Moessbauer and electronic spectral studies of iron(III) complexes of oximes.

Article abstract of DOI:10.1016/S1386-1425(02)00238-X

The hydroxo-bridge complexes of the type [Fe(2)(ligand-H)(4)(OH)(2)] with bidentate nitrogen-oxygen donor ligands, viz. 2-hydroxynaphthaldehydeoxime [hnoH(2)], 2-hydroxyacetphenoneoxime [haoH(2)], salicylaldooxime [SalH(2)], 2-hydroxypropiophenoneoxime [hnoH(2)] have been prepared. All the complexes have been characterized by elemental analysis, magnetic moments, electronic and Moessbauer spectral studies. Moessbauer parameters of the complexes clearly suggest high spin configuration of Fe(III) showing lower magnetic moment to that of the spin only value, i.e. 5.92 BM. It may be due to the antiferromagnetic interaction between Fe(III) centers.

Full text of DOI:10.1016/S1386-1425(02)00238-X

Spectrochimica Acta Part A 59 (2003) 755Á760
/
www.elsevier.com/locate/saa
Mossbauer and electronic spectral studies of iron(III)
¨
complexes of oximes
Sulekh Chandra *, Sangeetika, Sunil Dutta Sharma
Department of Chemistry, Zakir Hussain College, University of Delhi, J.L. Nehru Marg, New Delhi 110002, India
Received 15 February 2002; accepted 12 June 2002
Abstract
The hydroxo-bridge complexes of the type [Fe2(ligandꢀ
viz. 2-hydroxynaphthaldehydeoxime [hnoH2], 2-hydroxyacetphenoneoxime [haoH2], salicylaldooxime [SalH2], 2-
/
H)4(OH)2] with bidentate nitrogenÁoxygen donor ligands,
/
hydroxypropiophenoneoxime [hnoH2] have been prepared. All the complexes have been characterized by elemental
analysis, magnetic moments, electronic and Mossbauer spectral studies. Mossbauer parameters of the complexes clearly
¨
¨
suggest high spin configuration of Fe(III) showing lower magnetic moment to that of the spin only value, i.e. 5.92 BM.
It may be due to the antiferromagnetic interaction between Fe(III) centers.
# 2002 Published by Elsevier Science B.V.
Keywords: Fe(III); Oximes; Mossbauer; Magnetic moment; Electronic spectra
¨
1. Introduction
as semi-conducting materials [10,11]. The dioxime
and o-hydroxyoximes have also been used as
analytical reagent [12Á17] for the detection and
The metal complexes of o-hydroxyoximes re-
ceived considerable attention due to their struc-
/
determination of metal ions.
In this paper, we report the synthesis and
characterization of Fe(III) complexes of oximes,
viz. 2-hydroxynaphthaldehydeoxime [hnoH2] L1,
2-hydroxyacetphenoneoxime [haoH2] L2, salicyl-
aldooxime [SalH2] L3, 2-hydroxypropiophenone-
oxime [hnoH2] L4.
tural features which are of general interest [1Á5].
/
These features include short intramolecular hydro-
gen bonds and a packing configuration, which
gives rise to unusual optical properties. Hydro-
xyoximes are playing an important role as com-
mercial reagents in extractive metallurgy in both
solvent extraction and froth flotation [6,7]. Oximes
are also applicable as biochemical [8,9] models and
2. Experimental
All the chemicals used were of AnalaR grade.
All the solvents used were distilled before use.
* Corresponding author.
E-mail address: amit1984@mantraonline.com (S. Chandra).
1386-1425/03/$ - see front matter # 2002 Published by Elsevier Science B.V.
PII: S 1 3 8 6 - 1 4 2 5 ( 0 2 ) 0 0 2 3 8 - X

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S. Chandra et al. / Spectrochimica Acta Part A 59 (2003) 755Á760
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2.1. Preparation of the ligands
channel and the data from multichannel analyzer
were reduced by means of a least-square-fitting
programme run on IBM 360 computer.
A general method for the preparation of ligands
has been used. The ligands were prepared by
treating 0.05 mol of an ethanolic solution (20 ml)
of particular aldehyde or ketone with an ethanolic
solution (20 ml) of hydroxylamine hydrochloride
(0.1 mol, 6.95 g) containing an aqueous solution
(20 ml) of sodium acetate (0.15 mol, 12.30 g). The
4. Results and discussion
All the complexes were found to have general
solution was heated on water bath for about 2Á4 h
/
composition [Fe2(ligandꢀ
/
H)4(OH)2] where the
with constant stirring. On cooling the contents at
5 8C, ligands were precipitated out. They were
filtered, washed with ethanol and dried under
vacuum over P4O10.
ligands are of 2-hydroxynaphthaldehyde-
oxime [hnoH2] L1, 2-hydroxyacetophenoneoxime
[haoH2] L2 (Ia), salicylaldooxime [SalH2] L3, 2-
hydroxypropiophenoneoxime [hnoH2] L4 (Ib)
(Fig. 1). All the complexes are stable in air and
moisture. The analytical data of complexes with
the stoichiometries proposed are summarized in
Table 1.
2.2. Preparation of the complexes
A hot aqueous solution (20 ml) of ferric
perchlorate (0.1 mol) was mixed with the hot
ethanolic solution (20 ml) of the corresponding
ligand (0.2 mol). In the case of 2-hydroxynaphthal-
dehyde, aqueous solution of sodium hydroxide
was added dropwise until dark brown colour
complexes precipitated out. But in the case of
salicylaldehyde and 2-hydroxyacetophenone, aqu-
eous NH3 solution (1:1) was added dropwise until
the brown-coloured complexes precipitated out.
The coloured precipitate was filtered, washed with
absolute ethanol and dried under vacuum over
P4O10.
5. Magnetic moments
These complexes show magnetic moment in the
range 4.0Á4.3 BM which is lower than the spin
/
only value, i.e. 5.92 BM. Fe(III) d5 case, under
weak fields of Oh symmetry, the ground state is
6A1g(t23g, eg2) with Sꢀ
5/2 (high spin). Such system
/
exhibits magnetic moments close to spin only
value, i.e. 5.92 BM. In the presence of strong field
of Oh symmetry, the ground state is [2] T2g(t52g, eg0)
3. Physical measurements
with Sꢀ1/2 (low spin); in this case, the magnetic
/
moments are close to 2.0 BM. Deviation from the
spin only value of 1.73 BM is due to the small
contribution from the non-zero value of the orbital
angular momentum in the t52g configuration. The
magnetic moment is intermediate to high or low
spin values due arise when the ligand field strength
is comparable with the mean electronic pairing
energy of the d5 configuration. In such a case, the
Magnetic susceptibility on the solid complexes
were made at room temperature by Gouy method
using Hg[Co(CNS)4] (xgꢀ
/
16.44ꢁ
10ꢂ6 cgs units)
/
as the calibrating agent. Electronic spectra in
Nujol mull were recorded on Perkin-Elmer 137.
IR spectra were recorded on a Perkin-Elmer 621
automatic recording spectrophotometer in Nujol
mull. Microanalyses of C, H and N were per-
formed at the Microanalytical Laboratory, CDRI,
6
2
two possible ground states A1g and T2g are in
thermal equilibrium resulting in temperature-de-
pendent variation of magnetic moments between
Lucknow. Mossbauer measurements were carried
¨
out on a multichannel (512 channels) analyzer in
constant acceleration mode. Source (NEN) used is
Co57 in Pd matrix (15 mc) and was held at room
temperature. Sufficient counts were stored in each
the limiting values of 5.92Á2.0 BM. This has also
/
been confirmed by Mossbauer quadrupole split-
¨
ting.

S. Chandra et al. / Spectrochimica Acta Part A 59 (2003) 755Á
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757
Fig. 1. Structure of ligands.
Table 2
Infrared spectral bands in cmꢂ1 and their assignments
6. IR spectra
The most important bands in the IR spectra of
the ligands and their metal complexes are pre-
sented in Table 2 along with their tentative
assignments.
Complexes
[hnoH2]
n(OH) n(Cꢁ
/
N) n(Mꢀ
/
O) n(NꢀO)
/
3460s 1560m
Á/
Á/
398w
[Fe2(hnoHꢀ
[haoH2]
/
H)4(OH)2]
H)4(OH)2]
H)4(OH)2]
Á
/
1579m 471m
3475s 1560m
1580m 469m
1564m
1590m 470m
3470s 1575m
1590m 467m
Á/
Á/
393w
In the IR spectra of ligands, a strong band at
3450Á
3475 cmꢂ1 is assigned to n(OH) of the
[Fe2(haoHꢀ
[hSalH2]
/
Á/
3450
Á/
Á/
398w
/
[Fe2(SalHꢀ
[hmpH2]
/
Á/
oxime or phenolic group. The absence of this
band in the spectra of the metal complexes of these
ligands suggests coordination through the oxygen
Á/
Á/
397w
[Fe2(hmpHꢀ
/
H)4(OH)2]
Á/
of the phenolic group [18Á
band in the IR spectra of the ligands assignable to
n(CꢁN) appears at 1580Á
1590 cmꢂ1 and is shifted
to lower frequency (Â
25 cmꢂ1) in the spectra of
the complexes, suggesting involvement of this
group in chelation [21]. Some new bands also
/
20]. Another strong
/
/
appeared in the IR spectra of the complexes at
460Á475 and 398Á
393 cmꢂ1 which may be due to
the formation of n(Mꢀ
[22,23].
/
/
/
/
O) and n(Mꢀ
/N) bonds
Table 1
Colour melting point and composition of iron(III) complexes of oximes
Complexes
Colour
Melting point Yield Elemental analysis calculated
(8C)
(%)
(found) (%)
M
C
H
[Fe2(hnoHꢀ
[Fe2(haoHꢀ
[Fe2(SalHꢀ
[Fe2(hnoHꢀ
/
H)4(OH)2] Fe2C44H34N4O10
Dark brown
Dark brown
270
250
60
75
67
64
12.54 (12.14) 59.34 (59.11) 3.85 (3.42)
14.96 (14.44) 51.49 (51.14) 4.59 (4.12)
16.18 (16.38) 48.73 (48.23) 3.79 (3.32)
13.75 (13.33) 53.22 (52.84) 5.21 (5.56)
/H)4(OH)2] Fe2C32H34N4O10
/
H)4(OH)2] Fe2C28H26N4O10
Dark reddish-brown 255
Dark reddish-brown 265
/H)4(OH)2] Fe2C36H42N4O10

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S. Chandra et al. / Spectrochimica Acta Part A 59 (2003) 755Á760
/
7. Electronic spectra
Table 3
Electronic spectral bands and magnetic moment data in BM for
iron(III) complexes
The electronic spectra of the Fe(III) complexes
exhibit a number of fairly broad bands rather than
the series of narrow bands as expected [24]. The
complexes under study show three bands of
Complexes
lmax (cmꢂ1
)
meff (BM)
[Fe2(hnoHꢀ
/
10 125, 20 879, 21 690,
28 650
4.13
H)4(OH)2]
varying intensities at 16 320Á
/
20 879, 19 570Á
/
[Fe2(haoHꢀ
H)4(OH)2]
[Fe2(SalHꢀ
[Fe2(hmpHꢀ
H)4(OH)2
/
15 650, 16 320, 19 570,
21 690
4.09
26 900 and 28 560 cmꢂ1, respectively. These tran-
sitions may be assigned, respectively, to the
/
H)4(OH)2] 10 130, 16 360, 18 629
4.18
4.30
6
6
/
11 013, 18 621, 29 062
following transitions: A1g0
/
4T1g, A1g0
/
4T2g
6
and A1g0
/
4T1g,4Eg.
960 cmꢂ1 while the spectrum of other complexes
contains strong ligand bands at this position.
Mossbauer parameters for all the complexes are
¨
8. Mo¨ssbauer spectra
given in Table 4. Representative spectra are shown
in Fig. 3. The isomer shift value lie in the range
Mossbauer parameters of the complexes are
¨
clearly suggestive of high spin Fe(III) observed
lower magnetic moments as against 5.92 BM may
arise due to antiferromagnetic interaction between
Fe(III) centers. The alternative possibility of spin-
state equilibrium should lead to temperature-
0.54Á
an Sꢀ
values lie in the range 0.70Á
/
0.69 nm sꢂ1 (300 K), which is indicative of
/
5/2 iron(III) state [25]. Quadrupole splitting
0.97 nm sꢂ1 for high
/
spin iron(III) complexes. In iron(III) complexes,
there is no valence contribution to the QS. The
only source of QS, therefore, remains the lattice
contribution arising mainly from the asymmetry of
dependent Mossbauer quadrupole splitting [25],
¨
while the complexes under study show remarkably
temperature-independent QS values. Keeping in
view the composition of the complexes and
bidentate nature of the ligands, the following
dihydroxybridged structure may be considered
(Fig. 2).
Dihydroxybridging of this type may give rise to
moderate antiferromagnetic exchange interaction
causing only small lowering in the magnetic
moment value as observed in these complexes in
Table 3. The characteristics Feꢀ
metric vibrations in such complexes are known to
absorb at Â
950 cmꢂ1 in the IR spectra. [Fe2(S-
/
Oꢀ/Fe antisym-
/
alH)4(OH)2] show medium non-ligand bands at
Fig. 3. Mossbauer spectra of (a) [Fe (SalHꢀH)4(OH)2] and (b)
[Fe2(haoHꢀH)4(OH)2].
/
¨
2
Fig. 2. Structure of Fe(III) complexes.
/

S. Chandra et al. / Spectrochimica Acta Part A 59 (2003) 755Á
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759
Table 4
Mossbauer parameters for iron(III) complexes
¨
Complexes
[Fe2(hnoHꢀ
[Fe2(haoHꢀ
[Fe2(SalHꢀ
[Fe2(hmpHꢀ
Temperature (K) IS d (mm sꢂ1
)
QS DE (mm sꢂ1
)
HWh (mm sꢂ1
)
HW (mm sꢂ1
)
Hw/HW
/
H)4(OH)2]
300
78
0.65
0.79
0.98
0.95
0.58
0.45
0.48
0.40
1.20
1.12
/H)4(OH)2]
300
78
0.51
0.80
0.86
0.84
0.75
0.90
0.57
0.70
1.31
1.28
/
)4(OH)2]
300
78
0.63
0.77
0.97
0.94
0.64
0.94
0.57
0.77
1.12
1.22
/H)4(OH)2
300
78
0.62
0.78
1.33
1.34
0.31
0.44
0.41
0.38
0.76
1.16
the ligand field, which is further supported by the
temperature independence of the QS value.
All the complexes show asymmetry effect as
expected for dimeric iron(III) compounds [26]. The
half width ratios are temperature-independent for
[Fe2(SalH2)4(OH)2] and temperature-dependent
References
[1] Y.N. Kukushkin, M.V. Bovina, A.V. Zinchenko, V.K.
Belsky, V.Y. Kukushki, Polyhedron 16 (1997) 2429.
[2] A.A. Razik, A.K.A. Hadi, Trans. Met. Chem. 19 (1984)
84.
[3] K.H. Reddy, Y. Lingappa, Trans. Met. Chem. 19 (1994)
487.
for [Fe2(haoHꢀ
/
H)4(OH)2] and [Fe2(hnoHꢀ
/
[4] M.M. Aly, N.I.A. Shatti, Trans. Met. Chem. 23 (1998)
361.
H)4(OH)2]. The asymmetry of the quadrupole
doublet may be attributed to the interaction of
the nucleus with fluctuating electronic and mag-
netic field. Fluctuations due to spin lattice relaxa-
[5] Y. Gok, S. Karabocek, M.N. Misir, Trans. Met. Chem. 23
(1998) 333.
[6] A.W. Ashbrook, Coord. Chem. Rev. 16 (1975) 285.
[7] J.S. Preston, J. Inorg. Nucl. Chem. 42 (1980) 441.
[8] R.J. Whewell, C. Hanson, Ion Ex. Solvent Ext. 8 (1981) 1.
[9] A. Chakravorty, Coord. Chem. Rev. 13 (1974) 1.
[10] T.W. Thomas, A.E. Underhill, Chem. Soc. Rev. 1 (1972)
99.
tion cause
concentration-independent asymmetry and those
due to spinÁspin relaxation give temperature-
independent asymmetry [27Á29]. [Fe2(haoHꢀ
H)4(OH)2] and [Fe2(hnoHꢀH)4(OH)2] for which
asymmetry is temperature-dependent, involve
spinÁlattice relaxation, since concentration depen-
dence has not been studied, spinÁspin relaxation
a
temperature-dependent and
/
/
/
[11] A.E. Underhill, D.M. Watkins, R. Pethig, Inorg. Nucl.
Chem. Lett. 9 (1973) 1269.
/
[12] R.B. Lanjewar, A.N. Garg, Polyhedron 12 (1993)
2619.
/
/
[13] H. Yoshitomoto, M.A. Scialdone, W.E. Degrado, J. Am.
Chem. Soc. 121 (1999) 1636.
also not to be ruled out. [Fe2(SalH2)4(OH)2] shows
temperature-independent asymmetry and hence
[14] K. Bey, K. Mandal, D. Bandypadhyay, K.K. Nanda,
Indian J. Chem. 32 (1993) 358.
involves spinÁ
/
spin relaxation and not spinÁlattice
/
[15] E. Jackson, B.S. Nakani, J. Chem. Soc., Dalton Trans.
(1996) 1373.
relaxation.
[16] D. Black, A.T. Blake, K.P. Dancey, A. Harrison, M.M.
Cpartlin, S. Parrosu, P.A. Taskar, G. Whittakar,
M. Schsoder, J. Chem. Soc., Dalton Trans. (1998)
3953.
Acknowledgements
[17] Y. Pieg, Journoux, O. Kohn, Inorg. Chem. 28 (1989)
100.
[18] S. Serin, Trans. Met. Chem. 26 (2001) 300.
[19] K. Serbest, I. Degirmencioglu, S. Karabocek, S. Guner,
Trans. Met. Chem. 26 (2001) 232.
We are thankful to the Principal, Zakir Hussain
College, for providing laboratory facilities and
Department of Science and Technology, New
Delhi, for financial assistance.
[20] X. Ren, C. Duan, H. Zhu, Q. Meng, C. Hu, C. Lu, Y. Liu,
Trans. Met. Chem. 26 (2001) 295.

760
S. Chandra et al. / Spectrochimica Acta Part A 59 (2003) 755Á760
/
[21] K. Nonoyenaa, S. Tomito, K.K. Yamaekas, Inorg. Chim.
Acta 12 (1975) 33.
[25] N.N. Greenwood, T.C. Gibb, Mossbauer Spectroscopy,
¨
Chapman & Hall, London, 1971, pp. 162, 206.
[26] G.M. Boncroft, A.G. Maddock, R.P. Randl, J. Am.
Chem. Soc. A 90 (1968) 2939.
[22] K. Nakamoto, Infrared and Raman Spectra of Coordina-
tion Compounds, Wiley/Interscience, New York, 1970.
[23] D. Noboru, K. Nakamoto, Inorg. Chem. 10 (1975)
786.
[27] M. Blume, J.A. Jon, Phys. Rev. 165 (2) (1968)
446.
[24] ABP Lever, Inorganic Electronic Spectroscopy, 2nd ed.,
Elsevier, Amsterdam, 1984.
[28] J.W.G. Wignall, J. Chem. Phys. 44 (1966) 2461.
[29] B.N. Figgis, Trans. Faraday Soc. 57 (1961) 198.