Mossbauer spectral, magnetic moment and thermal decompositionstudies of unsymmetrically substituted

(N-alkyl,N?-hydroxyethyldithiocarbamato) iron(III) complexes

Sonal Singhal a, C.L. Sharma a, A.N. Garg a,*, K. Chandra b

a Department of Chemistry, Indian Institute of Technology, Roorkee 247 667, Indiab Institute Instrumentation Centre, Indian Institute of Technology, Roorkee 247 667, India

Received 17 June 2002; accepted 30 August 2002

Abstract

Four unsymmetrically substituted tris(N -alkyl,N ?-hydroxyethyldithiocarbamato) iron(III) complexes, [(OHCH2CH2)RNCS2]3Fe

with R�/CH3, C2H5, n -C3H7 and n -C4H9 have been synthesized and characterized by IR, electronic, Mossbauer spectral and

magnetic moment studies. Room temperature Mossbauer spectra of all the complexes exhibit an asymmetric doublet which could be

resolved into two doublets corresponding to high and low spin states in equilibrium. Variable temperature Mossbauer spectral and

magnetic moment studies suggest that all the complexes tend to become nearly low spin at 77 K. Isomer shift (d ) values show little

variation in the two spin states of the complexes but DEQ increases with increasing chain length from CH3 to n -C4H9. Mossbauer

spectra of heated products at 500 and 700 8C exhibit a doublet with sextet and sextet only, respectively, corresponding to the

formation of Fe2O3. In no case was Fe2S3 found to be formed. All the complexes undergo decomposition in two stages finally

yielding Fe2O3, but during the first stage it is a first order process. Various kinetic and thermodynamic parameters were calculated.

It is observed that the activation energy values increase with the molecular weight of the alkyl groups attached to the N atom. There

seems to occur an intramolecular rearrangement with restriction on the vibrational degrees of freedom.

# 2002 Elsevier Science Ltd. All rights reserved.

Keywords: Iron(III) dialkyldithiocarbamates; Mossbauer spectra; Magnetic moment; Thermal decomposition; Spin crossover

1. Introduction

Studies on spin-crossover in iron(III) systems have

been very fascinating for the past three decades [1,2].

Spin-crossover in the ferric state means an intramole-

cular transfer of two electrons between the t2g to eg

orbitals [3]. Rickards et al. [4] studied several tris(N ,N ?-dialkyldithiocarbamato) iron(III) complexes down to

4.2 K and in the presence of an external magnetic field

whereby a rate of exchange between the high and low

spin states were estimated to be greater than 107 s�1.

Leipoldt and Coppens [5] studied the temperature

dependent magnetic behaviour of iron(III) dithiocarba-

mates and assumed the existence of two almost equie-

nergetic ground states, the variation being a result of the

change in relative population of the two levels. Hall and

Hendrickson [6] suggested that both the high and low

spin states are very vibronic with a flipping rate of 1010

s�1. Pandeya et al. [7] have reported the synthesis and

Mossbauer spectral studies of a new complex,

[(OHCH2CH2)2NCS2]3Fe, with an unusually high quad-

rupole splitting having a flipping rate close to the inverse

of the Mossbauer time scale. Kopf et al. [8] reported an

intermediate spin state 3/2 for an iron(III) complex with

a mixed nitrogen sulfur coordinating sphere. The

synthesis, magnetic and spectral behaviour of a new

first spin-crossover chain compound was reported by

Koningsbruggen et al. [9]. Interestingly, Manikandan et

al. [10] reported the variable temperature (1.7�/300 K)

Mossbauer spectra of [FeL2](ClO4)2 �/CH3CN and

[FeL2](PF6)2 where L�/(2,6-bis(3,5-dimethylpyrazol-1-

yl methyl)pyridine) with an increased amount of low

spin form at high temperature. Such studies are of

* Corresponding author. Tel.: �/91-1332-85324; fax: �/91-1332-

73560

E-mail address: agargfcy@iitr.ernet.in (A.N. Garg).

Polyhedron 21 (2002) 2489�/2496

www.elsevier.com/locate/poly

0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.

PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 1 2 3 1 - 7

special interest as certain ferric cytochromes having a

FeS6 moiety are associated with electron transport in

biological systems and these are involved in spin

equilibrium suggesting that spin state conversion iscoupled to electron transport [11].

Thermal decomposition studies of iron(III) dithiocar-

bamates and related compounds have also attracted the

attention of several workers [12,13]. Thermogravimetric

studies of [Fe(S2CNEt2)3] by D’Ascenzo and Wendlendt

[14] have shown this to be completely volatile, whereas

Lanjewar and Garg [15] have reported volatile, non-

volatile and partially volatile natures depending onsymmetrical and unsymmetrical substituents. Earlier

we had reported Mossbauer spectral, magnetic moment

and thermal decomposition studies of some tris(N ,N ?-dialkyldithiocarbamato) iron(III) complexes wherein

Fe(SCN)3 was formed as an intermediate product [16].

In this paper we have reported the synthesis, IR

spectral, variable temperature magnetic moment, Moss-

bauer spectral and thermal decomposition studies of thefour unsymmetrically substituted complexes

[(OHCH2CH2)RNCS2]3Fe with R�/CH3, C2H5, n -

C3H7 and n -C4H9. Also from the TGA plots, the kinetic

and thermodynamic parameters were calculated using a

Freeman and Carroll method [17].

2. Experimental

All the chemicals used were of analytical/guaranteed

or high purity grade.

2.1. Preparation of the complexes

First the dithiocarbamate ligands were prepared as

sodium salts by the reaction of the respective secondary

amine in tetrahydrofuran with CS2 and adding sodiumhydroxide solution in equal mole ratio with vigorous

stirring for 5�/6 h at room temperature [16]. The crude

product was recrystallized from methanol. The purity of

ligands was checked by determining m.p. which matched

well with the literature values. 4 g of ferric nitrate was

dissolved in a minimum amount of absolute ethanol and

then a calculated amount of sodium N -alkyl,N ?-hydro-

xyethyldithiocarbamate was added with thorough stir-ring for 1�/2 h at room temperature as described earlier

[16]. In all cases a black coloured complex was formed.

These were washed with water and dried diethyl ether

and then dried over fused calcium chloride in a vacuum

desiccator overnight. Elemental analysis of the com-

plexes is given in Table 1.

2.2. Physical measurements

Mossbauer spectra were recorded using a constant

acceleration transducer driven Mossbauer spectrometer

(ECIL, Hyderabad) in conjunction with 1024 MCA

(Canberra). A 25 mCi 57Co(Rh) source procured from

Amersham, UK was used. The spectrometer was

calibrated using a natural iron foil as well as recrystal-

lized sodium nitroprusside dihydrate (SNP) as standards

at 295 K. The spectral data were least-square fitted.

Magnetic moments were measured at room temperature

(295 K) using a Vibrating Sample Magnetometer (VSM

Model 155, Princeton Applied Research, USA). Ther-

mograms were recorded on a thermogravimetric analy-

ser system, STA-780 series (Stanton Redcroft, UK) at a

heating rate of 10 8C min�1. All the measurements were

carried out in static air atmosphere using Al2O3 as

reference material. IR spectra in the range 4000�/400

cm�1 were recorded in KBr medium on a Perkin�/Elmer

1600, FT-IR Spectrophotometer. Further spectra were

also recorded down to 50 cm�1 at the RSIC, IIT-

Madras.

3. Results and discussion

All the four complexes were black solids, which are

stable under normal atmospheric conditions. Typical

Mossbauer spectra of the (N -methyl,N ?-hydroxyethyl-

dithiocarbamato) iron(III) complex from room tem-

perature (295 K) down to liquid nitrogen temperature

(77 K) are shown in Fig. 1. Mossbauer parameters

derived from these spectra after fitting are listed in Table

2. Variation of magnetic moment with temperature in

the 77�/295 K range for all the complexes, are shown in

Fig. 2. Typical thermograms (TG, DTG and DTA) of

the complexes, [(HOCH2CH2)RNCS2]3Fe having R�/

CH3 and C2H5 are shown in Fig. 3. Thermogravimetric

data and the kinetic and thermodynamic parameters for

all the complexes are listed in Table 3.

Tris(N ,N ?-dialkyldithiocarbamato) iron(III) com-

plexes have trigonally distorted octahedral geometry

with six sulfur donor atoms surrounding the central

iron(III) in D3 symmetry with a twist angle 8 varying

from about 338 to 408, depending on the nature of the

alkyl group [18]. Earlier we had studied the crystal

structure of the tris(N ,N ?-diallyl dithiocarbamato) iro-

n(III) complex and confirmed that the crystals are

monoclinic with space group C2/c where a�/18.737(5)

A, b�/10.229(3) A and c�/15.571(3) A and the angles

a�/908, b�/106.138 and g�/908. The bond lengths of

Fe�/S were found to be 2.3262, 2.3657 and 2.3488 A and

bond angles S�/Fe�/S were 74.258, 90.488, 94.588, 97.998,98.938 and 160.098 [19]. Since the basic nature of the

ligands remains the same, the molecular structure of the

presently studied unsymmetrically substituted com-

plexes is likely to remain similar and the possible

structure may be represented as I.

S. Singhal et al. / Polyhedron 21 (2002) 2489�/24962490

3.1. Magnetic moment

Magnetic moment studies of dialkyldithiocarbamato

iron(III) complexes have been reported by several

workers [3�/6]. On the basis of the room temperature

magnetic moments, all the complexes are in a mixed spin

state though these are predominantly in high spin state

(6A1g). This suggests that the complexes exhibit high

spin(HS)X/low spin(LS) equilibria at room tempera-

ture. As the temperature is lowered it is converted moreand more towards the low spin state (2T2g). This is quite

evident from the plots of variation of magnetic moment

with temperature as shown in Fig. 2. Also an interesting

relationship seems to exist between the nature of alkyl

group and the magnetic moment. Evidently as the

carbon chain length increases from methyl to n-butyl,

it tends to shift more towards a high spin state and the

same trend is observed at all temperatures. Apparentlythis is due to an increase in the electron density on the

Fe atom due to the positive inductive effect of the alkyl

group.

3.2. IR spectra

The metal�/ligand stretching band appearing in the far

IR region provides information about the strength of

the metal�/ligand bond and the spin state of the system

[20,21]. Ewald et al. [3] proposed the 300�/400 cm�1

region for both the high and low spin states of the Fe�/S

stretching band. Butcher et al. [20] examined the far IR

spectra of Fe(R2dtc)3 complexes using isotopic substitu-

tion, and assigned the high spin nFe�S at a lower energy

than that for the low spin mode, keeping both in the

300�/400 cm�1 region. In a further investigation of far

IR spectra of tris(N ,N ?-dialkyldithiocarbamato) iro-

n(III) complexes using 54Fe and 57Fe isotopes, Hutch-

inson et al. [21] showed that high spin nFe�S appears at

205�/250 cm�1, the low spin at 305�/350 cm�1 and the

intermediate spin nFe�S in both regions. Various assign-

ments for the IR stretching bands are listed in Table 1.

On the basis of literature reports the nFe�S stretching

band in the 226�/233 cm�1 region corresponds to the

high spin state and another strong band in the 332�/353

cm�1 region is attributed to the low spin state. Inter-

estingly, intensities of the two bands corresponding to

high and low spin states also vary depending on their

contributions in the equilibrium mixture.

Besides nFe�S, IR spectral assignments of other bands

are also reported. Chatt et al. [22] suggested resonance

structures on the basis of an intense band in the region

1550�/1480 cm�1 due to a C/� � �/N stretching vibration.

Bradley and Gitlitz [23] studied IR bands in several

metal N ,N ?-dialkyldithiocarbamates and reported the

thioureide (N/� � �/C) band near 1500 cm�1 as a character-

istic of the ligand indicating considerable double bond

character in the (S2)C/� � �/N(R2) bond. We have observed

n(N���C) in the 1492�/1496 cm�1 region, which matches

well with the literature value. Another strong band in

the 1165�/1190 cm�1 region may be attributed to N�/C2

Table 1

Analytical and infrared spectral data of tris(N -alkyl-N ?-hydroxyethyldithiocarbamato) iron(III) complexes

Complex [Fe(S2CNR1R2)3]

R1�CH2CH2OH

and R2�

Analytical Infrared

C (calc.) H (calc.) N (calc.) S (calc.) Fe (calc.) n(N�C) /n(N���C2 )/ /n(C���S)/ n(Fe�S)

HS LS

�CH3 28.46 4.74 8.30 37.94 11.07 1499 1190 985 233 332

(27.98) (4.71) (8.38) (36.54) (10.89) 1279

�C2H5 32.80 5.77 7.66 35.03 10.22 1492 1180 987 232 353

(32.85) (5.70) (7.45) (34.30) (10.34) 1238

n -C3H7 36.61 6.10 7.11 32.54 9.49 1493 1171 981 227 342

(35.91) (6.23) (6.98) (31.12) (9.53) 1224

n -C4H9 39.87 6.64 6.64 30.37 8.86 1496 1165 992 226 348

(40.05) (6.51) (6.72) (32.42) (8.79) 1327

S. Singhal et al. / Polyhedron 21 (2002) 2489�/2496 2491

for all the complexes. Strong bands at 981�/992 cm�1

and 1224�/1327 cm�1 due to n(C���S) are suggestive of the

chelating character of the dithiocarbamate ligand in all

cases [24].

An electronic spectrum of the complexes in acetone

exhibits a strong band at 28 600 cm�1 which corre-sponds to charge transfer (2T20/

4T1). Another weak

band at 19 600 cm�1 is due to a spin forbidden d �/d

transition (2T20/2T1). These observations are in accor-

dance with the literature [3].

3.3. Mossbauer spectra

Mossbauer spectra for all the complexes at 295 K

exhibit an asymmetric doublet, which can be resolvedinto two doublets corresponding to low and high spin

states. However, at temperatures 5/250 K the spectra

become increasingly symmetric with large line widths.

Typical Mossbauer spectra of tris(N -methyl,N ?-hydro-

xyethyldithiocarbamato) iron(III) complex at various

temperatures in Fig. 1 indicate two doublets correspond-

ing to high and low spin states in equilibrium at 295 K

and then the contribution of the HS state continuouslydecreases with the lowering of temperature. The isomer

shift (d ) values for both spin states do not vary

significantly. However, the quadrupole splitting (DEQ)

values for the low spin state are somewhat lower (0.27�/

0.44 mm s�1) compared to that for the high spin state

(0.42�/0.59 mm s�1). In general, the DEQ value increases

with decreasing temperature and on increasing the

number of carbon atoms in the alkyl group attachedto the N-atom of the ligand. Pandeya et al. [7] have

claimed the largest ever reported DEQ�/0.716 mm s�1

at 300 K in the complex tris[bis(hydroxyethyl)dithio-

carbamato)]iron(III) suggesting a large asymmetry of

the ligand field. In the present study, since one of the

hydroxyethyl groups has been replaced by alkyl groups,

still larger asymmetry was expected. However, in Table

2 the largest value of DEQ is 0.59 mm s�1 for tris(N -butyl,N ?-hydroxyethyldithiocarbamato) iron(III) at 295

K which increases to 1.28 mm s�1 at 77 K. It seems

asymmetric substitution at N-atoms does not necessarily

mean more asymmetry at the central Fe atom.

In order to find out the correlation, DEQ was plotted

with the molecular weight of the alkyl group and it

shows a linear increase in Fig. 4. Surprisingly DEQ for

both the spin states increases linearly with temperature.It is well known that by increasing the carbon chain

length, the positive inductive effect of the alkyl group

increases. This will result in an increase in s-electron

density at the Fe nucleus by way of donation. On going

down to 77 K all the complexes exhibit increasing

tendency towards low spin state (2T2g). In fact Moss-

bauer spectral results confirm our observation of

increasing contribution of the HS state with increasingcarbon chain length. However, an opposite trend is

observed for the LS state. Magnetic moments were also

calculated on the basis of estimated percent contribu-Fig. 1. Mossbauer spectra of the tris(N -methyl,N ?-hydroxyethyl-

dithiocarbamato) iron(III) complex at different temperatures.

S. Singhal et al. / Polyhedron 21 (2002) 2489�/24962492

tions of high and low spin states. The magnetic moments

so calculated compare well with the experimentally

determined values showing good agreement between

Mossbauer spectral and magnetic moment data (Table

2).

3.4. Thermogravimetric studies

Thermogravimetric studies suggest that all the com-

plexes, are stable up to �/140 8C, after which decom-

position starts and the whole process is completed at �/

650 8C in two stages. In all cases the first step is very

fast, corresponding to 65�/70% weight loss and it is

completed up to �/350 8C, as can be seen in Fig. 3.

Further decomposition takes place at �/550 8C and a

constant weight is obtained at 610�/650 8C (Table 3). In

all the complexes, the final weight matches well with the

expected weight of Fe2O3 and hence all the complexes

can be grouped as non-volatile. In earlier reports there

have been speculations about the formation of Fe2S3

[13,14] or a partially non-volatile group of complexes

yielding 70�/80% residual weight at 900 8C [15]. In the

present studies no Fe2S3 is formed. Incidentally melting

Table 2

Mossbauer parameters of high spin and low spin states in tris(N -alkyl,N ?-hydroxyethyldithiocarbamato) iron(III) complexes and calculated

magnetic moments

Complex [Fe(S2CNR1R2)3]

R1�CH2CH2OH

and R2�

High spin Low spin Estimated

percentage of

spin state

Magnetic moment a

meff (B.M.)

d b (mm s�1) DEQ (mm s�1) d b (mm s�1) DEQ (mm s�1) HS LS

�CH3 r.t. 0.39 0.42 0.42 0.27 45 55 3.53(3.61)

150 K 0.45 0.71 0.45 0.44 27 73 2.80(2.86)

77 K 0.48 0.98 0.49 0.58 6 94 1.87(1.98)

�C2H5 r.t. 0.37 0.48 0.39 0.31 61 39 4.17(4.28)

150 K 0.43 0.82 0.43 0.56 29 71 2.87(2.94)

77 K 0.45 1.11 0.45 0.75 17 83 2.37(2.44)

�n -C3H7 r.t. 0.36 0.52 0.32 0.38 65 35 4.37(4.45)

150 K 0.44 0.88 0.45 0.58 34 66 3.02(3.15)

77 K 0.46 1.21 0.46 0.81 22 78 2.57(2.65)

�n -C4H9 r.t. 0.36 0.59 0.34 0.44 70 30 4.58(4.66)

150 K 0.45 0.92 0.45 0.61 37 63 3.18(3.28)

77 K 0.47 1.28 0.47 0.84 26 74 2.78(2.82)

a In parentheses is meff calculated on the basis of percent contributions of high and low spin states.b With respect to iron as standard, 90.02 mm s�1.

Fig. 2. Variation of magnetic moment with temperature for tris(N -

alkyl,N ?-hydroxyethyl-dithiocarbamato) iron(III) complexes.

Fig. 3. TGA (*/), DTG (-----) and DTA (- �/ - �/ -) plots for some

typical iron(III) complexes.

S. Singhal et al. / Polyhedron 21 (2002) 2489�/2496 2493

Table 3

Thermogravimetric characteristics of tris(N -alkyl,N ?-hydroxyethyldithiocarbamato) iron(III) complexes

Complex [Fe(S2CNR1R2)3]

R1�CH2CH2OH

and R2�

Initial decomposition

temperature (8C)

DTA

peak

(8C)

Const. weight

temperature

(8C)

Final

wt. a

(%)

Activation energy

(Ea) (kJ mol�1)

Order of

reaction

(n )

Rate constant

(k �103) (s�1)

DH (kJ

mol�1)

DG (kJ

mol�1)

DS (J K�1

mol�1)

�CH3 140 300, 650 14.2 22.98 0.28 1.14 21.70 168.4 �266.7

169, (15.8)

94

C2H5 150 409, 610 14.8 29.06 0.64 1.42 26.13 167.5 �257.0

192, (14.6)

96

C3H7 150 310, 640 13.8 55.48 0.99 5.68 50.92 160.9 �200.8

237 (13.6)

C4H9 170 428, 630 14.0 78.50 1.48 13.56 71.27 157.0 �155.1

215 (12.7)

a In parentheses is the expected weight % of Fe2O3 on the basis of formula weight.

S.

Sin

gh

al

eta

l./

Po

lyh

edro

n2

1(

20

02

)2

48

9�

/24

96

24

94

points of all the complexes were observed in the range

170�/240 8C whereas the first exothermic DTA peak is

also observed in this temperature range only (Fig. 3). It

suggests that the first stage of decomposition involves

melting of the complex. In addition, another broad

exotherm is observed at �/350 8C. Kaushik et al. [25]

have attributed this to the conversion of iron sulfate to

iron oxide. However, we could not identify the forma-

tion of iron sulfate as an intermediate though we had

earlier confirmed the formation of Fe(SCN)3 in some

dithiocarbamates [16].

In order to identify the intermediate and final

products, Mossbauer spectra were recorded after heat-

ing the complexes at 500 and 700 8C. Typical Moss-

bauer spectra for the tris(N -ethyl,N ?-hydroxyethyldithiocarbamato) iron(III) complex after

heating at these temperatures in Fig. 5 show that a-

Fe2O3 starts forming at 500 8C as indicated by the

appearance of a sextet with Heff�/517 kOe and d�/0.37

mm s�1. A centrally located doublet is also observed

having d�/0.39 mm s�1 and DEQ�/0.51 mm s�1. It

suggests primarily an undecomposed compound in a

high spin state. After further heating up to 700 8C the

centrally located doublet disappears and a pure sextet is

observed with Heff�/514 kOe and d�/0.39 mm s�1.

These parameters correspond to that for a-Fe2O3 [26].

Therefore, no evidence was found for the formation of

Fe2S3. Undoubtedly the decomposition of unsymmetri-

cally substituted tris(N -alkyl,N ?-hydroxyethyldithiocar-

bamato)iron(III) complexes is affected by the nature of

alkyl substituents. However, intermediate products seem

to be different although we had earlier confirmed it to be

Fe(SCN)3 [16]. Finally a-Fe2O3 is formed in all cases.

From the thermograms of the complexes various

kinetic and thermodynamic parameters were calculated

using the Freeman and Carroll [17] method and these

are given in Table 3. From the linear plots of [Dlog(dw /

dt)/Dlog wr] vs. D(1/T )/Dlog wr, the activation energy

(Ea) and order of the reaction were calculated. The

Fig. 4. Variation of quadrupole splitting with molecular weight of

alkyl group for tris(N -alkyl,N ?-hydroxyethyldithiocarbamato) iro-

n(III) complexes.

Fig. 5. Mossbauer spectra of the tris(N -ethyl,N ?-hydroxyethyldithio-

carbamato) iron(III) complex at r.t., after heating at (b) 500 8C and (c)

700 8C for 1 h.

Fig. 6. Variation of the activation energy with molecular weight of

alkyl group for tris(N -alkyl,N ?-hydroxyethyldithiocarbamato) iro-

n(III) complexes.

S. Singhal et al. / Polyhedron 21 (2002) 2489�/2496 2495

frequency factor (ln A ) was calculated from the inter-

cept using the relationship:

lnda=dt

(1 � a)n� ln A�

Ea

RT

and then the rate constant was calculated. It is observed

that all these parameters vary with the nature of the

alkyl substituent suggesting strong dependence on the

nature of the substituent. A perusal of data in Table 3

shows that the activation energy varies in a wide rangeof 22.98�/78.50 kJ mol�1and a linear correlation is

observed between Ea and the molecular weight of the

alkyl group as shown in Fig. 6. Incidentally these do not

correlate with the spin state of the complexes. The order

of the reaction of the complexes is in the range 0.28�/

1.48, well within unity suggesting intramolecular re-

arrangement. Similarly the rate of the reaction decreases

as the molecular weight is increased as shown in Table 3.As the number of carbon atoms in the alkyl group is

increased the electron density at the iron atom increases

so that more energy is required to break the bond and

the reaction becomes slower. Possibly this is due to

positive inductive effect of the alkyl group causing

increased polarity in the molecule. In other words as

we move from CH3 to the bulkier n-C4H9 group, the

ionic character increases so that the Fe�/S bond becomesstronger.

The activation thermodynamic parameters, namely

enthalpy (DH ), entropy (DS ) and free energy (DG ), were

also evaluated (Table 3). The values of DS in all cases

were found in the range �/155.1 to �/266.7 J K�1

mol�1. This suggests that the decomposition process

involves molecular rearrangement whereby a significant

restriction is exerted on the vibrational degrees offreedom. However, during these processes an intermedi-

ate is likely to be formed which ultimately decomposes

into a-Fe2O3 at �/700 8C in air atmosphere.

Acknowledgements

Grateful thanks are due to the Council of Scientificand Industrial Research, New Delhi for the award of a

Senior Research Fellowship to S.S.

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