Novel nanohybrids of cobalt(III) Schiff base complexes and clay: Synthesis and structural determinations

Article abstract of DOI:10.1016/j.saa.2014.02.089

The [Co(Me₂Salen)(PBu₃)(OH₂)]BF ₄ and [Co(Me₂Salen)(PPh₃)(Solv)]BF_4, complexes were synthesized and characterized by FT-IR, UV-Vis, ¹H NMR spectroscopy and elemental a

Full text of DOI:10.1016/j.saa.2014.02.089

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 422–428
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Novel nanohybrids of cobalt(III) Schiff base complexes and clay:
Synthesis and structural determinations
b
a
b
Ali Hossein Kianfar a, , Wan Ahmad Kamil Mahmood , Mohammad Dinari , Mohammad Hossein Azarian ,
⇑
Fatemeh Zare Khafri c
a Department of Chemistry, Isfahan University of Technology, Isfahan 84156-83111, Iran
b Department of Chemistry, Universiti Sains Malaysia, Penang, Malaysia
c Department of Chemistry, College of Sciences Yasouj University, Yasouj, Iran
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
Novel cobalt Schiff base complexes
were prepared and their structures
were confirmed by different
techniques.
ꢀ
ꢀ
ꢀ
ꢀ
The X-ray crystallography results
show that they are hexacoordinated
in the solid state.
Nanohybrid of the above complexes
and MMT clay were prepared via ion-
exchange method.
FT-IR, TGA/DTG, XRD, SEM, EDX and
TEM were used for the
characterization of these materials.
SEM and TEM show the resulting
hybrid nanomaterials have layer
structures.
a r t i c l e i n f o
a b s t r a c t
Article history:
The [Co(Me2Salen)(PBu3)(OH2)]BF4 and [Co(Me2Salen)(PPh3)(Solv)]BF4, complexes were synthesized and
characterized by FT-IR, UV–Vis, 1H NMR spectroscopy and elemental analysis techniques. The coordina-
tion geometry of [Co(Me2Salen)(PPh3)(H2O)]BF4 was determined by X-ray crystallography. It has been
found that the complex is containing [Co(Me2Salen)(PPh3)(H2O)]BF4 and [Co(Me2Salen)(PPh3)(EtOH)]BF4
hexacoordinate species in the solid state. Cobalt atom exhibits a distorted octahedral geometry and the
Me2Salen ligand has the N2O2 coordinated environment in the equatorial plane. The [Co(Me2Salen)
(PPh3)(H2O)]BF4 complex shows a dimeric structure via hydrogen bonding between the phenolate oxygen
and hydrogens of coordinated H2O molecule. These complexes were incorporated into Montmorillonite-
K10 nanoclay. The modified clays were identified by FT-IR, XRD, EDX, TGA/DTA, SEM and TEM techniques.
According to the XRD results of the new nanohybrid materials, the Schiff base complexes are intercalated
in the interlayer spaces of the clay. SEM and TEM micrographs show that the resulting hybrid nanoma-
terials have layer structures. Also, TGA/DTG results show that the intercalation reaction was taken place
successfully.
Received 1 December 2013
Received in revised form 1 February 2014
Accepted 19 February 2014
Available online 1 March 2014
Keywords:
X-ray crystallography
Cobalt Schiff base complexes
Cobalt(III) phosphine complexes
Insertion compounds
Modified clay
Ó 2014 Published by Elsevier B.V.
⇑
Corresponding author. Tel.: +98 311 391 3245; fax: +98 311 391 2350.
E-mail addresses: akianfar@cc.iut.ac.ir, asarvestani@yahoo.com (A.H. Kianfar).
http://dx.doi.org/10.1016/j.saa.2014.02.089
1386-1425/Ó 2014 Published by Elsevier B.V.

A.H. Kianfar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 422–428
423
X-ray single crystal structure analysis was obtained by using Bru-
ker smart Apex II-2009 CCD area detector diffractometer. The X-ray
diffraction (XRD) was recorded on high resolution X-Ray diffrac-
tometer system model PANalytical X’PRO MRD PW3040. Transmis-
sion electron microscopy (TEM) studies were performed using
Zeiss LibraÒ120 TEM system. The thermal stability of specimens
was tested using PERKIN ELMER TGA7 1991 thermogravimetric
analyzer from ambient temperature to 900 °C at a heating rate of
20 °C/min under nitrogen gas. Scanning electron microscopy
(SEM) was recorded on QUANTA FEG 650 2012 SEM system. Energy
Dispersive X-ray Analysis (EDX) (EDAX Falcon System) was con-
ducted to analyze the presence of elements in the specimens that
have been sputtered with carbon black.
Introduction
During the past few years, terms like nanomaterials, nanocom-
posites and nanosystems have become designer. In fact anything
with ‘nano’ attached to it has nearly a magical effect – not so much
on performance as on expectations. There exceptional size-depen-
dent properties make these materials superior and indispensable
as they show unusual physical, chemical and biological properties
[1,2]. Along with the different nanomaterials, nanoclays compose a
multitalented area of exploration [3–6]. Due to its large value of as-
pect ratio, diameters in nanometer range, and thermal resistance,
clay minerals have many attentions in recent years [7]. Sodium
Montmorillonite (MMT) is the most commonly used clay owing
to its natural abundance, high aspect ratio and high cationic ex-
change capacity (about 80–120 meq/100 g) [8–10].
Synthesis of Schiff base ligands
Cobalt Schiff base complexes have been studied extensively.
They are investigated as models for the Cobalamine (B12) coen-
zymes [11] classified as an oxygen carrier [12]. They applied as a
catalyst for the preparative oxygenation of phenols [13] and
amines [14]. Cobalt(III) salen catalytic activity has been investi-
gated. The catalytically active species contains Co(III) oxidation
state [15].
The Schiff base ligand, H2Me2Salen, was prepared according to
the literature [26] by condensation between 1,2-etyhylenediamine
and 2-hydroxyacetophenone (1:2 mole ratio) in methanol and
recrystallized by dichloromethane/methanol mixed solvent
through the partial evaporation of dichloromethane.
Cobalt(III) Schiff base complexes with formula of [CoL(PR3)
(OH2)]+ (where L = tetradentate N2O2 Schiff bases) show that these
types of complexes are in equilibrium with phosphines and amines
to form [CoL(PR3)2]+ and [CoL(PR3)(amine)]+ [16–25], but there is
not any information about their structure. So to extension the
studies on the structure of these type of complexes, Me2Salen
(bis(2-hydroxyacetophenone)ethylenediamine) Schiff base was
prepared by the condensation of 2-hydroxyacetophenone within
1,2-ethylenediamine. The tertiary phosphine cobalt(III) complexes
of synthesized ligand were prepared in methanol solvent
(Scheme 1). The prepared complexes were identified by FT-IR, 1H
NMR, UV–Vis spectroscopy and elemental analysis. The coordina-
tion geometry of [Co(Me2Salen)(PPh3)2]BF4 was determined by
X-ray crystallography. The synthesized complexes were incorpo-
rated into Montmorillonite K-10 nanoclay. The modified clay was
identified and studied via FT-IR, XRD, TG/DTA, SEM, EDX and TEM.
Synthesis of metal Schiff base complexes
The general procedure for synthesis of [Co(Me2Salen)(PBu3)
(H2O)]BF4, [Co(Me2Salen)(PPh3)(H2O)]BF4 complexes is as follows:
an appropriate amount of cobalt(II)acetatetetrahydrate (0.249 g,
1.0 mmol), phosphine (1.0 mmol) were added to a methanolic
solution (40 mL) of H2Me2Salen (0.296 g, 1.0 mmol). The reaction
was refluxed for 1 h. The formed Co(II) complex was oxidized by
blowing air into the solution for 2 h, then it was filtered. To the fil-
trate, an appropriate amount of sodium tetrafluoroborate (.110 g,
1.0 mmol) was added. The green crystals formed after 48 h. The
crystals filtered off, washed with methanol and recrystallized from
2:1 ratio of methanol/ethanol and dried in vacuum at 65 °C.
[Co(Me2Salen)(PBu3)(OH2)]BF4 Yield (75%). Anal. calc. for
C
30H47N2O3PFCo: C, 60.89; H, 8.01; N, 4.73%. Found; C, 61.35; H,
8.12; N, 4.85%. FT-IR (KBr cmꢁ1
)
mmax 2956, 2921, 2863 (CAH),
À
Á
1597 (C@N), 1439 (C@C), 1085 BF4ꢁ
0.70–0.80 (t, 9H, CH3), 1.15–1.31 (m, 18H, CH2), 2.70 (s, 6H, CH3),
3.90–4.10 (d, 4H, CH2), 6.59–7.67 (m, 8H, Aromatic). UV–Vis, kmax
(nm) (Ethanol): 636 (780), 397 (5700), 336 (5600).
.
1H NMR (CDCl3, d, ppm):
Experimental
Materials
1/2[Co(Me2Salen)(PPh3)(CH3CH2OH)]BF4ꢂ1/2[Co(Me2-
Salen)(PPh3)(H2O)]BF4 Yield (80%). Anal. calc. for C37H37N2O3PF4-
BCo: C, 60.51; H, 5.08; N, 3.81%. Found; C, 61.44; H, 5.17; N,
All of the chemicals and solvents used for synthesis were of
commercially available reagent grade and they were used without
purification. Montmorillonite K-10 (MMT) with cation-exchange
capacity of 119 meq/100 g was provided by Aldrich.
3.83%. FT-IR (KBr cmꢁ1
)
mmax 3058 (CAH), 1592 (C@N), 1438
À
Á
(C@C), 1086 BFꢁ4
.
1H NMR (CDCl3, d, ppm): 2.30 (s, 3H, CH3, eth-
anol), 2.70 (s, 6H, CH3), 3.50–4.30 (m, 6H, CH2, ethanol and bridge
ethylene), 6.42–7.52 (m, 23H, Aromatic). UV–Vis, kmax (nm)
(Ethanol): 724 (1100), 405 (5700), 337 (10,000).
Characterizations
Fourier transform infrared (FT-IR) spectra were recorded as KBr
discs on a FT-IR JASCO-680 spectrophotometer in the 4000–
400 cmꢁ1. The elemental analysis was determined on a CHN–O–
Heraeus elemental analyzer. UV–Vis spectra were recorded on a
JASCO V-570 spectrophotometer in the 190–900 nm. The 1H NMR
spectra were recorded in CDCl3 on DPX-400 MHz FT-NMR. The
Synthesis of intercalation compounds
The 0.75 g of MMT was added to an ethanol solution containing
[Co(Me2Salen)(PBu3)(H2O)]BF4 or [Co(Me2Salen)(PPh3)(H2O)]BF4
(0.075 g) complexes. The reaction mixture was refluxed for 24 h
PR3
N
N
N
Methanol
Reflux
N
Co(OAc)2.4H2O
PR3
NaBF4
Co
BF4
O
OH HO
O
OH2
R:PhandBu
Scheme 1. The structure of Schiff base and its complexes.

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A.H. Kianfar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 422–428
and was filtered off. The green precipitate was washed with etha-
nol, methanol and acetone for several times, and then it was dried
at 65 °C.
A summary of the crystal data, experimental details and refine-
ment results are given in Table 1 for [Co(Me2Salen)(PPh3)(H2O)]BF4
complex. It is notable that, the asymmetric unit also contains sol-
vent molecules, which could not be modeled. Therefore, the dif-
fraction contribution of the solvent molecules was removed by
the subroutine SQUEEZE in PLATON. It is notable that although
the structure refined correctly for the complex but the high Rint
(0.1759) and R value (0.0978) is due to cracking of the crystal.
MMT white, FT-IR (KBr cmꢁ1
) mmax 2750–3600 (H2O), 1645
(OH), 900–1300 (SiAO), 527 (AlAO) and 462 (MgAO).
MMT–[Co(Me2Salen)(PBu3)(H2O)] (MMT–PBu3): color: green,
FT-IR (KBr cmꢁ1
) mmax 2750–3600 (H2O), 2959, 2933, 2873
(CAH), 1631 (OH), 1592 (C@N), 1440 (C@C), 900–1300 (SiAO),
524 (AlAO) and 470 (MgAO).
MMT–[Co(Me2Salen)(PPh3)(H2O)] (MMT–PPh3): color: green,
Results and discussion
FT-IR (KBr cmꢁ1
) mmax 2750–3600 (H2O), 1631 (OH), 1598 (C@N),
1439 (C@C), 900–1300 (SiAO), 524 (AlAO) and 468 (MgAO).
FT-IR characteristics
Crystal structure determination and refinement of
[Co(Me2Salen)(PPh3)(H2O)]BF4
The FT-IR spectra of the cobalt(III) complexes exhibit several
bands in the 400–4000 cmꢁ1 region (Section ‘Characterizations’).
The C@N bond vibrations appears in 1592 and 1597 cmꢁ1 region
for the synthesized complexes. These stretching are generally
shifted to a lower frequency relative to the free Schiff base, indicat-
ing a decrease in the C@N bond order due to the coordinate bond for-
mation between the metal and the imine nitrogen [31]. The CAH
stretching of PBu3 coordinated ligands were appeared in 2863,
2956 and 2921 cmꢁ1 region. The stretching vibration of BFꢁ4 counter
ion appear at about 1058 and 1086 cmꢁ1 for Co(Me2Salen)(PBu3)
(OH2)]BF4, [Co(Me2Salen)(PPh3)(OH2)]–BF4, respectively.
The MMT shows some peaks related to its functional groups. A
broad peak is seen in the range of 3600–2700 cmꢁ1 that is related
to the interlayer absorbed water molecules. A weak band is ap-
peared at 1645 cmꢁ1 which is related to the OH bending. The SiAO
stretching peak is appeared in the range of 1300–900 cmꢁ1. The
peaks at 462 and 527 cmꢁ1 are related to MgAO and AlAO, respec-
tively (Fig. 1).
The FT-IR spectra of intercalation compounds (MMT–PBu3 and
MMT–PPh3) show some changes relative to the pure MMT
(Fig. 1). Some peaks that are related to the complexes were seen
in the new intercalation compounds. The C@N band was appeared
at about 1600 cmꢁ1. The CH vibrations of PBu3 were seen in the
range of 2959–2873 cmꢁ1 and the C@C stretching was appeared
at about 1440 cmꢁ1. These observations confirm the formation of
the nanohybrid materials.
The X-ray diffraction measurements were made on a STOE
IPDS-2T diffractometer with graphite monochromated Mo K
radiation.
For [Co(Me2Salen)(PPh3)(H2O)]BF4 complex green plate crystal
with a dimension of 0.11 ꢃ 0.16 ꢃ 0.20 mm chosen and mounted
on a glass fiber and used for data collection. Cell constants and
an orientation matrix for data collection were obtained by
least-squares refinement of diffraction data from 17,496 unique
reflections. Data were collected at a temperature of 100(2) K to a
a
maximum 2h value of 58.00° in a series of
and integrated using the Stoe X-AREA software package. The
numerical absorption coefficient, for Mo radiation is
x scans in 1° oscillations
l
,
Ka
0.710 mmꢁ1. A numerical absorption correction was applied using
X-RED and X-SHAPE [27] software. The data were corrected for
Lorentz and Polarizing effects. The structures were solved by direct
methods [28] and subsequent difference Fourier maps and then
refined on F2 by a full-matrix least-squares procedure using aniso-
tropic displacement parameters [29]. All of hydrogen atoms were
located in a difference Fourier map and then refined isotropically.
Atomic factors are from International Tables for X-ray Crystallogra-
phy. All refinements were performed using the X-STEP32 crystallo-
graphic software package [30].
Table 1
Crystallographic and structure refinements data for [Co(Me2Salen)(PPh)(Solvent)]BF4.
Electronic spectra
Formula
Formula weight
C38H39CoN2O3P, C36H35CoN2O3P, 2(BF4)
1468.79
Temperature (K)
Wavelength k (Å)
Crystal system
100(2)
0.71073
Monoclinic
P21/c
0.11 ꢃ 0.16 ꢃ 0.20
21.2201(4)
15.5368(3)
20.4774(4)
90.00
The spectral data of the synthesized complexes were listed in
Section ‘Characterizations’. In both complexes, the band in the
Space group
Crystal size (mm3)
a (Å)
b (Å)
c (Å)
a
b (°)
102.554(1)
90.00
1.480
c
Density (calc.) (g cmꢁ1
)
h ranges for data collection
F(000)
1.8–29.0
3040
Absorption coefficient
Index ranges
0.633
ꢁ28 6 h 6 28
ꢁ21 6 k 6 21
ꢁ27 6 l 6 27
128,093
Data collected
Unique data (Rint
)
17496, (0.176)
871, 0
0.0978, 0.1720
0.1658, 0.1722
1.09
Parameters, restrains
a
Final R1, wR2 (obs. data)
a
Final R1, wR2 (all data)
Goodness of fit on F2 (S)
Largest diff peak and hole (e Å3)
0.86, ꢁ0.70
ꢅ
ꢂ
ꢃꢄ
ꢆ
1=2
ꢀ
ꢁ
ꢀ
ꢁ
2
2
F2o ꢁ F2c
Rw
Fo2
.
a
R1
=
R
||Fo| ꢁ |Fc||/
R
|Fo|, wR2
¼
R
w
Fig. 1. The FT-IR spectra of the hybrid materials.

A.H. Kianfar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 422–428
425
Table 2
transition was seen in the range of 600–750 nm for the complexes
[18,19].
Selected bond distances (Å) and bond angles (°) for [Co(Me2Salen)(PPh3)(EtOH)]BF4.
Bond distances
Bond angles
1H NMR spectra
Co1AN1
Co1AN2
Co1AO1
Co1AO2
Co1AOw
Co1AP1
O1AC19
O2AC34
N1AC25
N2AC28
N1AC26
N2AC27
O1WAH1W
1.910(4)
1.901(3)
1.871(3)
1.880(3)
2.107(3)
2.2222(12)
1.308(5)
1.319(5)
1.302(5)
1.295(5)
1.476(5)
1.477(5)
0.8476
P1ACo1AN1
P1ACo1AN2
P1ACo1AO1
P1ACo1AO2
P1ACo2AO1 WA
O1 WAACo1AN1
O1 WA ACo1AN2
O1 WA ACo1AO1
O1 WA ACo1AO2
O1ACo1AN2
96.29(11)
96.28(11)
87.24(9)
The chemical shift (d, ppm) of different protons of the cobalt(III)
complexes is presented in Section ‘Characterizations’. The 1H NMR
of complexes is in line with the proposed structures. The hydro-
gens of the tributyl phosphine in the [Co(Me2Salen)(PBu3)
(H2O)]BF4 were seen in the range of 0.70–1.31 ppm. The CH3 of
butyl was seen as triplet. The methylene groups were seen as
multiplet. The hydrogens of methyl groups of CH3 were seen as
singlet. The CH2 hydrogen of ethylene bridge were seen as doublet
at about 3.58–3.92 ppm. The hydrogens of aromatic rings were
seen in the range of 6.42–7.67 ppm. The complex of [Co(Me2Salen)
(PPh3)(H2O)]BF4 shows some additional protons related to ethanol
in 2.3 ppm and in the range of 3.50–4.30 ppm overlapped with
ethylene bridge.
88.55(9)
177.15(9)
85.74(14)
85.79(14)
90.64(13)
89.39(12)
176.24(14)
175.01(14)
85.78(12)
87.72(15)
93.22(14)
92.97(14)
O2ACo1AN1
O1ACo1AO2
N1ACo1AN2
O1ACo1AN1
O2ACo1AN2
Table 3
Selected bond distances (Å) and bond angles (°) for [Co(Me2Salen)(PPh3)(OH2)]BF4.
Description of the molecular structure of [Co(Me2Salen)(PPh3)
(H2O)]BF4
Bond distances
Bond angles
Co1AN1
Co1AN2
Co1AO1
Co1AO2
Co1AOw
Co1AP1
O1AC19
O2AC34
N1AC25
N2AC28
N1AC26
N2AC27
O1WAH1W
O1WBAH1WB
O1WBAH2WB
O1BAH2WB
1.898(4)
1.909(3)
1.879(3)
1.867(3)
2.102(3)
2.2475(12)
1.322(5)
1.315(5)
1.298(5)
1.293(5)
1.488(5)
1.475(5)
0.8476
P1ACo1AN1
P1ACo1AN2
P1ACo1AO1
P1ACo1AO2
94.84(11)
93.22(11)
91.87(9)
The [Co(Me2Salen)(PPh3)(H2O)]BF4 complex was characterized
by X-ray diffraction and crystallized in the Monoclinic space group
88.57(9)
P1ACo2AO1W
O1WAACo1AN1
O1WAACo1AN2
O1WAACo1AO1
O1WAACo1AO2
O1ACo1AN2
O2ACo1AN1
O1ACo1AO2
N1ACo1AN2
O1ACo1AN1
O2ACo1AN2
175.85(9)
89.30(13)
87.12(13)
87.74(12)
87.29(12)
174.84(14)
176.27(14)
85.45(13)
87.47(15)
92.90(14)
93.87(13)
0.8503
0.8535
2.020
253–255 nm region, involves
ring. The band in the 304–307 nm region, involves
p
?
p⁄ transition related to aromatic
p⁄ transi-
p
?
tion related to azomethine group. The cobalt(III) complexes show
an absorption band related to charge transfer transition (LMCT)
Fig. 3. Packing diagram of the unit cell of [Co(Me2nSalen)(PPh3)(Solvent)]BF4.
at about 395–412 nm region [16,32–38]. In addition,
a d–d
Fig. 2. The labeled diagram of [Co(Me2nSalen)(PPh3)(EthOH)]BF4(A) and [Co(Me2nSalen)(PPh3)(OH2)]BF4(B).

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A.H. Kianfar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 422–428
96.29(2)°. The CoAN1, CoAN2, CoAO1 and CoAO2 distances of
1.910(4), 1.901(3), 1.871(3) and 1.880(3) Å and 1.898(4),
1.909(3), 1.879(3) and 1.867(3) Å for A and B complexes, respec-
tively, are similar to those in N2O2–salen cobalt complexes [39–
41]. Interestingly the A and B complexes have a partial difference
in their structures. As can be seen in Fig. 2, molecule A has an eth-
anol group in an axial position trans to the PPh3 group while in B a
water molecule occupies this position. The Co–O distances
(1.871(3), 1.880(3)N2O2–salen cobalt
Å for A and 1.879(3),
1.867(3) Å for B) are smaller than the Co–Ow distances (2.107(3)
Å (A) and 2.102(3) Å (B)), due to the greater trans influence of
the P1 atom with respect to the N1 and N2 atoms. The CoAP bond
distances of apical positions are 2.222(1) and 2.247(1) for CoAP1A
and CoAP1B, respectively.
The extended network of complex is determined by intermolec-
ular bonds (for example the hydrogen bonding between the coor-
dinated phenolate oxygen and the coordinated water
(O1BAH2WB = 2.020 Å)) in molecule B which leads to aggregation
and to a supramolecular structure (Fig. 4).
Fig. 4. A view of the extended network of complex [Co(Me2nSalen)(PPh3)(Sol-
vent)]BF4 with the intermolecular hydrogen bonds (dashed red lines) between
molecules B. (For interpretation of the references to color in this figure legend, the
reader is referred to the web version of this article.)
All angles around the cobalt center deviate significantly from
90° indicating a regular distortion. For example in the complex A
the ligand–cobalt–ligand bond angles in the equatorial plane con-
sist of two angles that are larger than 90° (O1ACo1AN1)
(93.22(22)), (O2ACo1AN2) (92.97(22)) and two smaller angles
(O1ACo1AO2) (85.87(2)), (N1ACo1AN2) (87.72(2)) are similar to
those in N2O2–salen cobalt complexes [42]. Also the summations
of these angles are nearly 360° and shows that the cobalt atom is
in a square planer environment of N2O2 atoms.
X-ray diffraction
The XRD analysis confirmed that the intercalation reaction was
successful with the cationic complexes. The MMT layers were
propped apart upon swelling in ethanol and the basal distances be-
came higher after the ion-exchange process by the cationic com-
plexes compared to the original MMT, even after removing the
solvent and washing off excess metal complexes from the outer
surface of the clay. The d-spacing of unmodified MMT
(d = 1.006 nm) is calculated from the peak position at 2h = 8.78°
using Bragg’s equation. The diffraction peak of the MMT–PPh3
Fig. 5. The XRD patterns of the hybrid materials.
P21/a. X-ray diffraction data and selected bond lengths and angles
are listed in Tables 1–3, respectively. The complex crystallizes with
two independent molecules ([Co(Me2Salen)(PPh3)(EtOH)]BF4 (A
complex) and [Co(Me2Salen)(PPh3)(H2O)]BF4 (B complex)) in the
asymmetric unit (Fig. 2). The packing diagram of the complex is
shown in Fig. 3.
Each cobalt atom is coordinated in a distorted octahedral geom-
etry, the Me2Salen ligand has the N2O2 coordinated in the equato-
rial plane. PACoAN/O angles were distributed from 87.24(1)° to
and MMT–PBu3 nanohybrids shifts to
a new position at
2h = 4.63° (d = 1.906 nm) and at 2h = 5.26° (d = 1.678 nm) after
the ion-exchange reaction of MMT with the cationic complexes,
respectively (Fig. 5). An increase in the interlayer distance, leads
to a shift of the diffraction peak toward lower angles and confirms
that the intercalation reaction and surface modification of MMT are
occurred. This means that the basic structures of the MMT are kept,
the layers only propped open and the basal distances are increased
Fig. 6. The SEM.

A.H. Kianfar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 422–428
427
Fig. 7. The EDX of the MMT–PBu3.
Fig. 8. The TEM images of the MMT–PBu3.
significantly, providing evidence that the intercalation reaction has
occurred successfully.
Morphology analysis
The SEM images of the MMT–PBu3 were studied by SEM tech-
nique (Fig. 6). According to the SEM images, the MMT–PBu3 has a
layer structure. Further information was obtained using EDX.
Fig. 7 shows the EDX spectrum of the MMT–PBu3 particle. In the
EDX spectrum, ten elements can be observed, i.e. carbon (C), oxy-
gen (O), magnesium (Mg), aluminum (Al), silicon (Si), potassium
(K), sodium (Na), phosphor (P), nitrogen (N), and cobalt (Co). The
high percent of the carbon observed in the EDX is associated with
the coating materials sputtered on the sample. The present of Co, P
and N in the EDX confirms the presence of the Schiff base complex
in the interlayer of the MMT. All remaining elements represent
components of the MMT. Also the absent of the floure in the EDX
spectrum provided that the intercalation reaction has occurred
successfully.
TEM images of MMT–PBu3 nanohybrid is given in Fig. 8. Accord-
ing to the TEM images the thickness of the silicate layers of the
organoclay is about 2–5 nm and no aggregation was observed in
the TEM images of the MMT–PBu3. The spaces between silicate lay-
ers are around 2 nm. Therefore, these TEM micrographs confirmed
the results obtained by XRD in the form of small peaks.
Fig. 9. The TGA thermogram of the hybrid materials.
that the main weight losses (5.9%) occur at the temperature of
30–270 °C, which can be attributed to the loss of physically ad-
sorbed water. Second mass losses (1.9%) occur at the temperature
range of 270–540 °C, correspond to the loss of water which is
bonded to the clay layers. Last weight losses (2.2%), is due to
the loss of hydroxyl groups of clay. Decomposition of MMT–
PPh3 and MMT–PBu3 compounds occur in three steps, the mass
loss (1.7%) at the room temperature to 210 °C is due to the ad-
sorbed water. Second decomposition step (5.8%), in MMT–PPh3
starts at 210 °C and ended at 560 °C is according to decomposi-
tion of Schiff base complex [43–47] which intercalated to the clay
layers. In MMT–PBu3 the second step shows 8.7% weight loss at
the temperature of 220–750 °C. The weight loss in the third step
is 5.97% and 1.70% for MMT–PPh3 and MMT–PBu3, respectively.
Thermal degradation characteristics
The TGA and DTG curves of MMT, MMT–PPh3 and MMT–PBu3
are shown in Figs. 9 and 10. The thermal analysis of clay shows

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A.H. Kianfar et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 127 (2014) 422–428
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Appendix A. Supplementary materials
CCDC No. 965297 contains the supplementary crystallographic
data for [Co(Me2Salen)(PPh3(OH2)]BF4, respectively. These data
can be obtained at www.ccdc.cam.ac.uk/deposit {or from the Cam-
bridge Crystallographic Data Center 12, Union Road Cambridge CB2
1EZ, UK; Fax: (internet) +44-1223/336-033; E. mail: depos-
it@ccdc.cam.ac.uk). Supplementary data associated with this arti-
cle can be found, in the online version, at http://dx.doi.org/
10.1016/j.saa.2014.02.089.
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