Chromium(III) complexes of 1,2-di(imino-4′-antipyrinyl)ethane

Article abstract of DOI:10.1081/SIM-120016466

Chromium(III) complexes of the Schiff base 1,2-di(imino-4′-antipyrinyl)ethane (GA) have been synthesized and characterized by elemental analyses, electrical conductance in non-aqueous solvents, infrared and electronic spectra as well as magnetic susceptibility measurements. The complexes have the general formulae [Cr(GA)(ClO₄)](ClO₄)₂ and [Cr(GA)X₂]X (X = NO₃, Cl or Br). In the complexes, GA acts as a neutral tetradentate ligand coordinating through both carbonyl oxygens and both azomethine nitrogens. In the perchlorate complex one of the anions is coordinated in a bidentate fashion while in the corresponding nitrate and halide complexes two of the anions are coordinated to the metal ion. A distorted octahedral geometry is assigned around the Cr(III) ion in all of these complexes.

Full text of DOI:10.1081/SIM-120016466

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CHROMIUM(III) COMPLEXES OF 1,2-DI(IMINO-4′-ANTI
PYRINYL)ETHANE
V. T. Thomas a , N. T. Madhu a & P. K. Radhakrishnan b
a School of Chemical Sciences , Mahatma Gandhi University , Kottayam, Kerala, 686 560,
India
b School of Chemical Sciences , Mahatma Gandhi University , Kottayam, Kerala, 686 560,
India
Published online: 15 Feb 2007.
To cite this article: V. T. Thomas , N. T. Madhu & P. K. Radhakrishnan (2002) CHROMIUM(III) COMPLEXES OF 1,2-DI(IMINO-4′-
ANTI PYRINYL)ETHANE, Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry, 32:10, 1799-1809, DOI: 10.1081/
SIM-120016466
To link to this article: http://dx.doi.org/10.1081/SIM-120016466
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 32, No. 10, pp. 1799–1809, 2002
CHROMIUM(III) COMPLEXES OF
1,2-DI(IMINO-40-ANTIPYRINYL)ETHANE
V. T. Thomas, N. T. Madhu, and P. K. Radhakrishnan*
School of Chemical Sciences, Mahatma Gandhi
University, Kottayam 686 560, Kerala, India
ABSTRACT
Chromium(III) complexes of the Schiff base 1,2-di(imino-
40-antipyrinyl)ethane (GA) have been synthesized and
characterized by elemental analyses, electrical conductance in
non-aqueous solvents, infrared and electronic spectra as well
as magnetic susceptibility measurements. The complexes have
the general formulae [Cr(GA)(ClO4)](ClO4)2 and [Cr(GA)-
X2]X (X ¼ NO3, Cl or Br). In the complexes, GA acts as a
neutral tetradentate ligand coordinating through both car-
bonyl oxygens and both azomethine nitrogens. In the per-
chlorate complex one of the anions is coordinated in
a bidentate fashion while in the corresponding nitrate and
halide complexes two of the anions are coordinated to the
metal ion. A distorted octahedral geometry is assigned around
the Cr(III) ion in all of these complexes.
*Corresponding author. E-mail: mgu@md2.vsnl.net.in
1799
DOI: 10.1081=SIM-120016466
Copyright # 2002 by Marcel Dekker, Inc.
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com

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THOMAS, MADHU, AND RADHAKRISHNAN
INTRODUCTION
A number of workers have used antipyrine and its derivatives as
ligands in isolating solid complexes with transition metal ions.[1,2] Relatively
little is known about antipyrine complexes with Cr(III).[3,4] In view of this,
and as part of our continuing interest in Schiff base metal complexes,[5–7] we
report here the synthesis and structural investigation of Cr(III) complexes of
the Schiff base ligand 1,2-di(imino-40-antipyrinyl)ethane (GA) (Fig. 1),
which is an antipyrine derivative. Antipyrine and its derivatives possess
antibacterial[8] and anti-inflammatory[9] properties and, hence, the present
complexes would be of physiological importance.
RESULTS AND DISCUSSION
The formation of the complexes may be represented by the following
general equation.
CrX3 þ GA ! CrðGAÞX3 ðX ¼ ClO4; NO3; Cl or BrÞ
The analytical data (Table I) of the complexes indicate that the present
complexes may be formulated as Cr(GA)X3 (X ¼ ClO4, NO3, Cl or Br).
The molar conductance values of the complexes of GA (Table II) in
DMF, ethanol, methanol and nitrobenzene (10ꢀ3 M solutions) are in the
range expected for 1:2 electrolytes for the perchlorate complex while the
nitrate, chloride and bromide complexes behave as 1:1 electrolytes.[10] Thus,
the complexes may be formulated more precisely as [Cr(GA)X]X2
(X ¼ ClO4) and [Cr(GA)X2]X (X ¼ NO3, Cl or Br).
Figure 1. 1,2-Di(imino-40-antipyrinyl)ethane (GA).

CHROMIUM(III) COMPLEXES
1801

1802
THOMAS, MADHU, AND RADHAKRISHNAN
Table II. Molar Conductancea Data of the Cr(III) Complexes of GA
Molar Conductance
Complex
DMF
MeOH
EtOH
C6H5NO2
[Cr(GA)(ClO4)](ClO4)2
[Cr(GA)(NO3)2]NO3
[Cr(GA)Cl2]Cl
145.13
88.40
91.26
70.48
203.94
112.21
82.19
72.75
43.47
44.62
40.49
52.35
28.46
29.46
24.40
[Cr(GA)Br2]Br
85.45
aohmꢀ1 cm2 molꢀ1
.
Infrared Spectra
The important infrared spectral data of GA and its complexes are
presented in Table III. The strong band at 1650 cmꢀ1 due to the C¼O
stretching vibration of GA is shifted to the region 1600–1609 cmꢀ1 in the
complexes, showing the coordination of both carbonyl oxygens.[6,7] The
strong band at 1576 cmꢀ1 attributable to the C¼N stretching vibration of
GA is shifted to the region 1559–1562 cmꢀ1 in the complexes, indicating the
coordination of both azomethine nitrogens.[7]
In the perchlorate complex, the bands observed at 1140 and 1115 cmꢀ1
are due to the n8 and n6 vibrations, respectively, of the perchlorate ion of C2v
symmetry indicating the coordination thereof in a bidentate fashion.[7] The
strong band at 1086 cmꢀ1 and a medium band at 625 cmꢀ1 are assigned to
the n3 and n4 vibrations, respectively, of uncoordinated perchlorate ion
(Td).[7] Thus the presence of both, uncoordinated and bidentately coordi-
nated, perchlorate ions is indicated. The vibrational frequencies observed at
935 cmꢀ1 corresponding to the n2 vibration of the perchlorate (C2v) ion and
the band at 626 cmꢀ1 due to the n4 vibration of perchlorate (Td) ion, also
support the coexistence of both uncoordinated and bidentately coordinated
perchlorate ions in this complex.[7]
In the nitrate complex, two medium bands at 1491 and 1365 cmꢀ1 are
attributable to the n4 and n1 vibrations, respectively, of the nitrate ion of C2v
symmetry.[11] Since n4 ꢀ n1 ¼ 126 cmꢀ1, the nitrate ions are monodentate.[12]
A strong band at 1383 cmꢀ1 and a medium band at 831 cmꢀ1 are attributed
to the n3 and n2 vibrations of uncoordinated nitrate (D3h) ion.[11]
In the far-infrared spectra of the chloride and bromide complexes, the
Cr–Cl and Cr–Br stretching vibrations are at 407 and 376 cmꢀ1, respec-
tively,[7] and are absent in the spectrum of the ligand. Further, the n(Cr–O)
and n(Cr–N) stretching vibrations are observed at about 550 and 460 cmꢀ1
,
respectively, in all the complexes.[7]

CHROMIUM(III) COMPLEXES
1803

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THOMAS, MADHU, AND RADHAKRISHNAN
The above results, along with the conductance data, indicate that one
of the perchlorates as well as two of the nitrates, chlorides and bromides are
coordinated to the metal ion in these complexes.
Electronic Spectra
The electronic spectral bands of GA and its complexes with tentative
assignments are presented in Table IV. GA shows two band maxima at
26,180 and 39,220 cmꢀ1 corresponding to n ! pꢂ and p ! pꢂ transitions,
respectively.[6] In the complexes, the n ! pꢂ bands are found to be
Table IV. Electronic Spectral Data (in Nujol) and Magnetic Moments of the
Cr(III) Complexes of GA
Abs. Max.
(cmꢀ1
meff
(BM)
Compound
GA
)
Tentative Assignments
38,197
25,497
24,014
40,984
41,666
37,594
33,784
24,814
24,154
39,682
37,594
35,087
29,673
26,881
24,154
40,160
36,900
34,364
29,239
26,178
25,062
39,370
37,313
33,898
31,348
27,932
p ! pꢂ
n ! pꢂ
–
[Cr(GA)(ClO4)](ClO4)2
[Cr(GA)(NO3)2]NO3
[Cr(GA)Cl2]Cl
n ! pꢂ
3.81
p ! pꢂ
Charge transfer
A2g ! T1gðPÞ
A2g ! T1gðFÞ
A2g ! T2gðFÞ
n ! pꢂ
3.80
3.80
3.79
p ! pꢂ
Charge transfer
A2g ! T1gðPÞ
A2g ! T1gðFÞ
A2g ! T2gðFÞ
n ! pꢂ
p ! pꢂ
Charge transfer
A2g ! T1gðPÞ
A2g ! T1gðFÞ
A2g ! T2gðFÞ
n ! pꢂ
[Cr(GA)Br2]Br
p ! pꢂ
Charge transfer
A2g ! T1gðPÞ
A2g ! T1gðFÞ
A2g ! T2gðFÞ

CHROMIUM(III) COMPLEXES
1805
red-shifted to the region 24,014–25,062 cmꢀ1 and the p ! pꢂ bands are
found as blue-shifted to the region 39,370–40,984 cmꢀ1 compared to that of
GA. The absorption bands observed in the regions 33,898–37,594 cmꢀ1
,
29,239–33,784 cmꢀ1 and 24,814–27,932 cmꢀ1 in these complexes are in
4
4
4
4
4
accordance with A2g ! T1gðPÞ ðn3Þ; A2g ! T1gðFÞ ðn2Þ and A2g !
4
T2gðFÞ ðn1Þ transitions, respectively. These absorptions are consistent with
an octahedral geometry around Cr(III) in all of the complexes.[13,14] Fur-
thermore, the electronic spectra of all the complexes exhibit an intense
absorption band in the region 36,900–41,666 cmꢀ1, which might be due to a
charge transfer transition and there is no considerable change to it in dif-
ferent solvents.
Magnetic Moment Data
The magnetic moments of the complexes are presented in Table IV.
The values are in the range 3.79–3.81 BM, suggesting an octahedral geo-
metry around Cr(III) in these complexes.[15]
Based on the results of the present studies, we could not reach any
conclusion regarding the stereochemical behavior of the complexes and hence
the tentative structures shown in Fig. 2 may be assigned to the complexes.
EXPERIMENTAL
Materials
The metal salts, Cr(NO3)3ꢃ9H2O and CrCl3ꢃ6H2O were BDH AR
grade samples while Cr(ClO4)3ꢃ6H2O and CrBr3ꢃ6H2O were prepared from
Analar BDH chromium carbonate and the corresponding 50% acids and
crystallizing out the salts by evaporating the solution on a steam bath.
Preparation of the Ligand
The ligand 1,2-di(imino-40-antipyrinyl)ethane was prepared and
characterized as reported earlier.[7]
Preparation of Complexes
Perchlorate Complex
Cr(ClO4)3ꢃ6H2O (0.4584 g, 1 mmol) in ethyl acetate (10 mL) was added
to the boiling suspension of GA (0.5142 g, 1.2 mmol) in ethyl acetate

1806
THOMAS, MADHU, AND RADHAKRISHNAN
Figure 2. Tentative structures of chromium(III) complexes of GA.
(100 mL). This mixture was refluxed on a boiling water bath for about 3 h.
The resulting solution was then filtered and evaporated to half of its volume.
The complex precipitated on cooling to room temperature was filtered and
washed repeatedly with hot ethyl acetate. It was then recrystallized from
acetonitrile and dried under vacuum over P4O10. (Warning! Perchlorate salts
with organic compounds are potentially explosive. They should be handled in
small quantities and with caution.)
Nitrate, Chloride, and Bromide Complexes
A quantity of 1 mmol of Cr(NO3)3ꢃ9H2O (0.4002 g), CrCl3ꢃ6H2O
(0.2664 g) or CrBr3ꢃ6H2O (0.3998 g) in methanol (10 mL) was added to a

CHROMIUM(III) COMPLEXES
1807
boiling suspension of GA (0.5142 g, 1.2 mmol) in ethyl acetate (100 mL).
This mixture was refluxed on a boiling water bath for about 3 h. The dark
brown solution obtained on reflux was cooled and filtered. On partial eva-
poration of the solvent and subsequent cooling the complexes separated.
The mixture was filtered and the residue washed repeatedly with hot ethyl
acetate to obtain the pure complexes. They were then recrystallized from hot
acetonitrile and dried under vacuum over P4O10.
Physical Methods of Analysis
All the complexes were analyzed for metal and halide contents by
standard methods[16] and the perchlorate content by the Kurz method.[17]
The electrical conductance of the complexes in DMF, ethanol, methanol
and nitrobenzene (10ꢀ3 M solutions) were measured at room temperature
using a Toshniwal conductivity bridge with a dip-type conductance cell (cell
constant 0.9737). The infrared spectra of the ligands and the complexes were
recorded in the range 4000–400 cmꢀ1 on a Shimadzu IR 470 spectro-
photometer in KBr discs and in the range 500–100 cmꢀ1 on a Bruker IFS
66v FT-IR spectrophotometer in polyethylene powder. The electronic
spectra of the ligand and the complexes in the solid state (paste with Nujol)
were measured in the range 200–1100 nm on a Shimadzu UV 160 A
spectrophotometer. The elemental analyses (C, H and N) were carried out
on a Heraeus CHNO rapid analyzer. The magnetic moments were measured
at room temperature by the Gouy method using mercury(II) tetra-
thiocyanatocobaltate(II) as the calibrant.
ACKNOWLEDGMENTS
We thank the Head, Regional Sophisticated Instrumentation Centre,
Indian Institute of Technology, Chennai, for providing the experimental
facilities for this work. We also thank the authorities of the University
Grants Commission, New Delhi, India, for granting a Teacher Fellowship
to one of us (VTT).
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Received January 10, 2002
Accepted August 20, 2002
Referee I: D. N. Blauch
Referee II: L. J. Boucher