EPR, IR and electronic spectral studies on Ni(II) and Cu(II) complexes with N-donor tetradentate [N4] macrocyclic ligand

Article abstract of DOI:10.1016/j.saa.2007.08.027

Nickel(II) and copper(II) complexes are synthesized with a novel tetradentate macrocyclic ligand, i.e. 2,6,12,16,21,22-hexaaza;3,5,13,15-tetraphenyltricyclo[15,3,1,1^7-11] docosa;1(21),2,5,7,9,11(22),12,15,17,19-decaene (L) and characterized by the elemental analysis, magnetic susceptibility measurements, mass, ¹H NMR, IR, electronic and EPR spectral studies. All the complexes are non-electrolytic in nature. Thus, these may be formulated as [M(L)X₂] [M = Ni(II), Cu(II) and X = Cl^-, NO₃^- and (1/2)SO₄^2-]. Ni(II) and Cu(II) complexes show magnetic moments corresponding to two and one unpaired electron, respectively. On the basis of IR, electronic and EPR spectral studies an octahedral geometry has been assigned for Ni(II) and tetragonal geometry for Cu(II) complexes.

Full text of DOI:10.1016/j.saa.2007.08.027

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Spectrochimica Acta Part A 70 (2008) 1001–1005
EPR, IR and electronic spectral studies on Ni(II) and Cu(II) complexes
with N-donor tetradentate [N4] macrocyclic ligand
Sulekh Chandra∗, Archana Gautam
Department of Chemistry, Zakir Husain College, University of Delhi, JLN-Marg, New Delhi 110002, India
Received 16 March 2007; received in revised form 6 August 2007; accepted 12 August 2007
Abstract
Nickel(II) and copper(II) complexes are synthesized with a novel tetradentate macrocyclic ligand, i.e. 2,6,12,16,21,22-hexaaza;3,5,13,15-
tetraphenyltricyclo[15,3,1,17–11] docosa;1(21),2,5,7,9,11(22),12,15,17,19-decaene (L) and characterized by the elemental analysis, magnetic
susceptibility measurements, mass, 1H NMR, IR, electronic and EPR spectral studies.
−
All the complexes are non-electrolytic in nature. Thus, these may be formulated as [M(L)X2] [M = Ni(II), Cu(II) and X = Cl−, NO3 and
(1/2)SO42−]. Ni(II) and Cu(II) complexes show magnetic moments corresponding to two and one unpaired electron, respectively.
On the basis of IR, electronic and EPR spectral studies an octahedral geometry has been assigned for Ni(II) and tetragonal geometry for Cu(II)
complexes.
© 2007 Elsevier B.V. All rights reserved.
Keywords: Macrocycle; Nickel(II); Copper(II)
1. Introduction
In this paper, we report the spectral studies on Ni(II) and
Cu(II) complexes with a new aza-macrocyclic ligand (Fig. 1).
On the basis of analytical, magnetic and spectral data an octahe-
dral geometry for Ni(II) whereas tetragonal geometry for Cu(II)
complexes has been assigned.
The complexes of transition metal ions with macrocyclic lig-
ands are significant because of their resemblance with many
natural systems such as porphyrins and cobalamines [1,2]. The
main interest in new macrocyclic bifunctional chelating agents
arises due to their use in labeling monoclonal antibodies with
radioactive metals [3–5] and for cancer diagnosis [6,7].
The synthesis and characterization of coordination com-
pounds with aza-macrocyclic ligands have evolved as a main
research area during recent years [8,9]. Aza-type ligands appear
to be very promising for catalysis and have been discussed as
chelating systems in the literatures [10,11]. The complexation
capabilities of polyaza macrocycles are mainly governed by the
macrocyclic ring size [12].
2. Experimental
All the chemicals used were of AnalaR grade, and procured
fromFlukaandSigma–Aldrich. Metalsaltswerepurchasedfrom
E. Merck and were used as received.
2.1. Synthesis of ligand
Hot ethanolic solution (20 mL), of dibenzoylmethane (4.48 g,
0.02 mol), and a hot ethanolic solution (20 mL), of 2,6-
diaminopyridine (2.18 g, 0.02 mol) were mixed slowly with
constant stirring. This mixture was refluxed at 80 ◦C for 6 h
in presence of few drops of concentrated hydrochloric acid.
On cooling, light brown precipitate formed, which was filtered,
washed with cold EtOH, and dried under vacuum over P4O10.
Yield 70%, m.p. 85 ◦C. Elemental analysis found (%): C 80.82;
H 5.09; N 14.17. Calculated for C40H30N6 (atomic mass 594)
was C 80.80; H 5.05 and N 14.14%.
Aza-macrocyclic ligands, as well as their coordination and
organometallic compounds, play important roles in catalyti-
cally activating small molecules in electrochemically assisted
reactions with several substrates [13,14].
∗
Corresponding author. Tel.: +91 11 22911267; fax: +91 11 23215906.
E-mail addresses: schandra 00@yahoo.com (S. Chandra),
archanagautam 00@yahoo.com (A. Gautam).
1386-1425/$ – see front matter © 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2007.08.027

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S. Chandra, A. Gautam / Spectrochimica Acta Part A 70 (2008) 1001–1005
Fig. 1. Preparation and structure of the ligand (L).
2.2. Synthesis of complexes
Hot ethanolic (20 mL) solution of ligand (0.594 g, 0.001 mol)
and hot ethanolic solution of corresponding metal salts
(0.001 mol)weremixedtogetherwithconstantstirring. Themix-
ture was refluxed for 5–8 h at 70–80 ◦C. On cooling, coloured
complex precipitated out. It was filtered, washed with cold EtOH
and dried under vacuum over P4O10.
Fig. 2. Electron impact mass spectrum of the ligand (L).
cyclic moiety (C40H30N6)+ + 23 atomic mass of Na+ ion). It
also shows a series of peaks, i.e. 300 amu, 326 amu, 367 amu,
466 amu, 472 amu, 480 amu, 524 amu and 582 amu, etc. corre-
sponding to various fragments. Their intensity gives an idea of
stability of fragments. The 1H NMR spectrum of the ligand does
not give any signal attributable to primary diamine or alcoholic
protons. The presence of a sharp multiplet in the region, δ 7.28
may be assigned for the benzenoid hydrogen (6H) having the
same chemical shift and thus these behave as equivalent [15]. A
signal at δ 1.80–2.20 ppm may be assigned for (C–CH2–C, 4H)
and a strong triplet appeared for (C–C6H5, 20H). No IR spec-
tral bands appear corresponding to the free primary diamine or
hydroxyl group [16], which suggests the complete condensation
of keto group with amino group. The vibrations correspond-
ing to υ(C C) and υ(C N) skeletal are present in the region
1560 cm−1 shoulder and 1602 cm−1. The bands appearing at
924–805 cm−1 may be assigned to ring breathing mode, C–H
deformations, respectively. The strong frequencies 1597 cm−1
are usually associated to υ(CN) coupled with phenyl ring vibra-
tions. The band appearing at 1620–1580 cm−1 may be assigned
to symmetric or asymmetric υ(C N) vibrations. The shifting of
the υCN bands toward the lower side in the complexes indicate
that the coordination take place through the nitrogen of υC N
group, thus implying that the ligand is tetradentate.
2.3. Physical measurements
The C, H and N were analysed on a Carlo-Erba 1106 ele-
mental analyzer. Magnetic susceptibility was measured at room
temperature on a Gouy balance using CuSO4·5H2O as a cal-
ibrant. Electron impact mass spectra were recorded on TOF
1
MS ES+ mass spectrometer. H NMR spectra were recorded
on Hitachi FT-NMR, model R-600 spectrometer using DMF as
a solvent, chemical shifts are given in ppm relative to tetram-
ethylsilane. IR spectra (KBr) were recorded on a FTIR Spectrum
BX-II spectrophotometer. The electronic spectra were recorded
in DMF on Shimadzu UV mini-1240 spectrophotometer. EPR
spectra of the complexes were recorded as polycrystalline sam-
ple and in the solution of DMSO, at room temperature for Cu(II)
complexes on E4–EPR spectrometer using the DPPH as the
g-marker.
3. Result and discussion
On the basis of elemental analysis, the complexes were
assigned to possess the composition as shown in Table 1. The
molar conductance measurements of the complexes in DMF
correspond to non-electrolytic nature. These complexes may be
formulated as [M(L)X2] [M = Ni(II), Cu(II) and X = Cl−, NO3
3.1. IR bands due to anions
−
and (1/2)SO42−]. The electron impact mass spectra (Fig. 2) of
ligand (L) confirm the proposed formula by showing a peak
at 616 amu (i.e. atomic mass 594 corresponding to the macro-
IR spectra of nitrato complexes display three stretching
bandsat1455–1483 cm−1, 1228–1231 cm−1 and926–999 cm−1
Table 1
Elemental analysis data of the complexes
Complex
Atomic mass
Colour
m.p. (◦C)
Yield (%)
Elemental analysis data found (calculated) (%)
Metal
C
H
N
Ligand (L) C40H30N6
594
724
777
749
729
782
754
Light brown
Light green
Light green
Light green
Green
85
248
240
270
285
282
280
70
64
62
67
61
60
62
80.82 (80.80)
66.32 (66.30)
61.76 (61.78)
64.05 (64.08)
65.87 (65.84)
61.34 (61.38)
63.62 (63.66)
5.09 (5.05)
4.17 (4.14)
3.84 (3.86)
4.05 (4.00)
4.15 (4.12)
3.81 (3.84)
3.95 (3.98)
14.17 (14.14)
11.62 (11.60)
14.44 (14.41)
11.24 (11.21)
11.49 (11.52)
14.35 (14.32)
11.17 (11.14)
[Ni(L)Cl2] NiC40H30N6Cl2
[Ni(L)(NO3)2] NiC40H30N8O6
[Ni(L)SO4] NiC40H30N6O4S
[Cu(L)Cl2] CuC40H30N6Cl2
[Cu(L)(NO3)2] CuC40H30N8O6
[Cu(L)SO4] CuC40H30N6O4S
8.13 (8.11)
7.58 (7.55)
7.86 (7.84)
8.75 (8.78)
8.15 (8.18)
8.45 (8.49)
Green
Green

S. Chandra, A. Gautam / Spectrochimica Acta Part A 70 (2008) 1001–1005
1003
Fig. 3. IR spectral bands due to anions. (a) [Ni(L)(NO3)2], (b) [Cu(L)(NO3)2].
(Fig. 3). The position of the bands suggests that both the nitrate
groups are coordinated in unidentate manner.
the amount of tetragonal distortion due to ligand field and
Jahn–Teller distortion effect.
In the sulphato complexes, the presence of medium intensity
bands in the region 944–999 cm−1, 430–438 cm−1 and another
strong band appears in the region 1170–1183 cm−1, which splits
into two bands that suggest the coordinated behaviour of sul-
phate group in unidentate manner.
The EPR spectra of Cu(II) complexes were recorded as
polycrystalline sample and in the solution of DMSO at room
temperature. The spectra of the complexes exhibit a single
anisotropic broad signal. The study of the spectra give g
ꢀ
value in the range 2.0706–2.0906 and g value in the range
⊥
2.0382–2.0510 (Table 3(a) and (b)). The observed g value for
ꢀ
the Cu(II) complexes are less than 2.3 in agreement with the
4. Nickel(II) complexes
covalent character of the metal ligand bond. The values of g and
ꢀ
g are closer to 2 and g > g > 2.0023. This suggests distortion
Magnetic moment of the Nickel(II) complexes at room tem-
perature lie in the range 2.93–2.98 BM (Table 2). These values
are in tune with a high spin configuration and show the presence
of an octahedral environment [17] around the Ni(II) ion in the
complexes (Fig. 5).
⊥
ꢀ
⊥
in the Cu(II) complexes from Oh symmetry to D4h symmetry.
G = (g − 2)/(g − 2), which measure the exchange interac-
ꢀ
⊥
tion between the copper centres in a polycrystalline solid has
been calculated. According to Hathway and Billing [23,24], if
the value of ‘G’ less 4, indicates a considerable exchange inter-
action in the solid complex. In the complexes of Cu(II) reported
in this paper, the ‘G’ value are less than 4 indicating the exchange
interaction in solid complex.
The electronic spectra of the complexes (Fig. 4), exhibit four
bands in the range 10,395–10,526 cm−1, 18,621–18,460 cm−1
,
27,932–28,571 cm−1 and 36,231–38,022 cm−1. An examina-
tion of these bands indicates that the complexes have an
octahedral geometry and might possess D4h symmetry [18]. The
3
ground state of Ni(II) in an octahedral coordination is A2g.
6. Ligand field parameters
Thus, these bands may be assigned to the three spin allowed
3
3
3
3
transitions [19,20], A2g (F) → T2g(F), A2g(F) → T1g(F),
3A2g(F) → T1g(P), respectively and fourth one may be con-
3
Various ligand field parameters were calculated for the com-
plexes and are listed in Table 4. The values of Dq in Ni(II)
complexes were obtained from the first transition. Our results are
in agreement with the respective position of anions in the spec-
trochemical series. The Nephelauxetic parameter β was readily
sidered as charge transfer band (Fig. 5).
5. Copper(II) complexes
The magnetic moment measurements of the Cu(II) com-
plexes at room temperature lie in the range 1.95–2.12 BM
(Table 2) corresponding to one unpaired electron [16,21].
Electronic spectra of the copper complexes (Fig. 4)
recorded in DMSO possess absorption bands in the
Table 2
Magnetic moment and electronic spectral data of the complexes
Complex
μeff (BM)
λmax (cm−1
)
range 11,013–11,098 cm−1
,
16,583–18,621 cm−1
and
[Ni(L)Cl2]
2.98
2.95
2.93
1.98
1.95
2.12
10,416, 18,621, 28,571, 36,231
10,526, 18,621, 27,932, 36,496
10,395, 18,621, 28,571, 38,022
11,013, 18,621, 28,571
11,098, 18,621, 27,932
11,086, 16,583, 28,248
27,932–28,571 cm−1
.
These bands may be considered
[Ni(L)(NO3)2]
[Ni(L)SO4]
[Cu(L)Cl2]
[Cu(L)(NO3)2]
[Cu(L)SO4]
to the following three spin allowed [22] transitions:
2
2
2B1g → A1g(dx2−y2 → d ), 2B1g → B2g(dx2−y2 → dzy)
2
and 2B → Eg(dx2−y2 →zdzy, dyz), these transitions suggest
2
D4h symmetry. The energy level sequence will depend on

1004
S. Chandra, A. Gautam / Spectrochimica Acta Part A 70 (2008) 1001–1005
Table 3
EPR spectral data of the complexes
Complexes
(a) Data at LNT and room temperature (as
polycrystalline sample)
(b) Data at LNT and room temperature
(in solution of DMF)
g
ꢀ
g
⊥
giso
G
g
ꢀ
g
⊥
giso
G
[Cu(L)Cl2]
[Cu(L)(NO3)2]
[Cu(L)SO4]
2.0773
2.0773
2.0706
2.0382
2.0446
2.0446
2.0512
2.0597
2.0532
2.0235
1.5156
1.5829
2.0906
2.0839
2.0906
2.0446
2.0510
2.0510
2.0599
2.0619
2.0642
2.0313
1.6450
1.7764
Fig. 5. Sugge−sted structure of the complexes, where M = Ni(II) and Cu(II),
X = Cl−, NO3 and (1/2)SO4
.
2−
Table 4
Ligand field parameter of the complexes
Complex
Dq (cm−1
)
B (cm−1
)
β
LFSE (kJ mol−1
)
[Ni(L)Cl2]
[Ni(L)(NO3)2]
[Ni(L)SO4]
1041.6
1052.6
1039.5
1062
998
1067
1.02
0.96
1.02
149.51
151.09
149.21
obtained by using the relation
β = B(complex) × B(free ion)
where B(free ion) for Ni(II) is 1041 cm−1. The values of β
indicate the appreciable covalent character of metal ligand ‘σ’
bond.
7. Conclusion
Ni(II) and Cu(II) complexes with a tetradentate macrocyclic
ligand have been prepared and characterized. On the basis of
abovespectralstudies, anoctahedralgeometryhasbeenassigned
for Ni(II) and tetragonal geometry for Cu(II) complexes. Various
ligand field parameters have been calculated and discussed.
Acknowledgements
We are thankful to Principal, Zakir Husain College for
providing laboratory facilities, RSIC, IIT Mumbai, for record-
ing EPR spectra and DRDO, New Delhi, for financial
assistance.
Fig. 4. Electronic spectra of the complexes. (a) [Ni(L)Cl2], (b) [Ni(L)(NO3)2],
(c) [Cu(L)Cl2], (d) [Cu(L)(NO3)2].

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1005
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