Modern spectroscopic techniques in the characterization of Schiff base macrocyclic ligand and its complexes with transition metals

Article abstract of DOI:10.1016/j.saa.2004.12.044

Mn(II), Co(II), Ni(II), and Cu(II) complexes with a new azamacrocyclic tetradentate [N₄] ligand i.e. 2,3,9,10-tetraphenyl;l,4,8,11- tetraazacyclotetradeca;1,3,8,10-tetraene (L) have been synthesized and characterized by elemental analysis, mola

Full text of DOI:10.1016/j.saa.2004.12.044

Spectrochimica Acta Part A 62 (2005) 307–312
Modern spectroscopic techniques in the characterization of Schiff base
macrocyclic ligand and its complexes with transition metals
Sulekh Chandra∗, Lokesh Kumar Gupta
Department of Chemistry, Zakir Husain College, University of Delhi, JLN Marg, New Delhi 110002, India
Received 29 October 2004; accepted 16 December 2004
Abstract
Mn(II), Co(II), Ni(II), and Cu(II) complexes with a new azamacrocyclic tetradentate [N4] ligand i.e. 2,3,9,10-tetraphenyl;l,4,8,11-
tetraazacyclotetradeca;1,3,8,10-tetraene (L) have been synthesized and characterized by elemental analysis, molar conductance measure-
ments, magnetic susceptibility measurements, mass, 1HNMR, IR, electronic and EPR spectral studies. On the basis of their non-electrolyt−ic
nature, the probable formula of the complexes is proposed to be [M(L)X2], where M = Mn(II), Co(II), Ni(II), and Cu(II), X = Cl− and NO3
,
in dimethylformamide (DMF). All the complexes are of high-spin type and found to have six coordinated, octahedral geometry for Mn(II),
Co(II), and Ni(II) complexes, and tetragonal for Cu(II) complexes. Macrocyclic ligand and its complexes have also been screened against
pathogenic bacteria and fungi in vitro as growth inhibiting agent.
© 2005 Elsevier B.V. All rights reserved.
Keywords: Spectroscopic technique; Schiff base macrocyclic ligand; Transition metals
1. Introduction
2. Experimental
Synthetic macrocycles are a growing class of compounds
with varying chemistry a wide range of different molecular
topologies and sets of donor atoms [1–5]. The chemical
properties of macrocyclic complexes can be tuned to
force metal ions to adopt unusual coordination geometry.
Transition metal macrocyclic complexes have received
much attention as a active part of metalloenzymes [6] as
biomimic model compounds [7] due to their resemblance
with natural proteins like hemerythrin and enzymes. In view
of the above, in the present paper, we report the synthesis
and characterization of macrocyclic Mn(II), Co(II), Ni(II),
and Cu(II) complexes of a 14-membered tetradentate
(N4) macrocyclic ligand viz. 2,3,9,10-tetraphenyl;1,4,8,11-
tetraazacyclotetradeca;l,3,8,10-tetraene (L) Fig. 1. These
complexes are characterized by elemental analysis, molar
conductance, magnetic susceptibility measurements, mass,
1HNMR, IR, UV/visible and EPR spectral studies.
All the fine chemicals used were of AnalaR grade, and
procured from Fluka. Metal salts were purchased from E.
Merck and were used as received. All solvents were purified
before use according to standard procedures.
2.1. Synthesis of ligand
Hot ethanolic solution (20 mL) of benzil (9.30 g,
0.05 mol), and a hot ethanolic solution (20 mL) of 1,3-
diaminopropane (3.70 g, 0.05 mol) were mixed slowly with
constant stirring. This mixture was refluxed at 80 ◦C for 6 h in
the presence of few drops of concentrated hydrochloric acid.
On cooling, white colored precipitate was formed. It was fil-
tered, washed with cold EtOH, and dried under vacuum over
P4O10. Yield 84%, m.p. 237 ◦C. Elemental analysis found %
C 82.27; H 6.48; N 11.25. Calculated for C34H32N4 (atomic
mass calculated 496) was C 82.26; H 6.45 and N 11.29%.
2.2. Synthesis of complexes
∗
Corresponding author. Tel.: +91 11 229 11 267; fax: +91 11 232 15 906.
Hot ethanolic solution (20 mL) of the ligand (0.992 g,
0.002 mol) and hot ethanolic solution (20 mL) of a given
E-mail addresses: schandra 00@yahoo.com (S. Chandra),
lokesh kg@rediffmail.com (L.K. Gupta).
1386-1425/$ – see front matter © 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2004.12.044

308
S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 62 (2005) 307–312
Fig. 1. Structure of the ligand (L).
1
(C34H32N4)+. In the HNMR spectrum of the ligand, the
presence of the middle CH2 protons (4H) is confirmed by
the appearance of a signal at δ 1.9–2.2 [8], an expected quin-
tet. The presence of a multiplet in the region δ 7.38 may be
metal salt (0.001 mol) were mixed together with constant
stirring. The mixture was refluxed for 6–9 h at 79–80 ◦C.
On cooling, colored complex precipitated out. It was filtered,
washed with cold EtOH and dried under vacuum over P4O10.
assigned for the benzenoid hydrogen (20H). For CH2
N
(8H), the signal as a multiplet at δ 7.00–7.19 ppm was ob-
served. In the IR spectrum of ligand (L) the absence of bands
around ∼3400 cm−1 characteristic for hydroxyl group and
at ∼1720 cm−1 for free carbonyl group suggest complete
condensation of the two reactants and elimination of water
molecule. The appearance of bands at 1375 and 1428 cm−1
indicate the C CH3 and CH2 groups present in the ligand.
The characteristic IR band due to the phenyl rings is present in
the ligand and complexes in the region ∼700–770 cm−1. The
band at 1589 cm−1 may be assigned to ν (C N). The shifting
in the band of ν (C N) toward the lower side in the com-
plexes indicates that the coordination takes place through the
nitrogen of the ν (C N) group, thus implying that the ligand
(L) is tetradentate.
2.3. Physical measurements
The C, H and N were analysed on a Carlo-Erba 1106 el-
emental analyzer. Molar conductance was measured on a
ELICO (CM82T) conductivity bridge. Magnetic suscepti-
bility was measured at room temperature on a Gouy bal-
ance using CuSO4·5H2O as a callibrant. Electron impact
mass spectra were recorded on JEOL, JMS, DX-303 mass
spectrometer. 1HNMR spectra were recorded on Hitachi FT-
NMR, model R-600 spectrometer, using DMF (spectroscopic
grade) as solvent. Chemical shifts are given in ppm relative
to tetramethylsilane. 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 the complexes
were recorded as polycrystalline sample and in the solution
of DMF, at liquid nitrogen temperature for Co(II) and at
room temperature for Mn(II) and Cu(II) complexes on E4-
EPR spectrometer using the DPPH as the g-marker.
3.2. Complexes
On the basis of elemental analysis the complexes were
assigned to possess the composition listed in Table 1. The
molar conductance measurements of the complexes in DMF
correspond to be nonelectrolytic nature of the complexes.
Thus, the complexes may be formulated as [M(L)X2] where
M = Mn(II), Co(II), Ni(II) and Cu(II) and L is 2,3,9,10-
tetraphenyl;l,4,8,11-te−traazacyclotetradeca;l,3,8,10-tetraene
3. Results and discussion
3.1. Ligand
and X = Cl− and NO3
.
The electron impact mass spectrum of the ligand (L)
confirm the probable formula by showing a peak (Fig. 2)
at 495 amu, corresponding to the macrocyclic moiety
3.3. Infra-red spectral bands due to anion
IR spectra of the nitrato complexes Fig. 3(a–c), display
three, medium intensity bands, due to (N O) stretching in
the region ∼1418–1427 cm−1 (ν5), ∼1305–1311 cm−1 (ν1)
and ∼1003–1012 cm−1 (ν2). The difference between ν5 and
ν1, which is 107–119 [9], suggesting that both the nitrate
groups are coordinated to the central metal ion.
4. Manganese(II) complexes
The Mn(II) complexes show magnetic moments cor-
responding to five unpaired electrons (5.87–5.94 B.M.)
Fig. 2. Electron impact mass spectrum of the ligand (L).

S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 62 (2005) 307–312
309
Table 1
Molar conductance and elemental analysis data of the complexes
Compound
Molar conductance
−1 cm2 mol−1
( 2%)
Colour
M.P. (◦C) Yield (%) Elemental analysis data found (calculated) (%)
ꢀ
Metal
C
H
N
C34H32N4 (ligand)
[Mn(L)Cl2] C34H32MnN4Cl2
–
Off white
Light pink
Dark brown
Mauve pink
Blue
237
292
248
270
240
295
84
69
71
75
68
69
77
78
83
–
82.27 (82.26) 6.48 (6.45) 11.25 (11.29)
65.73 (65.78) 5.12 (5.15) 8.93 (8.95)
14.63
8.65(8.78)
[Mn(L)(NO3)2] C34H32MnN6O6 15.78
[Co(L)Cl2] C34H32CoN4Cl2 18.30
[Co(L)(NO3)2] C34H32CoN6O6 14.60
[Ni(L)Cl2] C34H32NiN4Cl2
[Ni(LXNO3)2] C34H32NiN6O6
[Cu(L)Cl2] C34H32CuN4Cl2
8.83 (8.87) 65.78 (65.81) 5.19 (5.16) 13.51 (13.55)
9.39 (9.35) 65.33 (65.36) 5.17 (5.12) 8.93 (8.89)
8.61 (8.63) 60.23 (60.29) 4.69 (4.72) 12.76 (12.71)
9.25 (9.32) 65.44 (65.39) 5.07 (5.12) 8.83 (8.90)
8.53 (8.60) 60.27 (60.31) 4.77 (4.73) 12.36 (12.31)
9.93 (10.01) 64.85 (64.89) 5.03 (5.08) 8.79 (8.83)
9.32 (9.24) 59.83 (59.89) 4.63 (4.69) 12.17 (12.22)
9.80
10.4
9.50
Brown
Light brown 288
Green 285
Dark brown >300
[Cu(LXNO3)2] C34H32CuN6O6 10.70
Fig. 3. IR spectral bands of anions (a) [Co(L)(NO3)2]; (b) [Ni(L)(NO3)2]; (c) [Cu(L)(NO3)2].
at room temperature (Table 2). These values are close
The calculated values of parameters B, C, Dq and β are
listed in Table 3. The values of B and C were calculated
by using the ν2 and ν3 transitions. This is due to the fact
the energies of these two transitions are independent of the
crystal field splitting energy and depend only on B and C
parameters.
to the spin only value of 5.92 B.M. Electronic spectra
of the Mn(II) complexes display four weak absorption
bands (ε = 43–121 L mol−1 cm−1) (Table 2) characteristic of
the octahedral geometry [10]. In these complexes, these
6
4
bands may be assigned to the transitions: A1g → T1g
(4G), 6A1g → Eg, 4A1g (4G) (10B + 5C), 6A1g → Eg (4D)
4
4
The EPR spectra of the complexes have been recorded as
polycrystalline sample and in DMF solution. Polycrystalline
(17B + 5C) and 6A1g → T1g (4P) (7B + 7C), respectively.
4
Table 2
Magnetic moment and electronic spectral data of the complexes
Complex
µeff B.M. ( 2%)
λmax (cm−1
)
ε (L mol−1 cm−1
)
[Mn(L)Cl2]
[Mn(L)(NO3)2]
[Co(L)Cl2]
[Co(L)(NO3)2]
[Ni(L)Cl2]
[Ni(L)(NO3)2]
[Cu(L)Cl2]
5.87
5.97
4.98
5.01
2.98
2.96
1.97
2.01
17698, 25090, 29279, 32421
18109, 24345, 28974, 32198
8970, 14410, 20110
43, 53, 67, 121
46, 49, 61, 115
67, 89, 94
9722, 14278, 20456
69, 83, 98
10065, 16065, 24513
10238, 15792, 24284
14224, 20484, 22697
14480, 20596, 23144
33, 87, 126
37, 79, 121
74, 93, 159
78, 96, 162
[Cu(L)(NO3)2]
Table 3
Ligand field parameters of the complexes
Complex
Dq (cm−1
)
B (cm−1
)
C (cm−1
)
β
F4
F2
hx
LFSE (kJ mol−1
)
[Mn(L)Cl2]
[Mn(L)(NO3)2]
[Co(L)Cl2]
[Co(L)(NO3)2]
[Ni(L)Cl2]
[Ni(L)(NO3)2]
1769.80
1810.90
1050.14
1014.44
1006.50
1023.80
598
661
1093.90
1056.71
692.20
624.10
3822
3547
0.76
0.84
0.87
0.84
0.66
0.60
109
101
–
–
–
1143
1166
3.43
2.29
–
–
–
–
–
–
–
–
–
–
–
–
–
–
10.37
96.96
144.30
146.70
–

310
S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 62 (2005) 307–312
Table 4
EPR spectral data of the complexes
Complexes
Polycrystalline sample
In DMF solution
g
g
giso
G
S
g
giso
G
ꢀ
⊥
ꢀ
⊥
[Mn(L)Cl2]a
–
–
2.17
2.13
2.18
2.16
–
–
2.11
2.09
2.05
2.12
2.03
2.08
2.13
2.10
2.09
2.13
–
–
1.54
1.44
3.60
1.33
–
–
2.13
2.10
2.14
2.12
–
–
1.92
1.93
2.05
2.04
2.02
2.06
1.99
1.99
2.06
2.05
–
–
1.62
1.43
2.80
3.00
[Mn(LXNO3)2]a
[Co(L)Cl2]b
[Co(L)(NO3)2]b
[Cu(L)Cl2]a
[Cu(L)(NO3)2]a
a
At room temperature.
At liquid N2 temperature.
b
samples gives one broad isotropic signal centered at approx-
imately the free electron ‘g’ value i.e. 2.0023 (Table 4) [10].
In DMF solution, Mn(II) complexes give EPR spectra
Fig. 4, containing the six lines arising due to the hyperfme
interaction between the unpaired electron with the 55Mn nu-
clear (l = 5/2). The nucler magnetic quantum number M1, cor-
responding to these lines are −5/2, −3/2, −1/2, +1/2, +3/2
and +5/2 from low to the high field.
6. Nickel(II) complexes
The magnetic moment of the Ni(II) complexes at room
temperature lie in the range 2.96–2.98 B.M. These values are
in tune with a high spin configuration [16,17] and show the
presence of an octahedral environment around the Ni(II) ion
in all the complexes reported in this paper.
These complexes display three electronic spectral bands
Fig. 5(c) and (d), at ∼10065–10238 (ν1), 15792–16065 (ν2)
and 24284–24513 cm−1 (ν3). These may be assigned to
3
3
5. Cobalt(II) complexes
the three spin allowed transitions A2g(F) → T2g (F) (ν1),
3
3
3
3A2g(F) → T1g (F) (ν2), A2g(F) → T1g (P) (ν3), respec-
tively. These bands indicate that the complexes have an octa-
hedral geometry and might possess D4h symmetry. The ν2/ν1
ratios lie in the range 1.47–1.66.
The magnetic moment measurements of the cobalt(II)
complexes at room temperature lie in the range
4.98–5.01 B.M.[11]. The electronic spectra of the Co2+
complexes are given in Fig. 5(a) and (b) and show three
bands, characteristic of an octahedral geometry. These bands
4
4
4
4
may be assigned to T1g(F) → T2g(F) (ν1), Tlg → A2g
7. Copper(II) complexes
4
4
(ν2) and Tlg(F) → T1g(P) (ν3) transitions, respectively
[12,13]. Various ligand field parameters have been calculated
[14,15] for the cobalt(II) complexes on the basis of electronic
spectra and are listed in the Table 3.
Magnetic moment of all the Cu(II) complexes at room
temperature lie in the range 1.97–2.01 B.M. corresponding
to one unpaired electron [18,19].
Three spin allowed transitions may be expected in the vis-
ible region and the Eg and T2g levels of 2D free ion will split
into B1g, A1g, B2g and Eg levels, respectively.
Electronic spectra of six coordinated copper com-
plexes display bands in the range 14224–14480 (ν1),
20484–20596 (ν2) and 22697–23149 cm−1 (ν3), correspond-
The g values of the Co(II) complexes, EPR spectra
ꢀ
recorded at liquid N2 temperature as polycrystalline and in
DMF solution, lie in the range 2.10–2.17 and the g values
⊥
are in the range 1.92–2.11 (Table 4). The deviation of the
‘g’ values from the spin only value (g = 2.0023) is due to the
angular momentum contribution.
Fig. 4. EPR spectra of [Mn(L)Cl2] recorded at room tempemture/DMF.

S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 62 (2005) 307–312
311
Fig. 5. Electronic spectra of the complexes (a) [Co(L)Cl2]; (b) [Co(L)(NO3)2]; (c) [Ni(L)Cl2]; (d) [Ni(L)(NO3)2].
2
2
8. Ligand field parameters
ing to the following transitions B1g → A1g (dx2−y2 →
2
2
2
2
dz2 ) ν1, B1g → B2g (dx2−y2 → dzy) ν2 and B1g → Eg
(dx2−y2 → dzy, dyz) ν3 (Table 2).
Various ligand field parameters were calculated for the
complexes and are listed in Table 3. The values of Dq in
Co(II)complexeswerecalculatedfromtransitionenergyratio
diagram using the ν3/ν2 ratio. Our results are in agreement
with the complexes reported earlier [5,15]. The nephelauxetic
parameter β is readily obtained by using the relation:
The EPR spectra of Cu(II) complexes were recorded
on X-Band at frequency 9.5 GHz under the magnetic field
strength 3200 band scan rate 2000, recorded at room tem-
perature. The EPR spectra (room temperature/DMF) of the
complexes exhibit a single anisotropic broad signal, while
splitting occurs in the solution phase, Fig. 6(a) and (b). The
absence of the band for the ꢁMs = 2 transition can ex-
plained by proposing the interaction between two param-
B(compIex)
β =
B(free ion)
where B (free ion) for Mn(II) is 786, for Ni(II) 1041 and
for Co(II) 1120 cm−1 [10,11]. The β values lie in the range
of 0.60–0.87. These values indicate the appreciable covalent
character of metal ligand ‘␴’ bond.
agnetic centers are negligible [20,21]. The spectra give g
value in the range 2.12–2.18 and g values in the range
2.04–2.12. The observed g value for the Cu(II) complexes
are less than 2.3, in agreement with the covalent charac-
ꢀ
ꢀ
ꢀ
ter of the M L bond. The ratio g > g > 2.0023 calculated
ꢀ
⊥
for Cu(II) complexes, suggest that the unpaired electron
is localized in dx2−y2 orbital and the spectral features are
characteristic of axial geometry and tetragonally elongated
geometry.
9. Biological screening
The macrocyclic ligand and its transition metal complexes
have been screened against a number of pathogenic bacte-
Fig. 6. EPR spectra recorded at R.T. in the solution of DMF. (a) [Cu(L)Cl2]; (b) [Cu(L)(NO3)2].

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S. Chandra, L.K. Gupta / Spectrochimica Acta Part A 62 (2005) 307–312
Acknowledgements
We are thankful to the Principal, Zakir Husain College
for providing research facilities and RSIC, IIT Mumbai for
recording EPR spectra. We also express our sincere thanks
to the UGC New Delhi for financial assistance.
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ria and plant pathogenic fiingi. For the study of antibacte-
rial activity the disc diffusion technique [22] was adopted
on the bacterial species, i.e. Sarcina lutea (gram positive),
Staphylococcus aureus and Escherchia coli (gram negative),
in vitro.
The results of the antibacterial study shown in Graph 1,
suggest the maximum inhibition capacity of the copper(II)
complexes, although all complexes are more efficient to
inhibit the bacterial growth as compare to the metal free
ligand.
Antifungal screening of the compounds was done in
vitro on Aspergilus niger, Aspergilus glaucus and Usti-
lago tritici by using the agar plate technique [22,23].
The results of the antifungal activity has been compared
with the results reported earlier [24,25]. Maximum fun-
gal growth inhibition was shown by the copper(II) com-
plexes (Graph 2) and the minimum by the manganese(II)
complexes.
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