Complexes of iron(III) with N,N′-bis (4-antipyrylmethylidene)ethylenediamine

Article abstract of DOI:10.1081/SIM-120016870

Iron(III) complexes of the Schiff base N,N′-bis(4-antipyrylmethylidene)-ethylenediamine (BAME) having the general formulae [Fe(BAME)₂X]X₂ (X = ClO₄ or NO₃) and [Fe(BAME)₂X₂]X (X = SCN, Cl or Br) have been s+ynthesized and characterized by elemental analyses, electrical conductance in non-aqueous solvents, infrared and electronic spectra, and magnetic susceptibility measurements. In these complexes, BAME acts as a neutral bidentate ligand coordinating through both azomethine nitrogen atoms. In the perchlorate and nitrate complexes, one of the anions is bidentate while in the thiocynate complex, two of the anions are bound in a monodentate fashion to the metal ion. In the chloride and bromide complexes, two of the halide ions are coordinated. A high-spin octahedral geometry is assigned around Fe(III) in all of these complexes.

Full text of DOI:10.1081/SIM-120016870

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Complexes of Iron(III) with
N,N′‐bis(4‐Antipyrylmethylidene)ethylenediamine
K. C. Raju a & P. K. Radhakrishnan a
a School of Chemical Sciences , Mahatma Gandhi University , Kottayam, 686‐560, Kerala,
India
Published online: 15 Aug 2006.
To cite this article: K. C. Raju & P. K. Radhakrishnan (2003) Complexes of Iron(III) with
N,N′‐bis(4‐Antipyrylmethylidene)ethylenediamine, Synthesis and Reactivity in Inorganic and Metal-Organic Chemistry, 33:1,
23-33, DOI: 10.1081/SIM-120016870
To link to this article: http://dx.doi.org/10.1081/SIM-120016870
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SYNTHESIS AND REACTIVITY IN INORGANIC AND METAL-ORGANIC CHEMISTRY
Vol. 33, No. 1, pp. 23–33, 2003
Complexes of Iron(III) with
N,N’-bis(4-Antipyrylmethylidene)ethylenediamine
*
K. C. Raju and P. K. Radhakrishnan
School of Chemical Sciences, Mahatma Gandhi University,
Kottayam, Kerala, India
ABSTRACT
Iron(III) complexes of the Schiff base N,N’-bis(4-antipyrylmethylidene)-
ethylenediamine (BAME) having the general formulae [Fe(BA-
ME)2X]X2 (X = ClO4 or NO3) and [Fe(BAME)2X2]X (X = SCN, Cl or
Br) have been s+ynthesized and characterized by elemental analyses,
electrical conductance in non-aqueous solvents, infrared and electronic
spectra, and magnetic susceptibility measurements. In these complexes,
BAME acts as a neutral bidentate ligand coordinating through both
azomethine nitrogen atoms. In the perchlorate and nitrate complexes, one
of the anions is bidentate while in the thiocynate complex, two of the
anions are bound in a monodentate fashion to the metal ion. In the
chloride and bromide complexes, two of the halide ions are coordinated.
A high-spin octahedral geometry is assigned around Fe(III) in all of
these complexes.
*
Correspondence: P.K. Radhakrishnan, School of Chemical Sciences, Mahatma
Gandhi University Kottayam, 686-560, Kerala, India; E-mail: mgu@vsnl.com.
23
DOI: 10.1081/SIM-120016870
0094-5714 (Print); 1532-2440 (Online)
www.dekker.com
Copyright D 2003 by Marcel Dekker, Inc.

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24
Raju and Radhakrishnan
INTRODUCTION
The biological activities of antipyrine based ligands and their metal
complexes are well known.[1,2] Iron complexes were the earliest metal
complexes used in the treatment of hypochromic anaemia.[3] In view of this
and as a continuation of our earlier investigation on Schiff base metal
complexes,[4–10] we report here the synthesis and characterisation of the
Fe(III) complexes of a Schiff base ligand, viz., N,N’-bis(4-antipyrylmethy-
lidene)ethylenediamine, which is an antipyrine derivative (Figure 1).
RESULTS AND DISCUSSION
The formation of the complexes may be represented by the general
equation shown below.
FeX3 þ 2BAME ! FeðBAMEÞ2X3ðX ¼ ClO4; NO3; SCN; Cl or BrÞ
The complexes are dark brown solids. They are soluble in acetonitrile,
DMF, ethanol, and nitrobenzene but insoluble in benzene, ethyl acetate, and
toluene. The analytical data (Table 1) show that the complexes can be
represented as: Fe(BAME)2X3 (X =ClO4, NO3, SCN, Cl or Br).
Electrical Conductance
The molar conductance values of the complexes (Table 2) in ace-
tonitrile, DMF and nitrobenzene fall in the range suggested for 1:2 elec-
trolytes for the perchlorate and nitrate complexes.[11] The thiocyanate,
chloride, and bromide complexes behave as 1:1 electrolytes. Thus, the
complexes may be formulated as [Fe(BAME)2X]X2 [X =ClO4 or NO3) and
[Fe(BAME)2X2]X (X =SCN, Cl or Br).
Figure 1. N,N’-Bis(4-antipyrylmethylidene)ethylenediamine.

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Complexes with Iron(III)
25

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26
Raju and Radhakrishnan
Table 2. Molar conductancea data of the iron(III) complexesb of BAME.
Complex
CH3CN
DMF
C6H5NO2
[Fe(BAME)2(ClO4)](ClO4)2
[Fe(BAME)2(NO3)](NO3)2
[Fe(BAME)2(SCN)2](SCN)
[Fe(BAME)2Cl2]Cl
307.44
296.46
120.78
126.27
153.72
170.19
153.72
74.66
77.96
88.9
61.49
57.09
19.76
21.41
25.25
[Fe(BAME)2Br2]Br
aOhm ꢀ 1 cm2 mol ꢀ 1
b10 ꢀ 3 M solution.
.
Infrared Spectra
The important infrared spectral bands of BAME and its complexes are
given in Table 3. The bands at 1650 and 1594 cm ꢀ 1 are attributable to the
stretching vibrations of the carbonyl and azomethine groups, respectively.[6]
In the complexes the band at 1594 cm ꢀ 1 is blue-shifted to the 1,607–1,612
region indicating the coordination of both azomethine nitrogens. But the
band at 1650 cm ꢀ 1 remains practically unaltered, suggesting non-coordi-
nation of both carbonyl oxygens in these complexes.[6]
In the perchlorate complex, the triply-split band maxima at 1142, 1110
and 1024 cm ꢀ 1 are due to the n8, n6 and n1 vibrations, respectively, of the
perchlorate group of C2n symmetry. This indicates that at least one of the
perchlorate groups must be coordinated in a bidentate fashion. The band at
1089 cm ꢀ 1 is assigned to n3 vibration of the ionic perchlorate of Td sym-
metry. The vibrational frequencies observed at 942 and 636 cm ꢀ 1 cor-
responding to n2 and n3 vibrations of the perchlorate group of C2n symmetry
and the band at 627 cm ꢀ 1 due to the n4 vibration of the ionic perchlorate,
which are not present in the spectrum of the free ligand, support the
coexistence of both ionic and coordinated perchlorate groups in this
complex.[6]
In the nitrate complex, two strong bands at 1475 and 1280 cm ꢀ 1 are
attributable to n4 and n1 stretching vibrations, respectively, of the coor-
dinated ion of C2n symmetry. Since n4 ꢀ n1 is 195 cm ꢀ 1, the nitrate ion is
bidentate.[12] A very strong band at 1380 cm ꢀ 1 and a medium intensity
band at 824 cm ꢀ 1 are due to n3 and n2 vibrations, respectively, of un-
coordinated nitrate ion of D3h symmetry.
In the thiocyanate complex, a sharp band at 2053 cm ꢀ 1 is attributable
to N-coordinated thiocyanate ion.[8] This is supported by the presence of a
medium intensity band at 478 cm ꢀ 1 and a weak band at 852 cm ꢀ 1
.

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Complexes with Iron(III)
27

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Raju and Radhakrishnan
In the spectra of halide complexes, Fe–Cl and Fe–Br stretching vib-
rations are observed at 310 and 289 cm ꢀ 1 which are absent in the ligand
spectrum.[8]
The above spectral observations along with the conductance data
indicate that one of the perchlorate and nitrate ions, two of the thiocyanates,
and both chloride and bromide ions are coordinated in these complexes.
Furthermore, Fe–N stretching vibrations are observed at about 450 cm ꢀ 1
in all these complexes.[8]
Electronic Spectra
The electronic spectral data of the ligand and complexes with their
tentative assignments are given in Table 4. BAME shows two absorption
maxima at 25,000 and 40,322 cm ꢀ 1, corresponding to n !p* and p! p*
Table 4. Electronic spectral data and magnetic moments of the iron(III) complexes
of BAME.
Abs. max.
(cm ꢀ 1
Tentative
assignment
meff
(B.M.)
Compound
BAME
)
25,000
40,322
24,390
40.485
n ! p*
–
p ! p*
[Fe(BAME)2(ClO4)](ClO4)2
[Fe(BAME)2(NO3)](NO3)2
[Fe(BAME)2 (SCN)2](SCN)
[Fe(BAME)2Cl2]Cl
n ! p*
5.84
p ! p*
33, 222
21,598
24,691
40,983
33,333
20,533
24813
40,485
33,898
21,645
24,630
40,650
33,333
21,978
24875
40,816
33,333
20,746
Charge transfer
4
6A1g ! T1g
n ! p*
5.96
5.88
5.71
5.74
p ! p*
Charge transfer
4
6A1g ! T1g
n ! p*
p ! p*
Charge transfer
4
6A1g ! T1g
n ! p*
p ! p*
Charge transfer
4
6A1g ! T1g
[Fe(BAME)2Br2]Br
n ! p*
p ! p*
Charge transfer
4
6A1g ! T1g

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Complexes with Iron(III)
29
transitions, respectively. In the complexes, n !p* transitions are red-shifted
to the regions 24,390–24,875 cm ꢀ 1, while p! p* transitions are blue-
shifted to the regions 40,485–40,983 cm ꢀ 1. The band in the region
6
4
20,533–21,978 cm ꢀ 1 of the complexes is attributed to the A1g ! T1g
transition, which is consistent with octahedral geometry around Fe(III)
ion.[13,14] An intense absorption band in the 33,222–33,898 cm ꢀ 1 region
may be due to a charge transfer process.
Magnetic Moment Data
The molar magnetic moments of the complexes are given in Table 4.
The values vary in the range 5.71–5.96 B.M., suggesting high-spin oc-
tahedral configuration around the Fe(III) ion.[15,16]
Based on the above observations the following tentative structures may
be assigned to the complexes (Figure 2).
EXPERIMENTAL
Materials
The metal salts were prepared from Analar ferric carbonate and the
respective 50% acids and crystallizing out the salts by evaporating the
solution on a steam bath. Ferric thiocyanate was prepared by the method
reported earlier.[17]
Preparation of the Ligand
The ligand N,N’-bis(4-antipyrylmethylidene)ethylenediamine was pre-
pared and characterized as described earlier.[6]
Preparation of BAME Complexes
Perchlorate, Nitrate, Thiocyanate and Bromide Complexes
A quantity of one mmol of Fe(ClO4)ꢁ6H2O (0.4623 g), Fe(SCN)3ꢁ6H2O
(0.3381 g) or FeBr3ꢁ6H2O (0.4037 g) in ethyl acetate (10 mL) or Fe(NO3)3ꢁ-
6H2O (0.3499 g) in methanol (10 mL) was added to a boiling suspension of
2.2 mmol (1.0044 g) of BAME in ethyl acetate (100 mL). The mixture was

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Raju and Radhakrishnan
Figure 2. Tentative structures of Fe(III) complexes of BAME.

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Complexes with Iron(III)
31
refluxed for about 3 h on a steam bath. The resulting solution was con-
centrated to half of its original volume and cooled. The complexes pre-
cipitated on cooling were filtered and washed several times with hot
benzene to remove the excess ligand. The complexes were dried under
vacuum over phosphorus(V) oxide.
Chloride Complex
A quantity of one mmol of FeCl3ꢁ6H2O (0.2703 g) in acetone (10 mL)
was added to a boiling suspension of 2.2 mmol (1.0044 g) of BAME in
acetone (100 mL). The complexes were separated by the same procedure as
described above.
Analyses and Physical Methods
All the complexes were analyzed for metal contents by the standard
method[18] and for perchlorate by the Kurz method.[19] The electrical
conductance of the complexes in acetonitrile, DMF and nitrobenzene (10 ꢀ 3
M solutions) were measured at room temperature using a Toshniwal con-
ductivity bridge with a dip-type conductance cell (cell constant =1.098).
The infrared spectra of the ligand and complexes were recorded in the
range 4,000–400 cm ꢀ 1 on a Shimadzu IR 470 spectrophotometer in KBr
disc and in the range 400–200 cm ꢀ 1 on a Perkin Elmer 983 IR spec-
trophotometer in polyethylene powder. Electronic spectra of the ligand and
the complexes in the solid state (using a paste with Nujol) were measured
in the range 200–1,100 nm on a Shimadzu UV 160A spectrophotometer.
The elemental analyses (C, H and N) were carried out on a Heraeus CHNO
rapid analyser. The magnetic moments were measured at room tempera-
ture by the Gouy method using mercury(II) tetrathiocyanatocobaltate(II) as
the calibrant.
ACKNOWLEDGMENTS
We wish to express our sincere thanks to the heads of the Regional
Sophisticated Instrumentation Centres at the Indian Institute of Technology,
Chennai, and the Indian Institute of Technology, Mumbai, for some ins-
trumental analysis. We also thank Mahatma Gandhi University, Kerala,
India, for providing laboratory facilities and the University Grants Com-
mission for awarding a Teacher Fellowship to one of us (KCR) under the

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32
Raju and Radhakrishnan
faculty improvement programme. We also wish to express our sincere thanks
to Dr. Siby Joseph and Dr. N. T. Madhu for some fruitful discussions.
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Received May 2, 2002
Accepted August 22, 2002
Referee I: J. D. Protasiewicz
Referee II: M. Bayachou