accepted 18 January 2013
Available online 19 February 2013
Keywords:
Macrocyclic ligand
Pendant-arm
Cadmium complexes
X-ray crystal structure
1. Introduction
cyclic ligand as they can encapsulate the metal ion into the macro-
cyclic hole [11]. In this way, some macrocyclic ligands were
The oxaaza and azamacrocyclic ligands have been a subject of
extensive investigation in the coordination chemistry research
during last decades [1–3]. It is mainly due its ability to form
complexes with different metal ions or anionic species with
considerable potential in such areas as catalysis, modelling of
metalloenzyme, molecular recognition, etc. [4–6].
The host–guest interactions and the selectivity of metal ions
with this sort of ligand is governed, between other factors, on the
cavity and chelate ring size, ligand rigidity and the number and
nature of the donor atoms. The presence of pendant-arms into
the macrocyclic skeleton have attracted a great deal of interest ow-
ing to the fact that the ligating groups attached to the macrocyclic
backbone can offer additional donor groups to produce important
changes in the control of the stability, selectivity, stereochemistry
and certain thermodynamic parameters [7–10], or promote the
formation of dinuclear or polynuclear metal complexes with inter-
action between the metal centres. The use of pendant-armed
groups can also increase the coordination capability of the macro-
designed to act as selective sequestering agents for ‘‘soft’’ metal
ions of environment importance such as cadmium, mercury or lead
[12–14]. In particular, cadmium is an environment pollutant which
inhibits RNA polymerase activity in vivo [15,16], and reacts readily
with proteins and other biological molecules, and so the macrocy-
clic chemistry of cadmium complexes with multidentate ligands
such that may have important utility as antagonist for treatments
of heavy-metal poisoning have attracted much attention [17–20].
Although many studies have been made on cadmium(II) macrocy-
clic complexes, no many crystal structures have been reported and
most of them resulted to be mononuclear [21–24].
As continuation of our work on the coordination capability of
oxa and azamacrocyclic ligands [25–28] and in order to gain in-
sight into the structures and stabilities of macrocyclic coordination
complexes with Cd(II) ion, we report in this paper the coordination
ability of two new pendant-arm macrocyclic ligands, L1 and L2
(Scheme 1). The X-ray crystal structure of cadmium perchlorate
complexes is also reported.
2. Experimental
⇑
Corresponding authors. Addresses: Departamento de Química Inorgánica,
Facultad de Química, Avenida de las Ciencias s/n, 15782 Santiago de Compostela,
Spain. Tel.: +34 981 528073; fax: +34 981597525 (R. Bastida). Departamento de
Química Inorgánica, Facultad de Química, As Lagoas-Marcosende, 36310 Vigo,
Pontevedra, Spain. Tel.: +34 986 812313; fax: +34 986 813797 (L. Valencia).
E-mail addresses: qibastid@usc.es (R. Bastida), qilaura@uvigo.es (L. Valencia).
2.1. Chemicals and starting materials
The precursor macrocyclic ligand L0 [29] and 2,20-(etane-1,2-
diildiamine)bisbenzaldehyde [30], were synthesized as described
0277-5387/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.poly.2013.01.040

M. López-Deber et al. / Polyhedron 54 (2013) 54–59
55
in the literature. Salicylaldehyde, tris(2-aminoethyl)amine, anhy-
MS (m/z): 555 [CdL2(NO3)]+, 494 [CdL2]+. KM
/X
ꢁ1 cm2 molꢁ1 (in
drous Na2SO4, NaBH4, nitrate and perchlorate salts were commer-
cial products (from Alpha and Aldrich) and were used without
further purifications. Solvents were of reagent grade and were
purified by the usual methods.
Caution: Although no problems were encountered during the
course of this work, attention is drawn to the potentially explosive
nature of perchlorates.
CH3CN): 148 (1:1). Colour: white.
2.3.4. [CdL2](ClO4)2
Anal. Calc. for C22H34N6O8Cl2Cd: C, 38.1; H, 4.9, N, 12.1. Found:
C, 37.9; H, 4.7, N, 11.8%. Yield: 53%. IR (KBr, cmꢁ1): 3156 [
(N–H)],
(ClO4ꢁ)]. FAB-MS (m/z):
ꢁ1 cm2 molꢁ1 (in CH3CN):
m
1605, 1500, 1460 [m(C@C)], 1100, 625 [m
594 [CdL2(ClO4)]+, 494 [CdL2]+. KM
/X
300 (2:1). Colour: white.
2.2. Synthesis of macrocyclic ligands
2.4. Physical measurements
Ligand L1: To a hot methanol (30 ml) solution of the precursor
macrocyclic ligand L0 (1 mmol, 0.38 g), salicylaldehyde (1 mmol,
0.12 g) dissolved in methanol (30 ml) was added dropwise. The
mixture was refluxed during 1 h. After the solution was allowed
to cool to room temperature, NaBH4 (0.38 g, 10 mmol) was added
slowly. The solution was concentrated to dryness and the crude so-
lid was extracted with water–chloroform. The organic layer was
dried over anhydrous Na2SO4 and evaporated until 5 ml. The addi-
tion of ether caused separation of a pale yellow solid characterized
as L1: C29H38N4O3 (MW: 490): C, 68.5; H, 7.8; N, 11.0. Found: C,
68.4; H, 7.7; N, 10.6%. Yield: 45%. IR (KBr, cmꢁ1): 3670–3580
Elemental analyses were performed in a Carlo-Erba EA micro-
analyser. IR spectra were recorded as KBr discs on a Bruker IFS-
66V spectrophotometer. FAB mass spectra were recorded using a
Kratos-MS-50T spectrometer connected to a DS90 data system
using 3-nitrobenzyl alcohol as the matrix. Conductivity measure-
ments were carried out in 10ꢁ3 mol dmꢁ3 acetonitrile solutions
at 20 °C using a WTW LF3 conductivimeter. NMR spectra were re-
corded on a Bruker 500 MHz.
2.5. Crystal structure determination
[
m
(O–H)], 3434 [
m(N–H)], 1594, 1544, 1492 [m(C@C)]. FAB-MS, m/
z: 491 [L1+H]+. Colour: pale yellow.
Measurements were made on a Bruker SMART CCD 1000 area
diffractometer. All data were corrected for Lorentz and polarization
effects. Empirical absorption corrections were also applied for all
the crystal structures obtained [31]. Complex scattering factors
were taken from the program package SHELXTL [32]. The structures
were solved by direct methods which revealed the position of all
non-hydrogen atoms. All the structures were refined on F2 by a
full-matrix least-squares procedure using anisotropic displace-
ment parameters for all non hydrogen atoms. The hydrogen atoms
were located in their calculated positions and refined using a riding
model, except the hydrogen atoms from the amine groups in
[CdL2](ClO4)2 which were located and refined isotropically.
The ligand L2 was prepared by addition of (tris(2-amino-
ethyl)amine) (2 mmol, 0.30 mL) dissolved in methanol to a hot
solution in methanol (75 ml) of 2,20-(ethane-1,2-diildiamine)bis-
benzaldehyde (2 mmol, 0.54 g). The mixture was refluxed for 4 h
and after the solution was allowed cool to room temperature,
NaBH4 (0.76 g, 20 mmol) was added slowly, the solid filtered off
and evaporated to dryness. The residue was then extracted with
water–chloroform and the organic layer was dried over anhydrous
Na2SO4 and evaporated to yield a white oil. By recrystallization of
this oil in acetonitrile the ligand L2 was obtained as white solid.
Anal. Calc. for C22H34N6 (MW: 382): C, 69.1; H, 8.9; N, 22.0. Found:
C, 69.0; H, 8.6; N, 21.8%. Yield: 52%. IR (KBr, cmꢁ1): 3269 [
m
(N–H)],
1604, 1514, 1458 [
white.
m
(C@C)]. FAB-MS, m/z: 383 [L2+H]+. Colour:
3. Results and discussion
2.3. Synthesis of metal complexes-general procedure
L1 and L2 pendant-armed macrocyclic ligands were each readily
obtained from a one-pot synthesis from the precursors reagents in
satisfactory yield and purity without the need for column chroma-
tography. The ligands were characterized by different techniques:
elemental analysis, FAB-MS, IR, 1H and 13C NMR spectroscopy.
FAB mass spectrometry provides evidence for the presence of
only L1 (m/z 491, assignable to [L1+H]+), and L2 (m/z 383, assignable
to [L2+H]+). The IR spectra show no bands corresponding to pri-
mary amino-group in L1 and carbonyl group in L2, further confirm
that the introduction of the pendant-arm in L1 and the cyclization
for L2 took place.
The appropriate metal salt (0.25 mmol) in a 1:1 Cd:Ln molar ra-
tio was dissolved in acetonitrile (10 ml) and added to a stirred and
refluxing solution of the macrocyclic ligand (0.25 mmol) in aceto-
nitrile (30 ml). The reaction mixture was refluxed for 3 h and con-
centrated in a rotary evaporator until ca. 5–6 ml. The product
obtained was filtered off and dried.
2.3.1. [CdL1](NO3)2
Anal. Calc for C29H38N6O9Cd: C, 47.9; H, 5.2; N, 11.6. Found: C,
47.8; H, 5.4; N, 10.9%. Yield: 62%. IR (KBr, cmꢁ1): 3260 [
m
(N–H)],
(NO3ꢁ)]. FAB-
/X
MS (m/z): 665 [CdL1(NO3)]+, 603 [CdL1]+. KM ꢁ1 cm2 molꢁ1 (in
The NMR spectra of both ligands were recorded using deuter-
ated chloroform as solvent, and confirm the integrity of the ligands
and their stability in solution. The assignment of the signals was
based upon standard COSY, DEPT-135 and HMQC measurements.
The aromatic region of the 1H NMR spectrum of L1 shows two mul-
tiplet signals at d 7.5–6.5 ppm belonging to the aromatic rings; the
ethylene protons signal appears at d 4.4 ppm as a singlet. The ben-
zyl and salicyl protons appear as a singlet and multiplet at d 3.7
and 3.6 ppm, respectively. The signal of the ethylene groups of
the macrocyclic framework is observed at d 2.5 ppm as a multiplet.
Finally, the ethylenic protons of the pendant-arm are observed as
triplet at d 2.4 and 2.2 ppm.
1608, 1492, 1458 [m(C@C)], 1383, 1080, 832, 766 [m
CH3CN): 152 (1:1). Colour: white.
2.3.2. [CdL1(CH3CN)](ClO4)2ꢀCH3CN
Anal. Calc. for C33H44N6O11Cl2Cd: C, 45.9; H, 5.1; N, 9.7. Found:
C, 46.0; H, 5.0; N, 9.5%. Yield: 78%. IR (KBr, cmꢁ1): 3262 [
m
(N–H)],
(ClO4ꢁ)]. FAB-MS (m/z):
/X
703 [CdL1(ClO4)]+, 603 [CdL1]+. KM ꢁ1 cm2 molꢁ1 (in CH3CN):
1605, 1493, 1458 [m(C@C)], 1100, 622 [m
268 (2:1). Colour: white.
2.3.3. [CdL2](NO3)2ꢀH2O
The 1H and 13C NMR signal data, together with the labelling
scheme, for L2 is collected in Table 1. The proton spectrum shows
a multiplet signal due to the aromatic proton in the range d 7.4–
Anal. Calc. for C22H34N8O7Cd: C, 41.6; H, 5.3; N, 17.6. Found: C,
42.2, H, 5.4; N, 17.5%. Yield: 47%. IR (KBr, cmꢁ1): 3168 [
1607, 1499, 1458 [ (C@C)], 1384, 1082, 825, 760 [
(NO3ꢁ)]. FAB-
m(N–H)],
m
m
6.6 ppm. The signals of the tris-ethylene amine protons (H9–H12)

56
M. López-Deber et al. / Polyhedron 54 (2013) 54–59
L1. The crystal structure of the [CdL1(CH3CN)](ClO4)2ꢀCH3CN and
Table 1
1H and 13C NMR spectra assignment for L2 in CDCl3.
[CdL2](ClO4)2 complexes is also reported.
3.1.1. Crystal structure of CdL1(CH3CN)](ClO4)2ꢀCH3CN
By slow concentration of a solution of the perchlorate Cd(II)
complex with L1 in acetonitrile, crystals suitable for X-ray diffrac-
tion with formula CdL1(CH3CN)](ClO4)2ꢀCH3CN were obtained. The
molecular structure of the complex and selected bond lengths (Å)
and angles (°) relating to the coordination environment of the me-
tal are given in Fig. 1. Crystal data and structure refinement are gi-
ven in Table 2.
The molecular structure shows a mononuclear endomacrocyclic
complex in a distorted pentagonal bypyramid environment, being
the metal atom coordinated by the three nitrogen and two oxygen
donor atoms from the macrocyclic backbone and the amino nitro-
gen atom from the pendant-arm. The seventh coordination posi-
tion is occupied by an acetonitrile molecule, remaining the
phenoxy group from the pendant-arm uncoordinated and proton-
ated. The equatorial plane of the distorted pentagonal bipyramid
can be considered to be formed by the all macrocyclic backbone
donor atoms [N(1)N(2)N(3)O(1)O(2), rms = 0.5104(2) Å]. The axial
positions are formed by the secondary amino-group of the pen-
dant-arm, N(4), and the coordinated acetonitrile molecule, N(1S),
as these two donor atoms show the biggest angle to the metal
ion N(4)–Cd(1)–N(1S) 162.52(15)°.
The Cd–N bond distances corresponding to the acetonitrile
group [Cd(1)–N(1S), 2496(5) Å] and the tertiary amine [Cd(1)–
N(2), 2.426(4) Å] are longer than the corresponding to the second-
ary amines (average value, 2.345 Å). The longest coordinated bond
distances correspond to the ether group, which coordinates to the
metal ion in asymmetric mode [Cd(1)–O(2) 2.547(5) and Cd(1)–
O(1) 2.652(3) Å].
The macrocyclic ring is slightly twisted, showing a perpendicu-
lar disposition of the aromatic rings, with a dihedral angle between
the planes that contain the rings of 78.34°.
The crystal structure shows that one oxygen atom of a perchlo-
rate group is disordered in two positions. The perchlorate ions do
not participate in the coordination to the metal ion, but they are
involved in hydrogen bond interactions with the amino-groups
from the macrocycle. Also, an intramolecular hydrogen bond inter-
action between the amino-group N4–H4A and the ether oxygen
atom O3 has been observed.
1H
13C
Assignment
d (ppm)
Assignment
d (ppm)
C1
C2
42
H1
H8
H10
H9, H12
H11
3.5 (s, 4H)
3.8 (s, 4H)
2.5 (m, 4H)
2.6 (m, 6H)
2.4 (m, 2H)
7.4–6.6 (m, 8H)
148
130–109
124
52
46
53
C3, C4, C5, C6
C7
C8
C9
C10
C11
C12
H3, H4, H5, H6
56
39
appear as different multiplets in the range d 2.6–2.4 ppm, whilst
the other ethylene protons (H1) are singlet at d 3.5 ppm. Finally,
the benzyl protons appear as singlet at d 3.8 ppm.
The coordination capability of L1 and L2 towards Cd(II) hydrated
nitrate and perchlorate salts was studied. The complexes were
characterized by elemental analysis, IR, molar conductivity, FAB-
MS and NMR spectroscopy.
3.1. Structural studies of the complexes
Adequate crystals for suitable X-ray diffraction of formulae
CdL1(CH3CN)](ClO4)2ꢀCH3CN and [CdL2](ClO4)2 were obtained by
recystallization of the complexes in acetonitrile. The details of
the X-ray crystal structures solution and refinement are given in
Table 2. The X-ray studies reveal the presence of similar mononu-
clear endomacrocyclic complexes consistent with the cation
[CdLn]2+ and two well separated perchlorate ions. One acetonitrile
molecule is also coordinated to cadmium ion in the complex with
3.1.2. Crystal structure of [CdL2](ClO4)2
The molecular structure of the cation belonging to [CdL2]2+
complex, together with selected bond lengths and angles relating
to the coordination environment of the metal is present Fig. 2.
The metal ion present a N6 coordination environment inside the
O
O
O
O
NH
HN
HN
NH
HN
NH
HN
NH
N
N
N
NH
OH
NH2
NH2
L 0
L 1
L2
Scheme 1.

M. López-Deber et al. / Polyhedron 54 (2013) 54–59
57
Table 2
Crystal data and structure refinement for [CdL1(CH3CN)](ClO4)2ꢀCH3CN and [CdL2](ClO4)2.
[CdL1(CH3CN)](ClO4)2ꢀCH3CN
[CdL2](ClO4)2
Empirical formula
Formula weight
T (K)
C33H44N6O11Cl2Cd
884.04
298(2)
C22H34N6O8Cl2Cd
693.85
293(2)
k (Å)
0.71073
0.71073
Crystal system
Space group
Unit cell dimensions
a (Å)
b (Å)
c (Å)
triclinic
P1
monoclinic
P2(1)/c
ꢀ
11.0786(18)
12.600(2)
14.498(2)
8.7909(19)
18.282(4)
17.348(4)
a
b (°)
(°)
100.148(3)
98.381(3)
102.133(4)
c
(°)
97.437(3)
1945.7(5)
V (Å3)
2725.8(10)
4
1.691
1.055
1416
Z
2
Dcalc (Mg mꢁ3
)
1.509
0.762
908
Absorption coefficient (mmꢁ1
F(000)
)
Crystal size (mm3)
h (°)
0.40 ꢂ 0.09 ꢂ 0.09
1.66–26.43
ꢁ13 6 h 6 13,
ꢁ15 6 k 6 15,
0 6 l 6 18
0.55 ꢂ 0.40 ꢂ 0.33
1.64–27.15
ꢁ11 6 h 6 11,
0 6 k 6 23,
0 6 l 6 22
Index ranges
Reflections collected
22111
32850
Independent reflections (Rint
Completeness to h
Absorption correction
)
7940 (0.0372)
99.3% (26.43°)
empirical
6000 (0.0292)
99.2% (27.15°)
empirical
Maximum and minimum transmission
Refinement method
0.9345 and 0.7502
full-matrix least-squares on F2
7940/0/480
1.059
0.7222 and 0.5946
full-matrix least-squares on F2
6000/0/386
1.057
Data/restraints/parameters
Goodness-of-fit (GOF) on F2
Final R indices [I > 2
r
(I)]
R1 = 0.0456,
wR2 = 0.1060
R1 = 0.0790,
wR2 = 0.1272
0.834 and ꢁ0.520
R1 = 0.0309,
wR2 = 0.0848
R1 = 0.0376,
wR2 = 0.0886
0.886 and ꢁ5.62
R indices (all data)
Largest difference peak and hole (e Åꢁ3
)
macrocyclic hole by the five nitrogen donor atoms from the macro-
cyclic backbone and the nitrogen amino-group from the pendant-
arm. The geometry around the metal ion can be described as dis-
torted trigonal prism. The triangular faces of the trigonal prism
are defined by N(1)N(2)N(5) and N(3)N(4)N(6) with a dihedral an-
gle between the faces of 5.41°, and the Cd2+ ion slightly displaced
towards N(1)N(2)N(5) face.
The longest Cd–N bond distance do not corresponds to the ter-
tiary amine [Cd(1)–N(1) 2.426(2) Å], but for one of the secondary
amines [Cd(1)–N(3) 2.447(2) Å]. The other Cd–N amines are similar
[range 2.336(2)–2.396(2) Å].
In this case, the ligand is folded with a dihedral angle between
the planes containing the aromatic rings of 82.17°, as the ligand
must accommodate all the nitrogen atoms near the metal center.
Again, the perchlorate anions remain without coordination to
the metal, but numerous hydrogen bond interactions between
them and the amino-groups of the ligand are present in the crystal
structure.
spectra of the nitrate complexes the band at 1380 cmꢁ1 associated
with the presence of ionic nitrate [33],is accompanied by several
bands in the region associated with nitrate vibrations and these
clearly identify the coordinated nitrate groups [34]. The perchlo-
rate complexes feature absorptions attributable to ionic perchlo-
rate at 1100 and 626 cmꢁ1 [35]. The lack of splitting of this band
indicates that these groups are not coordinated to the metal cen-
tres [33,35b].
Molar conductivity data measured at room temperature using
acetonitrile as solvent showed the presence of ionic counterions
since they are in the range reported in that solvent for 1:1 electro-
lytes in the case of nitrate complexes, and 2:1 for the percl-
orates[36]. Those values are indicative of the different
coordinative capacity between nitrate and perchlorates anion and
are in agreeing with the results obtained from the IR and X-ray
studies.
The 1H NMR spectra of Cd(II) complexes with L2 were recorded
immediately after dissolution in CD3CN at different temperatures
(between 238 and 338 K).
The spectra are similar, and at room temperature the aliphatic
signals show a poor resolution and are broadened, suggesting the
presence of different conformers in solution, probably due to the
rapid coordination/decoordination of the amine pendant group in
the NMR time scale. When the temperature is decreased from
298 to 238 K, even better resolution of the aliphatic region of the
spectrum is observed, a higher number of signals are present due
the presence of the conformers, resulting a more complicated
spectra.
3.2. Spectroscopic studies
Microanalytical data of the complexes were in accord in all
cases with the presence of mononuclear species of the type [CdLn]
X2. xH2O. yCH3CN (X = NO3 or ClO4ꢁ).
ꢁ
FAB mass spectra confirm the mononuclear nature of the com-
plexes. All complexes show the peaks attributable to different frag-
mentation species, including [CdL(X)]+ or [CdL]2+
.
The secondary amine stretches m(N–H) that appear at 3434 and
3269 cmꢁ1 in the IR spectrum of the free ligands, L1and L2, respec-
tively, undergo a shift toward high frequencies in the IR spectra of
the complexes, suggesting the coordination to the metal ion. In the
If the temperature is raised from 298 to 338 K a better resolu-
tion of the aliphatic region of the spectrum is observed, due prob-
ably to the increase in the interchange rate between the different

58
M. López-Deber et al. / Polyhedron 54 (2013) 54–59
Table 3
1H and 13C NMR spectra assignment for [CdL2](ClO4)2 in CD3CN at 338 K.
1H
13C
Assignment
d (ppm)
Assignment
d (ppm)
H1
3.5 (m, 2H)
3.7 (m, 2H)
7.5–7.2 (d, t, 8H)
4.5 (sb, 2H)
3.8 (db, 2H)
2.9 (m, 2H)
2.6 (m, 6H)
2.3 (sb, 2H)
1.8 (sb, 2H)
C1
C2
43
H10
145
134–116
127
53
48
56
H3, H4, H5, H6
H8
H80
C3, C4, C5, C6
C7
C8
C9
C10
C11
C12
H9
H09, H10
H11
H12
56
40
and 1.85 ppm, respectively. The signals of the primary and second-
ary amines are also observed as broad signals at different chemical
displacements in the spectrum.
For complexes with L1 in CD3CN the 1H NMR spectra presented
broad signals showing probably a rapid conformational intercon-
version in solution, again due to the coordination/decoordination
of the pendant group. However, the different temperatures NMR
study was not useful in the assignment of the spectra. They
showed that, in general, all the proton resonances are shifted
downfield when compared with the free ligand due to the
complexation.
Fig. 1. Crystal structure of [CdL1(CH3CN)]2+ ion; Selected bond lengths (Å) and
angles (°): Cd(1)–N(3) 2.312(4), Cd(1)–N(1) 2.329(4), Cd(1)–N(4) 2.393(3), Cd(1)–
N(2) 2.426(4), Cd(1)–N(1S) 2.496(5), Cd(1)–O(2) 2.547(3), Cd(1)–O(1) 2.652(3),
N(3)–Cd(1)–N(1) 131.57(14), N(3)–Cd(1)–N(4) 101.76(13), N(1)–Cd(1)–N(4)
109.25(13), N(3)–Cd(1)–N(2) 76.80(14), N(1)–Cd(1)–N(2) 75.23(14), N(4)–Cd(1)–
N(2) 76.88(13), N(3)–Cd(1)–N(1S) 84.35(15), N(1)–Cd(1)–N(1S) 77.10(14), N(4)–
Cd(1)–N(1S) 162.52(15), N(2)–Cd(1)–N(1S) 120.59(15), N(3)–Cd(1)–O(2)
144.36(12), N(1)–Cd(1)–O(2) 78.99(12), N(4)–Cd(1)–O(2) 79.06(11), N(2)–Cd(1)–
O(2) 136.18(12), N(1S)–Cd(1)–O(2) 86.46(14).
Titrations by 1H NMR of L2 with Cd(II) nitrate and perchlorate
salts were carried out in CD3CN at room temperature. In both cases
the signals of the ligand shift slightly at downfield due to the coor-
dination to the metal ion. Also, those signals are broad and de-
crease in intensity as more salt is added, due to a slow ligand/
complex interchange in the NMR time scale. This phenomenon is
well appreciated in the aromatic region, but the aliphatic signals
are poorly resolved, probably due the presence of different con-
formers in solution at room temperature. From this titration we
can conclude the existence only the 1:1 metal/ligand of the species,
because once 1:1 relation is reached, not changes are observed in
the spectra when the metal salt concentration is increased. How-
ever, the formation constant of those complexes could not be
determined.
4. Conclusion
Two new pendant-arms macrocyclic ligands (L1 and L2) derived
from a dioxotriaza 17-membered and pentaaza 17-membered pre-
cursors, respectively, have been synthesized and characterized. The
coordination behaviour of those ligands with nitrate and perchlo-
rate cadmium(II) salts was studied. The synthesis of the complexes
was carried out in acetonitrile in a 1:1 cadmium:ligand molar ratio.
Mononuclear species were obtained in all cases. The crystal struc-
ture of [CdL1(CH3CN)](ClO4)2ꢀCH3CN and [CdL2](ClO4)2 were deter-
minated by X-ray diffraction. In both cases the Cd ion is
endomacrocyclicly coordinated by all the donor atoms of the mac-
rocyclic backbone and the pendant-arm group. In the first case the
heptacoordination environment around the metal is completed by
an acetonitrile molecule and the geometry can be described as dis-
torted pentagonal bipyramid. The coordination geometry around
cadmium in [CdL2](ClO4)2 complex can be better described as dis-
torted trigonal prism.
Fig. 2. Crystal structure of [CdL2]2+; Selected bond lengths (Å) and angles (°): Cd–
N(2) 2.336(2), Cd–N(6) 2.365(2), Cd–N(5) 2.365(2), Cd–N(4) 2.396(2), Cd–N(1)
2.426(2), Cd–N(3) 2.447(2), N(2)–Cd–N(6) 107.41(10), N(2)–Cd–N(5) 106.34(9),
N(6)–Cd–N(5) 127.59(9), N(2)–Cd–N(4) 151.98(8), N(6)–Cd–N(4) 87.66(9), N(5)–
Cd–N(4) 80.58(8), N(2)–Cd–N(1) 77.01(8), N(6)–Cd–N(1) 73.91(9), N(5)–Cd–N(1)
76.09(8), N(4)–Cd–N(1) 130.66(8), N(2)–Cd–N(3) 82.09(8), N(6)–Cd–N(3) 93.92(8),
N(5)–Cd–N(3) 129.60(8), N(4)–Cd–N(3) 73.23(8), N(1)–Cd–N(3) 151.10(8).
conformers. For sample, the 1H NMR spectrum at 338 K for com-
plex [CdL2](ClO4)2 (Table 3) shows the aromatic protons at down-
field as two triplets and two doublets. Between d 4.5 and 3.6 ppm
two signals are assigned to the geminal H8 and H08 protons. The sig-
nals of H1 and H01 protons of the ethylene bridge between the aro-
matic rings, H1 and H01, are observed at d 3.55 ppm as two broad
multiplets. The H9 and H09 as consequence of the coordination are
not equivalent and are showing at d 2.6 and 2.9 ppm together with
Acknowledgment
We thank Xunta de Galicia 10PXIB209028PR for financial
support.
H10. Finally, at highfield appear the signals of H11 and H12 at d 2.35

M. López-Deber et al. / Polyhedron 54 (2013) 54–59
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Appendix A. Supplementary material
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CCDC 912578 and 912579 contain the supplementary crystallo-
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