Spectral studies with coordination behaviour of (NO3) and (NCS) anions and EPR parameters of chromium(III) complexes which have different chromospheres macrocyclic ligands: Synthesis and electronic spectroscopy

Article abstract of DOI:10.1016/j.saa.2006.02.024

New macrocyclic ligands were prepared and chromium(III) stability in the marcrocyclic cavities are reported. Two of them have four-coordinate [N₂O₂]:[N₄], third one has five-coordinate [N₂O₂S] and the

Full text of DOI:10.1016/j.saa.2006.02.024

Spectrochimica Acta Part A 66 (2007) 74–80
Spectral studies with coordination behaviour of (NO3) and (NCS)
anions and EPR parameters of chromium(III) complexes which
have different chromospheres macrocyclic ligands:
Synthesis and electronic spectroscopy
Sulekh Chandraa,b, Rajiv Kumara,b,∗
a Department of Chemistry, Zakir Husain College (University of Delhi) Jawahar Lal Nehru Marg,
New Delhi 110002, India
b Department of Chemistry, University of Delhi, New Delhi 110007, India
Received 7 November 2005; received in revised form 14 February 2006; accepted 17 February 2006
Abstract
New macrocyclic ligands were prepared and chromium(III) stability in the marcrocyclic cavities are reported. Two of them have four-coordinate
[N2O2]:[N4], third one has five-coordinate [N2O2S] and the last one has six-coordinate [N4O2] donor macrocyclic cavities. These macrocyclic
ligands have been synthesized with their chromium(III) complexes which have mononuclear nature and their structural features have been discussed
on the basis of: elemental analysis, magnetic moment, electronic, IR, 1H NMR, and EPR spectral studies. All the chromium(III) complexes show
magnetic moments in the range of 3.74–3.80 B.M. corresponding to high-spin configuration. However, the interaction of oxygen to the chromium
ion in complexes is much weaker than that of other donor atoms. The spin–orbit coupling parameter, z, gives no significance because the splitting
of doublet transition lines are too large to be explained by spin–orbit coupling. The β values (0.75–0.79) indicate the covalent character, which is
due to the presence of ␴ bond between the metal/ligand. λ values indicate that the complexes under study have substantial covalent character and
their g-values have also been calculated by using spin–orbital coupling constant (λ).
© 2006 Elsevier B.V. All rights reserved.
Keywords: Macrocyclic ligands; 1H NMR; IR; EPR; Chromium(III) complexes
1. Introduction
of clearly defined spin forbidden transitions specially based on
UV–vis absorption [6,7].
The synthesis of macrocyclic ligands and their transition
metal complexes is a growing area of research in inorganic
and bioinorganic chemistry in view of their presence in many
biologically significant systems [1–3]. Macrocyclic metal com-
plexes are considered to be the model of metalloporphyrins and
metallocorrins due to their intrinsic structural properties. The
synthesis and study of macrocycles have undergone tremendous
growth and their complexation chemistry with a wide variety
of metal ions has been extensively studied [4,5]. In particular,
chromium(III) complexes are quite useful for this purpose since
they are so kinetically inert that various complexes could be iso-
lated and show three spin allowed transition bands and a number
The biological significance of chromium is still a matter of
considerable discussion [8–10]. The glucose tolerance factor
(GTF) [11], an active chromium(III) substance, has never been
isolatedinpureform, andtheotherbiologicalproductcontaining
chromium, called low molecular weight chromium (LMWCr)
[12,13], which was obtained in milligram amounts. Its structure
has not as yet been determined and here is still some skepticisms
in the literature regarding any positive role for chromium(III) in
biological systems [14].
As the ternary complexes seem to be better models for the
chromium(III) active substances than the binary ones, in this
paper we report the isolation of the chromium(III) complexes
with the mixture of organic skeleton containing macrocyclic
ligands.
∗
Macrocycles find wide applications in medicine, cancer diag-
nosis and in treatment of tumors, in metal ion techniques
Corresponding author. Tel.: +91 1234276530; fax: +91 1234276530.
E-mail address: chemistry rajiv@hotmail.com (R. Kumar).
1386-1425/$ – see front matter © 2006 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2006.02.024

S. Chandra, R. Kumar / Spectrochimica Acta Part A 66 (2007) 74–80
75
ene [N2O2]ane; ligand L2: 2,4,9,11-tetraphenyl-6,13-dimethyl-
1,5,8,12-traazacyclotertr-adeca-1,4,8,11-tetraene
[N4]ane;
ligand L3: 1,7-diaza-4-monothia-10,14-dioxo-8,9:15,16-cyclo-
hexadecane [N2O2S]ane and ligand L4: 4,13-diaoxo-1,7,10,16-
terazacyclooctadecane [N4O2]ane.
2. Experimental
2.1. Materials and instrumentation
All the chemicals used in the present investigation were of
AR grade, purchased from Sigma Chemical Co, USA. Elemen-
tal analysis (CHN) of these complexes were carried out on a
Carlo-Erba 1106 Elemental Analyzer. Molar conductance was
measured on an ELICO conductivity bridge (Type CM82T).
Magnetic susceptibility measurements were made on Gouy Bal-
ance at room temperature using CuSO4·5H2O as calibrant.
Infrared spectra were recorded on a Perkin Elmer 137 instru-
ment as KBr pellets. Electronic spectra were recorded in DMSO
solution on a Shimadzu UV mini-1240 spectrophotometer. EPR
spectra of the chromium(III) complexes were recorded as pow-
der samples at room temperature on an E-4 EPR spectrometer
using DPPH as the g-marker.
2.2. Preparation and characterization of macrocyclic
ligands
The proposed chemical structures of the prepared macro-
cyclic ligands were in good agreement with the stoichiometries
concluded from their analytical, 1H NMR, and IR spectral data
and related structures are given in Fig. 1.
Fig. 1. Structures of macrocyclic ligands.
2.2.1. Ligand L1: 2,4-diphenyl-1,5-diaza-8,12-dioxo-
6,7:13,14-dibenzocyclotetradeca-1,4-diene[N2O2]ane
ToanEtOHsolutionof(25 ml)dibenzoylmethane(0.05 mol),
an EtOH solution (25 ml) of 1,2-di(o-aminophenoxy)propane
(0.05 mol) was added in the presence of a few drops (∼1 ml) of
conc. HCl. The solution was refluxed on a water bath at ∼82 ◦C
for 3–4 h. The solution was then concentrated to half of it’s
volume under reduced pressure and kept over night at ∼5 ◦C.
The off-white crystals formed were filtered, washed with EtOH,
and dried under a vacuum over P4O10.
and treatment of kidney stone. Macrocyclic ligands have been
used successfully for diverse processes such as separation of
ions by transport through artificial and natural membrane,
liquid–liquid or solid–solid phase transfer reaction, prepara-
tion of ion-selective electrodes, isotope separation and in the
understanding of some natural processes through mimicry of
metalloenzymes [15,16].
In this article we have developed some new chromium(III)
complexes with the mixture of organic skeleton containing
macrocyclic ligands (Fig. 1). Namely Ligand L1: 2,4-diphenyl-
1,5-diaza-8,12-dioxo-6,7:13,14-dibenzocyclotetradeca-1,4-di-
For L1 Formula: C30H26N2O2. C 80.69 (80.10); H 5.87
(5.12): N: 6.27 (6.10).
Table 1
H NMR spectral data of the macrocyclic ligands L1, L2, L3 and L4
Ligand
Phenyl
Benzene (subst.)
NH
Ph CH2 Ph
4.1 (2H, s)
O
CH2
S
CH2
NH CH2
L1 C30H26N2O2
7.1–7.25 (10H, m)
7.1–6.9 (2H, m) (2H, d, J = 7.2)
(2H, d, J = 7.1) (2H, m)
–
–
–
3.4 (4H, m)
–
–
–
–
L2 C36H36N4
L3 C19H24N2O2S
7.20–7.30 (20H, m)
–
4.4 (4H, m)
–
–
7.2–6.5 (4H, m) (2H, d, J = 7.2)
5.2 (2H, s)
3.2 (4H, m)
2.8 (4H, s)
3.2 (4H, m)
(2H, d, J = 7.0)
–
L4 C12H28N4O2
–
9.2 (4H, s)
–
3.25 (8H, m)
–
3.2 (16H, m)

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S. Chandra, R. Kumar / Spectrochimica Acta Part A 66 (2007) 74–80
Table 2
Important I.R. absorption bands (cm−1) of nitrato and thiocyanato chromium(III) complexes of L1, L2, L3, and L4
Compound
υC
υNi
υNi
υNi
␷
NO
3
υNCS
N
N
O
S
[Cr(L1)(NO3)2](NO3)
[Cr(L2)(NO3)2](NO3)
[Cr(L3)(NO3)](NO3)2
[Cr(L4)](NO3)3
[Cr(L1)(NCS)2](NCS)
[Cr(L2)(NCS)2](NCS)
[Cr(L3)(NCS)](NCS)2
[Cr(L4)](NCS)3
1610
1601
–
624
615
611
625
618
620
622
620
510
–
520
–
511
–
514
–
–
1421, 1309and1385
1420, 1301and1384
1420, 1308and1382
1385
–
–
–
–
–
310
–
–
–
–
1607
1602
–
2084, 2050
2081, 2051
2089, 2049
2052
315
–
–
Table 3
Analytical data of chromium(III) complexes
Complexes/empirical formula
Yield (%) Molar conductance
Color
Elemental analysis calcd. (found%)
ꢀ cm2 mol−1
)
Cr
C
H
N
[Cr(L1)(NO3)2](NO3) CrC30H26N5O11
[Cr(L2)(NO3)2](NO3) CrC36H36N7O9
40
45
56
50
86.0
94.0
165
Green
7.60 (7.50)
52.64 (52.32)
56.69 (56.12)
39.18 (39.01)
28.92 (28.56)
58.91 (58.65)
62.38 (62.11)
34.73 (34.65)
37.02 (36.85)
3.83 (3.56)
4.76 (4.41)
4.15 (4.12)
5.66 (5.23)
3.90 (3.65)
4.83 (4.74)
5.44 (5.33)
5.80 (5.45)
10.23 (10.11)
12.86 (12.45)
12.02 (11.99)
19.67 (19.32)
10.41 (10.26)
13.06 (12.99)
18.90 (18.48)
20.15 (20.01)
Dark green
Dark green
Green
Reddish-brown
Green
6.82 (6.74)
8.93 (8.63)
10.43 (10.12)
7.73 (7.45)
6.92 (6.68)
10.02 (9.98)
10.69 (10.22)
[Cr(L3)(NO3)](NO3)2 CrC19H24N5O11
[Cr(L4)](NO3)3 CrC12H28N7O11
S
245
[Cr(L1)(NCS)2](NCS) CrC33H26N5O2S3 58
90.0
93.0
189
[Cr(L2)(NCS)2](NCS) CrC39H36N7S3
[Cr(L3)(NCS)](NCS)2 CrC21H24N7O2S4 61
[Cr(L4)](NCS)3 CrC15H28N7O2S3
65
54
Dark green
Dark green
250
2.2.2. Ligand L2: 2,4,9,11-tetraphenyl-6,13-dimethyl-
1,5,8,12-traazacyclotertr-adeca-1,4,8,11-tetraene
[N4]ane
under a vacuum over P4O10. L3 Formula: C19H24N2O2S1 C:
66.25 (66.12); H: 7.02 (6.95), N: 8.13 (8.11).
This ligand prepared as reported earlier [5].
2.2.4. Ligand L4:
4,13-dioxo-1,7,10,16-teraazacyclooctadecane[N4O2]ane
To an EtOH solution (20 ml) of bis(2-chloroethayl)thiol
(0.05 mol), an EtOH solution (20 ml) of diaminoethane
(0.05 mol) was added. The resulting solution was refluxed on
a water bath at ∼72 ◦C for 3–4 h. The solution was then con-
centrated to half of it’s volume under reduced pressure and kept
overnight at ∼5 ◦C. The white crystals formed were filtered,
washed with EtOH, and dried under a vacuum over P4O10. L4
Formula: C12H28N4O2 C: 55.35, (55.23); H: 10.84, (10.47); N:
21.52 (21.0).
2.2.3. Ligand L3: 1,7-diaza-4-monothia-10,14-dioxo-
8,9:15,16-cyclohexadecane[N2O2S]ane
To an EtOH solution (25 ml) of bis(2-chloroethayl)ether
(0.05 mol), an EtOH solution (25 ml) of 1,2-di(o-
aminophenoxy)propane (0.05 mol) was added. The resulting
solution was refluxed on a water bath at ∼72 ◦C for 5–6 h. The
solution was then concentrated to half of it’s volume under
reduced pressure and kept overnight at ∼5 ◦C. The off-white
crystals formed were filtered, washed with EtOH, and dried
Table 4
Magnetic moment, electronic spectral data of the chromium(III) complexes with all ligands in DMSO
Complexes
Magnetic moments (B.M.)
υ2
υ1
Transitions
[Cr(L1)(NO3)2](NO3)
[Cr(L1)(NCS)2](NCS)
[Cr(L2)(NO3)2](NO3)
[Cr(L2)(NCS)2](NCS)
[Cr(L3)(NO3)](NO3)2
[Cr(L3)(NCS)](NCS)2
[Cr(L4)](NO3)3
3.80
3.74
3.79
3.75
3.80
3.74
3.79
3.75
17241
17543
16393
16949
18181
16806
17857
16499
11235
11235
11098
11764
17494
11764
12048
11627
4
4A2g(F) → T2g(F)
and
4
4A2g(F) → T1g(F)
[Cr(L4)](NCS)3

S. Chandra, R. Kumar / Spectrochimica Acta Part A 66 (2007) 74–80
77
Fig. 2. UV spectra of the complexes [Cr(L3)(NO3)](NO3)2 for A and
[Cr(L3)(NCS)](NCS)2 for B.
Fig. 3. UV spectra of the complexes [Cr(L4)](NO3)3 for A and [Cr(L4)](NCS)3
for B.
Fig. 5. E.P.R. spectrum of the complex [Cr(L3)(NCS)](NCS)2.
All the ligands were also characterized by 1H NMR and the
1H NMR spectral data are giving in Table 1.
2.3. Preparation of chromium(III) complexes
EtOH solution of (25 ml) corresponding macrocylic ligands
L1, L2, L3 or L4 was added to an EtOH solution of the (20 ml)
Fig. 6. EPR spectrum of the complexes [Cr(L4)](NCS)3 for
[Cr(L4)](NO3)3 for B.
A
and
Fig. 4. EPR spectra of the complex [Cr(L1)(NO3)2](NO3).

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S. Chandra, R. Kumar / Spectrochimica Acta Part A 66 (2007) 74–80
Fig. 7. Structure of the complex [Cr(L1)(NCS)2](NCS).
hydrated chromium(III) salts (1m mol). The resulting solution
was refluxed on a water bath at 75–85 ◦C for several hours.
The solution was then concentrated to half of its volume under
reduced pressure and kept over night at ∼5 ◦C. The colored
crystals formed were filtered off, washed with EtOH and finally
dried in a vacuum desiccator over P4O10.
Fig. 9. Structure of the complex [Cr(L2)(NCS)2](NCS).
the low frequency region for (Ni O) at 520–510 cm−1, (Ni S)
at 315–310 cm−1 and (Ni N) at 624–611 cm−1[1].
3.1.1. Bands due to thiocyanate anions
In the IR spectra of thiocyanato complexes of L1, L2 and
L3 ligands show N-bonded coordination and shows band shows
at 2089–2081 cm−1 and second type coordination corresponds
to uncoordinated behaviour of this group and shows band at
2051–2049 cm−1. Thus, these result proved two types of coor-
dination behaviour of this group in these complexes.
L4 complexshowsbandat2052 cm−1 whichiscorresponding
to uncoordinated nature of this ion [3].
3. Results and discussion
3.1. IR spectra of the chromium(III) complexes
The infrared spectrum of these ligands L1 and L2 show bands
at 1610–1601 cm−1 which may be assigned to C N respectively
[1]. The IR spectra of both L3 and L4 ligands show characteristic
bands at 3280–3310 cm−1 corresponding to υ (NH). On com-
plexation these bands shift to the lower frequency ∼10 cm−1. It
proved diversion of electron clouds from the nitrogen donor of
C N and NH groups, thereby resulting in the formation of the
metal nitrogen bond and related data are given in Table 2.
In the IR spectrum of L3, bands due to Ph O CH2 at
520–510 cm−1 are also shift to lower side on complexation and it
also indicates the formation of metal–oxygen/sulphur bond. Due
to the formation of new bonds, another new bands appeared in
3.1.2. Bands due to nitrate anions
In the IR spectra nitrato complexes of ligand L1 and L2
show bands at 1421–1420 and 1301–1309 cm−1 correspond-
ing to monodentate nature of this group and also show a sharp
band at 1385–1384 cm−1 which is corresponding to uncoordi-
Fig. 8. Structure of the complex [Cr(L1)(NO3)2](NO3).
Fig. 10. Structure of the complex [Cr(L2)(NO3)2](NO3).

S. Chandra, R. Kumar / Spectrochimica Acta Part A 66 (2007) 74–80
79
Fig. 13. Structures of [Cr(L4)](NO3)3.
4.2. Electronic spectroscopy
Fig. 11. Structure of the complex [Cr(L3)(NCS)2](NCS).
The electronic spectra of the complexes recorded in DMSO
and the observed values are reported with their possible transi-
tions [17,18]. Table 4 and Figs. 2 and 3.
The positions of the important bands indicate that these com-
plexes exhibit six coordinate octahedral geometry, consistent
with D4h symmetry around the metal ion.
nated nature of this group. Thus, these result proved two types
of coordination behaviour of this group in these complexes.
L4 complexshowsbandat1385 cm−1 whichiscorresponding
to uncoordinated nature of this ion.
4. Results and discussion
4.3. Ligand field parameters
4.1. Chromium(III) complexes
Various ligand field parameters Dt, Ds, Dq, B, C, λ and β have
been calculated and their values have a good agreement with data
earlier reported [1]. The values of the ligand field parameters are
consistent with octahedral geometry for the complexes. How-
ever, the interaction of oxygen to the chromium in complexes
are much weaker than that of other donor atoms. The ligand field
strength, 10 Dq, can be estimated roughly for each ligand by the
relationship of nonlinear, anisotropic ligands. The ligand field
parameters from the best-fit parameter set yield the Δ values.
Large variance of spin-orbit coupling parameter, z, gives no sig-
nificance because the splitting of doublet transition lines are too
large to be explained by spin-orbit coupling [19,20].
The isolated complexes are stable in air, completely soluble in
DMSO. All of the complexes are found to have the composition
Cr(L)(X)3 (where L = Ligands L1, L2, L3, and L4X = SCN and
NO3). The elemental analysis data obtained for the complexes
are listed in Table 3.
All the complexes show magnetic moment corresponding to
three unpaired electrons (i.e. 3.74–3.80 BM), which is approxi-
mately equal to spin only value [1].
All the complexes show molar conductances in the range of
86–94, 165–189 and 245–250 ꢀ−1 cm2 mol−1 as 1:1, 1:2 and
1:3 electrolytes. Therefore, these complexes may be formulated
as [Cr(L1 or L2)(X2)]X, [Cr(L3)X]X2 and [Cr(L4)]X3, respec-
tively. H1 NMR spectra of the complexes are also studied and
compared with the H1 NMR spectra of their macrocyclic lig-
ands, which proved metal to ligand complexation.
The β values (0.75–0.79) indicate the covalent character,
which is due to the presence of ␴ bond between the metal/ligand.
Δ values indicate the energy difference between the principle
bands, which are formed due to ligand field absorption. This
Fig. 12. Structure of the complex [Cr(L3)(NO3)](NO3)2.
Fig. 14. Structures of [Cr(L4)](NCS)3.

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S. Chandra, R. Kumar / Spectrochimica Acta Part A 66 (2007) 74–80
type of complexes may have either C4v or D4h symmetry which
is arising from the lifting of the degeneracy of the orbital triplet
(in octahedral symmetry) in the order of increasing energy or
assuming D4h symmetry. The C4v symmetry has been ruled out
because of higher splitting of the first band. This suggests that
it possess distorted octahedral geometry around the metal ion.
Mohit Krishan, Computer Programmer, CSL Delhi University
Delhi, for providing computer facilities. Thanks to the Univer-
sity Grants Commission, New Delhi, for financial assistance.
Thanks to I.I.T. Bombay, for recording the EPR spectra. Thanks
are also due to the Solid State Physics Laboratory, India, for
recording magnetic moments.
4.4. EPR spectra of chromium(III)
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as polycrystalline sample as well as solution at room temperature
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which correspond to six coordinated geometry. It is possible to
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5. Conclusion
A series of chromium(III) complexes with macrocyclic lig-
ands have been prepared and fully characterized. The coordinat-
ing behavior in the complexes of chromium(III) effected by the
coordination stereochemistry of the macrocyclic ligands NCS
and NO3. Due to these coordinating sites of the ligands are
affecting coordination behaviors of the NO3 and NCS ions. On
the basis of above studies suggested structures of the complexes
are given in Figs. 7–14.
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Acknowledgements
One of the authors (Rajiv Kumar) gratefully acknowledges
his younger brother Bitto for motivation. Special thanks to
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