Template synthesis and characterization of 12 and 14-membered pendant-armed tetraazamacrocyclic transition metal complexes: A photoelectron spectroscopic study

Article abstract of DOI:10.1081/SIM-200026581

A new series of 12 and 14-membered tetraazamacrocyclic complexes, [ML ¹X₂] and [ML²X₂] [M = Mn(II), Zn(II), Co(II), Ni(II), X = Cl]; [ML¹X₂] and [ML ²X₂] [M = Cu(II), X = Cl or NO₃, L¹ and L² - 12 and 14-membered tetraazamacrocyclic ligands] have been prepared via the template condensation of 1,2-dibromoethane or 1,3-dibromopropane with aniline. The complexes have been characterized by elemental analyses, conductivity, IR, UV-VIS, ¹H NMR, magnetic susceptibility measurements, and x-ray photoelectron spectra. An octahedral geometry has been assigned for all of the prepared metal complexes.

Full text of DOI:10.1081/SIM-200026581

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Template Synthesis and
Characterization of
12 and 14‐Membered
Pendant‐Armed
Tetraazamacrocyclic
Transition Metal Complexes:
A Photoelectron
Spectroscopic Study
Shekhar Srivastava a & Abul Kalam a
a Department of Chemistry , Allahabad
University , Allahabad, 211 002, India
Published online: 16 Nov 2010.
To cite this article: Shekhar Srivastava & Abul Kalam (2004) Template Synthesis
and Characterization of 12 and 14‐Membered Pendant‐Armed Tetraazamacrocyclic
Transition Metal Complexes: A Photoelectron Spectroscopic Study, Synthesis
and Reactivity in Inorganic and Metal-Organic Chemistry, 34:9, 1529-1541, DOI:
10.1081/SIM-200026581
To link to this article: http://dx.doi.org/10.1081/SIM-200026581
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 34, No. 9, pp. 1529–1541, 2004
Template Synthesis and Characterization
of 12 and 14-Membered Pendant-Armed
Tetraazamacrocyclic Transition
Metal Complexes: A Photoelectron
Spectroscopic Study
*
Shekhar Srivastava and Abul Kalam
Department of Chemistry, Allahabad University, Allahabad, India
ABSTRACT
A new series of 12 and 14-membered tetraazamacrocyclic complexes,
[ML1X2] and [ML2X2] [M ¼ Mn(II), Zn(II), Co(II), Ni(II), X ¼ Cl];
[ML1X2] and [ML2X2] [M ¼ Cu(II), X ¼ Cl or NO3, L1 and L2 ¼ 12
and 14-membered tetraazamacrocyclic ligands] have been prepared via
the template condensation of 1,2-dibromoethane or 1,3-dibromopropane
with aniline. The complexes have been characterized by elemental
analyses, conductivity, IR, UV-VIS, 1H NMR, magnetic susceptibility
*
Correspondence: Shekhar Srivastava, Department of Chemistry, Allahabad Univer-
sity, Allahabad 211 002, India; E-mail: shekharsri1@rediffmail.com.
1529
DOI: 10.1081/SIM-200026581
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright # 2004 by Marcel Dekker, Inc.

1530
Srivastava and Kalam
measurements, and x-ray photoelectron spectra. An octahedral geometry
has been assigned for all of the prepared metal complexes.
Key Words: Magnetic susceptibility measurements; X-ray photo-
electron spectra; Metal complexes; Template condensation.
INTRODUCTION
Transition metal complexes of macrocyclic ligands have been studied for
many years.[1] Recently, interest has drawn by their catalytic properties, which
led to industrial applications.[2,3] Macrocyclic complexes are significant as
they can be used as catalysts in many organic oxidation reactions[3] and
they have been found to act as possible models for biochemically important
proteins and enzymes.[4–8] Macrocyclic polyamides of different ring sizes
have been reported extensively in the literature.[9–17] Macrocyclic compounds
containing nitrogen and other heteroatoms as ring components have usually
been prepared by use of either the high dilution technique[13–15,18–20] or by
metal template reactions.[21–25] Recently, a new route for the preparation of
14–22 membered tetraamide macrocyclic ligands using dicyclohexylcarbo-
diimide and 4-(dimethylamino)pyridine as condensing reagents was
reported.[26] Herein, we report the synthesis and characterization of a new
series of 12 and 14-membered pendant-armed tetraazamacrocyclic transition
metal complexes (Fig. 1), obtained by the template condensation reaction of
1,2-dibromoethane or 1,3-dibromopropane with aniline.
RESULTS AND DISCUSSION
The complexes may be synthesized by the following general method.
Pendant-armed tetraazamacrocyclic transition metal complexes ([ML1X2],
[ML2X2]) can be conveniently be prepared in fair to good yields by the
interaction of aniline,1,2-dibromoethane and 1,3-dibromopropane with
metal salt under anhydrous condition.
4ArNH2 þ 4BrCH2CH2Br þ MX2 ꢀ! ½ML1X2ꢁ
ð1Þ
4ArNH2 þ 2BrCH2CH2CH2Br þ 2BrCH2CH2Br þ MX2 ꢀ! ½ML2X2ꢁ
ð2Þ
M ¼ MnðIIÞ; CoðIIÞ; NiðIIÞ; CuðIIÞ; ZnðIIÞ; X ¼ Cl; X ¼ NO3
for CuðIIÞ

A Photoelectron Spectroscopic Study
1531
Figure 1. 12 and 14-Membered pendant-armed tetraazamacrocyclic transition metal
complexes.
All the complexes have shown high melting points. Elemental analyses were
within +0.5% for C, H, N, Cl, and M and the molar conductance values for
all the compounds in DMSO lie in the 12–25 cm2 V21 mol21 range, which
supports[34] the contention that the nature of these complexes is non-ionic.
(Table 1). However, we could not grow single crystals suitable for x-ray
crystallographic studies.
Infrared Spectra
All of the complexes show bands in at 1150–1210cm21 which may be
assigned to n(C–N) modes. The presence of a band in the region

1532
Srivastava and Kalam
l
m

A Photoelectron Spectroscopic Study
1533

1534
Srivastava and Kalam
330–380 cm21 in the spectra of all of the complexes is assignable to n(M–N)
vibrations.[24] Bands appearing in the region 3000–3100, 650–750,
1580–1600, and 1460–1500cm21 may be assigned as, n(C–H) aromatic,
d(C–H) aromatic, n(C55H) aromatic and n(C–H) aliphatic, respectively.[24]
All of the complexes shown bands in the region 265–310 cm21 assignable
to n(M–Cl) vibrations. Bands in the regions 1230–1245, 1000–1030, and
850–875 cm21 for the nitrate complexes indicate the presence of monodentate
coordinated nitrate groups.[30]
Electronic Spectra and Magnetic Moments
The electronic spectra of the cobalt(II) complexes show two bands in
the 14,200–14,650 and 21,350–21,700 cm21 regions, which may be
4
4
4
4
assigned[31,32] to the T1g(F) ! A2g(F) and A1g(F) ! T2g(P) transitions,
respectively, suggesting an octahedral geometry around the cobalt(II) ion,
which is further confirmed by the observed magnetic moment (4.05–4.20
B.M.). The macrocyclic complexes derived from Ni(II) ions show two
bands in their electronic spectra in the regions 14,900–15,800 and 23,750–
3
3
25,000 cm21 which may be assigned[31,32] to the A2g(F) ! T1g(F) and
3
3A2g(F) ! T1g(P) transitions, respectively, suggesting an octahedral geome-
try around the nickel(II) ions, which is further confirmed by the observed
magnetic moment values (3.10–3.13 B.M.). The electronic spectra all Cu(II)
complexes show broad band maxima at 18,200–19,000 cm21 with a shoulder
on the low-energy side at 15,280–16,620 and 19,100–19,750 cm21, which
2
1
may be assigned to the 2B1g ! Eg and 2B1g ! B2g transitions, respectively,
corresponding to octahedral geometry around the copper(II) ion.[31] The mag-
netic moment values (1.72–1.82 B.M.) further confirm the proposed geome-
try. The electronic spectra of the Mn(II) complexes show three bands in the
ranges at 22,500–22,800 and 32,000–32,300 cm21 and the magnetic
moment values of all Mn(II) metal complexes (5.62–5.82 B.M.) suggest octa-
hedral geometry around the Mn(II) ion.
1H NMR Spectra
1
The H NMR spectra of the [ML1X2] and [ML2X2] complexes show
a multiplet in the region 2.16–2.20 ppm with an intensity ratio of 16 : 20
corresponding to the middle-CH2 protons.[33] All of these complexes show a
multiplet in the region 7.18–7.30 ppm region due to phenyl ring protons.[30]
In this region, two peaks, a triplet and a multiplet, corresponding to two
side CH2 groups and two middle-CH2 groups are seen, respectively.

A Photoelectron Spectroscopic Study
Photoelectron Spectroscopy
1535
The photoelectron peak binding energy (BE) data of all metal ions
(M2p3/2,1/2), Cl2p and N1s for MCl2, [MLC12] [where M ¼ Mn(II), Co(II),
Ni(II), Zn(II)] and for MX2 and [MLX2] [where M ¼ Cu(II), X ¼ Cl, NO3]
are listed in Table 2. It may be seen that the M2p3/2,1/2 photoelectron peak
BE values were observed higher (from 1.8 to 2.2 eV) in metal salts than in
the metal complexes (Fig. 2), suggesting that the metal ions have higher elec-
tion density in the metal complexes than the metal salts due to involvement of
the metal ions in coordination.[28] Further, the N1s photoelectron peaks have
shown higher BE values for all of these metal complexes (402.6–402.8 eV)
than free nitrogen atoms (ꢀ399 eV), which suggest a more effective positive
charge on the nitrogen atom in the metal complexes.[28] From these M2p3/2
and N1s XPS data one can conclude that the nitrogen atom in these metal
complexes are coordinated to the metal ion.[28] Furthermore, in the case of
[CuL(NO3)2] (where L ¼ L1 and L2) complexes, two nitrogen peaks were
observed at 402.8 and 408.4 eV in a 2 : 1 intensity ratio, out of these two
Table 2. Binding energies (eV) in [MLCl2] [M ¼ Mn(II), Co(II), Ni(II), Zn(II)] and
in [MLX2] [M ¼ Cu(II), X ¼ Cl, NO3].
Metal ion
Nitrogen (N1s)
Complexes
M2p1/2
M2p3/2
Cl2p
N
NO3
MnCl2
653.6
652.4
652.4
794.8
793.0
793.0
—
640.6
638.8
638.8
779.8
778.0
778.0
855.6
853.4
853.4
1,021.8
1,020.0
1,020.0
931.8
929.8
929.8
931.6
929.6
929.6
199.2
201.2
201.2
199.4
201.4
201.4
199.6
201.6
201.6
199.6
201.4
201.4
199.8
201.6
201.6
199.4
201.4
201.4
—
—
—
[MnL1Cl2]
[MnL2Cl2]
CoCl2
402.6
402.6
—
—
—
[CoL1Cl2]
[CoL2Cl2]
NiCl2
[NiL1Cl2]
[NiL2Cl2]
ZnCL2
[ZnL1Cl2]
[ZnL2Cl2]
CuCl2
[CuL1Cl2]
[CuL1Cl2]
Cu(NO3)
[CuL1(NO3)2]
[CuL2(NO3)2]
402.8
402.8
—
—
—
—
—
—
—
402.6
402.6
—
—
—
—
—
402.8
402.8
—
—
—
—
—
—
—
—
—
402.6
402.6
—
—
—
—
—
402.8
402.8
408.4
408.4
—

1536
Srivastava and Kalam
Figure 2. Mn2p3/2 BEs (eV) in MnCl2 and [MnLCl2] (L ¼ L1 or L2) complexes.
N1s photoelectron peaks, one N1s photoelectron peak with low intensity
(BE ¼ 408.4 eV) should be due to the NO3 group and may be assigned to
be in inner-sphere coordination.[28–30,34]
The Cl2p photoelectron spectra of all complexes have shown higher BE
values in the range 201.2–201.4 eV than the starting materials MCl2 (Table 2),
which suggest that in all of the metal complexes chloride ion is coordinated in
the inner coordination sphere of the metal ion.[30]
The M3s photoelectrons of all of these metal complexes have shown mul-
tiple splitting,[30] suggesting paramagnetic behaviour, as is consistent with the
electronic spectral and magnetic moment data during the present study.
EXPERIMENTAL
.
The metal salts MnCl2 4H2O, NiCl2 6H2O, CoCl2 6H2O, CuCl2 2H2O,
.
.
.
.
Cu(NO3)2 3H2O, ZnCl2 (all BDH) were commercially available pure
samples. 1,2-Dibromoethane (Fine Chem.), 1,3-dibromopropane and aniline
(BDH) were used after purification.[37] Solvents were distilled and dried
by conventional methods.[37] Elemental analyses were obtained at the Micro-
analytical Laboratory of CDRI, Lucknow, India. Conductance measurements
were obtained in DMSO at room temperature using a Digisun electronic
conductivity bridge. The UV-Vis spectra of the compounds in DMSO were

A Photoelectron Spectroscopic Study
1537
recorded on a Pye-Unicam 8800 spectrophotometer at room temperature. The
IR spectra. (4000–200 cm21) of all prepared complexes were recorded as KBr
discs on a Perkin-Elmer 621 spectrophotometer. 1H NMR spectra, recorded in
DMSO-d6 using a Bruker AC 200 E spectrometer with Me4Si as an internal
standard, were obtained at the IIT Kanpur, India. Metals and chloride were
determined volumetrically[35] or gravimetrically,[36] respectively. The
magnetic susceptibility was measured by the Faraday method using a Cahn
magnetic susceptibility system. Hg[Co(CNS)4] was used as a standard for cali-
bration.[27] The x-ray photoelectron spectra were recorded on a V.G. Scientific
ESCA-3MK II electron spectrometer. The MgKa x-ray line (1253.6 eV) was
used for photo-excitation. The Cu2p3/2 (BE ¼ 932.8 + 0.2) and Au4f7/2
(BE ¼ 83.8 + 0.1) lines were used to calibrate the instrument and Ag3d5/2
(BE ¼ 368.2) was used for cross checking.[28] All spectra were recorded
using the same spectrometer parameters of 50 eV pass energy and 4 mm slit
width. The reduced full width at half height maximum (FWHM) at the
Au4f7/2 (BE ¼ 83.8 eV) level under these conditions was 1.2 eV. The pow-
dered sample was mixed with high-purity silver powder to reduce the charging
effect. A thin layer of such a sample was pressed on a gold metal gauze which
was welded to a nickel sample holder. The Ag3d5/2 level (Eb 368.2 eV)
obtained from this sample was sharp and did not show any observable shift.
Thus, the charging of the sample, if at all present, was negligible.[28] The
spectra were recorded in triplicate in the region of interest. In most cases,
the BEs were reproducible within +0.1 eV. The usual least-squares fitting
procedure of determining peak positions, line widths and areas was used.
Synthesis of the Complexes
[ML1X2]
The divalent metal salts (1 mmol) were dissolved in methanol (15 mL)
in a round bottom flask and aniline (1.8 mL, 4 mmol) in methanol (10 mL)
and 1,2-dibromoethane (1.8 mL, 4 mmol) in methanol (10 mL) were added
drop-wise to the round bottom flask and the resulting mixture was refluxed
for 3 hr until a precipitate appeared which was filtered and washed with
methanol and dried in vacuo. It was further purified on an alumina
column using a solution in DMSO and ethylacetate (85%), methanol
(10%) and acetic acid (5%) as eluent. The purity of the final product was
checked by TLC of the complexes in DMSO solution using ethylacetate
(85%), methanol (10%), and acetic acid (5%) as eluent. Only one spot
was observed in each case after developing in an iodine chamber, indicating
that the compounds were pure.

1538
Srivastava and Kalam
[ML2X2]
The same procedure was adopted as above but using 1,3-dibromopropane
(2 g, 2 mmol) and 1,2-dibromoethane (0.9 mL, 2 mmol) in place of 1,2-
dibromoethane. It was further purified on an alumina column using a solution
in DMSO and ethylacetate (85%), methanol (10%) and acetic acid (5%) as
eluent. The purity of the recrystallized products (in DMSO and pet.-ether
9 : 1) in both cases was checked by the TLC technique described previously.
On the basis of all of above mentioned results, the proposed structure of
[MLX2] complexes (where L ¼ L1 and L2, X ¼ Cl or NO3) may be assigned
as shown in Fig. 1.
ACKNOWLEDGMENTS
The authors thank, the Head, Department of Chemistry, University of
Allahabad, Allahabad, India, for providing chemicals and laboratory facilities
during this work. One of the author (A. K.) is thankful to CSIR, New Delhi for
providing financial assistance.
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Received April 19, 2002
Accepted April 23, 2004