Spectroscopic characterization and EPR spectral studies on transition metal complexes with a novel tetradentate, 12-membered macrocyclic ligand

Article abstract of DOI:10.1016/j.saa.2005.12.042

Complexes of Cr(III), Mn(II), Co(II), Ni(II) and Cu(II) containing a tetradentate macrocyclic N-donor ligand have been prepared via template reaction of 2,3-pentanedione, ethylene-di-ammine and transition metal ions. The complexes have been characterized on the basis of the elemental analysis, molar conductance, magnetic moment susceptibility, IR, electronic and EPR spectral studies. The complexes are of high spin type and possess four coordinate tetrahedral five coordinate square pyramidal and six coordinated octahedral/tetragonal geometry.

Full text of DOI:10.1016/j.saa.2005.12.042

Spectrochimica Acta Part A 65 (2006) 792–796
Spectroscopic characterization and EPR spectral studies on transition metal
complexes with a novel tetradentate, 12-membered macrocyclic ligand
∗
Lokesh Kumar Gupta, Sulekh Chandra
Department of Chemistry, Zakir Husain College (University of Delhi), JLN-Marg, New Delhi 110002, India
Received 6 November 2005; accepted 6 December 2005
Abstract
Complexes of Cr(III), Mn(II), Co(II), Ni(II) and Cu(II) containing a tetradentate macrocyclic N-donor ligand have been prepared via
template reaction of 2,3-pentanedione, ethylene-di-ammine and transition metal ions. The complexes have been characterized on the basis
of the elemental analysis, molar conductance, magnetic moment susceptibility, IR, electronic and EPR spectral studies. The complexes
are of high spin type and possess four coordinate tetrahedral five coordinate square pyramidal and six coordinated octahedral/tetragonal
geometry.
©
2006 Elsevier B.V. All rights reserved.
Keywords: Macrocyclic ligands complexes; Magnetic moment; Spectral studies
1
. Introduction
used as received and the solvents used were of spectroscopic
grade.
The tetraaza macrocyclic ligands and their metal complexes
have attracted interest among the coordination chemists [1].
The metal ions directs the reaction preferentially towards cyclic
rather than oligomeric or polymeric products [2]. The study
of synthetic macrocyclic compounds is a very important area
of chemistry in view of their presence in many biological sig-
nificant naturally occurring metal complexes [3]. Keeping in
mind the importance of such type of compounds, in this paper
we report the synthesis and characterization of Cr(III), Mn(II),
Co(II), Ni(II) and Cu(II) complexes with a new macrocyclic lig-
and (L) (Fig. 1).
2
.1. Preparation of complexes
A template reaction was carried out for the formation of the
complexes. A hot ethanolic solution (20 ml) of the metal salt
0.025 mol) was mixed with a hot ethanolic solution (20 ml)
of ethylene-di-ammine (0.05 mol). Then an ethanolic solution
20 ml) of 2,3-petanedione (5.0 g, 0.05 mol) in the presence
(
(
of ethanolic lithium hydroxide solution (0.42 g, 0.01 mol) was
added to the resultant solution under constant stirring. This
solution was refluxed for 8 h. On cooling a colored complex
precipitated out. The complexes were filtered, washed with cold
ethanol and dried under vacuum over P4O10.
2
. Experimental
Synthesis of macrocyclic ligands often involved multi-step
2.2. Physical measurements
process and the products are generally obtained in poor yields.
The use of metal templates in the preparation of macrocyclic
complexes has been well established as a simple method by
which high yields of the target compound can be obtained.
All chemicals used, were of AnalaR grade and procured
from Fluka (USA) and E. Merck (Germany). Metal salt were
The C, H and N were analysed on a Carlo-Erba 1106
elemental analyzer. Molar conductance was measured on a
ELICO (CM82T) conductivity bridge. Magnetic susceptibility
was measured at room temperature on a Gouy balance using
CuSO4·5H2O as a callibrant. IR spectra (KBr) were recorded on
a Perkin-Elmer FTIR Spectrum BX-II spectrophotometer. The
electronic spectra were recorded in DMF on a Shimadzu UV
mini-1240 spectrophotometer. EPR spectra of all the complexes
were recorded as polycrystalline sample on E4-EPR spectrome-
∗
Corresponding author. Tel.: +91 11 229 112 67; fax: +91 11 232 15 906.
E-mail addresses: lokesh kg@rediffmail.com (L.K. Gupta),
schandra 00@yahoo.com (S. Chandra).
1
386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2005.12.042

L.K. Gupta, S. Chandra / Spectrochimica Acta Part A 65 (2006) 792–796
793
Fig. 1. Structure of the ligand (L).
Fig. 2. IR spectral bands of the complexes.
ter using the DPPH as the g-marker. The purity of the compounds
has been checked on high performance liquid chromatogra-
phy (HPLC), Waters Alliance Model 2695, by using Thermo-
Hypersil BDS (250 mm long, i.d. 4.6 ␮m and particle size 5 ␮m)
column. The mixture of potassium-dihydrogen-orthophosphate
buffer (pH 4.5) and acetonitrile in the ratio of 70:30, used as
attributed to ν(M N), which provides strong evidence for the
involvement of nitrogen in coordination [6]. Hence, we con-
clude out that the ligand is tetradentate coordinating through
four nitrogen atoms.
−
1
mobile phase, with the flow rate of 1.0 ml min
. Results and discussion
On the basis of elemental analysis, complexes were assigned
.
3
.1. IR bands due to anions
3
The IR spectra of the Cr(III) nitrate complex exhibit bands
corresponding to coordinated as well as uncoordinated nitrate
group. The cobalt nitrate complex shows the peak at 1385 cm
−1
the composition shown in Table 1. The molar conductivity val-
ues of the complexes recorded at room temperature in DMSO
solvent. The complexes of Cr(III) are found to be 1:1 elec-
corresponding to uncoordinated nitrates (Fig. 2), while other
nitrato complexes are found to be coordinated to the central
metal ion in unidentate manner (Table 2). In the IR spectra of
the thiocyanato complexes the peaks in the range ∼2089–2092,
−
trolyte [4] and may be formulated as [Cr(L)X2]X, where X = Cl
−
and NO3 . All other complexes, except the cobalt nitrate,
−
1
∼
855–865 and ∼410–498 cm could be assigned to ν(N C),
are non-electrolytic in nature while cobalt nitrate is 1:2 elec-
trolyte [5], these complexes may be formulated as [M(L)X2]
and [Co(L)](NO3)2, respectively.
ν(C S) and ν(NCS) bending vibrations, respectively. The posi-
tion of the bands is in favor of monodentate coordination through
the N-atom of the NCS group. The positions of IR peaks in the
sulphato complexes are in the tune of monodentate coordinated
sulphate group.
In the IR spectra of the complexes the absence of the bands
−
1
characteristic for free carbonyl group (∼1720 cm ) and pri-
−
1
mary ammines (∼3400 cm ) suggests that the complete con-
densation had occurred. The appearance of a new, strong inten-
−
1
sity, band in the region 1620–1660 cm , attributed to the char-
3.2. Chromium(III) complexes
acteristic stretching frequencies of the imino linkage ν(C N)
[
6], provides strong evidence in favor of the formation of cyclic
Cr(III) complexes shows magnetic moments correspond-
ing to three unpaired electrons, i.e. 3.72–3.82 B.M. Expected
−
1
product. Another IR spectral peak in the region 405–475 cm
,
Table 1
Elemental analysis, color and molar conductance data of the complexes
Complex
Yield (%) Color
Molar conductance
Calculated (found) (%)
−
1
2
−1
(
ꢀ
cm mol )
C
H
N
M
[
[
[
[
[
[
[
[
[
[
[
[
[
Cr(L)Cl2]Cl CrC14H24N4Cl3
Cr(L)(NO3)2]NO3 CrC14H24N7O9
Mn(L)Cl2]MnC14H24N4Cl2
Co(L)Cl2] CoC14H24N4Cl2
Co(L)(NCS)2] CoC16H24N6S2
Co(L)](NO3)2 CoC14H24N6O6
Co(L)SO4] CoC14H24N4SO4
Ni(L)Cl2] NiC14H24N4Cl2
Ni(L)(NO3)2] NiC14H24N6O6
Ni(L)(NCS)2] NiC16H24N6S2
Cu(L)Cl2] CuC14H24N4Cl2
Cu(L)(NO3)2] CuC14H24N6O6
Cu(L)SO4] CuC14H24N4SO4
77
66
78
65
82
70
78
62
62
72
82
73
66
Green
Grey
Light brown
Pink
Redish brown
Grey
Pink
Dark brown
Brown
Green
Brown
92.23
84.86
10.42
12.24
16.96
205.95
12.08
12.84
12.56
14.92
14.45
17.06
13.65
41.34 (41.27)
34.57 (34.51)
44.94 (44.92)
44.46 (44.53)
45.38 (45.47)
38.99 (38.76)
41.69 (41.72)
44.49 (44.62)
39.01 (39.08)
45.41 (45.54)
43.93 (44.12)
38.57 (38.65)
41.22 (41.34)
5.95 (5.91)
4.97 (4.86)
6.46 (6.53)
3.73 (3.81)
5.71 (5.84)
3.27 (3.33)
5.99 (6.04)
6.40 (6.46)
5.61 (5.67)
5.71 (5.79)
6.32 (6.45)
5.55 (5.62)
5.93 (5.98)
13.78 (13.67)
20.16 (20.22)
14.97 (15.03)
14.81 (14.88)
19.85 (19.96)
19.48 (19.56)
13.89 (13.97)
14.82 (14.95)
19.49 (19.59)
19.86 (19.82)
14.64 (14.89)
19.28 (19.34)
13.73 (13.91)
12.78 (12.84)
10.69 (10.76)
14.68 (14.59)
15.58 (15.63)
13.91 (14.02)
13.66 (13.72)
14.61 (14.76)
15.53 (15.67)
13.61 (13.67)
13.86 (13.97)
16.60 (16.82)
14.58 (14.66)
15.58 (15.67)
Light green
Black

7
94
L.K. Gupta, S. Chandra / Spectrochimica Acta Part A 65 (2006) 792–796
Table 2
Table 4
IR spectral bands of the complexes
Ligand field parameters of the complexes
Dq (cm 1)
−
B (cm
−1
)
β
−1
LFSE (kJ mol )
Complexes
ν(C N) ν(M N) ν(M X)
ν(C H)
Complexes
[
[
[
[
[
[
[
[
[
[
[
[
[
Cr(L)Cl2]Cl
Cr(L)(NO3)2]NO3 1632
Mn(L)Cl2]
Co(L)Cl2]
Co(L)(NCS)2]
Co(L)](NO3)2
Co(L)SO4]
Ni(L)Cl2]
Ni(L)(NO3)2]
Ni(L)(NCS)2]
Cu(L)Cl2]
1625
420
450
440
470
410
425
405
424
435
475
452
438
455
362
3003
2958
2900
2940
2976
2950
2948
2956
2987
2943
2980
2995
[Cr(L)Cl2]Cl
[Cr(L)(NO3)2]NO3
[Mn(L)Cl2]
1494
1577
824
948
1013
301
1140
945
986
659
796
749
987
1055
684
660
775
791
0.72
0.86
0.79
0.88
0.90
0.61
0.63
0.74
0.76
21400
226.00
–
90.60
96.82
43.15
163.44
135.48
141.36
1236, 1033, 802
–
316
2089, 855
1230, 1030, 800
940, 1040, 1188
304
1235, 1028, 802
2092, 865
–
1640
1620
1648
1660
1624
1644
1628
1640
1650
1638
1656
[Co(L)Cl2]
[Co(L)(NCS)2]
[Co(L)](NO3)2
[Ni(L)Cl2]
[Ni(L)(NO3)2]
[Ni(L)(NCS)2]
Cu(L)(NO3)2]
Cu(L)SO4]
1232, 1024, 806
946, 1048, 1192, 640 2978
The EPR spectra recorded as polycrystalline sample at room
temperature and the g-values has been calculated by using the
expression: g = 2.0023(1 − 4λ/10 Dq), where λ is the orbit spin
coupling constant for the metal ion in the complexes. The g-
values are 1.97–1.99.
Table 3
Electronic spectral and magnetic moment data of the complexes
λMax (cm 1)
−
μeff (at room
Complexes
3.3. Manganese(II) complex
temperature)
[
[
[
[
[
[
[
[
[
[
[
[
[
Cr(L)Cl2]Cl
Cr(L)(NO3)2]NO3
Mn(L)Cl2]
14347, 21367, 28688
15772, 23201, 26315
18270, 24650, 28930, 30487
8090, 16500, 20921
8650, 15480, 21300, 34450
5400, 14706, 22222, 30824
12400, 15504, 21368
11402, 18620, 25500
9450, 18692, 21277
9860, 18797, 22650, 29540
13600, 22422
3.82
3.72
5.94
5.05
5.08
4.66
4.98
3.12
3.04
3.20
1.90
2.02
1.94
The room temperature magnetic moment of the complex is
.94 B.M. It corresponds to the five unpaired electrons, high spin
5
Co(L)Cl2]
octahedral configuration [8]. The electronic spectra of the com-
plexes give four weak intensity peaks (Table 3), which may be
assigned to the transitions, characteristic to the octahedral geom-
Co(L)(NCS)2]
Co(L)](NO3)2
Co(L)SO4]
6
4
4
6
4
4
4
6
4
4
etry A1g → T1g( G), A1g → Eg A1g( G), A1g → Eg( D)
Ni(L)Cl2]
6
4
4
Ni(L)(NO3)2]
Ni(L)(NCS)2]
Cu(L)Cl2]
Cu(L)(NO3)2]
Cu(L)SO4]
and A1g → T1g( P), respectively. By the help of above transi-
tions various ligand field parameters have been calculated and
are listed in Table 4.
11050, 17452
12500, 20600
TheEPRspectrumofthecomplexrecordedaspolycrystalline
sample and in DMSO solution at room temperature. The poly-
crystalline sample gives one broad isotropic signal centered at
1
.9892, it is near to the free electron value, i.e. 2.0023 (Table 5).
to high spin octahedral Cr(III) complexes [7]. The electronic
spectra recorded in DMSO solution gives well resolved three
peaks (Table 3 and Fig. 3), which may be assigned to the
3
.4. Cobalt(II) complexes
4
4
4
4
4
4
A2g(F) → T2g(F), A2g(F) → T1g(F)and A2g(F) → T2g(P)
The magnetic moment of the cobalt(II) complexes recorded
transition, respectively. The energy of the first spin allowed tran-
4
4
at room temperature lies in the range 4.66–5.08 B.M. It may
be possess for the four coordinated tetrahedral, five coordinated
square pyramidal and six coordinated octahedral geometry. The
geometry of the present complexes have been elucidated on the
basis of electronic spectra, discussed below.
sition A2g(F) → T2g(F), directly gives the value of the 10 Dq.
The values of the Racah parameter ‘B’ have been calculated
2
2
by using the formula: B = (2ν + ν − 3ν1ν3)/(15ν2 − 27ν1).
1
2
The low ‘B’ values indicate the greater degree of the co-valance
in M N bond.
Fig. 3. Electronic spectra of the complexes.

L.K. Gupta, S. Chandra / Spectrochimica Acta Part A 65 (2006) 792–796
795
Table 5
EPR spectral data of the complexes
Complexes
Temperature
g||
g⊥
giso
g3
g2
g1
R
G
[
[
[
[
[
[
[
[
[
[
Cr(L)Cl2]Cl
Cr(L)(NO3)2]NO3
Mn(L)Cl2]
RT
RT
RT
LNT
LNT
LNT
LNT
RT
–
–
–
–
–
–
1.982
1.984
1.982
4.002
2.854
2.715
2.731
2.131
2.177
2.231
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
–
4.45
4.13
–
Co(L)Cl2]
5.871
4.254
3.902
4.232
2.271
2.308
–
5.871
4.254
3.902
4.232
2.061
2.075
–
Co(L)(NCS)2]
Co(L)](NO3)2
Co(L)SO4]
Cu(L)Cl2]
Cu(L)(NO3)2]
Cu(L)SO4]
RT
RT
–
–
–
–
4.424
2.177
2.092
0.344
RT, room temperature; LNT, liquid nitrogen temperature.
3
3
3
3
3
.5. Co(L)Cl2 and Co(L)(NCS)2
ration transitions: A2g(F) → T2g(F), A2g(F) → T1g(F) and
3
3
A2g(F) → T1g(P), respectively.
The electronic spectra of complexes prepared from CoCl2
and Co(NCS)2 are characteristic of octahedral cobalt(II)
9–10]. They show three peaks (Table 3), corresponding
The Naphelauxetic parameter β is calculated by using the
relation: β = B(Complex)/B(Free ion), where B is the Racah inter-
electronic repulsion parameter. The values of B, lowered than
the free Ni(II) ion, i.e. 1041 cm , suggesting 24–37% covalent
character in the M N linkage. Other ligand field parameter are
also calculated and are listed in Table 4.
[
4
4
4
4
4
4
4
4
−
1
to T1g( F) → T2g( F), ν1; T1g( F) → A2g( F), ν2 and
4
4
4
4
T1g( F) → T1g( P), ν3 transitions, respectively. The EPR
spectra of the complexes under study were recorded at liq-
uid nitrogen temperature because we found that the rapid
relaxation of Co(II) broadened the lines at higher temperature
3
.9. Copper(II) complexes
(
g|| = 4.254–5.871 and g⊥ = 2.154–3.067). The large deviations
of the g-values from the spin only value (g = 2.0023) is due to
The room temperature magnetic moment values of the Cu(II)
the large angular momentum contribution.
complexes (1.90–2.02 B.M.) indicates the monomeric nature of
the complexes. The values correspond to one unpaired electron
and the complexes may be considered as tetragonal geometry,
except the sulphato complex whish possess five coordinated
square pyramidal geometry and Cu2 ion and anions occupies
the axial position. The chloro and nitrato complexes of the Cu(II)
3
.6. Co(L)(NO3)2
+
The electronic spectra of the tetrahedral and octahedral
cobalt(II) complexes are almost similar. The remarkable differ-
−
1
2
2
ence is the presence of a band at ∼5000 cm , in the tetrahedral
givestwoelectronicpeaks(Table3)assignedtothe B → A
1
g
1g
2
2
complexes, which is absent in the octahedrals. In the present
and B1g → E transitions, characteristic for tetragonal geom-
g
−
1
case the presence of the band at 5400 cm , suggests tetrahe-
dral geometry of this complex [11].
etry. The copper(II) sulphato complex gives the electronic peaks
comparable with five coordinate square pyramidal geometry.
The complexes have anisotropic EPR spectra, characteristic
to tetragonal geometry [14]. The g-values have been calculated
by the method published earlier [15–16], and are summarized in
Table 5. The value of G = (g − 2)/(g − 2) which measure the
3
.7. Co(L)SO4
The electronic spectra of the sulphate complex display three
||
⊥
−
1
−1
−1
bands at ∼12,400 cm , ν1; ∼15,504 cm , ν2; ∼21,368 cm
,
exchange interaction between the copper centers in polycrys-
talline samples. If the value of G > 4, the exchange interaction is
negligible but the G < 4 value suggest considerable interaction
between the solid complex. The value of G in the complexes
reported here is G > 4, suggesting that there is no interaction
between the copper centers.
ν3, corresponding to the square pyramidal geometry [9]. Ligand
field parameters for the complex have been calculated and are
in the tune of the results published earlier [12].
3
.8. Nickel(II) complexes
Five coordinated copper(II) complex may possess two
geometries, i.e. trigonal bi-pyramidal and square pyramidal [17],
All complexes are of high spin type and show room temper-
ature magnetic moments in the range 3.04–3.20 B.M. (Table 3),
correspond to two unpaired electrons. High spin Ni(II) com-
plexes may be four coordinated tetrahedral and six coordi-
nated octahedral. The observed μeff values are low for tetra-
hedral Ni(II) complexes, which is known to show magnetic
moments in the range 3.40–4.12 B.M. The electronic spec-
tra are in favor of octahedral geometry [13]. It shows three
bands (Table 3) which are assignable to octahedral configu-
which are characterized by ground states d
2
2
or dz , respec-
2
x −y
tively [18]. The EPR spectra provides an excellent basis for
distinguishing between these two ground states. For system with
g3 > g2 > g1 the ratio (g2 − g1)/(g3 − g2) called the parameter
‘R’, is very useful for this purpose. If the ground state predom-
inantly, dz
2
, the value of R is greater than 1, and the value of R
less than 1 is in the case of d
g1, g2, g3 and R (Table 5) for the complex under study suggest
2
2
ground state. The value of
x −y

7
96
L.K. Gupta, S. Chandra / Spectrochimica Acta Part A 65 (2006) 792–796
[7] B.N. Figgis, Introduction to Ligand Field Theory, Wiley, New York, 1978.
the d
Cu(II) ion.
2
2
ground state (square pyramidal geometry) around the
x −y
[
[
8] N.K. Singh, S.K. Kushwaha, Indian J. Chem. 39 (2000) 1070.
9] A.B.P. Lever, Electronic Spectra of Inorganic and Coordination Com-
pounds, John Wiley, New York, 1968.
Acknowledgements
[
10] E.Q. Gao, S. Bi, H. Sun, S. Liu, Synth. React. Inorg. Met.-Org. Chem. 27
1997) 1115;
S. Chandra, L.K. Gupta, Spectrochim. Acta A 60 (2004) 1563.
(
We are thankful to the Department of Science & Technol-
ogy and Defence Research & Development Organization for
financial assistance. We are also thankful to the Regional Sophis-
ticated Instrumentation Center, Indian Institute of Technology
Mumbai for recording the EPR spectra.
[11] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry,
Wiley/Interscience Publication, New York, 1988.
[
12] S. Chandra, L.K. Gupta, Spectrochim. Acta A 60 (2004) 1751;
S. Chandra, L.K. Gupta, Spectrochim. Acta A 60 (2004) 2767.
[
13] M. Shakir, A.K. Mohamed, O.S.M. Nasman, Polyhedron 15 (1996)
3490.
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