Spectroscopic studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with a N4-macrocylic ligands

Article abstract of DOI:10.1016/j.saa.2007.11.005

Complexes of cobalt(II), nickel(II), copper(II) and zinc(II) with a new tetraaza macrocyclic ligand have been synthesized and characterized by microanalyses, molar conductance, magnetic susceptibility, mass, thermogravimetric (TGA), IR, ¹H and ¹³C NMR, electronic and ESR spectral studies. All the complexes are found to have the formula [MLX₂]·nH₂O and are six-coordinated with distorted octahedral geometry.

Full text of DOI:10.1016/j.saa.2007.11.005

Available online at www.sciencedirect.com
Spectrochimica Acta Part A 70 (2008) 929–933
Short communication
Spectroscopic studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes
with a N4-macrocylic ligands
S.J. Swamy∗, Someshwar Pola
Department of Chemistry, Kakatiya University, Vidyaranyapuri, Warangal 506009, India
Received 1 January 2007; accepted 15 November 2007
Abstract
Complexes of cobalt(II), nickel(II), copper(II) and zinc(II) with a new tetraaza macrocyclic ligand have been synthesized and characterized by
microanalyses, molar conductance, magnetic susceptibility, mass, thermogravimetric (TGA), IR, 1H and 13C NMR, electronic and ESR spectral
studies. All the complexes are found to have the formula [MLX2]·nH2O and are six-coordinated with distorted octahedral geometry.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Macrocyclic ligands; Transition metal complexes; Mass spectroscopy; 1H NMR; Electronic; IR; ESR
1. Introduction
ring sizes by non-template synthetic methods [18]. Herein, we
report the preparation and characterization of the complexes
of Co(II), Ni(II), Cu(II) and Zn(II) with three new ligands:
dibenzo[e,m][1,4,8,11]tetraazacyclotetradecine-5,14-dione
There is a continuing interest in the chemistry of polyaza
macrocycles because of their ability to interact with both
metal cations and anionic species [1–3]. Transition metal
complexes of polyaza macrocyclic ligands with functional
groups have been synthesized in order to investigate how
the functional groups affect their coordination geometry and
chemical properties [4,5]. Complexes of macrocyclic ligands
have become very important building blocks of ligand-bridged
complexes that possess various dimensional structures and
fascinating magnetic properties [6–9]. The large polyazamacro-
cyclic molecules, containing six or more nitrogen atoms, are
known to form stable metal complexes, with one or more
metal ions, due to their large number of nitrogen atoms [10].
They find applications in different areas such as catalysis,
bioinorganic, biomimetic and coordination chemistry [11].
Metal complexes of macrocycles are also tested in medicine,
radio immunotherapy [12–14] cancer diagnosis and treatment
of tumor [15]. The complexes of manganese and iron with
macrocyclic ligands are used as antimicrobial, antifertility,
anti-inflammatory and analgesic agents [16,17]. In view of
the interest and importance of nitrogen macrocycles, we have
reported the preparation of new tetraaza macrocycles of variable
(L1),
dibenzo[e,n][1,4,8,12]tetraazacyclotetradecine-6,15-
dione(L2)andtribenzo[b,f,m][1,4,8,11]tetraazacycclotetradecine-
5,14-dione (L3).
2. Experimental
All the chemicals used were of AnalaR grade, and purchased
from Sigma–Aldrich. Metal salts were procured from E. Merck
and were used as received. The preparation of ligands was
described elsewhere [18].
2.1. Synthesis of complexes
The general method used for the preparation of the com-
plexes is: to 10 ml warm solution of the corresponding metal
salt [0.001 mol, chloride in the case of Co(II), Ni(II) and
Cu(II) and acetate in the case of Zn(II)] the solution (10 ml)
of the respective ligand (0.001 mol) in methanol was added
and refluxed for 5 h at 60 ◦C. The solid complex obtained
was collected on a fine frit and washed with cold methanol
and then with acetone. The complexes were dried in vacuo
over fused calcium chloride till no change in weight was
noticed.
∗
Corresponding author. Tel.: +91 870 2438369; fax: +91 870 2453533.
E-mail address: sj swamy@yahoo.com (S.J. Swamy).
1386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.11.005

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S.J. Swamy, S. Pola / Spectrochimica Acta Part A 70 (2008) 929–933
2.2. Physical measurements
plexes as [MLX2]·H2O, where M = Co(II), Ni(II) and Cu(II)
and X = Cl−. The mass spectrum of [Zn(L3)(OAc)2] exhibits
the m/z peaks at 555.2, 496.3 and 437 which are assignable
to the species [Zn(L3)(OAc)2], [Zn(L3)(OAc)] and [Zn(L3)],
respectively. Further, all the species containing metal ion were
confirmed by good agreements between the observed and cal-
culated isotopic distributions [20].
The percentages of C, H and N were determined using a
PerkinElmer CHN analyzer-2400. Molar conductance was mea-
sured on the Digisun digital DI-909 conductivity bridge. TGA
curveswererecordedusingMettler–Toledo, DSCandTGA822e
series instrument. Magnetic susceptibility was measured at room
temperature on a Gouy balance using Hg[Co(CNS)4] as calli-
brant. The mass spectrum was recorded on CEC-21-110B and
3.3. Thermal analysis
1
Finnigan MAT-1210 mass spectrometers. H NMR spectrum
was recorded using a Jeol 200 MHz FT-NMR spectrometer in
d6-DMSO. Chemical shifts are given in ppm relative to tetram-
ethylsilane. IR spectra were recorded on a PerkinElmer BX
series spectrometer using KBr pellets in the IR region and as
nujol mulls between CsI plates in the far-IR region. The elec-
tronic spectra were recorded in DMF solutions on a Shimadzu
UV–vis spectrophotometer model 2401 PC. ESR spectra of the
Cu(II) complexes were recorded at liquid nitrogen tempera-
ture on JEOL-JES-PE-3X ESR spectrometer using DPPH as
the g-marker.
The thermograms of the complexes of Co(II), Ni(II) and
Cu(II) show initial weight loss in the temperature range of
60–150 ◦C, corresponding to one water molecule. The presence
of water molecule in these complexes is further confirmed by an
endothermic peak in this temperature range. The loss in the low
temperature region indicates that the water molecule is lattice
held [21].
On further heating, the complexes exhibit mass loss curve
beyond 180 ◦C and continues to a temperature around 750 ◦C,
after which the TG becomes parallel to the temperature axis.
The percentage of the residue left was found to be the respective
metal oxide, Co3O4, NiO, CuO and ZnO [22].
3. Results and discussion
3.1. Complexes
3.4. IR spectra
All the complexes are stable, non-hygroscopic and soluble
in DMF and DMSO but insoluble in methanol, ethanol, acetone
and benzene. The analytical data of the metal chelates presented
in Table 1 indicate that the metal ions are coordinated to one
ligand molecule and two chloride or acetate ions. The low molar
conductivities of all the complexes in DMF indicate that they are
non-electrolytic in nature [19].
The characteristic absorptions of the N4-macrocyclic ligands
containing two amide and two amine groups have been dis-
cussed in an earlier communication [18]. The spectra of the
corresponding complexes exhibit these absorptions at differ-
ent frequencies indicating the coordination of the ligands. The
ν(N–H) and amide-II (Table 2) stretching frequencies shift by
50–100 and 20–30 cm−1, respectively, towards lower frequency
side. The C O stretching frequency shifts by 10–20 cm−1
towards high frequency side indicating that the amide oxy-
gen is not coordinated [23]. The IR spectra of Co(II), Ni(II)
and Cu(II) complexes exhibit a broad absorption between 3500
and 3250 cm−1. This broad absorption is the characteristic of
ν(O–H) of water molecule. The water molecule in a complex
may be as lattice held or as coordinated. The coordinated water
molecules exhibit a characteristic absorption around 850 cm−1
in the IR spectra of complexes. The close examination of the
3.2. Mass spectra
The mass spectra of all complexes exhibit high mass peak
corresponding to [(MLX2)·H2O]7+. Another ion that confirms
the coordination of the ligand to the metal ion is the appear-
ance of ML7+ fragment. The other fragment peaks are as
observed in the mass spectrum of the ligand. The mass spectral,
analytical and thermal data confirm the formulae of the com-
Table 1
Analytical and physicochemical data of the complexes
S. no.
Compound
m/z (amu)
% Yield
Dc. comp.
% M
% C
% H
% N
ꢀ◦ (ꢁ−1 cm2 mol−1
)
1
2
3
4
5
6
7
8
9
[CoL1Cl2]
[NiL1Cl2]
[CuL1Cl2]
[ZnL1(OAc)2]
[CoL2Cl2]
[NiL2Cl2]
[CuL2Cl2]
[ZnL2(OAc)2]
[CoL3Cl2]
[NiL3Cl2]
[CuL3Cl2]
[ZnL3(OAc)2]
475.2 (472)
473.82 (472)
478.16 (476)
507
488.93 (486)
487.82 (486)
490.8 (490)
522.8 (522)
522.2 (520)
520.6 (520)
526.54 (524)
555.2 (555)
62
64
59
65
70
63
68
60
59
61
69
54
284
276
288
292
254
262
274
268
290
286
278
292
12.34 (12.42)
12.52 (12.46)
13.16 (13.23)
12.29 (12.38)
11.98 (12.06)
12.39 (12.30)
12.89 (12.96)
12.12 (12.06)
11.27 (11.33)
11.21 (11.29)
12.19 (12.11)
11.28 (11.39)
45.71 (45.76)
45.72 (45.76)
45.26 (45.37)
50.19 (50.28)
46.83 (46.91)
46.86 (46.91)
46.49 (46.53)
51.26 (51.21)
50.68 (50.79)
50.76 (50.81)
50.26 (50.34)
54.35 (54.41)
4.59 (4.66)
4.73 (4.66)
4.56 (4.62)
5.24 (5.33)
5.01 (4.94)
4.88 (4.94)
4.85 (4.89)
5.63 (5.56)
4.21 (4.26)
4.18 (4.26)
4.18 (4.22)
4.84 (4.92)
11.92 (11.86)
11.79 (11.86)
11.81 (11.70)
10.72 (10.67)
11.61 (11.52)
11.61 (11.57)
11.51 (11.43)
10.31 (10.39)
10.69 (10.77)
10.71 (10.77)
10.74 (10.67)
9.81 (9.76)
10.2
11.8
12.1
10.6
13.4
10.9
12.7
11.1
12.6
13.2
9.3
10
11
12
12.5

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931
Table 2
Infrared spectral data (cm−1) and their assignment
S. no.
Complex
ν(N–H)
Amide bands
I
ν(M–N)
ν(M–Cl)
ν(M–O)
II
III
1
2
3
4
5
6
7
8
9
[CoL1Cl2]
[NiL1Cl2]
[CuL1Cl2]
[ZnL1(OAc)2]
[CoL2Cl2]
[NiL2Cl2]
[CuL2Cl2]
[ZnL2(OAc)2]
[CoL3Cl2]
[NiL3Cl2]
[CuL3Cl2]
[ZnL3(OAc)2]
3447
3435
3458
3364
3424.5
3432
3436
3408
3382
3368
3354
3408
1674
1671
1654
1654
1664
1658
1656
1664
1644
1658
1670
1664
1560
1595
1591
1586
1588
1572
1546
1584
1561
1594
1612
1546
1224
1245
1238
1253
1227
1242
1234
1256
1231
1229
1219
1246
447
450
418
472
332
358
444
490
438
458
421
503
342
–
–
–
372
–
–
–
390
–
–
–
354
350
–
452
448
342
–
348
354
352
–
10
11
12
403
spectra of the complexes did not reveal any new absorption
around 850 cm−1 indicating that the water molecule is not coor-
dinated. Hence, it may be proposed that the water molecule is
lattice held and the thermal data (loss of mass in the low temper-
ature region) also confirms the same. The absorption between
418 and 450 cm−1 in the far-IR spectra of the complexes may
be attributed to ν(M–N), and it provides a strong evidence for
the involvement of nitrogen atoms in coordination [24]. The
spectra of Co(II), Ni(II) and Cu(II) complexes exhibit another
absorption around 260 cm−1 characteristic of ν(M–Cl). The far-
IR spectra of the Zn(II) complexes show an absorption around
400 cm−1. This may be assigned to ν(M–O) confirming that
acetate ions are coordinated to the metal ion [25]. Further, the
absorptions at 1606 and 1400 cm−1, confirm the monodentate
nature of the acetate ion in these complexes [26].
The Cu(II) complexes exhibit the magnetic moment values of
1.86, 1.89 and 1.87μB corresponding to one unpaired electron.
These values are higher than the spin-only value, i.e. 1.73μB
for one unpaired electron. This reveals that these complexes are
monomeric in nature without any of metal–metal interactions
[27] but with same orbital contribution at room temperature.
3.6. Electronic spectra
3.6.1. Cobalt complexes
The electronic spectral data of all complexes along with
derived parameters are presented in Table 3. The three spec-
tral absorptions of Co(II) complexes may be assigned to
4T1g(F) → T2g(F), 4T1g(F) → A2g(F) and 4T1g(F) → T1g(P)
transitions. The position of the bands suggests octahedral
geometry around the Co(II) ion [27]. The various ligand
field parameters were calculated for the Co(II) complexes.
The value of Dq has been calculated using the ν3/ν1 ratio.
The nephelauxetic parameter β is obtained using the relation:
β = B(complex)/B(free ion), where B(free ion) is 1120 cm−1 [28], the
value of β is in the range of 0.769–0.82 and this indicates that the
covalent character of metal ligand ␴ bond is low. The LFSE val-
ues of the complexes have been evaluated and given in Table 3.
4
4
4
3.5. Magnetic moment
The magnetic moment values of the Co(II) complexes
measured at room temperature are found to be 4.94,
4.96 and 4.98μB These high spin values of Co(II) com-
plexes confirm that the complexes have octahedral geometry
[27].
The magnetic moment values of all the Ni(II) complexes lie
in the range 2.97, 2.94 and 3.11μB and corresponding to two
unpairedelectrons. Themagneticmomentvaluesareintunewith
high spin configuration of octahedral Ni(II) complexes [27].
3.6.2. Nickel complexes
Electronic spectra of Ni(II) complexes show three transitions
in the region 9425–24,690 cm−1 and these transitions may be
Table 3
Electronic spectral absorptions and ligand field parameters of the complexes
S. no.
Complex
Spectral bands (cm−1
)
ν3/ν1
Dq (cm−1
711.76
)
B (cm−1
747.46
793.2
664.1
689.5
797.7
745.9
–
)
β
LFSE (kJ mol−1
)
1
2
3
4
5
6
7
8
9
[CoL1Cl2]
[CoL2Cl2]
[CoL3Cl2]
[NiL1Cl2]
[NiL2Cl2]
[NiL3Cl2]
[CuL1Cl2
[CuL2Cl2]
[CuL3Cl2]
8,970, 14,970, 23,152
9,124, 15,002, 24,268
8,794, 14,441, 21,902
10,060, 16,103, 24,420
9,425, 15,551, 24,690
9,695, 16,060, 24,213
14,220
2.35
2.23
2.49
2.43
2.62
2.51
–
0.67
0.71
0.60
0.66
0.76
0.72
–
68.02
70.84
72.18
76.92
78.67
74.56
–
1232
996.6
1006
942.5
969.5
–
14,493
14,588
–
–
–
–
–
–
–
–
–
–

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S.J. Swamy, S. Pola / Spectrochimica Acta Part A 70 (2008) 929–933
3
3
3
3
assigned to A2g(F) → T2g(F) (ν1), A2g(F) → T1g(F) (ν2)
and 3A2g(F) → T1g(P) (ν3), respectively. These transitions are
3
characteristic of the octahedral Ni(II) species [27]. The vari-
ous ligand field parameters [28] are calculated by using Orgel
diagrams and are given in Table 3.
3.6.3. Copper(II) complexes
The electronic spectra of the Cu(II) complexes show a
broad absorption in the range 14,220–14,588 cm−1 assignable
to 2B1g → A1g transition [29]. This broad absorption suggests
2
distorted octahedral geometry as expected from the Jahn–Teller
effect in hexa-coordinated d9 metal ion.
Fig. 1. Suggested structures of M = Co(II), Ni(II) and Cu(II), X = Cl− and
M = Zn(II), X = CH3COO−.
3.7. ESR spectra
complexes show two new signals at 181.46 and 21.94 which
are corresponding to –O–C O– and CH3 of acetate ion. The
rest of the carbon atoms are similar as found in the spectra of
the free ligand.
On the basis of elemental analyses, molar conductance, ther-
mogravimetric analyses, magnetic susceptibility, IR, electronic,
ESR and 1H NMR spectral data the following structure may be
proposed for all the complexes (Fig. 1).
ESR spectra of Cu(II) complexes are recorded at liquid nitro-
gen temperature. The absence of Cu–Cu interactions can be
explained by proposing transitions, i.e. ꢂMs = 2 between two
paramagnetic centers is negligible [30]. The analysis of spec-
tra gave g = 2.2301–2.2913 and g = 2.078–2.098. The values
ꢀ
⊥
g > g indicates that the unpaired electron lies in the dx2−y2
ꢀ
⊥
orbital giving 2B1g as the ground state. This supports that there
is a considerable mixing of ground and excited state terms and
also reflected in the magnetic moment values which are slightly
greater than the spin-only value for Cu(II), i.e. 1.73μB, which is
indicating the formation of mononuclear copper(II) complexes.
The ratio g > g > gave > 2.0023 evaluated for all Cu(II) com-
Acknowledgement
The financial assistance from Department of Science and
Technology, Government of India, New Delhi (SP/S1/F17/98-
PRU) is gratefully acknowledged.
ꢀ
⊥
plexes, suggests that the unpaired electron is localized in dx2−y2
orbital and the spectral features are characteristic of tetragonally
distorted octahedron.
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3.8. 1H and 13C NMR spectra of Zn(II) complexes
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