Synthesis and structure of iron (III) and iron (II) complexes in S4P2 environment created by diethyldithiocarbamate and 1,2-bis(diphenylphosphino)ethane chelation: Investigation of the electronic structure of the complexes by M?ssbauer and magnetic studies

Article abstract of DOI:10.1016/j.ica.2009.04.007

Iron (II) and iron (III) complexes, [Fe^II(DEDTC)₂(dppe)] · CH₂Cl₂ (1), [Fe^II(ETXANT)₂(dppe)] (2) (DEDTC = diethyldithiocarbamate, ETXANT = ethyl xanthate, dppe = 1,2-bis (diphenylphosphino) ethane), and [Fe^III(DEDTC)₂(dppe)] [Fe^IIICl₄] (3) have been synthesized and characterized. Since 3 contains two magnetic centers, an anion metathesis reaction has been conducted to replace the tetrahedral FeCl₄^- by a non-magnetic BPh₄^- ion producing [Fe^III(DEDTC)₂(dppe)]BPh₄ (4) for the sake of unequivocal understanding of the magnetic behavior of the cation of 3. With the similar end in view, the well-known FeCl₄^- ion, the counter anion of 3, is trapped as PPh₄[Fe^IIICl₄] (5) and its magnetic property from 298 to 2 K has been studied. Besides the spectroscopic (IR, UV-Vis, NMR, EPR, Mass and XPS) characterization of the appropriate compounds, especially 2, others viz. 1, 3 and 4 have been structurally characterized by X-ray crystallography. While Fe^II complexes, 1 and 2, are diamagnetic, the Fe^III systems, namely the cations of 3, and 4 behave as low-spin (S = 1/2) paramagnetic species from 298 to 50 K. Below 50 K 3 shows gradual increase of χ_MT up to 2 K suggesting ferromagnetic behavior while 4 exhibits gradual decrease of magnetic moment from 60 to 2 K, indicating the occurrence of weak antiferromagnetic interaction. These conclusions are supported by the Mo?ssbauer studies of 3 and 4. The Mo?ssbauer pattern of 1 exhibits a doublet site for diamagnetic (2-400 K) Fe^II. The compounds 1, 2 and 4 encompass interesting cyclic voltammetric responses involving Fe^II, Fe^III and Fe^IV.

Full text of DOI:10.1016/j.ica.2009.04.007

Inorganica Chimica Acta 362 (2009) 3583–3594
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
Synthesis and structure of iron (III) and iron (II) complexes in S4P2
environment created by diethyldithiocarbamate and
1,2-bis(diphenylphosphino)ethane chelation: Investigation of the electronic
structure of the complexes by Mössbauer and magnetic studies
Tanmay K. Jana a, Dhurjati P. Kumar a, Rabindranath Pradhan a,c, Subhajit Dinda a,
Pradip N. Ghosh a, Corine Simonnet b, Jérome Marrot b, Inhar Imaz c, Alain Wattiaux c,
Léopold Fournès c, Jean-Pascal Sutter c,d, ,1, Francis Sécheresse b, ,2, Ramgopal Bhattacharyya a,
*
*
*
a Department of Chemistry, Jadavpur University, Kolkata, West Bengal 700032, India
b Institut Lavoisier, Université de Versailles Saint- Quenten-en-Yvelines. 45, Avenue des Etats Unis, F-78035 Versailles Cedex, France
c Institut de Chimie de la Matière Condensée de Bordeaux-CNRS, Université Bordeaux 1, F-33608 Pessac, France
d Laboratoire de Chimie de Coordination du CNRS, Université Paul Sabatier, F-31077 Toulouse, France
a r t i c l e i n f o
a b s t r a c t
Iron (II) and iron (III) complexes, [FeII(DEDTC)2(dppe)] ꢀ CH2Cl2 (1), [FeII(ETXANT)2(dppe)] (2) (DED-
TC = diethyldithiocarbamate, ETXANT = ethyl xanthate, dppe = 1,2-bis (diphenylphosphino) ethane),
and [FeIII(DEDTC)2(dppe)] [FeIIICl4] (3) have been synthesized and characterized. Since 3 contains two
Article history:
Received 11 October 2008
Received in revised form 19 March 2009
Accepted 3 April 2009
ꢁ
magnetic centers, an anion metathesis reaction has been conducted to replace the tetrahedral FeCl4
Available online 18 April 2009
by a non-magnetic BPh4ꢁ ion producing [FeIII(DEDTC)2(dppe)]BPh4 (4) for the sake of unequivocal underꢁ-
standing of the magnetic behavior of the cation of 3. With the similar end in view, the well-known FeCl4
ion, the counter anion of 3, is trapped as PPh4[FeIIICl4] (5) and its magnetic property from 298 to 2 K has
been studied. Besides the spectroscopic (IR, UV–Vis, NMR, EPR, Mass and XPS) characterization of the
appropriate compounds, especially 2, others viz. 1, 3 and 4 have been structurally characterized by X-
ray crystallography. While FeII complexes, 1 and 2, are diamagnetic, the FeIII systems, namely the cations
of 3, and 4 behave as low-spin (S = 1/2) paramagnetic species from 298 to 50 K. Below 50 K 3 shows grad-
Keywords:
Iron complexes
Sulfur and phosphorous donors
Crystal structure
Mössbauer spectra
Magnetic studies
Cyclic voltammetry
ual increase of
vMT up to 2 K suggesting ferromagnetic behavior while 4 exhibits gradual decrease of
magnetic moment from 60 to 2 K, indicating the occurrence of weak antiferromagnetic interaction. These
conclusions are supported by the Mössbauer studies of 3 and 4. The Mössbauer pattern of 1 exhibits a
doublet site for diamagnetic (2–400 K) FeII. The compounds 1, 2 and 4 encompass interesting cyclic vol-
tammetric responses involving FeII, FeIII and FeIV
.
Ó 2009 Published by Elsevier B.V.
1. Introduction
properties to liquid crystalline materials [8] and to the naturally
occurring spin crossover type Fe (III)–porphyrin systems [9,10]
stimulated an enormous interest in the synthesis and study of
new spin–transition complexes. It is well known that strength of
crystal field splitting parameter, Do (of octahedral transition metal
complexes) can be expressed as Do = f ꢂ g, where f = the field
strength of the ligands and the g-factor is the characteristic of
the actual metal ions involved [11]. The field strength of the li-
gands depends largely on the donor atoms, which can be arranged
in increasing ligand field order as ClSONPC; the metal g-factor,
with its usual trends also depends on the oxidation states of metal
ions concerned. In this regard the cases of CoII and FeII in octahedral
environment are interesting. CoII when bound to strong field li-
gands generates CoIII complexes and the reverse is the case for FeII,
which is very much stable when surrounded by strong field li-
gands, but becomes oxidized to FeIII when liganded with weak field
Pioneering observation of Cambi and Szego [1,2] of the unusual
temperature dependence of magnetic moments of various tris-
(N,N-dialkyldithiocarbamato) iron (III) complexes was attributed
[3] to the spin-crossover phenomenon in octahedral transition me-
tal complexes originating from two types of arrangements of the
five 3d electrons depending on the strength of the ligand field. Re-
cent discovery of the application of spin–transition systems in
optoelectronics [4,5], information storage [6,7], imparting special
* Corresponding authors. Tel.: +91 33 24327159; fax: +91 33 24137902.
E-mail addresses: sutter@lcc-toulouse.fr (J.-P. Sutter), secheres@uvsq.chimie.fr
(F. Sécheresse), aargibhatta@yahoo.com (R. Bhattacharyya).
1
Tel.: +33 561333157; fax: +33 561553003.
Tel.: +33 139254389; fax: +33 139254381.
2
0020-1693/$ - see front matter Ó 2009 Published by Elsevier B.V.
doi:10.1016/j.ica.2009.04.007

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T.K. Jana et al. / Inorganica Chimica Acta 362 (2009) 3583–3594
species [12–16]. This is quite understandable from the pairing en-
ergy of the electrons and electronic arrangement of the above men-
tioned transition metal ions in their t2g and eg orbitals. The above
kinetic instability of the said bonds should be the root of the inter-
est developed along with the problem created in unequivocally
interpreting the magnetic and Mössbauer behavior of those two
complexes. Notably not many 3d metal complexes are known with
S4P2 coordination sphere [26] and low-spin Fe (III) complexes are
not numerous [27] compared to its high spin analogues and before
10 years their numbers were really low [12–16,27]. The recent
surge of synthesis of low-spin FeIII complexes and detailed studies
of their electronic structure including ST behavior is mainly due to
Weighardt and his group [28,29]. The aims and objective of this
work is to set the right hand boundary of the mixed ligand FeIII–
DEDTC systems which remains a low-spin species from 2 to
300 K, with an ulterior motive to derivatize the ligands used or
to change the ring size of the P–P chelates so that the resulting
Fe (III) complexes may show spin–transition properties. Similarly,
the left hand boundary (the resulting Fe (III) complexes showing
pure high spin behavior from 2 to 300 K) can be set in our forth-
coming work by replacing P–P chelates by N–N chelates. Both
the boundaries being thus known, we hope to play in the mid-field
to take command over the situation, leading to the discoveries of
diverse spin-crossover systems.
explanation is supported by relevant E0 and
D
G0 values of the
appropriate CoII ꢀ CoIII and FeII ꢀ FeIII systems. Hence, besides
FeIII, CoII also should show spin–transition behavior and it really
does so [17,18]. FeIII and even FeII solutions in presence of air have
a strong tendency to generate [FeIIIS6] functions when bidentate S–
S ligands like dialkyldithiocarbamates or alkyl xanthates [19] are
used, apparently indicating the weak field character of S-ligands,
but since CoII also displays similar behavior affording Co(S–S)3
where S–S = RRDTC and RXANT, the said apparent conclusion is
not tenable. Moreover, the ligandꢁfield splitting (
D) and Racah
parameter B generated by RR0NCS2 (= RR0DTC = dialkyldithiocar-
bamate ion) ligands in [FeIII(RR0NCS2)3] type complexes are well
known [1–3] to create a situation which place the said complex
at the 6A1 ? 2T2 electronic crossover [20] and changes in R substit-
uents are known to change the position of the spin state equilib-
rium via the difference in their resonance, inductive and steric
effect [21] apparently indicating that S-ligands of these dithio-acid
groups are not typical weak field ligands like disubstituted dithio-
phosphates, sulfides, and thioethers and N,N0-pyrrolydyl dithiocar-
bamates [22]. Actually, Tanabe–Sugano diagrams which consider B
as a fundamental parameter are more realistic, and considering
higher covalency effect of S-ligands, (specially in Fe–S systems
[23]) such as dithiocarbamates and xanthates, consideration of
merely the position of these ligands in spectrochemical series
should not be the only guide for expecting the electronic crossover.
The mixed ligand Fe–S complexes, where, besides S-ligands other
donor atoms present should be considered and given due impor-
tance. In the present paper, however, we are not reporting any
new ST material, but are giving an account of a systematic study
in order to arrive at a situation whereby one can have an insight
in predicting the directed synthesis of spin–transition compounds.
With this end in view we undertook a study on the substitution of
one of the DEDTC ligand in [FeIII(DEDTC)3] (DEDTC = diethyldithio-
2. Experimental
2.1. Materials
Anhydrous iron (III) chloride, iron (II) chloride, 1,2-bis(diphen-
ylphosphino)ethane (dppe) were obtained from Aldrich and used
as received. Iron (II) chloride tetrahydrate, Mohr’s salt [FeS-
O4,(NH4)2SO4,6H2O], tetraethylammonium chloride and tetraphen-
ylphosphonium chloride of G.R. grade were obtained from E. Merck
(Germany). Acetonitrile, nitrobenzene, dichloromethane, hexane,
carbon disulfide, P4O10, KOH and NaClO4 of G.R. grade were ob-
tained from E. Merck (India). Sodium salt of diethyl dithiocarba-
mate was the extrapure product of Loba chemie (India). Ethanol
(90%) was obtained from Bengal Chemicals and Pharmaceuticals
Ltd., Calcutta, was treated with lime (CaO) and kept for 48 h and
distilled before use. Mineral acids and alkalies were of G.R. (E.
Merck, India) grade. Commercially available distilled water was
further [once using KMnO4 (G.R.)] distilled (all glass) twice and this
water was used for all experimental purposes. Acetonitrile used for
synthetic, spectroscopic and other physicochemical measurements
was further purified by refluxing with P4O10 and distilling out the
solvent, which was again treated with fresh P4O10, refluxed and
distilled and the process was repeated until a fresh P4O10 was
not stained yellow when added to the last (fresh) distillate. For
electrochemical studies this solvent was further purified by treat-
ment with CaH2 (overnight) followed by successive distillation
over Li2CO3, KMnO4 and P4O10. Pure tetraethyl ammonium per-
chlorate (for electrochemical studies) was obtained by the anion
metathesis of tetraethyl ammonium chloride with perchloric acid
in aqueous medium and then recrystallizing the product from
water. The quality of other chemicals used is mentioned in proper
places in the text. Potassium o-ethyl xanthate was synthesized
from carbon disulfide, ethanol and KOH, following literature proce-
dure [30].
carbamate) with bidentate
p-acidic P-donor ligand, namely, 1,2
bis(diphenylphosphino) ethane, (dppe), which possesses high cov-
alency as well as ligand field effect [24] to enforce a drastic change
in magnetic and other behavior of the resulting compound. We ex-
pected the introduction of dppe would impose such a field strength
that the ground state term of the resulting complexes would be
placed at the right hand side of the respective Tanabe Sugano dia-
gram and so the synthesized Fe (III) complexes would be the pure
low-spin species without exhibiting any ST property. So it was of
interest to study (i) physicochemical characterization and struc-
ture of the synthesized new mixed ligand complexes and (ii)
ground state configuration and associated magnetic behavior of
the compounds in the temperature range of 2–300 K to bring out
magneto structural relationship in the context of the introduction
of phosphorus donors in iron–sulfur environment. Hence, in this
paper we report the synthesis and structure of a series of [FeS4P2]
complexes [FeII(DEDTC)2(dppe)] (1), [FeII(ETXANT)2(dppe)] (2),
[FeIII(DEDTC)2(dppe)][FeIIICl4] (3) and [FeIII(DEDTC)2(dppe)][BPh4]
(4). Compound 2 is not structurally characterized by X-ray crystal-
lography but its adequate spectroscopic characterization indicate
that its structure is similar to that of 1. For the unequivocal under-
standing of the magnetic and Mössbauer behavior of the low-spin
Fe (III) complexes 3 and 4, we also had to prepare and characterize
PPh4[FeCl4] (5) [25] for the anion of which the detailed magnetic
behavior below 80 K has not yet been reported but we need to
know the same since it exists as counter anion in 3, to confirm
whether or not there exists any magnetic interaction between
the two FeIII centers at 298–50 K. Furthermore, the FeIII ion being
a hard acceptor, FeIII–phosphorus bonds existing in 3 and 4 are
formed by hard–soft interactions and so the thermodynamic and
2.2. Physical measurements
Electrolytic conductance in CH3CN solution was measured on a
Philips PR 9500 conductivity bridge and the molecular weights of
the complexes were determined in nitromethane solution using a
KNAUR (Berlin) vapor pressure osmometer using benzyl
(PhCOCOPh) as a calibrant. Infrared spectra in the range 4000–
200 cmꢁ1 were recorded using a Perkin–Elmer 597 IR spectropho-

T.K. Jana et al. / Inorganica Chimica Acta 362 (2009) 3583–3594
3585
tometer and those in the range 4000–400 cmꢁ1, using a Perkin–El-
mer 883 FT-IR spectrophotometer. The electronic spectra were ob-
tained on a Hitachi model U-3410 UV–Vis–NIR spectrophotometer
and when required, by Perkin–Elmer Lambda 25 UV–Vis–NIR spec-
trophotometer attached with GAUSSIAN03 W attachment. The 1H
NMR spectrum of 1 in CDCl3 was recorded with a Varian EM 390
spectrometer using TMS as a calibrant and the 13C NMR spectrum
was recorded in a BRUKER DPX-300 spectrometer using the same
calibrant in CDCl3. The EI mass spectrum of 1 was recorded on a
the cases of special equipments necessary for a particular experi-
ment, the details of those will be quoted in the proper place.
2.3. Preparation of the complexes
2.3.1. [FeII{(C2H5)2NS2)2}{(C6H5)2P-CH2-CH2-P(C6H5)2}] ꢀ CH2Cl2:
[FeII(dppe)(DEDTC)2] ꢀ CH2Cl2 (1)
Method 1 from Fe (II) starting material: FeCl2 ꢀ 4H2O (0.25 g;
1.25 mmol) was dissolved in 15 mL of ethanol and to it a CH2Cl2
(30 mL) solution of dppe (0.76 g; 1.9 mmol) was added under
nitrogen atmosphere. An ethanolic solution (10 mL) of Na-DED-
TC ꢀ 3H2O (0.56 g; 2.48 mmol) was added dropwise to the above
solution under stirring while a green compound separated. The
product was filtered off and washed with ethanol (0.5 mL) and
diethyl ether. The compound thus obtained was recrystallized from
CH2Cl2–hexane mixture (6:1) to obtain deep green needles. Yield
0.210 g (55%). Anal. Calc. for C37H46N2S4P2Cl2Fe: C, 53.17; H, 5.56;
N, 3.35; S, 15.34; P, 7.41; Cl, 8.48; Fe, 6.68. Found: C, 52.5; H,
6.00; S, 17.0; P, 8.30; Cl, 7.98; Fe, 6.50%. M.W., 828 g molꢁ1. IR
(KBr disc) cmꢁ1: 3120(w), 3000(w) 2960(w), 1505(s), 1430(s),
1380(w), 1360(w), 1270(s), 1230(m), 1200(w), 1150(m), 1100(w),
1020(w), 1000(w), 920(w), 880(w), 810(w), 790(w), 770(m),
740(m), 730(s), 700(s), 680(m), 500(s), 480(m), 460(m), 440(w),
Varian MS
9 mass spectrometer operating at a pressure of
10ꢁ8 mm of Hg at 70 ev. Perfluorobutyl amine (Fischer analytical)
was used as a calibrant. FAB mass spectra in a m-nitrobenzyl alco-
hol (G.R., E. Merck) matrix were obtained by using a Jeol SX 102
mass spectrometer applying the DA-6000 data system and utilizing
xenon as the FAB gas. The electrospray mass spectrum of 3 was re-
corded on a MICROMASS QUATTRO-II triple-Quadruple spectrom-
eter. The magnetic measurements of 3, 4 and 5 have been
performed with a Quantum design MPMS-5S Squid magnetometer.
The temperature dependence of the molar magnetic susceptibility,
vM, for each compound was collected in the temperature range 2–
300 K. The data have been corrected for diamagnetic contributions
deduced from Pascal’s constants. The field dependence of magneti-
zation at 2 K was measured up to 5 T.
The Mössbauer spectra were recorded on a HALDER spectrome-
ter with a constant acceleration and a 57Co source (Rh matrix)
working at room temperature. The finely ground powdered sam-
ples containing ca. 10 mg iron/cm2 were maintained in an airtight
holder between two aluminum foils. For such concentration line
broadening effects can be neglected. Isomer shifts are expressed
370(w), 330(w), UV–Vis [kmax/nm (e
/Mꢁ1 cmꢁ1)]: 288(8925),
440(1540), 585(330). The compound prepared by either ways is
soluble in chloroform, dichloromethane, acetonitrile and acetone.
Method 2 from Fe (III) starting material: FeCl3 ꢀ 6H2O (0.15 g;
0.50 mmol) was dissolved in 20 mL of ethanol, warmed (60–
70 °C) and to this solution a 10 mL ethanolic solution of ascorbic
acid (0.53 g, 3.0 mmol) was added dropwise with stirring when
the yellow brown color of the original solution was changed to yel-
lowish green. To this, a CH2Cl2 (20 mL) solution of 1,2 bis (diphen-
ylphosphino) ethane (dppe) (0.31 g, 0.77 mmol) was added while
stirring and heating at ꢃ55 °C. Heating and stirring were continued
for another one and a half hour when an orange yellow solution re-
sulted which was cooled to room temperature and the precipitate
appeared during cooling was redissolved with minimum amount
of CH2Cl2. Na-DEDTC (0.23 g; 1.0 mmol) dissolved in 10 mL of
90% ethanol was then added dropwise to the above solution when
a deep green solid separated. The solid was filtered off and washed
with ethanol (0.5 mL) and diethyl ether. The compound was
recrystallized from CH2Cl2–hexane mixture (6:1) to obtain deep
green needles of [Fe(dppe)(DEDTC)2] ꢀ CH2Cl2. Yield 0.210 g (54%).
Anal. Found: C, 52.9; H, 5.70; N, 3.44; S, 14.8; P, 8.07; Cl, 8.01;
Fe, 6.50%. M.W., 795 g molꢁ1 (determined experimentally by vapor
with respect to
a-Fe at 293 K. For each of the compounds 3, 4
and 5 data have been collected at 293 K and 4.2 K. Spectra fittings
have been carried out into two stages. First Lorentzian peak profile
was assumed and the position, amplitude, and width of each peak
were refined. This preliminary analysis allowed to determine the
experimental hyperfine parameter for the various iron sites pres-
ent in the compounds. When the width was too large, a second
refinement was performed in terms of quadrupole splitting distri-
bution, P(D), and hyperfine field distribution, P(H), using the meth-
od of Hesse and Rubartsch [31]. This method is often used for
materials showing disorder and a significant surrounding distribu-
tion, which give rise to strong line broadening and a line shape
deviating from a Lorentzian profile. In the procedure, the band
widths (C )
) are fixed (typically between 0.40 and 0.25 mm sꢁ1
and the isomer shifts (d) used are deduced by fitting a Lorentzian
profile to the experimental data. For each Fe site, either a distribu-
tion of a quadrupole splitting or a distribution of hyperfine fields
can thus be obtained from which a mean quadrupole splitting
pressure osmometric method) M.W., 835.78 g molꢁ1
.
(D
) or a mean hyperfine field (H) are deduced.
2.3.2. [Fe(C2H5OCS2)2{(C6H5)2PCH2CH2P(C6H5)2}]
The XPS studies were carried out on an ESCALAB 503 X-ray pho-
[Fe(dppe)(ETXANT)2] (2)
toelectron spectrometer. The Al K
excitation source. The spectra were calibrated by using the C1S
a
line (1486.6 ev) was used as the
An aqueous ethanolic (90% ethanol, 10% water, v/v) solution
(10 mL) of ascorbic acid (1.06 g; 6 mmol) was slowly added with
stirring to an ethanolic (90%) solution (20 mL) of FeCl3 ꢀ 6H2O
(0.27 g; 1.0 mmol). The temperature of the solution was then
raised to 70 °C when the yellow–brown color of the solution was
discharged. To the hot solution was then added with stirring a
10 mL of dichloromethane solution of dppe (0.40 g; 1.0 mmol).
Stirring and heating was continued for another 15 min. The orange
yellow solution so produced was cooled to room temperature and
an ethanolic (90%) solution (20 mL) of Na-ETXANT (0.32 g;
2.0 mmol) was added to it and a brown black precipitate appeared.
The separated solid was filtered off, washed with water, ethanol
and diethyl ether. The substance was purified by recrystallization
from chloroform–diethyl ether mixture (4:1). Yield 0.62 g (88%).
Anal. Calc. for C32H34O2P2S4Fe: C, 55.17; H, 4.93; P, 8.89; S, 18.41;
Fe, 8.02; M.W., 696.67 g molꢁ1. Found: C, 54.8; H, 5.10; P, 8.80; S,
18.1; Fe, 7.80%. M.W., 680 g molꢁ1. IR (KBr disc) cmꢁ1: 3080(w),
1/2
binding energy (at 285.0 ev) from pump oil as an internal standard
[32,33]. Electrochemical measurements like cyclic voltammetry
were done by using a PAR model 378-1 electrochemistry system
incorporating the following components: 174 A polarographic ana-
lyzer, 175 universal programmer, RE 0074 XY recorder, 173 poten-
tiostat and 377 cell system. All experiments were performed under
a nitrogen atmosphere. A stout platinum wire working electrode, a
platinum foil auxiliary electrode and an aqueous saturated calomel
reference electrode (SCE) were used in the three electrode config-
uration. All experimental data were collected at 298 K and are
uncorrected for the junction potentials. The data were also cali-
brated observing ferrocene–ferrocenium couple under the same
experimental condition. X-ray powder diffractograms were re-
corded with a XRD powder diffractometer (PW 1730/1770) at
22 °C operating at 40 kV and 20 mA with 2° minꢁ1 scan rate. In

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T.K. Jana et al. / Inorganica Chimica Acta 362 (2009) 3583–3594
3060(w), 2990(w), 1588(w), 1578(w), 1482(w), 1465(w), 1435(s),
1418(w), 1403(w), 1385(m), 1295(w), 1015(m), 870(m), 800(w),
755(m), 742(m), 700(s), 678(m), 650(w), 620(w), 518(s), 478(w),
422(w), 342(w), 330(w). The powder X-ray diffractogram for this
compound can be found in the supporting information (Fig. SI-1).
tion. A yellow solid separated, collected by filtration and washed
with 4 M HCl solution. The product was then dried in vacuo and
purified by recrystallization from methanol. Anal. Calc. for
C
24H20PCl4Fe: C, 53.67; H, 3.76; P, 5.77; Cl, 26.40; Fe, 10.40. Found:
C, 53.3; H, 3.7; P, 6.0; Fe, 10.3; Cl, 27.0%. IR (KBr disc cmꢁ1):
3050(w), 1580(w), 1520(s), 1440(s), 1340(m), 1310(w), 1200(w),
1175(w), 1100(s), 1020(w), 1000(w), 920(w), 750(m), 730(s),
2.3.3. [FeIII{(C2H5)2NCS2}2 {C6H5)2PCH2CH2P(C6H5)2}] FeIIICl4:
[FeIII(dppe)(DEDTC)2] FeIIICl4 (3)
690(s), 530(s), 390(s), 310(w). UV–Vis [kmax/nm (e
/Mꢁ1 cmꢁ1)]:
FeCl3 ꢀ 6H2O (0.14 g; 0.50 mmol) was dissolved in 15 mL of eth-
anol, warmed a little and then 2–3 drops of concentrated HCl were
added to the clear solution. To this solution was added dropwise an
ethanol (90%, 10 mL) solution of NH2OH ꢀ HCl (0.12 g, 17.2 mmol)
under constant stirring, the color of the solution changed from
deep brown to light yellow. The solution was warmed at 60–
70 °C, stirred for 10 min, filtered through a Whatman 40 filter pa-
per (in case of appearance of any turbidity). To the filtrate a CH2Cl2
(20 mL) solution of dppe (0.40 g, 1.0 mmol) was added with stir-
ring when an orange yellow color developed. Stirring was contin-
ued for another 15–20 min and the solution was filtered out
from any solid separated at this stage. The solution was then kept
on a steam bath for 15 min to remove CH2Cl2, cooled, and in case of
separation of any precipitate, the same was dissolved by adding a
minimum volume of CH2Cl2. Then an ethanol (90%, 10 mL) solution
of Na-DEDTC (0.12 g, 0.50 mmol) was added (concentration of
DEDTCꢁ was kept low to avoid formation of [Fe(DEDTC)3]) to the
clear solution, dropwise and under constant stirring. The separated
black needles were filtered off, washed with water (to remove the
precipitate of NaCl) and then with 90% ethanol and finally with
diethyl ether. The solid was collected by filtration and was recrys-
tallized from CH2Cl2–ether (6:1) mixture to obtain shining black
needles. Yield 0.21 g (55%). Anal. Calc. for C36H44N2S4P2Cl4Fe2: C,
45.6; H, 4.69; N, 2.95; P, 4.53; S, 13.5; Cl, 14.95; Fe, 11.80; M.W.,
948.50 g molꢁ1. Found: C, 45.9; H, 4.7; N, 3.07; P, 6.60; S, 13.8;
361(6735), 312(6405), 275(7610), 268(8535), 262(7510).
2.4. Crystal structure determination of 1, 3 and 4
Compound 1:
A
deep green crystal of dimensions,
0.40 ꢂ 0.20 ꢂ 0.08 mm3, was mounted with Paratone-N oil (Hamp-
ton Research) coating. X-ray intensity data were collected at 296 K
on a Bruker-Nonius X8-APEX2 CCD area-detector diffractometer
using Mo K
frames (10 s per frame) were collected at different values of h for
5 and 1 initial value of / and , respectively, using 0.5° increments
of / or . Data reduction was accomplished using SAINT V7.03 [31].
a radiation (kmax = 0.71073 Å). Six sets of narrow data
x
x
The substantial redundancy in data allowed a semi-empirical
absorption correction (SADABS V2.10) [34] to be applied, on the basis
of multiple measurements of equivalent reflections. The structure
was solved by direct methods, developed by successive difference
Fourier syntheses, and refined by full-matrix least-squares on all F2
data using SHELXTL V6.14 [35]. Hydrogen atoms were included in cal-
culated positions and allowed to ride on their parent atoms. (3). A
black crystal of dimensions 0.40 ꢂ 0.30 ꢂ 0.25 mm3 was selected
for indexing and intensity data collection. Measurements were car-
ried out on a Siemens SMART three circle diffractometer equipped
with a CCD bi-dimensional detector. The crystal to detector dis-
tance was 45 mm allowing the data collection up to 20–65°. An
empirical absorption correction was applied using SADABS Program
[36] based on the Blessing method [37]. The structure was solved
by direct methods followed by Fourier difference syntheses using
the SHELXTL package [38]. All atoms except hydrogen atoms, C9
and C10 carbon atoms, were anisotropically refined. Hydrogen
atoms were refined with geometrical constraints 4. A black crystal
of dimension 0.10 ꢂ 0.08 ꢂ 0.06 mm3 was isolated for intensity
data collection. Single crystal diffraction data were collected on a
Nonius Kappa CCD diffractometer at 298 K (k (Mo
Cl, 14.09, Fe, 12.0%; M.W., 925 g molꢁ1. IR (KBr pallet) cmꢁ1
:
3020(w), 2460(w), 1515(s), 1490(w), 1470(w), 1440(s), 1390(w),
1360(w), 1280(s), 1210(w), 1160(m), 1100(m), 1000(w), 870(w),
850(w), 815(m), 750(m), 720(m), 695(s), 680(w), 650(w), 525(s),
515(m), 390(s), 380(s), 260(w). UV–Vis [kmax/nm (e
/Mꢁ1 cmꢁ1)]:
270(2880), 360(3400), 492(125), 581(88), 662(113).
It may be noted here that the above synthetic protocol if applied
by using NaETXANT instead of NaDEDTC, the compound [FeII(ETX-
ANT)2(dppe)] (2) is generated, once again demonstrating that the
ETXANT is a stronger and more reducing ligand that DEDTC. It is
diamagnetic and its IR spectra is superimposable with that of 2.
Ka
) = 0.71073 Å). The structures were solved by direct methods
and refined by full-matrix least-squares on F2 values using SHELXL
-
97 [39]. Selected crystallographic data together with the refine-
ment details of compounds 1, 3 and 4 are given in Table 1.
2.3.4. [FeIII{(C2H5)2NCS2}{(C6H5)2PCH2CH2P[C6H5)2}]BPh4:
[Fe(dppe)(DEDTC)2]BPh4 (4)
3. Results and discussion
Compound 3 (0.10 g; 0.10 mmol) was dissolved in 20 mL of eth-
anol and to it was added solid NaBPh4 (0.04 g; 0.1 mmol). The mix-
3.1. Synthetic aspects
ture was stirred for 5 min when
a brown black compound
separated. The substance was filtered off, washed with water, eth-
anol and diethyl ether. The solid was then recrystallized from
CH2Cl2–hexane (6:1) solvent mixture. The black needles were col-
lected and vacuum dried. Yield 0.90 g (85%). Anal. Calc. for
C60H64BFeN2P2S4: C, 67.34; H, 6.04; N, 2.62; S, 11.98; P, 5.79; Fe,
5.22. Found: C, 67.1; H, 5.9; N, 2.8; S, 12.3; P, 5.7; Fe, 4.9%. IR
(KBr pallet cmꢁ1): 3040(w), 2960(w), 1570(w), 1505(s), 1445(s),
1375(w), 1350(m), 1275(s), 1210(m), 1160(m), 1100(s), 1030(w),
1000(w), 865(w), 805(w), 800(w), 750(s), 730(s), 710(s), 700(s),
Since dppe was used as one of the ligands, a non-aqueous med-
ium was necessary for the synthetic protocol in general and
FeCl2 ꢀ 4H2O or FeCl3 ꢀ 4H2O were chosen as the starting materials.
The appropriate iron salt and two equivalents of Na-DEDTC or Na-
ETXANT were taken in ethanol, and dppe in dichloromethane, to
obtain the products 1 and 2 as described in Section 2. If pure
FeCl2 ꢀ nH2O is not available, FeCl3 ꢀ nH2O may also be used but in
that case ascorbic acid must be used to reduce FeIII to FeII for
obtaining
1 and 2. When saturated aqueous solution of
615(m), 530(s), 520(w), 515(w), 400(w), 265(w). UV–Vis [kmax
/
nm (
e
/Mꢁ1 cmꢁ1)]: 275(28 000), 485(88), 550(188), 650(250).
NH2OH ꢀ HCl in presence of 2 drops of concentrated HCl was used
as reducing agent for FeIII, the resulting solution on experimental
work up generated a species, [FeIII(dppe)(DEDTC)2]FeIIICl4 (3),
2.3.5. Preparation of PPh4[FeIIICl4] (5)
FeCl3 ꢀ 6H2O (0.14 g: 0.50 mmol) was dissolved in 20 mL of 6 M
aqueous HCl solution and stirred. Then 0.19 g (0.50 mmol) of
PPh4Cl dissolved in 0.5 mL of water was added to the above solu-
ꢁ
where FeCl4 is the counter anion for the monocationic FeIII com-
plex while with ETXANT the FeII derivative [FeII(ETXANT)2(dppe)]
(2) was obtained as the reaction product. Compound 3 on anion

T.K. Jana et al. / Inorganica Chimica Acta 362 (2009) 3583–3594
3587
Table 1
Selected crystallographic data together with the refinement details are given for the compounds 1, 3 and 4.
1
3
4
Empirical formula
Formula weight
a (Å)
b (Å)
c (Å)
C37H46N2P2S4Cl2Fe
835.69
C36H44N2P2S4Cl4Fe2
948.41
19.0170(9)
11.7288(5)
20.1715(9)
90
101.2740(10)
90
4412.4(3)
4
C60H64N2P2S4BFe
1070.01
10.479(4)
11.8234(6)
18.0164(9)
71.378(2)
78.843(2)
81.354(2)
2065.9(1)
2
11.706(1)
18.517(2)
26.747(3)
99.95(4)
99.48(4)
95.56(5)
5585.5(1)
2
a
(°)
b (°)
c
(°)
V (Å3)
Z
Crystal System
Space group
qcalc (g/cm3)
triclinic
P1
1.343
0.71069
296
monoclinic
P21/n
1.428
0.71073
296
triclinic
P1
1.273
0.71073
298
ꢀ
ꢀ
l
(Mo K
T (K)
Crystal size
(mmꢁ1
a
) (mmꢁ1) k (Å)
0.40 ꢂ 0.20 ꢂ 0.08
0.40 ꢂ 0.30 ꢂ 0.25
0.10 ꢂ 0.08 ꢂ 0.06
l
)
0.802
1.189
0.517
h Limits (°)
1.21–30.11
63 947
12056
8780
1.092
1.35–25
22 667
7754
3611
0.933
2.07–26.37
44 847
22851
11900
1.024
Number of data collected
Number of unique data
Number of data used for refinement (I) > 0(Fo)2
Goodness-of-fit (GOF) on F2
R1a(Fo)
0.0625
0.1528
0.0612
0.1270
0.0651
0.1783
WR2 (Fo)2
b
a
R1
=
R
||Fo| ꢁ |Fc||/
R|Fo|.
P
P
2
2 1=2
WR2 ¼ ½ ½WðF2o ꢁ Fc2Þ = ½wðF2oÞ ꢄ
.
b
metathesis with NaBPh4 in ethanolic medium gave
[FeIII(ꢁdppe)(DEDTC)2]BPh4 (4). The PPh4 salt of the well-known
FeCl4 (seems as yet unreported), was obtained quite easily as
PPh4[FeCl4] (5). Compounds 4 and 5 were synthesized and charac-
terized insofar as the measurement of magnetic susceptibility and
Mössbauer spectroscopy of these two compounds were necessary
for explaining the magnetic and Mössbauer behavior of the cation
of 3.
curs as a very prominent band at 390 cmꢁ1 which is split as a shoul-
der at 380 cmꢁ1 due to the isotopic factor involved in 35Cl and 37Cl.
This is considered diagnostic [47,48] for Td FeCl4ꢁ otherwise absent
in 1, 2 and 4 but present in 3, besides occurring as a strong band in 5.
Compound 5 shows five electronic spectral bands of which those at
361 nm (e e )
= 6735 Mꢁ1 cmꢁ1) and at 312 nm ( = 6405 Mꢁ1 cmꢁ1
are due to the Clꢁ ? Fe (III) LMCT transition and the other three
+
are due to the PPh4 ion. Complex 3 shows the above transition at
360 nm (
e = 3400) whereas the higher wave length bands are due
3.2. General characterization
to ligand field transitions of strong field Fe (III), namely,
2T2g ? 2T1g 2T2g ? 2A2g and 2T2g ? 2Eg (Fig. 1, these terms origi-
,
While compounds 3, 4 and 5 are 1:1 electrolytes (observed mo-
lar conductance, KM = 150 ohmꢁ1 cm2 molꢁ1) in acetonitrile [40] 1
and 2 are non-electrolytes, as expected. The molecular weight data
indicate that the compounds are discrete molecules in CH3CN at
nated from the 2I field free ionic term of the Fe3+ ion [49]). Com-
pound 4 also shows similar high wavelength d–d bands (Fig. 1)
with high
e
(Mꢁ1 cmꢁ1) in both the complexes (see Section 2) but
obviously no band at 360 nm (Fig. 1). The diamagnetic complexes
room temperature.
A
strong vibrational band appears at
1 and 2 show two bands in the visible region (see Section 2).
1478 cmꢁ1 in the IR spectrum of Na-DEDTC ꢀ 3H2O which can be as-
signed as
m
(CN) (here thiouride band) vibration which is very much
3.3. Proton NMR spectroscopy of 2
characteristic of this ligand [41,42]. In complexes 1, 3 and 4 this
band appears at a higher wave member region (see Section 2) due
to enhanced double bond character of the C–N bond after metal
The proton NMR of 2, whose structure is expected to be similar
to that of 1 (two DEDTC are substituted by two ETXANT) consti-
tutes a triplet (J = 6 Hz) at d = 0.9 ppm (6H) due to the methyl
coordination. The
m(CS) stretch in the three DEDTC complexes is un-
iquely represented by a medium intensity band at 1000 cmꢁ1
.
groups of the two xanthate ligands, a quartet (J = 6 Hz) at
Occurrence of no other DEDTC band between the spectral region
d = 3.9 ppm (4H) due to two CH2 groups of the two xanthate li-
gands and a singlet at d = 2.6 ppm (4H) due to four CH2 protons
of the dppe ligand. The appearance of a single proton signal for
two CH2 groups of the dppe ligand is a consequence of the fact that
a C2 axis of the molecule 2 bisects the C–C bond of the two CH2
groups establishing a magnetic equivalence of all the four protons
of the ethene residue. This supports the structural similarity be-
tween the complexes 1 and 2.
Mass spectrometry: (a) Electron impact mass spectroscopy. The
peaks observed in 2 are at m/e = 89 (C2H5OS) 108 (PPh2), 121
(EtOCS2), 262 (Ph3P), 370 (Ph2P–PPh2) 398 (dppe) and 269 (proba-
bly corresponding to [FeII(COS2) (ETXANT)]) [26]. As usual the sa-
tellite peaks are due to the isotopic compositions of sulfur,
carbon, nitrogen, etc, as may be the case here.
1420 and 1480 cmꢁ1 indicates that in all the three complexes DED-
TC functions as a bidentate ligand [42]. Absorption due to m(NC2,
ethyl C) of free DEDTC (1200 cmꢁ1) suffers a lower wave number
shift (ca. 150 cmꢁ1) in all the three DEDTC complexes. The complex
2 is characterized by m(C–O–C@S) vibration at 1030(w), 1180(w),
1080(w), 1210(s) which is typical for the bidentate xanthate ligand
[43,44]. In all the complexes the strong to medium intensity bands
around 1500, 1440, 1120, 750, 725, 700 and 520 cmꢁ1 appear due to
the dppe vibrations. The m
(FeII–P) vibration [45] in 1 and 2 occurs at
330 cmꢁ1, while the same in 3 and 4 appears around 260 cmꢁ1 indi-
cating that the FeIII–P bond is much weaker than the corresponding
FeII–P bond. The (FeII–S) vibrations [46] in all the DEDTC complexes
appear at 350 cmꢁ1 but in xanthate complex at 380 cmꢁ1 suggest-
ing that the ETXANT is a stronger ligand than DEDTC in Fe (III) as
(b) FAB (Fast Atom Bombardment) mass spectroscopy. Besides
X-ray crystallography complexes 1 and 3 have been further
well as Fe (II) complexes. In compound 3, the m(Fe–Cl) vibration oc-

3588
T.K. Jana et al. / Inorganica Chimica Acta 362 (2009) 3583–3594
higher and Fe2p binding energies lower than those of the FeII com-
plexes. This is clear indication that the DEDTC ligand binds more
strongly to the FeIII than to FeII. For all practical purposes it should
be borne in mind that
negligible.
p-acidity of DEDTC and ETXANT are
3.5. Molecular structure of 1, 3 and 4
The crystal of compound 1 contains discrete monomeric units of
[Fe(dppe)(DEDTC)2] and a molecule of CH2Cl2 per unit, held in the
lattice. A view of compound 1 is shown in Fig. 2. A packing diagram
(Fig. 3) showing of four unit cells in bc plane exhibiting the lattice
held CH2Cl2 one in each formula unit. The closest approach of C–H
hydrogens towards the chlorine atoms of CH2Cl2 does not show
any H-bonding (as examined by using a MERCURY software) interac-
tion. Structure of the cationic part of complex 3[Fe(dppe)(DED-
TC)2]+ is analogous to compound 1, but complex 3 has another
tetrahedral Fe (III) center, FeCl4ꢁ, held in the lattice. A view of
the cationic part of 3 is shown in Fig. 4. The crystal structure of
compound 4 consists of the cationic [Fe(dppe)(DEDTC)2]+ complex
associated with BPh4ꢁ. Two cation–anion moieties are found in the
asymmetric crystal unit.
A view of the cationic units of
[Fe(dppe)(DEDTC)2]BPh4 (4) which are non-enantiomers is shown
in Fig. 5. A view of the asymmetric unit with the atom numbering
information scheme is provided as Supporting material (Fig. SI-2).
The molecular structure of the cationic unit of [Fe(dppe)(DEDTC)2]+
for both 3 and 4 as well as the two molecules in 4 are very similar
(see Table 3) and the values of angles around the atoms are shown
in Table 4. It is obvious from Fig. 3 that the very small differences of
bond lengths and inter-bond angles (Table 4) are due to the nature
of crystal packing. Figs. 2–4 and the bond length and bond angle
data in Tables 3 and 4 indicate that the geometry around the Fe
(II) and Fe (III) centers can be best described as distorted octahe-
dral. The Fe (III)–P distances are remarkably longer than those in
Fe (II)–P bond lengths as shown in Table 3, in contrast Fe (III)–S
are shorter than those in Fe (II)–S bond lengths Iron (II) being a less
hard (borderline) acceptor than Iron (III), the FeIII–P bond distances
in 3 and 4 are obviously (Table 3) longer than those in 1, since
Fig. 1. Electronic Spectra (Gaussian Analyzed) of 3 (————) and 4 (——).
characterized using FAB mass spectroscopy. In the positive ion
mode 1 shows a distinct and intense molecular ion peak at
m/z = 750 amu [Fe(Ph2PCH2CH2PPh2){(C2H5)2 NCS2}2]+. Besides
this, other peaks observed at m/z = 602, 399, 352 and 204 amu cor-
respond to [Fe(dppe)(DEDTC)]+, (dppe)+, [Fe(DEDTC)2]+ and
Fe(DEDTC)]+ ions, respectively. In the negative ion mode the peak
at m/z = 148 and 204 amu are due to (DEDTC)ꢁ and {Fe(DEDTC)}ꢁ
ions, respectively. In complex 3 an intense molecular ion peak is
observed at m/z = 950 amu for the [{Fe(dppe)(DEDTC)2}FeCl4]+
ion in the positive ion mode. In the negative ion mode a distinct
and intense peak at m/z = 198 amu is obtained for the [FeCl4]ꢁ
ion, otherwise absent in 1.
phosphorus donors are moderately good p-accepting and soft do-
nor [for HSAB principles and details see Refs. [50,51]. Sulfur atom
belonging to the period 3 of the periodic table is labeled as soft do-
nor because in principle it can use its 3d orbitals for back accep-
tance of metal electrons but the phosphorus donors are always
3.4. X-ray photoelectron spectroscopy
Inner electron binding energies of S2p, Fe2p1/2 as recorded in
Table 2, for 1 and 2 signify that as usual ETXANT is a stronger li-
gand than DEDTC, since the S2p binding energy of the coordinated
ETXANT ligand has a slightly higher value (ev) than that of coordi-
nated DEDTC indicating that a greater amount of electron density
of the xanthate ligand is transferred to the metal ion compared
to that of the DEDTC ligand. On the other hand the appropriate
binding energies from XPS results of two iron 2p multiplets are
higher in energy for the complex 1 than for complex 2, implying
that electron density enrichment of the Fe2p orbital in 1 is lower
than in 2 due to the weaker S-coordination in the former than that
of the later. The S2p binding energy of the FeIII complex, 4 is a bit
Table 2
Relevant inner electron binding energies of S2p and Fe2p electrons of 1, 2 and 4 from
XPS results.
Complex
Binding energy (ev)
S2p
Fe2p3/2
Fe2p1/2
[FeII(DEDTC)2(dppe)]CH2Cl2 (1)
[FeII(ETXANT)2(dppe)] (2)
162.5
163.0
163.8
709.3
708.5
707.4
724.5
722.0
720.1
[FeIII(DEDTC)2(dppe)]BPh4 (3)
Fig. 2. View of [Fe(dppe)(DEDTC)2] (1). Displacement ellipsoids are scaled to
enclose 30% probability levels. Hydrogen atoms are not represented.

T.K. Jana et al. / Inorganica Chimica Acta 362 (2009) 3583–3594
3589
Fig. 3. The packing diagram for compound 1, [Fe(dppe)(DEDTC)2] showing the
lattice held solvent molecules.
Fig. 5. View of the cationic moiety of [Fe(dppe)(DEDTC)2]BPh4 (4). Displacement
ellipsoids are scaled to enclose 30% probability levels. Hydrogen atoms are not
represented.
Table 3
Main bond distances (Å) for compounds 1, 3 and 4.
1
3
4
Fe–P2
Fe–P1
Fe–S2
Fe–S4
Fe–S3
Fe–S1
2.1945(8)
2.1942(8)
2.3110(9)
2.3083(9)
2.3586(9)
2.3571(9)
2.3064(18)
2.3178(18)
2.2906(18)
2.2880(19)
2.2981(17)
2.2937(17)
2.3088(1) 2.3056(12)
2.3164(13) 2.3147(12)
2.2875(13) 2.2875(12)
2.2898(13) 2.2826(12)
2.3024(13) 2.3022(12)
2.3044(13) 2.3071(13)
Table 4
Main bond angles (°) for compounds 1, 3 and 4.
1
3
4
Fig. 4. View of the cationic moiety of [Fe(dppe)(DEDTC)2]FeCl4 (3). Displacement
ellipsoids are scaled to enclose 30% probability levels. Hydrogen atoms are not
represented.
S4–Fe–S2 162.94(4)
S1–Fe–S3 165.88(7)
S3–Fe1–S1 165.65(5)
S5–Fe2–S8 164.08(5)
S2–Fe1–P2 168.02(5)
S7–Fe2–P4 169.32(5)
S4–Fe1–P1 167.65(5)
S6–Fe2–P3 167.19(5)
P2–Fe–S1 170.18(3)
P1–Fe–S3 171.49(4)
S4–Fe–P2 169.92(7)
S2–Fe–P1 168.15(7)
better p-acids than the S-donors. This explains the nature of iron–
phosphorous and iron–sulfur bond lengths. However, the Fe–S dis-
tances observed here are a bit more prominent [52] since the FeII–S
bond lengths are a part of the molecular species 1 which is neutral
but that of FeIII–S belongs to a molecule which carries a positive
charge. Pauling’s electro-neutrality principle suggests that in 3
the iron (III) ion will get a good share of the 1+ charge rendering
it electron poorer enough to enforce S-atoms of DEDTC to make a
[Fe(dppe)(DEDTC)]+. Below 50 K,
vMT increases and reaches a value
of 5.55 cm3 K molꢁ1 at 2 K (vide infra for discussion). The field
dependence of the magnetization at 2 K for this compound is de-
picted as inset in Fig. 6.
more effective overlap with the said FeIII empty d
r orbitals than
that furnished with neutral FeII system, in 1.
For the highest field investigated, the magnetization tends to a
saturation value of 6 lB in agreement with the contribution of six
unpaired electrons.
3.6. Magnetic properties
The temperature dependence of the molar magnetic suscepti-
bility, M, for compounds 3–5 have been investigated in the tem-
perature range 2–300 K. The results are plotted as MT versus T
[Fe(dppe)(DEDTC)2]BPh4 (4). For this compound the value of vMT
v
between 300 and 60 K is constant and amounts to
v
0.46 cm3 K molꢁ1 in agreement with low-spin Fe (III) as in 3. Below
in Figs. 6–8 together with the field dependence of their magnetiza-
60 K v
MT decreases rapidly and reaches 0.21 cm3 K molꢁ1 for 2 K,
tion at 2 K.
suggesting the occurrence of weak antiferromagnetic interactions
among the spin carriers. This is confirmed by the magnetization
curve (Fig. 7) recorded at 2 K which reaches just 0.61 lB in an ap-
plied field of 5T.
[Fe(dppe)(DEDTC)2][FeCl4] (3). The
vMT for compound 3 between
300 and 50 K remains invariant with a value of 4.91 cm3 K molꢁ1
.
This value is in good agreement with that anticipated for two
non-interacting spins with S = 5/2 and S = ½ (4.75 cm3 K molꢁ1
assuming g = 2). These spins are attributed respectively to the Td
Fe (III) unit, [FeCl4]ꢁ, and to the octahedral low-spin Fe (III) moiety,
PPh4[FeCl4] (5): Compound
behavior down to very low temperature with a
4.40 cm3 K molꢁ1 in agreement with a S = 5/2 spin ground state
5
exhibits
a
paramagnetic
v
MT value of

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T.K. Jana et al. / Inorganica Chimica Acta 362 (2009) 3583–3594
5.6
5.5
5.4
5.3
5.2
5.1
5.0
4.9
4.8
4.6
6.0
5.0
4.0
3.0
2.0
1.0
0.0
4.4
5.0
4.2
4.0
3.8
3.6
3.4
3.2
3.0
4.0
3.0
2.0
1.0
0.0
0
10
20
H (kOe)
30
40
50
0
10
20
H (kOe)
30
40
50
0
50
100
150
T (K)
200
250
300
0
50
100
150
T (K)
200
250
300
Fig. 8. Temperature dependence of
of the magnetization at 2 K.
vMT for PPh4FeCl4 (5). Inset: Field dependence
Fig. 6. Temperature dependence of
Field dependence of the magnetization at 2 K.
vMT for [Fe(dppe)(DEDTC)2]FeCl4 (3). Inset:
counter-ions. Thus the magnetic behavior of [Fe(dppe)(DED-
TC)2]FeCl4 (3) in the temperature domain 40–300 K is simply the
sum of the contribution of each Fe moiety in its ligand surround-
ing. This is also confirmed by the Mössbauer studies (vide infra).
However, the magnetic behavior of compound 3 is characterized
0.50
0.45
0.70
by an increase of
nor for 5.
vMT below 20 K, which is found neither for 4
0.60
0.40
Two hypotheses can be invoked to explain this increase. The
first possibility is that the spin state for cation of 3 is modified at
low temperature. This could result from a structural evolution
affecting the octahedral coordination sphere and subsequently
the ligand field strength, allowing a crossover from S = ½ spin to
a larger spin state. However, no evidence for such a process is de-
tected by Mössbauer spectroscopy (see later). The second possibil-
ity is the occurrence of weak intermolecular ferromagnetic
interaction among the Fe centers. The structural data for com-
0.50
0.40
0.35
0.30
0.30
0.25
0.20
0.20
0.10
0.0
pound
3
permit to identify
a
short S–S contact (S2ꢀ ꢀ ꢀS2,
0
10
20
30
40
50
4.03(11) Å; S7ꢀ ꢀ ꢀS7, 4.19(12) Å) between two adjacent
[Fe(dppe)(DEDTC)2]+ cations in the crystal lattice (Fig. 9). Such a
contact can propagate weak exchange interaction between the
magnetic centers. In the present case, these contacts lead to ferro-
magnetic interactions. This latter hypothesis is more realistic and
is supported by the ferromagnetic ordering found for [Fe(DED-
TC)2Cl] [55].
H (kOe)
0
50
100
150
T (K)
200
250
300
Fig. 7. Temperature dependence of vMT for [Fe(dppe)(DEDTC)2]BPh4 (4). Inset: Field
dependence of the magnetization at 2 K.
3.7. Magnetic behavior of the diamagnetic compound
(Fig. 8). This is also supported by the field dependence of the mag-
netization that tends to 5 lB for the highest field investigated.
These data are consistent with those reported for related [FeCl4]ꢁ
salts [53].
[Fe(dppe)(DEDTC)2] (1)
Recording the variable temperature magnetic moment of the
low-spin diamagnetic compound 1 in the temperature range
400–2 K shows typical diamagnetic behavior with out any spin
crossover with T. This was quite expected since the compound is
diamagnetic at 298 K and it is almost a ‘‘truth” that ‘diamagnetism
is independent of temperature’. There is no way that it can acquire
paramagnetism at lower temperature because energies involved
are insignificant enough to cause any spin decoupling. This state-
ment will remain valid even if some phase transition due to struc-
ture distortion occurs [22] and occurrence of that too is very
remote at lower temperature. At the higher temperature 300–
The magnetic behavior for compounds 3 and 4 clearly show that
Fe (III) has low-spin with S = ½ in [Fe(dppe)(DEDTC)2]+. Moreover,
no evidence was found for a crossover to a higher spin state with
temperature as often observed for related Fe–DEDTC complexes
[19,54]. This low-spin state can be attributed to the octahedral
coordination sphere of Fe (III), which excludes the possibility for
intermediate spin state S = 3/2, because of a stronger ligand field
induced by the dppe ligand. It is important to note that for the
[Fe(dppe)(DEDTC)]+ cation and the [FeCl4]ꢁ anion the magnetic
behaviors are the same whether these species are combined as in
compound 3 or taken individually in salts with non-magnetic
400 K
vMT versus T plot (given as Fig. SI-3) for the compound
shows a little deviation which is due to the oxidation of FeII to FeIII

T.K. Jana et al. / Inorganica Chimica Acta 362 (2009) 3583–3594
3591
Mössbauer spectra for compounds 3, 4, and 5 at 293 K and at
4.2 K. Results are displayed in Fig. 10 and Tables 5–7.
Behavior at 293 K: For all three compounds, the spectra obtained
at 293 K have been analyzed by considering the contributions from
one octahedral (Oh) iron site (with S = ½) and from a tetrahedral
(Td) Fe site (with S = 5/2). For [FeIII(dppe)(DEDTC)2]FeCl4 3 a 1:1
distribution of Oh and Td sites is anticipated, but a discrepancy is
found (65:35). It can be stressed that the purity of the microcrys-
talline powder used for Mössbauer studies was checked by powder
X-ray diffraction. The experimental diffractogram matches with
the diffractogram calculated with the crystal data of the structure
of 3 (Fig. SI-4) confirming that the sample corresponds to the
known (structurally confirmed) compound and does not contain
detectable amounts (more than ca. 5%) of other species. So, the rea-
son for this discrepancy is not obvious at present. The above ratio
was different for an aged sample (Table 5). In Fig. 10 are compared
the spectra obtained initially for compound 3 and for the same
sample several months later (aged). It appears clearly that aging
leads to an increase of the contribution attributed to Td sites with
respect to the octahedral (Oh) Fe center. This suggests that the evo-
lution of compound 3 involves a modification of the coordination
sphere of the {Fe(DEDTC)2(dppe)} unit. For [FeIII(dppe)(DED-
TC)2]BPh4 (4) the data confirm the main occurrence of the expected
Oh site but some Td sites are also found. In view of qualitative tests
conducted for Clꢁ ion showing negative response, we attribute the
presence of Td sites in 4 to the decomposition product of the Oh Fe
center as evidenced above. Finally, data and analysis for
PPh4[FeCl4] (5) are in agreement with the anticipated parameters
for a Td Fe (III) center with S = 5/2. A very good fit has been ob-
tained when considering the contribution of an Oh impurity but
its amount (<3%) clearly underlines the purity of the sample.
Behavior at 4.2 K: The experimental and curve fitted spectra at
4.2 K for compounds 3–5 are depicted in Fig. 10. Based on the data
obtained at 293 K, a first refinement with a Lorentzian peak profile
yielded rather large peak width values. Therefore the spectra have
Fig. 9. View of the short Sꢀ ꢀ ꢀS contact (dotted line) existing between the cationic
[Fe(dppe)(DEDTC)2]+ units of 3 in the solid.
which occurs almost in all cases studied, even by diluting the FeII
compound via solid solution formation [56]. The compound starts
decomposing above 400 K. Strictly speaking a very little FeIII impu-
rity cannot be ruled out from
v
MT (cm3 K molꢁ1) versus tempera-
ture (400–298 K) plot, which has been explained by many
authors working with other Fe (II) systems.
3.8. Mössbauer spectroscopy for compounds 3, 4, and 5
In order to evaluate the spin states of these Fe derivatives and
their possible evolution with temperature we have recorded the
at293K
at293K
at293K
-3
0
at4.2K
at4.2K
at4.2K
]BPh
]
PPh 5
4[FeCl
4
[Fe(dppe)(DEDTC)2
[Fe(dppe)(DEDTC)2]FeCl43
4
4
Fig. 10. Experimental (h) and simulated (––) Mössbauer spectra for (left) compound 3, (middle) compound 4, and (right) compound 5 at respectively, (top) 293 K and (bottom)
4.2 K.

3592
T.K. Jana et al. / Inorganica Chimica Acta 362 (2009) 3583–3594
Table 5
parameters deduced from the data of all compounds at 4.2 K is ob-
served (Table 6). From the data of compound 5 at 293 K and 4.2 K
we can conclude that the hyperfine parameters obtained at 4.2 K
are those of the Td Fe (III) center with S = 5/2 [57]. Distribution
DIS1 corresponds to what is expected for Fe (III) in a four-ligand
surrounding, the difference of isomer shift between 293 K
(d293 = 0.21 mm sꢁ1) and 4.2 K (d4.2 = 0.33 mm sꢁ1) is due to a sec-
ond order Doppler effect which leads to an increase of d when T is
lowered. Formally, DIS3 should correspond to a second Fe (III) site
which however, is not detected at 293 K. Therefore, we suppose
that this second site simply result from a geometrical distortion
Hyperfine parameters at 293 K for compounds 3, 4, and
simulation by considering the contributions from one octahedral site (1) and from
one tetrahedral site (2).
5 deduced from curve
a
b
c
Fe site
d (mm sꢁ1
)
D
(mm sꢁ1
)
C
(mm sꢁ1
)
%
Compound 3 (initial)
1 (Oh)
2 (Td)
0.265(3)
0.215(12)
1.150(3)
0.312(12)
0.284(4)
0.466(30)
65
35
Compound 3 (aged)
1 (Oh)
2 (Td)
0.263(4)
0.217(7)
1.142(4)
0.332(7)
0.225(3)
0.393(6)
37
63
Compound 4
1 (Oh)
2 (Td)
ꢁ
of the Td FeCl4 unit at low temperature.
0.260(1)
0.218(14)
1.202(1)
0.340(14)
0.235(3)
0.40(1)
62
38
For compound 3 we get the two distributions (DIS1 and DIS3)
found for 5 and a third contribution (DIS2), which is not perturbed
by a magnetic exchange interaction. The hyperfine parameters
associated to this latter distribution are attributed to the Fe (III)
in octahedral surrounding, i.e. [Fe(DEDTC)2(dppe)]+. As mentioned
previously, the difference between the isomer shift found at 293 K
Compound 5
1 (Oh)
2 (Td)
0.25(22)
0.216(4)
1.60(22)
0.340(4)
0.49(13)
0.426(5)
3
97
a
d = isomer shift.
b
c
D
= quadrupole splitting.
= band width.
(d293 = 0.26 mm sꢁ1) and that at 4.2 K for DIS2 (d4.2 = 0.37 mm sꢁ1
)
C
is due to the second order Doppler effect. For compound 4, best
analysis has been obtained when the same contributions as for
compound 3 were considered; the results are very similar as far
as hyperfine parameters are concerned. This confirms that com-
pound 4 contains the expected Oh unit but also some amount of
a tetrahedral component that can be attributed to sample aging.
The population obtained for the octahedral and tetrahedral sites
both at 293 K and 4.2 K are summarized in Table 7. For compounds
4 and 5 the populations are found to be very similar at 293 K and
4.2 K, some deviation is observed for compound 3. For the latter
compounds, a 1:1 ratio between the Oh and Td sites is found at
4.2 K but this ratio deviates significantly for the chemical composi-
tion at 293 K with 65% Oh sites. This discrepancy might be attrib-
Table 6
Hyperfine parameters at 4.2 K for compounds 3, 4, and
simulation by considering distributions of quadrupole splitting (DIS1 and DIS3), and
hyperfine fields (DIS2).
5
deduced from curve
a
b
c
Distribution
d (mm sꢁ1
)
D
(mm sꢁ1
)
C
(mm sꢁ1
)
%
H (T)d
Compound 3
DIS1
DIS2
0.33
0.37
0.21
0.35
0.22
0.30
38
4.2
1.75
0.39
52.0
10
DIS3
Compound 4
DIS1
DIS2
0.33
0.37
0.21
0.35
0.22
0.30
23
68
9
4.1
6.8
1.72
1.39
uted
to
the
Lamb
Mössbauer
parameters
(f)
for
DIS3
[Fe(DEDTC)2(dppe)]+ and [FeCl4]ꢁ that could be very similar at
4.2 K but different at high temperature yielding populations much
closer to reality at low temperature.
Compound 5
DIS1
DIS2
0.33
0.21
0.35
0.25
67
33
DIS3
0.37
3.9. Mössbauer spectroscopy for 1
a
d = isomer shift.
b
c
D
C
= mean quadrupole splitting.
= band width.
The magnetic behavior discussed earlier (Section 3.7) is fully
supported (100%) by the Mössbauer data (Fig. 11). The signal ob-
tained (doublet 1) is in agreement with low-spin (S = 0) FeII, which
overlaps with the simulated signal (doublet 1). A small amount of
impurity, however, appears as doublet 2 (see also Fig. 11).
d
Mean hyperfine field.
Table 7
Population of octahedral and tetrahedral sites at 293 K and 4.2 K for compounds 3–5
deduced from spectra simulations.
3.10. Electrochemical redox responsivity of DEDTC complexes
3
3 Aged
4
5
The cyclic voltammograms of the isolated complexes 1, 3 and 4
have been recorded in acetonitrile/TEAP medium using Pt-wire
working electrode. The results are summarized in Table 8 and
the voltammograms in Fig. 12.
Comparing the cyclic voltammetric data as well as the voltam-
mograms of complex 1 (Fig. 12A) with those of [Fe(DEDTC)3] [25],
it becomes apparent that two metal centered redox responses ob-
served represent the electrochemical redox reactions shown in Eqs.
(1) and (2) in 1.
At 293 K
Oh sites
Td sites
65%
35%
37%
63%
62%
38%
3%
97%
At 4.2 K
DIS2
DIS1 + DIS3
52%
48%
68%
32%
0%
100%
been analyzed by considering either one or two quadrupole split-
ting distributions and one hyperfine field distribution (see Section
2). The values for the chemical shifts allow for attributing each dis-
tribution to Fe (III) in two environments. Hence, distribution DIS2
concerns the Fe in Oh surrounding whereas DIS1 and DIS3 apply to
Td sites. Thus, for compounds 3 and 4, two distributions of the
quadrupole splitting (DIS2 and DIS3) have been considered as well
as a hyperfine fields distribution (DIS1) whereas for compound 5 a
hyperfine field distribution and only one quadrupole splitting dis-
tribution have been considered. A very good agreement of the
ꢁe
½FeIIðdppeÞðDEDTCÞ2ꢄ
ꢀ
½FeIIðdppeÞðDEDTCÞ2ꢄþ
ð1Þ
þe
E0298¼ꢁ0:25 V
ꢁe
½FeIIIðdppeÞðDEDTCÞ2ꢄþ
ꢀ
½FeIVðdppeÞðDEDTCÞ2ꢄ
ð2Þ
2þ
þe
E0298¼ꢁ0:83 V
However, a quantitative comparison of the above results with
the potential of the redox cycle [FeIII(DEDTC)3] ꢀ [FeIV(DEDTC)3],
conveys that the substitution of one DEDTC-ligand by dppe the

T.K. Jana et al. / Inorganica Chimica Acta 362 (2009) 3583–3594
3593
Fig. 12. (A and B) Cyclic voltammograms of compounds 1 and 4 in CH3CN/TEAP
medium at scan rate of 50 mV/S.
þe
½FeIIIðdppeÞðDEDTCÞ ꢄ½BPh4ꢄꢁ
ꢀ
½FeIIðdppeÞðDEDTCÞ ꢄ þ ½BPh4ꢄꢁ
2
2
ꢁe
E0298¼þ0:35 V
ð7Þ
It is well known that various cationic iron (IV) complexes can be
made by chemical and electrochemical oxidation of Fe (III) com-
plexes [58]. Hence it is quite expected that all the complexes stud-
ied here will show a FeIII ꢀ FeIV response, which is actually the
case. Attention may be drawn to Eqs. (2) and (3) and the irreversible
process represented by Eq. (6), which all represents the oxidation of
the same complex ionic species. The difference lies in the
FeIII ꢀ FeIV potential as shown in Eq. (2) and the same cation asso-
ciated with tetrahedral counter anions containing FeIII in Eq. (3) and
Fig. 11. Mössbauer spectra of the diamagnetic compound 1, [Fe(dppe)(DEDTC)2].
0
E298 of the reaction undergoes remarkable increase insofar as the
P–P donor is a reasonably strong p-acid. The M L p-back donation
reduces the metal electron density and hence further oxidation to
metal center requires higher energy. Interestingly, the FeIII com-
plex cation, 3 having FeCl4ꢁ as the counter anion exhibits three vol-
tammetric cyclic responses (Fig. 12B). The redox steps for the cyclic
responses in this case is shown as Eqs. (3)–(5). Surprisingly the oxi-
dative response of 4 is irreversible and is assignable as Eq. (6) but
the reductive response (FeIII FeII) is reversible (Eq. (7)).
B
III in Eq. (6). An association of the counter ion is not responsible for
the difference in electrode potential as can be seen from Eqs. (2) and
(6). But in Eq. (3) we deal with the [FeS4P2]+ system associated with
the [FeIIICl4]ꢁ counter anion and the electrode potential for the cyc-
lic response is lower than that represented by Eqs. (2) and (6),
although of course in (6) the represented response is acyclic.
In a dipolar solvent both two FeIII centers of 3, whose redox
behavior is represented in Eq. (3), will be solvent clustered and
electron transfer from clustered [FeIII]ꢁ to clustered [FeIII]+ may
ꢁe
½FeIIIðdppeÞðDEDTCÞ2ꢄþ
ꢀ
½FeIVðdppeÞðDEDTCÞ2ꢄ2þ þ ½FeCl4ꢄꢁ
þe
E0298¼þ0:45 V
slightly increase (
D
E0 = E0C ꢁ E0A) the electron density of the posi-
ð3Þ
ð4Þ
tively charged iron center and it requires less energy (hence lower
potential) for its oxidation to FeIV. Concisely in 1 and 4 (if we ignore
the irreversibility of the oxidation reaction in 4) the overall redox
series is represented as:
þe
1ꢁ
2ꢁ
½FeCl4ꢄ
ꢀ
½FeCl4ꢄ
ꢁe
E0298¼þ0:05 V
eꢁ
1ꢁ
2ꢁ
þe
2þ
½FeIIIðdppeÞðDEDTCÞ2ꢄþ
ꢀ
½FeIIðdppeÞðDEDTCÞ2ꢄ
ð5Þ
ð6Þ
½FeCl4ꢄ ꢀ ½FeCl4ꢄ
ð8Þ
ꢁe
E0298¼ꢁ0:35 V
Interestingly in 3 we get the above equilibria along with another
one which is:
ꢁe
½FeIIIðdppeÞðDEDTCÞ ꢄþ½BPh4ꢄꢁ
!
½FeIVðdppeÞðDEDTCÞ2ꢄ
2þ
eꢁ
2
½FeIIIðdppeÞðDEDTCÞ2ꢄþ ꢀ ½FeIIðdppeÞðDEDTCÞ2ꢄ
Ea¼þ0:87 V
þ ½BPh4ꢄꢁ
eꢁ
ꢀ ½FeIðdppeÞðDEDTCÞ2ꢄꢁ
ð9Þ
Table 8
Cyclic voltammetric parameters of 1, 3 and 4. Potentials are in volts (V) vs. SCE at 25 °C and 760 mm.
Entry
Anodic potential (Epa)
Catholic potential (Epc)
D
Er (mv)
Assignment
1 [Fe(dppe)(DEDTC)2]CH2Cl2
+0.86
ꢁ0.22
+0.48
+0.05
ꢁ0.30
+0.87
ꢁ0.22
+0.80
ꢁ0.28
+0.42
+0.04
ꢁ0.40
60
60
60
90
100
FeIII ꢁ FeIV
FeIII ꢁ FeII
FeIII ꢁ FeIV
3 [FeIII(dppe)(DEDTC)2]FeIIICl4
[FeCl4]ꢁ
FeIII ꢁ FeII for the anion
FeIII ꢁ FeII for the cation
Epa of FeIII ? FeIV
FeIII ꢁ FeII
4 [Fe(dppe)(DEDTC)2]BPh4
ꢁ0.31
90

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T.K. Jana et al. / Inorganica Chimica Acta 362 (2009) 3583–3594
[11] C.K. Jorgensen, Modern Aspects of Ligand Field Theory, Elsevier, New York,
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This redox picture actually attests the molecular composition of the
complexes studied, besides displaying the potentials (in Volts ver-
sus SCE) of the redox reactions.
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4. Concluding remarks
This work discovers that iron (III) complexes with FeIIIS4P2
functionality for example, 3 and 4 (see text) possessing two N,N-
diethyldithiocarbamate (DEDTC; S4) and one 1,2-bis (diphenyl-
phosphino) ethane (dppe; P2) ligands, lie on the right side of spin
crossover zone of the Tanabe Sugano diagram. So, these types of
Fe (III) complexes are all expected to show low-spin behavior in
the entire temperature range of 2–300 K. We expect that our
(immediate) next work will be able to define the left side bound-
aries of the said diagram and the Fe (III) complexes lying on the left
side of that boundary will exhibit only high spin behavior in the
said temperature range. Then we shall get an entire midfield range
accessible by the directed synthesis of Fe (III) complexes possess-
ing slightly lower field strength than the right siders and also by
the complexes having a little higher field strength than the left sid-
ers. Midfielder molecules can be synthesized by modifying or
changing the ligand, so as to posses the right ligand field effect.
All those molecules will then show spin–transition behavior and
can be used in optoelectronics, information storage and other
important properties as mentioned in Section 1.
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Acknowledgements
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The authors namely T.K.J., D.P.K., S.D. and R.B. thank Depart-
ment of Science and Technology (DST), Govt. of India for financial
assistance in the form of a Project (Project No. SR/S1/IC-12/2002).
T.K.J. thanks DST and D.P.K. thank CSIR, Govt. of India, for fellow-
ship. The magnetic and Mössbauer studies have been supported
by the Centre Franco-Indien pour 1a promotion de 1a Recherche
Avancee/Indo-French Centre for the Promotion of Advanced Re-
search under Project No. 3108-3.
}
}
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Appendix A. Supplementary material
CCDC 639617, 639618 and 639619 contain the supplementary
crystallographic data for 1, 3 and 5. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associ-
ated with this article can be found, in the online version, at
doi:10.1016/j.ica.2009.04.007.
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