Spectroscopic approach in characterization of chromium(III), manganese(II), iron(III) and copper(II) complexes with a nitrogen donor tetradentate, 14-membered azamacrocyclic ligand

Article abstract of DOI:10.1016/j.saa.2004.06.060

The complexes of Cr(III), Mn(II), Fe(III) and Cu(II) were synthesized with the macrocyclic ligand i.e. 2,3,9,10-tetraketo-1,4,8,11- tetraazacyclotetradecane. The ligand was prepared by the [2 + 2] condensation reaction of diethyloxalate and 1,3-diamino propane. These complexes were found to have the general composition M(L)X₃ and M′(L)X₂ [where M = Mn(II) and Cu(II), M′ = Cr(III) and Fe(III), L = ligand (N ₄) and X = Cl^-, NO₃^-, 1/2SO ₄^2- and [CH₃COO^-]. The ligand and its transition metal complexes were characterized by the elemental analyses, molar conductance, magnetic susceptibility, mass, IR, electronic, and EPR spectral studies. On the basis of IR, electronic and EPR spectral studies an octahedral geometry has been assigned for Cr(III), Mn(II) and Fe(III) and a tetragonal geometry for Cu(II) complexes.

Full text of DOI:10.1016/j.saa.2004.06.060

Spectrochimica Acta Part A 61 (2005) 2139–2144
Spectroscopic approach in characterization of chromium(III),
manganese(II), iron(III) and copper(II) complexes with a
nitrogen donor tetradentate, 14-membered azamacrocyclic ligand
Sulekh Chandra∗, Lokesh Kumar Gupta
Department of Chemistry, Zakir Husain College, University of Delhi, JLN-Marg, New Delhi 110002, India
Received 12 April 2004; accepted 16 June 2004
Abstract
The complexes of Cr(III), Mn(II), Fe(III) and Cu(II) were synthesized with the macrocyclic ligand i.e. 2,3,9,10-tetraketo-1,4,8,11-
tetraazacyclotetradecane. The ligand was prepared by the [2 + 2] condensation reaction of diethyloxalate and 1,3-diamino propane. These
complexes were found to have the general composition M(L)X3 and Mꢀ(L)X2 [where M = Mn(II) and Cu(II), Mꢀ = Cr(III) and Fe(III), L
= ligand (N4) and X = Cl−, NO3−, 1/2SO4 and [CH3COO−]. The ligand and its transition metal complexes were characterized by the
2−
elemental analyses, molar conductance, magnetic susceptibility, mass, IR, electronic, and EPR spectral studies.
On the basis of IR, electronic and EPR spectral studies an octahedral geometry has been assigned for Cr(III), Mn(II) and Fe(III) and a
tetragonal geometry for Cu(II) complexes.
© 2004 Elsevier B.V. All rights reserved.
Keywords: Azamacrocyclic; Chromium(III); Manganese(II); Iron(III); Copper(II)
1. Introduction
In this paper, we report the synthesis and character-
ization of Cr(III), Fe(III), Mn(II) and Cu(II) complexes
with 2,3,9,10-tetraketo-1,4,8,11-tetraazacyclotetradecane
(Fig. 1). The possible geometry for complexes has been
deduced by the elemental analyses, molar conductance,
magnetic susceptibility, IR, electronic and EPR spectral
studies.
The complexes of metal ions with macrocyclic ligands are
significant because of there resemblance with many natural
systems, such as porphyrins and cobalamines [1,2] The main
interest in new macrocyclic bifunctional chelating agents
arise due to their use in labeling monoclonal antibodies with
radioactive metals [3–5] and for cancer diagnoses [6,7] as
well as with permagnetic ions for magnetic resonance imag-
ing [8].
2. Experimental
The attachment of metal ions to proteins such as mono-
clonal antibodies can create new tools for use in biology and
medicine [9]. This type of ligands has theoretical importance
also because they are capable of furnishing an environment
with controlled geometry and ligand field strength [10,11].
The reagents used for such attachments are called bifunc-
tional chelating agents [12]. They have shown to be efficient
catalyst for cleavage of the phosphate ester bond [13].
All the chemicals used were of AnalaR grade, and pro-
cured from Sigma-Aldrich, USA and E. Merck, Germany.
Metal salts were purchased from E. Merck and Ranbaxy and
were used as-received.
2.1. Synthesis of ligand
The hot ethanolic solution (20 mL), of diethyloxalate
(2.9228 g, 0.02 mol), and a hot ethanolic solution (20 mL) of
1,3-diaminopropane (1.4826 g, 0.02 mol) were mixed slowly
∗
Corresponding author.
E-mail address: schandra00@yahoo.com (S. Chandra).
1386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2004.06.060

2140
S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 61 (2005) 2139–2144
Fig. 1. Synthesis and structure of ligand (L).
with constant stirring. This mixture was refluxed at ∼78 ◦C
for 7 h in the presence of few drops of concentrated hy-
drochloric acid. On cooling a solid cream-colored precipi-
tate formed, which was filtered, washed with cold EtOH, and
dried under vacuum over P4O10. Yield ∼78%, m.p. 240 ◦C.
Elemental analyses found (%): C, 46.79; H, 6.31; N, 21.83.
Calculated for C10H16N4O4 (atomic mass 256) was C, 46.88;
H, 6.25 and N, 21.87%.
2.2. Synthesis of complexes
The hot ethanolic solution (20 mL), of ligand (0.5120 g,
0.002 mol)andhotethanolicsolution(20 mL), ofcorrespond-
ing metal salt (0.001 mol) were mixed together with constant
stirring. The mixture was refluxed for 4–9 h at 78 ◦C. On cool-
ing, colored complex precipitated out. It was filtered, washed
with cold EtOH and dried under vacuum over P4O10 and
recrystallised.
2.3. Physical measurements
The C, H and N were analysed on a Carlo-Erba 1106
elemental analyzer. IR spectra (KBr) were recorded on an
FTIR Spectrum BX-II spectrophotometer. The electronic
spectra were recorded in DMSO on Shimadzu UV mini-1240
spectrophotometer. Molar conductance was measured on an
ELICO (CM82T) conductivity bridge. Magnetic susceptibil-
ity was measured at room temperature on a Gouy balance
using CuSO4·5H2O as a callibrant. Electron impact mass
spectra were recorded on Jeol, JMS, DX-303 mass spec-
trometer. 1H NMR spectra were recorded on Hitachi model
R-600FT-NMRspectrometerusingCDCl3 assolvent, chemi-
cal shifts are given in ppm relative to tetramethylsilane. EPR
spectra of the complexes were recorded as polycrystalline
sample at RT on E4-EPR spectrometer using the DPPH as
the g-marker.
3. Results and discussion
On the basis of elemental analyses, the complexes were as-
signed the composition shown in Table 1. The molar conduc-
tance measurements in DMSO correspond to 1:1 electrolytic
nature for Cr(III) and Fe(III) complexes and non-electrolytes
for the Mn(II) and Cu(II) complexes. Thus the complexes

S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 61 (2005) 2139–2144
2141
3.1. Chromium(III) complexes
Chromium(III) complexes show magnetic moment in the
range 3.68–3.72 BM recorded at room temperature, corre-
sponding to three unpaired electrons (Table 3). This value
is close to the spin only value. IR spectrum (Fig. 3b) of
Cr(III) nitrate complex shows three IR bands ν5, ν1 and ν2 at
1437, 1318 and 1021 cm−1, respectively. The difference of
two highest frequency bands (ν5 − ν1) is 119 cm−1, charac-
teristics for unidentate behavior of nitrate ion. A sharp strong
band at 1379 cm−1 confirms the presence of a uncoordinated
nitrate ion.
Fig. 2. Electron impact mass spectrum of the ligand (L).
The electronic spectra (Fig. 3) of Cr(III) complexes
recorded in DMSO solution at room temperature, display
three bands in the range 18,586–18,605 (ε = 41–42 L mol−1
may be formulated as [M(L)X2]X and [Mꢀ(L)X2], respec-
tively [where M = Mn(II) and Cu(II), Mꢀ = Cr(III) and Fe(III),
L = ligand and X = Cl−, NO3−, and CH3COO−].
cm−1) (ν1), 22,290–22,386 (ε = 56–58 L mol−1 cm−1
)
The mass spectra of ligand (L) (Fig. 2) confirm the pro-
posed formula by showing a peak at 255 amu correspond-
ing to the macrocyclic moiety [(C10H16N4O4)+ calculated
atomic mass = 256 amu]. It also shows a series of peaks at
42, 56, 72, 128, 184 and 200 amu corresponding to various
fragments. Their intensity gives an idea of stability of frag-
ments. The 1H NMR spectrum of the metal-free ligand does
not give any signal corresponding to primary diamine and
ketonic group. It shows a signal at δ3.7(q) ppm, attributed to
amide ( CH2 NH C ) protons (4H). The signals appeared
at δ2.6(m) ppm and δ1.4(q) ppm may be assigned to methylene
protons [14]. IR spectrum of the ligand does not exhibit any
band corresponding for the free primary diamine and ketonic
group. Four new bands, Table 2, appear in the spectrum of
ligand [15] in the regions 1651, 1518, 1226 and 762 cm−1 are
assignable to amide-I ν(C O), amide-II [ν(C N) + δ(N H)],
amide-III [δ(N H)] and amide-IV [ϕ(C O)] bands, respec-
tively. This supports the macrocyclic nature of the ligand.
A single sharp band observed at 3298 cm−1, may be due to
ν(N H) of the secondary amino group [16]. On complexa-
tion the position of ν(N H) bands shifted to lower frequency
compared to the macrocyclic ligand and a new medium in-
tensity band appears at 418–490 cm−1 attribute to ν(M N),
it provide, strong evidence for the involvement of nitrogen
in coordination. IR spectrum indicates that the ligand act as
tetradentate coordinating through nitrogen [N4].
(ν2) and 24,920–24,948 (ε = 65–67 L mol−1 cm−1), char-
acteristic to an octahedral geometry [17] (Fig. 4). These
4
4
bands may be assigned to the transitions A2g → T1g
4
4
(F) ν2 and A2g → T2g (F) ν1, respectively, and third
one is due to the charge transfer. Various ligand field
parameters are calculated and given in Table 4. Dq values
have been evaluated by using Orgel energy level diagram.
The Nephelauxetic parameter β is obtained by using the
relation: β = B(Complex)/B(Free ion). The β values indicate
that the complexes have appreciable covalent character. EPR
spectra were recorded as a polycrystalline sample at room
temperature. An isotropic EPR spectra of Cr(III) complexes
recorded at room temperature as polycrystalline sample
shows the giso values in the range 1.9965–2.0016 (Table 5).
3.2. Manganese(II) complexes
The room temperature magnetic moment of the man-
ganese(II) complexes lies in the range 5.89–5.93 BM cor-
responding to five unpaired electrons.
IR spectrum of Mn(II) sulphate complex exhibits three
bands at ∼1123–1151, 970 and 617–609 cm−1, assigned to
ν3, ν1 and ν4, respectively. Both the bands ν3 and ν4 splits into
two bands. It can be explained by assuming the lowering in
symmetry from Td to C3v (unidentate manner of coordination
of sulphate group), Fig. 5.
Table 2
IR spectral data and their assignments in cm−1
Complexes
ν(N H)
Amide-I [ν(C=O)]
Amide-II [ν(C N) + δ(N H)]
Amide-III [␦(N H)]
Amide-IV [φ(C=O)]
[ν(M N)]
Ligand (L)
3298
3296
3299
3295
3298
3293
3297
3284
3289
3296
3298
1651
1653
1647
1649
1655
1652
1647
1650
1651
1657
1648
1518
1502
1505
1495
1499
1506
1497
1501
1490
1503
1492
1226
1209
1202
1210
1197
1211
1205
1201
1199
1215
1206
762
759
756
766
759
763
762
755
762
757
760
–
[Cr(L)Cl2]Cl
[Cr(L)(NO3)2]NO3
[Mn(L)Cl2]
487
463
488
452
481
467
438
479
465
459
[Mn(L)SO4]
[Fe(L)Cl2]Cl
[Fe(L)(NO3)2]NO3
[Cu(L)Cl2]
[Cu(L)(NO3)2]
[Cu(L)SO4]
[Cu(L)(CH3COO)2]

2142
S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 61 (2005) 2139–2144
Table 3
Magnetic moment and electronic spectral data of the complexes
Complex
µeff (BM)a
λmax (cm−1
)
Extinction coefficient, ε (L mol−1 cm−1
)
[Cr(L)Cl2]Cl
[Cr(L)(NO3)2]NO3
[Mn(L)Cl2]
[Mn(L)SO4]
[Fe(L)Cl2]Cl
[Fe(L)(NO3)2]NO3
[Cu(L)Cl2]
[Cu(L)(NO3)2]
[Cu(L)SO4]
3.68
3.72
5.89
5.93
5.91
5.98
1.92
2.01
1.97
1.90
18586, 22290, 24920
18605, 22386, 24948
41, 58, 65
42, 56, 67
46, 51, 59, 74
47, 53, 58, 76
73, 84, 97
18349, 22883, 28329, 38462
19685, 23474, 28011, 38610
18939, 21008, 27027, 37037
18627, 20593, 26762, 37842
15878, 20315, 31328
16705, 20527, 31272
16764, 20109, 31478
16837, 20768, 31517
71, 80, 96
52, 68, 134
54, 69, 133
54, 76, 135
55, 70, 136
[Cu(L)(CH3COO)2]
a
Error limit 4%.
Table 4
Ligand field parameters of the complexes
Complex
Dq (cm−1
)
B (cm−1
)
C (cm−1
)
β
LFSE (kJ mol−1
)
[Cr(L)Cl2]Cl
[Cr(L)(NO3)2]NO3
[Mn(L)Cl2]
[Mn(L)SO4]
[Fe(L)Cl2]Cl
2229.00
2238.60
1834.90
1968.50
1893.90
1862.70
329.15
336.54
778.00
648.15
859.86
881.29
1316.60
1314.16
3020.60
3398.50
2481.88
2356.02
0.36
0.37
0.89
0.83
–
319.57
320.95
00.00
00.00
00.00
00.00
[Fe(L)(NO3)2]NO3
–
4Eg, 4A1g(4G) (10B + 5C) and A1g → Eg(4D) (17B +
6
4
Electronic spectra of Mn(II) complexes exhibit
four weak intensity absorption bands in the range
18,349–19,685 (ε = 46−47 L mol−1 cm−1), 22,883–23,474
5C), 6A1g → T1g(4P) (7B + 7C), respectively.
4
The value of B and C were calculated from the second
and third transitions, because these transitions are free from
the crystal field splitting and depend on B and C parameters
[18,19]. The calculated values of the ligand field parameters
are given in Table 4.
(ε
=
51−53 L mol−1 cm−1), 28,011–28,329 (ε
=
58−59 L mol−1 cm−1), and 38,462–38,610 cm−1 (ε
=
74−76 L mol−1 cm−1). These bands may be as-
6
4
signed to the transitions: A1g → T1g(4G), 6A1g
→
EPR spectra were recorded at room temperature as poly-
crystalline sample and in DMSO solution. The polycrys-
talline spectra were isotropic and exhibit the giso value in the
range 1.9980–2.0018. The EPR spectra recorded in DMSO
solution give well defined six line, arising due to the hyper-
fine interaction between the unpaired electron with the 55Mn
nuclear (l = 5 ). The nuclear magnetic quantum number M1,
2
5
3
1
corresponding to these lines are −2 , −2 , −2 , +12 , +23 and
5
+
from low to the high field.
2
Fig. 3. Electronic spectra of the complexes.
Fig. 4. Suggested structures of the complexes.

S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 61 (2005) 2139–2144
2143
Table 5
EPR spectra of iron(III) complexes were recorded as poly-
crystalline sample at room temperature. The isotropic spectra
gives the giso values in the range 2.0402–2.0468.
EPR spectral data of the complexes
Complexes
Data at room temperature
g
g
g
iso/g
G
||
⊥
[Cr(L)Cl2]Cl
[Cr(L)(NO3)2]NO3
[Fe(L)Cl2]Cl
[Fe(L)(NO3)2]NO3
[Mn(L)Cl2]
[Mn(L)SO4]
[Cu(L)Cl2]
[Cu(L)(NO3)2]
[Cu(L)SO4]
–
–
–
–
–
–
–
–
–
–
–
–
1.9965
2.0016
2.0402
2.0468
1.9980
2.0018
2.0665
2.1090
2.1254
2.0482
–
–
–
–
–
–
3.4. Copper(II) complexes
The magnetic moment measurements of the Cu(II) com-
plexes at room temperature lie in the range 1.90–2.01 BM
corresponding to one unpaired electron. The complexes may
be considered to possess a tetragonal geometry.
The IR spectra of Cu(II) nitrate complex displays three
bands (ν5, ν1 and ν2) at 1429, 1325 and 1017 cm−1. The
position of these bands suggests the coordinated behavior of
nitrate group as unidentate.
2.0998
2.2224
2.2107
2.0973
2.0499
2.0531
2.0828
2.0236
2.0000
4.1890
2.5568
4.1229
[Cu(L)(CH3COO)2]
IR spectrum of sulphate complex exhibits four bands at
1098–1033, 986, 639–581 and 467 cm−1. Assigned to ν3, ν1,
ν4, and ν2, respectively. The ν3 and ν4 each splits into two
bands. It suggests the unidentate behavior of the sulphate ion
[21].
3.3. Iron(III) complexes
These complexes show magnetic moments correspond-
ing to five unpaired electrons [20], which lie in the range
5.91–5.98 BM.
The IR spectrum of Cu(II) acetate complex shows the
medium intensity bands at 1619 and 1332 cm−1, assigned
to νa(C O) and νs(C O), respectively. The difference be-
tween these two frequencies is ∼287 cm−1, which is greater
than that for uncoordinated acetate ion by ∼143 cm−1 and
for bidentate acetate ion by ∼217 cm−1. It strongly support
that both the acetate ions are coordinated to the metal ion in
the unidentate fashion [21].
IR spectrum of iron nitrate complex (Fig. 5(b)) shows
bands corresponds to bidentate nature. The presence of an
uncoordinated nitrate group is also confirmed by the band
(strong) present at 1386 cm−1, in the IR spectra of the Fe(III)
sulphate complex [21].
Electronic spectra of these complexes display three bands
in the range 18,627–18,939 (ε = 71−73 L mol−1 cm−1),
20,593–21,008 (ε = 80−84 L mol−1 cm−1) and 26,762–
27,027 cm−1 (ε = 96−97 L mol−1 cm−1). The assignments to
these bands are difficult.
Electronic spectra of copper complexes display bands
in the range 15,878–16,764 (ε = 52–55 L mol−1 cm−1
)
(ν1), 20,109–20,768 (ε = 67–70 L mol−1 cm−1) (ν2) and
31,272–31,517 cm−1 (ε = 133–136 L mol−1 cm−1) (ν3), cor-
responding to the following transitions: 2B1g → A1g (dx2−y2
2
2
2
→ dz2 ) ν1, 2B1g → B2g (dx2−y2 → dzy) ν2 and 2B1g → Eg
(dx2−y2 → dzy, dyz) ν3, respectively. These three spin allowed
transitions may be expected in the visible region, suggesting
D4h or C4v symmetry.
The complexes exhibit anisotropic EPR spectra character-
istic of tetragonal copper. The observed g values are in the
range 2.0482–2.1090.
G = (g||−2)/(g⊥−2), which measure the exchange interac-
tion between the copper centers in a polycrystalline solid has
been calculated. According to Hathaway and Billing [22] and
Chandra [23] if G > 4, the exchange interaction is negligible
but G < 4 indicates considerable exchange interaction in the
solid complexes. The G value for chloride and sulphate com-
plexes are <4, it indicates a considerable exchange interaction
between two molecules of the complex while in the nitrate
acetate complexes the value of G is >4 suggest the vice versa
position.
Acknowledgements
We are thankful to the Principal, Zakir Husain College,
for providing research facilities. ACBR Delhi University, for
Fig. 5. IR spectral bands of the anions.

2144
S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 61 (2005) 2139–2144
recording IR spectra, RSIC, IIT Mumbai, for recording EPR
spectra and UGC, New Delhi, for financial assistance.
S. Chandra, K. Gupta, Trans. Met. Chem. 27 (2002) 329.
[12] S. Chandra, N. Gupta, L.K. Gupta, Synth. React. Inorg. Met.-Org.
Chem. 34 (2004) 919;
A.K. Mishra, J.F. Chatal, New J. Chem. 25 (2001) 336;
L. Broge, I. Sotofte, C.E. Olsen, J. Springborg, Inorg. Chem. 40
(2001) 3124.
References
[13] V. Alexander, Chem. Rev. 95 (1995) 273.
[14] P.S. Kalsi, Spectroscopy of Organic Compounds, fourth ed., New
Age International (P) Ltd. Publisher, New Delhi, 2001.
[15] M. Shakir, O.S.M. Nasman, A.K. Mohamed, S.P. Varkey, Ind. J.
Chem. 35A (1996) 770.
[1] F.H. Fry, B. Graham, L. Spiccia, D.C.R. Hockles, E.R.T. Tiekink, J.
Chem. Soc., Dalton Trans. (1997) 827.
[2] M. Rosignoli, P.V. Bernhardt, G.A. Lawrence, M. Maeder, J. Chem.
Soc., Dalton Trans. (1997) 323.
[3] S. Brandes, F. Denat, S. Lacour, F. Rabiet, F. Barbette, P. Pulumbi,
R. Guilard, Eur. J. Org. Chem. (1998) 2349.
[16] U.K. Pandey, S.K. Sengupta, S.C. Tripathi, Polyhedron 6 (1987)
1611.
[4] W. Niu, E.H. Wong, G.R. Weisman, K.C. Lam, A.L. Rheingold,
Inorg. Chem. Com. 2 (1999) 361.
[5] L. Broge, U. Pretzmann, N. Jensen, I. Sotofte, C.E. Olsen, J. Spring-
borg, J. Inorg. Chem. 40 (2001) 2323.
[17] S. Chandra, L.K. Gupta, Orient. J. Chem. 19 (2003) 571;
S. Chandra, K. Gupta, Trans. Met. Chem. 27 (2002) 196.
[18] S. Chandra, L.K. Gupta, D. Shukla, J. Saudi Chem. Soc. 7 (2003)
336;
[6] S. Chandra, L.K. Gupta, Spectrochim. Acta A 60 (2004) 1563;
Y. Liu, C. Wu, Pure Appl. Chem. 63 (1991) 427.
[7] S. Chandra, L.K. Gupta, J. Saudi Chem. Soc. 8 (2004) 85;
B.W. Wessels, R.D. Rogus, Med. Phys. 11 (1984) 638.
[8] P. Caravan, J. Ellison, T.J. Memurry, R.B. Lauffer, Chem. Rev. 99
(1999) 2293.
S. Chandra, S.D. Sharma, J. Ind. Chem. Soc. 79 (2002) 495.
[19] C. Preti, G. Tosi, Aust. J. Chem. 20 (1976) 543.
[20] F.A. Cotton, G. Wilkinson, Advanced Inorganic Chemistry, second
ed., Wiley, London;
S. Chandra, D. Jain, L.K. Gupta, J. Saudi Chem. Soc. 7 (2003)
243.
[9] S. Chandra, L.K. Gupta, Spectrochim. Acta A 60 (2004) 1751;
C.F. Meeres, T.G. Wensel, Ace. Chem. Res. 17 (1984) 202.
[10] J. Gao, A.E. Martell, Inorg. Chim. Acta 122 (2002) 329.
[11] S. Chandra, L.K. Gupta, D. Jain, Spectrochim. Acta A 60 (2004)
2411;
[21] K. Nakamoto, Infrared Spectra of Inorganic and Coordination Com-
pounds, Wiley/Interscience, New York, 1970.
[22] B.J. Hathaway, D.E. Billing, Coord. Chem. Rev. 6 (1970) 143.
[23] S. Chandra, X. Sangeetika, Spectrochim. Acta
147.
A 60 (2004)