Accepted Manuscript Immobilization of cobalt(III) Schiff base complexes onto montmorillonite-K10: Synthesis, experimental and theoretical structural determination Ali Hossein Kianfar, Wan Ahmad Kamil Mahmood, Mohammad Dinari, Hossein Farrokhpour, Majid Enteshri, Mohammad Hossein Azarian PII: DOI: Reference:

S1386-1425(14)01548-0 http://dx.doi.org/10.1016/j.saa.2014.10.051 SAA 12866

To appear in:

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy

Received Date: Revised Date: Accepted Date:

17 August 2014 28 September 2014 15 October 2014

Please cite this article as: A.H. Kianfar, W.A.K. Mahmood, M. Dinari, H. Farrokhpour, M. Enteshri, M.H. Azarian, Immobilization of cobalt(III) Schiff base complexes onto montmorillonite-K10: Synthesis, experimental and theoretical structural determination, Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy (2014), doi: http://dx.doi.org/10.1016/j.saa.2014.10.051

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Revised Immobilization

of

cobalt(III)

Schiff

base

complexes

onto

montmorillonite-K10: Synthesis, experimental and theoretical structural determination Ali Hossein Kianfar1a, Wan Ahmad Kamil Mahmoodb, Mohammad Dinaria, , Hossein Farrokhpoura, Majid Enteshria and Mohammad Hossein Azarianb a

Department of Chemistry, Isfahan University of Technology, Isfahan, Iran, 84156-83111

b

School of Chemical Sciences, Universiti Sains Malaysia,11800 Minden, Penang, Malaysia

Abstract The

[Co(naphophen)(PPh3)(OH2)]ClO4

and

[Co(naphophen)(PBu3)(OH2)]BF4

(where

naphophen = bis(naphthaldehyde)1,2-phenylenediimine) complexes were synthesiszed and chracterized by FT-IR, UV-Vis, 1H NMR,

13

C NMR spectroscopy and elemental analysis

techniques. The coordination geometry of the synthezised complexes were determined by X-ray crystallography. Cobalt (III) complexes have six-coordinated pseudo-octahedral geometry in which the O(1), O(2), N(1) and N(2) atoms of the Schiff base forms the equatorial plane. These complexes showed a dimeric structure via hydrogen bonding between the phenolate oxygen and the hydrogens of the coordinated H2O molecule. The theoretical calculations were also performed to optimize the structure of the complexes in the gas phase to confirm the structures 1

Ali Hossein Kianfar, E-mail: [email protected] ; [email protected]

Tel : +98-31-33913251 Fax : +98-31-33912350

1

proposed by X-ray crystallography. In addition, UV-Visible and IR spectra of complexes were calculated and compared with the corresponding experimental spectra to complete the experimental structural identification. The synthesized complexes were incorporated onto the Montmorillonite-K10 nanoclay via simple ion-exchange reaction. The structure and morphology of the obtained nanohybrids were identified by FT-IR, XRD, TGA/DTA, SEM and TEM techniques. Based on the XRD results of the new nanohybrid materials, the Schiff base complexes were intercalated in the interlayer spaces of clay. SEM and TEM micrographes of the clay/complex shows that the resulting hybrid nanomaterials has layer structures.

Keywords: X-Ray crystallography; Cobalt Schiff base Complexes; DFT calculation; Insertion compounds; Montmorillonite-K10; Modified clay

1. Introduction Montmorillonite (MMT) is a typical 2:1 phyllosilicate in which the negative layer charge is electrically balanced by the equal charge of exchangeable cations, such as Na+, Ca2+ or K+ [1,2]. Due to its large availability, large specific surface area, swelling behavior, ion exchange, low cost, low toxicity and good biocompatibility, the properties and industrial applications of the MMT have been extensively investigated [3-6]. Taking advantage of these characteristic features of MMT, the constructions, properties and applications of the MMT have been extensively reported [7,8]. Surface modifications of clay minerals have received attention because it allows production new materials and new applications. There are several routes which can be used to modify clays 2

and clay minerals. Modified clays can be used in different areas such as adsorbents of organic pollutants in soil, water, and air; rheological control agents; paints; cosmetics; refractory varnish; thixotropic fluids, polymer nanocomposites and etc [9,10]. Cobalt Schiff base complexes have been investigated as models for the Cobalamine (B12) coenzymes [11] and classified as an oxygen carrier [12]. They are also applied as a catalyst for the preparative oxygenation of phenols [13] and amines [14]. The catalytic activity of the cobalt(III) salen with the active species containing Co(III) oxidation state has been investigated [15]. The thermodynamic and electrochemical studies of [CoL(PR3)(OH2)]+ (where L = tetradentate N2O2 Schiff bases) complexes were investigated previously [16-25]. To extend the studies on the structure of these type of complexes, H2 naphophen (bis(2hydroxynaphthaldehyde)phenylenediimine) Schiff base was prepared by the condensation reaction of the 1,2-phenylenediamine with 2-hydroxynaphthaldehyde and then, the cobalt(III) complexes of this ligand were synthesized in methanol solvent (Scheme 1). The [Co(naphophen)(PBu3)(H2O)]BF4 and [Co(naphophen)(PPh3)(OH2)]ClO4 complexes were identified by FT-IR, 1H NMR,

13

C NMR, UV-Vis spectroscopy and elemental analysis

techniques. The coordination geometry of these compounds was determined by X-ray crystallography. Nanohybrid of the synthesized complexes and Montmorillonite K-10 (MMTK10) were prepared in ethanol and the structure and morphology of the hybrid materials were determined by different techniques. In addition, density functional theory (DFT) calculations were performed to optimize the structures of complexes in the gas phase to confirm the geometrical structures obtained from X-ray crystallography data. Time-dependent density functional theory (TD-DFT) was also employed to calculate the UV-Vis spectra of

3

Co(naphophen)(PBu3)(H2O)]+ and [Co(naphophen)(PPh3)(OH2)]+ complexes in the gas phase and compared them with the corresponding spectra recorded in ethanol solvent. 2. Experimental 2.1. Materials All of the chemicals and solvents used for synthesis were of commercially available reagent grade and they were used without purification. MMT-K10 with cation-exchange capacity of 119 meq/100 g was provided by Aldrich chemical Co.

2.2 Characterizations Fourier transform infrared (FT-IR) spectra were recorded as KBr disks on a FT-IR JASCO680 spectrophotometer in the 4000 - 400 cm-1. The elemental analysis was determined on a CHN-O-Heraeus elemental analyzor. UV-Vis spectra were recorded on a JASCO V-570 spectrophotometer in the 190 - 900 nm. The 1HNMR and

13

C NMR spectra were recorded in

DMSO-d6 on Bruker-500 MHz. The X-ray single crystal structure analysis was obtained by using bruker smart Apex II-2009 CCD area detector diffractometer. The X-ray diffraction (XRD) was recorded on high resolution X-Ray diffractometer system model PAN analytical X'PRO MRD PW3040. Scanning electron microscopy (SEM) was recorded on QUANTA FEG 650 2012 SEM system. Transmission electron microscopy (TEM) was performed using Zeiss Libra®120 TEM system. The thermal stability of specimens was tested using PERKIN ELMER TGA7 1991 thermogravimetric analyzer from ambient temperature to 900 ºC at a heating rate of 20 ºC/min under nitrogen gas.

2.3 Synthesis of the Schiff base ligands 4

The Schiff base ligand, H2naphophen, was prepared according to the literature by condensation between 1,2-phenylenediamine and 2-hydroxynaphthaldehyde(1:2 mole ratio) in methanol and recrystallized by dichloromethane/methanol mixed solvent through the partial evaporation of dichloromethane [26]. H2naphophen; FT-IR (KBr cm-1) νmax 1620 (C=N), 1569 (C=C), 1320 (C-O). 1H NMR (DMSO-d6, δ, ppm): 7.07-7.08 (d, 2Ar-H, 3J = 5.5), 7.36-7.39 (t, 2Ar-H, 3J = 8), 7.44-7.46 (m, 2Ar-H), 7.54-7.57 (t, 2Ar-H, 3J = 7.5), 7.80-7.83 (d, 2Ar-H, 3J = 13.5), 7.95-7.97 (d, 2Ar-H, 3J = 10.5), 8.53-8.55 (d, 2Ar-H, 3J = 10), 9.69 (s, 2H, HC=N) and 15.12 (s, 2H, OH). 13C NMR (DMSO-d6, δ, ppm): 109, 119, 120, 121, 123, 126, 127, 128, 129, 133, 136, 138, and 157 (C Ar), 168 (CH=N). UV-Vis, λmax (nm) (Ethanol): 453 (16000), 389 (20000), 319 (17000).

2.4 Synthesis of the metal Schiff base complexes The general procedure for the synthesis of cobalt complexes is as follows: an appropriate amount of cobalt(II)acetatetetrahydrate (0.249 g, 1.0 mmol) and phosphine (1.0 mmol) were added to a methanolic solution (40 mL) of H2 naphophen (0.416 g, 1.0 mmol) and was refluxed for 1h. The synthesized Co(II) complex was oxidized by blowing air into the solution for 2 h and then, it was filtered. To filtrate, an appropriate amount of sodium tetraflouroborate (0.110 g, 1.0 mmol) or sodium perchlorate (0.140 g, 1.0 mmol) was added and the resulting crystals were formed after 4 days. [Co(naphophen)(PBu3)(OH2)]BF4, yield (80%). Anal, calc. for C40H47BCoF4N2O3P: C, 61.55; H, 6.08; N, 3.59%. Found; C, 62.15; H, 6.23; N, 3.45%. FT-IR (KBr cm-1) νmax 2958, 2929 and 2870 (C-H), 1606 (C=N), 1531 (C=C), 1189 (C-O), 1053 (BF4-). 1H NMR (DMSOd6d6, δ, ppm): 0.61-0.65 (t, 9H, CH3, 3J = 10), 1.03-1.26 (m, 18H, CH2), 7.37-7.44 (t, 2Ar-H, 3J 5

= 18), 7.46-7.55 (d, 2Ar-H, 3J = 18), 7.56-7.58 (br, 2Ar-H), 7.61-7.66 (t, 2Ar-H, 3J = 10), 7.847.86 (d, 2Ar-H, 3J = 10), 7.97-8.01 (d, 2Ar-H, 3J = 15.5), 8.62-8.65 (d, 2Ar-H, 3J = 12.5), 8.72 (br, 2Ar-H) and 9.57 (s, 2HC=N) . 13C NMR (DMSO-d6, δ, ppm): 13 (CH3), 21, 23 and 24 (CH2), 109, 117, 120, 123, 124, 126, 127, 128, 129, 133, 137,144, and 152 (C-Ar), 168 (CH=N). UV-Vis, λmax (nm) (Ethanol): 650 (270), 517 (11300), 497 (10600), 394 (20500), 349 (11300), 331(11000. [Co(naphophen)(PPh3)(OH2)]ClO4, yield (80%). Anal, calc. for C46H35ClCoN2O7P: C, 64.76; H, 4.14; N, 3.28%. Found; C, 65.36; H, 4.27; N, 3.43%. FT-IR (KBr cm-1) νmax 1600 (C=N), 1532 (C=C), 1191 (C-O), 1105 (ClO4 -).1H NMR (DMSO- d6, δ, ppm): 7.25-7.55 (m, 23 H, Ar-H), 7.74-7.75 (d, 2Ar-H, 3J = 7.5), 7.84-7.85 (d, 2Ar-H, 3J = 7.5), 8.35-8.37 (d, 4Ar-H, 3J = 12), and 9.57 (s, 2H, HC=N) . 13C NMR (DMSO-d6, δ, ppm): 109, 117, 120, 123, 124, 126, 127, 128, 129, 133, 137,144, and 152 (C Ar), 168 (CH=N). UV-Vis, λmax (nm) (Ethanol): 700 (655), 512 (14600), 488 (13000), 392 (23700), 345 (20800), 332 (20800).

2.5 Synthesis of intercalation compounds The

0.75g

of MMT-K10

[Co(naphophen)(PBu3)(H2O)]BF4

or

was

added

to

an

ethanolic

solution

[Co(naphophen)(PPh3)(H2O)]ClO4

containing

(about

0.08g)

complexes. The reaction mixture was refluxed for 24h and then, was filtered off. The brown precipitates were washed with ethanol, methanol and acetone for several times, and then it was dried at 65°C. K10-[Co(naphophen)(PBu3)(H2O)] (K10-CoPBu3): color: brown, FT-IR (KBr cm-1) νmax 2750-3600 (H2O), 1633 (OH), 1534 (C=N), 1350(C=C), 900-1300 (Si-O), 527 (Al-O) and 469 (Mg-O). 6

K10-[Co(naphophen)(PPh3)(H2O)] (K10-CoPPh3): color: brown, FT-IR (KBr cm-1) νmax 2750-3600 (H2O), 1627 (OH), 1534 (C=N), 1370(C=C), 900-1300 (Si-O), 527 (Al-O) and 457 (Mg-O).

2.5. Crystal structure determination and refinement of [Co(naphophen)(PBu3)(H2O)]BF4 and [Co(naphophen)(PPh3)(H2O)]ClO4 The X-ray diffraction measurements were made on a STOE IPDS-2T diffractometer with graphite monochromated Mo-Kα radiation. The red brown crystal of [Co(naphophen)(PBu3)(H2O)]BF4 complex with a dimension of 0.28 × 0.15 × 0.09 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 10920 unique reflections. Data were collected at a temperature of 100(2) K to a maximum 2θ value of 60.2° in a series of ω scans in 1° oscillations and integrated using the Stoe X-AREA software package. The numerical absorption coefficient, µ, for Mo-Kα radiation is 0.710 mm-1. For [Co(naphophen)(PPh3)(H2O)]ClO4 complex, brown crystal with a dimension of 0.41 × 0.26 × 0.21 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 8840 unique reflections. Data were collected at a temperature of 100(2) K to a maximum 2θ value of 55.2° in a series of ω scans in 1° oscillations and integrated using the Stoe X-AREA software package.

The numerical absorption coefficient, µ, for Mo-Kα

radiation is 0.710 mm-1.

7

A numerical absorption correction was applied using X-RED and X-SHAPE softwares [27]. 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 fullmatrix least-squares procedure using anisotropic displacement parameters [29]. All of hydrogen atoms were located in a difference Fourier map and then refined isotropically. Atomic factors were from International Tables for X-ray Crystallography. All refinements were performed using the X-STEP32 crystallographic software package [30]. A summary of the crystal data, experimental details and refinement results are given in Table 1 for [Co(naphophen)(PBu3)(H2O)]BF4 [Co(naphophen)(PPh3)(H2O)]ClO4 complexs. It is notable that, the asymmetric unit also contains solvents molecules, which could not be modeled. Therefore, the diffraction contribution of the solvent molecules was removed by the subroutine SQUEEZE in PLATON.

3. Results and discussion 3.1 FT-IR characteristics The FT-IR spectra of the Schiff base ligand and cobalt (III) complexes exhibit several bands in the 400-4000 cm-1 region (sections 2.2-2.5). The azomethine vibration of the Schiff base ligand was appeared at 1620 cm-1. Because of bond formation between the metal and the imine nitrogen, the C=N bond stretching was shifted to lower frequencies relative to the free Schiff base and appeared in 1606 and 1600 cm-1 for [Co(naphophen)(PBu3)(OH2)]BF4 and [Co(naphophen)(PPh3)(OH2)]ClO4 complexes, respectively [31]. The C-H stretching of PBu3 coordinated ligands appeared in the 2870-2958 cm-1 region. The stretching vibrations of BF4- and ClO4 - counter ions were appeared at 1053 and 1105 cm-1, respectively. 8

For MMT-K10 a broad peak is seen in the range of 3600-2700 cm-1 that is related to the interlayer absorbed water molecules. A weak band is appeared at 1645 cm-1 which is related to the OH bending. The Si-O stretching peak is appeared in the range of 1300-900 cm-1. The peaks at 463 and 529 cm-1 are related to Mg-O and Al-O, respectively [32]. The FT-IR spectra of the intercalation compounds (MMT-CoPBu3 and MMT-CoPPh3) 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 stretching band of the complexes was appeared at about 1630 cm-1 in the hybrid materials. Other characteristic bonds around 15001300 cm-1 confirmed the presence of the complexes intercalated between the MMT layered.

3.2. Electronic spectra The UV-Vis spectral data (300-800 nm) of the ligand and synthesized complexes were listed in sections 2.2. and 2.3. All the bands lower than 400 nm are involved π → π* transition related to aromatic ring. In the Schiff base ligand, the band at 453 nm, involves π → π* transition related to azomethine group. This band was shifted to higher wavelengths and appeared at about 490 nm in mixed with charge transfer transition. The cobalt(III) complexes show an absorption band related to charge transfer transition (MLCT) at about 512 and 517 nm region [16, 33-38]. In addition,

a

d-d

transition

[Co(naphophen)(PBu3)(H2O)]BF4

was and

seen

at

about

650

and

700

[Co(naphophen)(PPh3)(H2O)]ClO4

nm

for

complexes,

respectively [18, 19]. It is notable that there is a complete assignment of the UV-Visible spectra of complexes, based on the TD-DFT calculations presented in the theoretical part of paper.

9

3.3. 1HNMR and 13CNMR spectra The 1HNMR data of the Schiff base ligand and the cobalt(III) complexes were presented in sections 2.2. and 2.3. The aromatic hydrogens of ligand were seen in the range of 7.07-8.55 ppm. The imine and the phenolic (OH) hydrogens were appeared at 9.69 and 15.12 ppm, respectively. The phenolic hydrogens were disappeared in the synthesized complexes. The hydrogens of the PBu3 in the [Co(naphophen)(PBu3)(H2O)]BF4 were appeared in the range of 0.60-1.25 ppm. For the synthesized complexes, the hydrogens of aromatic rings also existed in the range of 7.25-8.73 ppm and the imine hydrogens were seen at 9.57 ppm as a singlet. The structures of the synthesized ligand and complexes were also confirmed by

13

C NMR

techniques. The fourteen different lines belong to aromatic carbons of Schiff base ligand were seen in the range of 109-157 ppm. The imine carbon was appeared at 168 ppm. For the [Co(naphophen)(PBu3)(H2O)]BF4 complex, the carbons of PBu3 were seen in the range of 13-24 ppm. The aromatic carbons were appeared in the range of 109-152 ppm and the iminic carbon was seen at 168 ppm. In the [Co(naphophen)(PPh3)(H2O)]ClO4 complex, the aromatic carbons were seen in the range of 109-152 ppm for Schiff base ligand and triphenylphosphine and the C=N carbon was appeared at 167 ppm.

3.4 Description of the molecular structure of the [Co(naphophen)(PBu3)(H2O)]BF4 and [Co(naphophen)(PPh3)(H2O)]ClO4 The structure of the [Co(naphophen)(PBu3)(H2O)]BF4 and [Co(naphophen)(PPh3)(H2O)]ClO4 complexes were determined by X-ray diffraction and crystallized in the Triclinic space group P1. X-ray diffraction data and selected bond lengths and angles of [Co(naphophen)(PBu3)(H2O)]BF4 and [Co(naphophen)(PPh3)(H2O)]ClO4 complexes were listed in Tables 2 and 3, respectively. 10

The

asymmetric

unit

of

[Co(naphophen)(PBu3)(H2O)]BF4

and

[Co(naphophen)(PPh3)(H2O)]ClO4 complexes were shown in Figs. 2 and 3, respectively. In both complexes, each cobalt atom is coordinated in a distorted octahedral geometry and the naphophen ligand has the N2O2 coordinated in the equatorial plane. In the [Co(naphophen)(PBu3)(H2O)]BF4 complex, P-Co-N/O angles are distributed from 90.37(3) to 94.73(4)°, while O1w-Co-N/O angles are distributed from 86.40(5) to 88.01(5)°. The Co-N1, Co-N2, Co-O1 and Co-O2 distances also appear in the range of 1.8830 (12), 1.8790 (12), 1.8843 (10) and 1.8686 (10) Å, respectively. These results are similar to those in N2O2-salen cobalt complexes [39-41]. The Co-P bond distance of apical position is 2.2216(4) for Co-P1. The Co−O distances (1.8843(10), 1.8686(10)Å) are smaller than the Co−Ow distance 2.1193(11) Å, due to higher trans influence of the P1 atom with respect to the N1 and N2 atoms. In the [Co(naphophen)(PPh3)(H2O)]ClO4 complex P-Co-N/O and O1w-Co-N/O angles were distributed from 94.21(8) to 94.60(8)° and 85.02(7) to 85.73(8)°, respectively. The Co-N1, CoN2, Co-O1 and Co-O2 distances appear in the range of 1.878 (2), 1.8825 (19), 1.8760 (15) and 1.8726 (16) Å, respectively. In this compound, due to lower trans effect of PPh3 relative to PBu3, the

Co−Ow

(2.0983

(17)Å)

is

shorter

than

the

similar

bond

in

the

[Co(naphophen)(PBu3)(H2O)]BF4 complex while the Co-P bond distance of apical position shows a reveres trend. The extended network of the complexes is due to the hydrogen bonding in molecules which leads to aggregation to supramolecular structures (Fig.4 and 5). In [Co(naphophen)(PBu3)(H2O)]BF4 the hydrogen bonding between the phenolate oxygen and the hydrogens of coordinated water (O1-H1W = 2.058 Å and O2-H1W = 2.565 Å) leads to a dimer structure (Fig.4). In addition, to hydrogen bonding with hydrogen of coordinated water 11

(F4-H2W1(2.080Å)), the BF4 - counter ion collected 4 asymmetric units to create the extended network

of

[Co(naphophen)(PBu3)(H2O)]BF4

complex

via

[F1-H21A(2.347Å),

F1-

H16A(2.495Å), F2-H29B(2.410Å) F2-H27A(2.590Å), F3-H6A(2.539Å), F3-H11A(2.467Å), F3-H13A(2.485Å), F4-H27A(2.438Å)) hydrogen bonding. In [Co(naphophen)(PPh3)(H2O)]ClO4 complex, the hydrogen bonding between the phenolate oxygen and the hydrogens of coordinated water (O1-H1W(2.476Å) and O2-H1W(2.133Å) leads to a dimer structure (Fig. 5). The perchlorate counter ion is bonded to coordinated water (O5H2W(2.767Å)) and the hydrogens on the Schiff base (O5-H27A(2.587Å) and (O2-H16A(2.717Å))

via hydrogen bonding, helps to forming dimer structure. Also the perchlorate ion is bonded to the other asymmetric units via hydrogen bonding between oxygens of perchlorate and hydrogens on aromatic rings to create the extended network of [Co(naphophen)(PPh3)(H2O)]ClO4 complex. All angles around the cobalt center deviate significantly from 90° indicating a regular distortion. The ligand-cobalt-ligand bond angles in the equatorial plane consist of two angles that are larger and two smaller angles than 90° (Table 2 and 3) are similar to those in N2O2-salen cobalt complexes [42]. The summations of these angles are nearly 360° and shows that the cobalt atom is in a square planer environment of N2O2 atoms.

3.5 X-ray diffraction Fig. 6 demonstrated the XRD pattern of the K10, K10-CoPBu3 and K10-CoPPh3. The dspacing of unmodified clay (K10) which was calculated from the peak position at 2θ = 8.78o using Bragg’s equation is 1.006 nm. The diffraction peak of the K10-CoPBu3 and K10-CoPPh3 shifted to a new position at 2θ = 4.01o (d = 2.20 nm) and at 2θ = 4.25o (d = 2.08 nm) after the ion-exchange reaction of MMT with the cationic complexes, respectively (Fig. 6). An increase in 12

the interlayer distance, lead to a shift of the diffraction peak toward lower angles and confirmed that the intercalation reaction and surface modification of MMT-K10 were occurred. These results confirmed that the intercalation reaction has occurred successfully.

3.6 Theoretical studies The

structures

of

the

synthesized

complexes

[Co(naphophen)(PPh3)(OH2)]+

and

[Co(naphophen)(PBu3)(OH2)]+, without counter ions, were fully optimized using Gaussian 2009 software [43]. The primary full optimization was performed using PM6 semi-empirical method. The initial geometries of complexes for this optimization were obtained from the experimental X-ray date reported in this paper. The PM6 optimized structures were used as initial geometry for further optimization the structures at the DFT method. The functional M062X [44] was used for the optimization and the extremely tight optimization convergence criteria was set. The standard relativistic effective core pseudo potential LANL2DZ was used for Co atom and 631G(d) basis set for P, O, N and C atoms. The frequency calculations were performed at the DFT level of theory using M062X functional and the same basis set to check the position of the optimized structures on their potential energy surfaces. There was no imaginary frequency which confirmed that the optimized structures were at the minima stationary points on their potential energy

surfaces.

The

optimized

structures

of

[Co(naphophen)(PBu3)(OH2)]+

and

[Co(naphophen)(PPh3)(OH2)]+ complexes have been shown in Figures 2 and 3, respectively. Some calculated bond lengths and bond angles of these two complexes were compared with the corresponding experimental values obtained from X-ray data in Table 2. As seen in Table 2, the bond length of Co1-N1 and Co1-N2 in gas phase has been slightly decreased in both complexes compared to solid state. In addition, a slightly increase in the other bond length 13

shown in the tables is observed. Generally, it can be seen that the calculated structures of complexes in gas phase strongly confirms the solid state structures of complexes. However, there are two differences between the solid and gas phase structures. The first, in both complexes, is related to the orientation of the coordinated water relative to the phenolic oxygen atoms (O1 and O2). There are two intermolecular hydrogen bondings as O1-H1W and O2-H2W in solid state which causes that the hydrogen atoms of water coordinated are located far away from the phenolic oxygen atoms in the complex. The opposite orientation is seen in the gas phase so that the hydrogen atoms of water coordinated are toward phenolic oxygen atoms because of the intramoleculare hydrogen bonding. The second difference is due to the deviation of the Schiff base from the planarity especially for the [Co(naphophen)(PPh3)(OH2)]+ complex in the gas phase. This can be attributed to the cone angle of PPh3 ( 145) relative to PBu3 (132) [45]. The precense of high strain from PPh3 in the [Co(naphophen)(PPh3)(OH2)]+ complex leads to the deviation of Schiff base from planarity. In the solid state, the precense of hydrogen bonding between two different molecules (Fig. 5) nearly resulted planarity of Schiff base ligand in equatorial plane of the complex. The structural deformation also leads to longer bond length of Co1-P1 in the solid stae (2.24) compared to the gas phase (2.11). Figures 7 and 8 compares the calculated IR spectra of the [Co(naphophen)(PPh3)(OH2)]+ and [Co(naphophen)(PBu3)(OH2)]+ complexes in the gas phase with the corresponding experimental spectra of these complexes containing their counter ions in the solid state. As seen, there is a good agreement between theory and experiment. The calculated frequency of C=N stretching of imine for both [Co(naphophen)(PPh3)(OH2)]+ and [Co(naphophen)(PBu3)(OH2)]+ is about 1696 cm-1 which is close to the experimental values reported in section 3-1 (1606 and 1600 cm-1). The features related to C-H streching of PBu3 coordinated ligands are appeared in the range of 306414

3145 cm-1. It is interesting to notice that the peaks related to the counter ions are absent in the calculated spectra. As seen in Figures 7 and 8, there is an energy shift between the calculated and experimental IR spectra which can be attributed to three facts including: the calculations were performed in the gas phase, the vibrational modes have been considered harmonics and the counter ion is absent in the calculations. Figures 9 and 10 compare the calculated gas phase absorption spectra of [Co(naphophen)(PBu3)(OH2)]+ and [Co(naphophen)(PPh3)(OH2)]+

with the corresponding

recorded spectra of complexes in ethanol solvent. As seen, there is relatively good agreement between the theroy and experiment which shows that there is similarity between the structures of complexes in the gas phase with those in the solvent. For calculating the absorption spectra, The time-dependent density function theory (TD-DFT) along with the same functional and basis set was used for calculations. Only ten absorption bands were incorporated in calculating the absorption spectra. The first feature in the recorded spectrum of [Co(naphophen)(PBu3)(OH2)]+, located between 600 to 700 nm is composed of three absorbtion bands based on the theoretical calculations. The most intense absorption line of this feature is due to the excitation from molecular orbitat of azomethine to the empty d atomic orbital of cobalt. The second and third feature of experimental spectrum are composed of only one absoprtion line. The second feature is due to two excitions including π of aromatic rings of ligand and σ (C-H) of tert-butyl to cobalt d orbital. The third feature in the experimental spectrum is due to HOMO→LUMO excitation which the HOMO is d orbital of central metal and LUMO is the empty π* of Schiff base ligand. The most intense feature in the experimental spectrum is composed of two excitations bands. These two excitation bands are mainly related to metal to ligand charge transfer (MLCT). A detail information about 15

the excitation bands of [Co(naphophen)(PBu3)(OH2)]+ have been reported in Table 3. In addition, the shape of molecular orbitals involved in the transitions of this complex has been shown in Table 1 (suplementary materials). The first feature in the experimental spectrum of [Co(naphophen)(PPh3)(OH2)]+ located at about 700 nm corresponds to the feature of the theoretical spectrum at about 822 nm. Comparison of theory with experiment shows that this feature composed of three absorption lines. The first absorption band of this feature is due to the excitation from d orbital of the metal to π* of Schiff base ligand. The second feature of the experimental spectrum composed of three lines which the most intense line in this feature is related to the promotion of electron from d orbitals of the metal to π* of Schiff base ligand. Theoretical calculation shows that the third feature in the experimental spectrum is due to HOMO→LUMO excitation which the HOMO is d orbital of central metal ion and LUMO is the empty π* of Schiff base ligand. The most intense feature in the experimental spectrum is composed of two excitations bands. These two excitation bands are mainly related to metal to ligand charge transfer (MLCT). A detail information about the excitation bands of [Co(naphophen)(PPh3)(OH2)]+ have been reported in Table 4. In addition, the shapes of molecular orbitals involved in the transitions of this complex have been shown in Table 2 (suplementary).

3.7 Morphology analysis A fracture surface of K10-CoPPh3 was examined by SEM technique. As seen in Fig. 11, smooth fractured surface observed on this compound and it has a layer structures.

16

TEM images of K10-CoPPh3 nanohybrid is presented in Fig. 12. According to the TEM images, the thickness of the silicate layers of the organoclay is about 2-5 nm and no aggregation is observed in the TEM images of this compound. 3.8 Thermal properties The TGA and DTG curves of MMT-K10, K10-CoPPh3 and K10-CoPBu3 are shown in Figs. 13 and 14, respectively. The thermal analysis of clay shows a weight loss about 5.9% for physically adsorbed water at the temperature of 30 to 270oC. The loss of water which is bonded to the clay layers is about 1.9% at the temperature range of 270 to 540oC. Last weight loss (2.2%), is due to the loss of hydroxyl groups of the clay. The K10-CoPPh3 decomposes in three steps; the mass loss (1.2%) at room temperature to 175oC is owing to the adsorbed water. Second decomposition step (6.8%), in K10-CoPPh3 starts at 175oC and ended at 765oC is according to decomposition of Schiff base complex which intercalates to the clay layers [46-50]. The last weight loss (1.2%) is accrued between 760 to 900oC. The K10-CoPBu3 compound decomposes in four steps. The water mass loss is happened between 30-180oC. The second step shows 4% weight loss at the temperature of 180oC to 534oC. The weight loss in the third (2.7%) and last (1.6%) steps is occurred in the range of 534oC to 747oC and 747oC to 900oC, respectively. The residue for K10-CoPBu3 and K10-CoPPh3 is about 90.3% and 90.9%, respectively.

4. Conclusions In summery,

[Co(naphophen)(PPh3)(OH2)]ClO4

and

[Co(naphophen)(PBu3)(OH2)]BF4

complexes were synthesized and their structures were identified by different techniques. The FTIR, 1H NMR,

13

C NMR and X-ray crystallography results confirmed that the synthesized

complexes contain Schiff base, phosphine and counter ions. According to the X-ray 17

crystallography results, the synthesized complexes were hexacoordinated in the solid state. Theoretical calculations of the structures of complexes, their UV-visible and IR spectra were performed for the characterization of complexes and confirmation of experimental results. From the ion-exchange reaction of the above complexes and MMT-K10, new nanohybrids of these materials were prepared in ethanol solution and they were characterized by FT-IR, TGA/DTG, XRD, SEM and TEM. SEM and TEM micrographs show that the resulting nanohybrid had layer structures.

5. Supplementary material CCDC No. 965298 and 965299 contains the supplementary crystallographic data for [Co(naphophen)(PPh3)(OH2)]ClO4 and [Co(naphophen)(PBu3)(OH2)]BF4, respectively. These data can be obtained at www.ccdc.cam.ac.uk/deposit {or from the Cambridge Crystallographic Data Center 12, Union Road Cambridge CB2 1EZ, UK; Fax: (internet) +44-1223/336-033; E. mail: [email protected]).

Acknowledgements We wish to express our gratitude to the Research Affairs Division Isfahan University of Technology (IUT), Isfahan, for partial financial support. Further financial support from National Elite Foundation (NEF), Iran Nanotechnology Initiative Council (INIC) and Center of Excellency in Sensors and Green Chemistry Research (IUT) is gratefully acknowledged.

References

18

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22

Scheme 1. The structure of Schiff base and its complexes

Fig 1. The FT-IR spectra of the MMT-K10 and hybrid materials.

23

Fig 2. (a) The labeled diagram of [Co(naphophen)(PBu3)(OH2)]BF4 showing 80% probability thermal ellipsoids, (b) The optimized structures of (a) [Co(naphophen)(PBu3)(OH2)]+ calculated at the M062X/LANL2DZ/6-31G(d).

24

Fig 3. (a) The labeled diagram of [Co(naphophen)(PPh3)(OH2)]ClO4 showing 80% probability thermal ellipsoids, (b) The optimized structures of (a) [Co(naphophen)(PPh3)(OH2)]+ calculated at the M062X/LANL2DZ/6-31G(d).

25

Fig. 4. A view of the extended network of complex [Co(naphophen)(PBu3)(OH2)]BF4 showing 50% probability thermal ellipsoids with the intermolecular hydrogen bonds (dashed lines).

26

Fig. 5. A view of the extended network of complex [Co(naphophen)(PPh3)(OH2)]ClO4 showing 50% probability thermal ellipsoids, with the intermolecular hydrogen bonds (dashed lines).

27

Fig 6. The XRD patterns of the MMT-K10 and its hybrid materials.

28

theor etical

Figure 7. The experimental and theoretical IR spectra of [Co(naphophen)(PBu3)(OH2)]+.

29

theor etical

Figure 8. The experimental and theoretical IR spectra of [Co(naphophen)(PPh3)(OH2)]+.

30

Figure 9. The experimental (in ethanol) and theoretical electronic spectra of [Co(naphophen)(PBu3)(OH2)]+. 31

Figure 10. The experimental (in ethanol) and theoretical electronic spectra of [Co(naphophen)(PPh3)(OH2)]+. 32

Fig 11. The SEM images of the K10-CoPPh3 nanohybrid.

Fig 12. The TEM images of the K10-CoPPh3 nanohybrid.

33

Fig 13. The TGA thermogram of the (a) MMT-K10, (b) K10-CoPPh3 nanohybridand (c) K10CoPBu3 nanohybrid.

Fig 14. The DTG thermogram of the (a) MMT-K10, (b) K10-CoPPh3 nanohybridand (c) K10CoPBu3 nanohybrid.

34

Table 1. Crystallographic and structure refinements data for [Co(naphophen)(PBu3)(OH2)]BF4 (A), [Co(naphophen)(PPh3)(OH2)]ClO4 (B). Compound Formula Formula weight Temperature /K Wavelength λ /Å Crystal system Space Group Crystal size /mm3 a /Å b /Å c /Å α /° β /° γ /° Density (calc.) /g cm-1 θ ranges for data collection F(000) Absorption coefficient Index ranges

(A) C40H47BCoF4N2O3P 780.51 100 0.710 Triclinic P1 0.28 × 0.15 × 0.09 11.7629 (5) 11.9816 (5) 14.7570 (7) 71.724 (1) 71.903 (1) 84.918 (1) 1.381 1.5-30.1 816 0.560 -16 ≤ h ≤ 16 -16 ≤ k ≤ 16 -20 ≤ l ≤ 20 Data collected 39862 Unique data (Rint) 10920, (0.035) Parameters, restrains 487, 0 a Final R1, wR2 (Obs. data) 0.0358 , 0.1088 Final R1, wR2a (All data) 0.0476 , 0.0997 2 Goodness of fit on F (S) 1.033 Largest diff peak and hole 0.84, −0.59 /e Å3 a

(B) C46H35ClCoN2O7P 853.11 100 0.710 Triclinic P1 0.41 × 0.26 × 0.21 11.7465 (2) 13.3022 (3) 13.9315 (3) 100.375 (1) 109.775 (1) 102.613 (1) 1.475 1.9-27.6 880 0.616 -15 ≤ h ≤ 15 -17 ≤ k ≤ 17 -18 ≤ l ≤ 18 33632 8840, (0.055) 531, 0 0.0453 , 0.1077 0.0651 , 0.1207 1.036 0.80, −0.62

R1 = Σ||Fo|-|Fc||/Σ|Fo|, wR2 = [Σ(w(Fo2-Fc2)2)/Σw(Fo2)2]1/2

35

Table 2. Selected bond distances (Å) and bond angles (°) for [Co(naphophen)(PBu3)(OH2)]BF4 (A), [Co(naphophen)(PPh3)(OH2)]ClO4 (B).

Bond distances

X-ray

Co1-N1 Co1-N2 Co1-O1 Co1-O2 Co1-O1W Co1-P1 O1-C1 O2-C28 N1-C11 N2-C18 N1-C12 N2-C17 O1W-H1W1 O1W-H2W1 O1B-H1W O2B-H1W O1-H2W O2-H1W F2-H29B O5-H2W Bond angles O2-Co1-N2 O2-Co1-N1 N2-Co1-N1 O2-Co1-O1 N2-Co1-O1 N1-Co1-O1 O2-Co1-O1W N2-Co1-O1W N1-Co1-O1W O1-Co1-O1W N1-Co1-P1 N2-Co1-P1 O1-Co1-P1 O2-Co1-P1 O1W-Co1-P1

1.8830 (12) 1.8790 (12) 1.8843 (10) 1.8686 (10) 2.1193 (11) 2.2216 (4) 1.3082 (16) 1.3030 (16) 1.3092 (18) 1.3096 (17) 1.4217 (18) 1.4207 (17) 0.79 (3) 0.74 (2) 2.058 2.565 2.410 -

(A) M062X/LANL2DZ/ 6-31G(d) 1.84108 1.84615 1.92465 1.93658 2.12449 2.11130 1.29316 1.28939 1.33406 1.33294 1.44425 1.44178 0.99319 0.97859 2.74262 2.09862 -

94.66 (5) 173.67 (5) 86.00 (5) 84.19 (4) 176.13 (5) 94.75 (5) 87.33 (4) 88.01 (5) 86.40 (5) 88.25 (4) 94.73 (4) 93.36 (4) 90.37 (3) 91.52 (3) 178.29 (3)

94.02777 173.16195 89.46542 82.81700 175.17915 94.05333 78.13410 88.80705 96.08735 94.08747 91.81096 99.72058 76.90110 93.38770 168.44120

36

1.878 (2) 1.8825 (19) 1.8760 (15) 1.8726 (16) 2.0983 (17) 2.2434 (7) 1.310 (3) 1.308 (3) 1.312 (3) 1.309 (3) 1.417 (3) 1.420 (3) 0.79 (3) 0.77 (4) 2.004

(B) M062X/LANL2DZ/ 6-31G(d) 1.85002 1.84929 1.92988 1.92341 2.14527 2.14249 1.29520 1.29208 1.33160 1.33034 1.44128 1.44120 0.97914 0.97964 -

94.60 (8) 173.79 (8) 85.73 (8) 85.02 (7) 175.86 (8) 94.21 (8) 86.41 (8) 87.30 (8) 87.41 (8) 88.56 (7) 95.98 (6) 95.31 (6) 88.82 (5) 90.17 (5) 175.86 (6)

93.19430 177.10890 89.47394 83.93234 177.08343 93.38927 95.71080 85.19356 85.61529 95.57117 101.92510 104.77695 74.09269 76.32006 167.39210

X-ray

Table 3. All singlet-singletcalculated excitations of [Co(naphophen)(PBu3)(OH2)]+ using TDDFT method. Exc 1

2 3

4

5 6

7 8

9

10

Composition

E(eV)

H–35 (πSb(C=N-C) + σSb(Ar)) → L+3 (d) (17%) H-34 (πSb(C=N-C) + σSb(Ar)) → L+3 (d) (14%) H–36 (σBu ) → L+3 (d) (12%) H–41 (σBu ) → L+3 (d) (12%) H–33 (σSb ) → L+2 (π*Sb ) (11%) H–33 (σSb ) → L+2 (π*Sb ) (16%) H-1 (dz2 ) → L+2 (π*Sb ) (15%) H–33 (σSb ) → L+3 (d) (16%) H–37 (πSb(Ar)+ σBu ) → L+2 (π*Sb ) (12%) H–35 (πSb(C=N-C) + σSb(Ar)) → L+3 (d) (12%) H–33 (σSb ) → L+3 (d) (16%) H (d) → L+2 (π*Sb ) (14%) H–37 (πSb(Ar)+ σBu ) → L+2 (π*Sb ) (12%) H-1 (dz2 ) → L+3 (d) (12%) H–37 (πSb(Ar)+ σBu ) → L+3 (d??) (10%) H–28 (σBu(C-H)) → L+3 (d??) (10%) H (d) → L (π*Sb ) (50%) H-1 (dz2 ) → L (π*Sb ) (22%) H-1 (dz2 ) → L+1 (σ*P-Co ) (17%) H–37 (πSb(Ar)+ σBu ) → L+2 (π*Sb ) (16%) H-34 (πSb(C=N-C) + σSb(Na)) → L+2 (π*Sb) (13%) H (d) → L+1 (σ*P-Co ) (45%) 2 H-1 (dz ) → L (π*Sb ) (28%) H (d) → L+2 (π*Sb ) (27%) H (d) → L+2 (π*Sb ) (47%) 2 H-1 (dz ) → L (π*Sb ) (25%) H (d) → L+1 (σ*P-Co ) (19%) H-1 (dz2 )→ L (π*Sb ) (33%) H (d) → L+1 (σ*P-Co ) (26%) H (d) → L+3 (d) (21%) H (d) → L (π*Sb ) (20%)

1.6646

Oscillator Strength(f) 0.0021

λtheo (scaled (nm)) 744

λexp (nm) 650

Ass.

LMCT LMCT LMCT LMCT ILCT

1.6709

0.0014

742

1.7811

0.0005

696

LLCT MLCT LMCT ILCT LMCT

2.5683

0.0023

482

517

LMCT MLCT ILCT d-d

2.6396

0.0279

469

LMCT LMCT

2.8113

0.1718

441

MLCT MLCT MLCT

2.9960

0.0004

413

3.1303

0.1780

396

394

ILCT ILCT MLCT MLCT MLCT

3.1877

0.1063

388

MLCT MLCT MLCT

3.4961

0.0015

354

331

MLCT MLCT d-d MLCT

H−1 = HOMO−1, H = HOMO, L = LUMO, L+1 = LUMO +1 etc. Sb = Schiff base, Bu = Butyl, Ar = Aromatic, ILCT= inter-ligand charge transfer; MLCT= metal to ligand charge transfer; LMCT= ligand to metal charge transfer, Exc. = excitation, Ass. = assignment.

37

Table 4. All singlet-singletcalculated excitations of [Co(naphophen)(PPh3)(OH2)]+ using TDDFT method. Exc 1

2 3 4

5

6

7 8

9 10

Composition

E(eV)

H–1 (d) → L+1 (π*Sb) (17%) H-31 (σSb ) → L+1 (π*Sb ) (17%) H-45 (σSb ) → L+1 (π*Sb ) (13%) H–33 (πPh) → L+3 (π*Sb ) (25%) H-44 (σSb ) → L+3 (π*Sb ) (13%) H–28 (σPh ) → L+1 (π*Sb ) (13%) H-31 (σSb ) → L+3 (π*Sb ) (11%) H–1 (d) → L+3 (π*Sb) (12%) H-31 (σSb ) → L+3 (π*Sb ) (12%) H–28 (σPh ) → L+1 (π*Sb ) (11%) H-45 (σSb ) → L+3 (π*Sb ) (11%) H–28 (σPh ) →L+3 (π*Sb ) (15%) H–1 (d) →L+1 (π*Sb) (13%) H-37 (σSb ) →L+3 (π*Sb) (12%) H (d) → L+1 (π*Sb ) (29%) H–33 (πPh ) →L+1 (π*Sb) (20%) H–12 (πPh ) →L+1 (π*Sb) (11%) H (d) → L (π*Sb) (69%) H–1 (d) → L+2 (σ*P-Co) (31%) H (d) → L+1 (π*Sb ) (33%) H–33 (πPh )→L+1 (π*Sb) (14%) H–35 (πPh )→L+1 (π*Sb) (12%) H–1 (d) → L (π*Sb ) (51%) H (d) → L+2 (σ*P-Co ) (49%) H (d) → L+3 (π*Sb ) (29%) H–1 (d) → L+2 (σ*P-Co ) (12%)

1.5068

Oscillator Strength(f) 0.0028

λtheo (scaled (nm)) 822

λexp (nm)

Ass.

MLCT ILCT ILCT

1.5840

0.0007

782

1.6356

0.0013

758

2.4693

0.0034

502

700

LLCT ILCT LLCT ILCT MLCT LLCT LLCT ILCT

2.5411

0.0144

487

512

LLCT MLCT ILCT

2.6399

0.0013

469

MLCT LLCT LLCT

2.8629

0.1689

433

3.1544

0.0111

393

488

MLCT MLCT MLCT LLCT

392 3.1796

0.2349

389

3.5640

0.0135

347

LLCT MLCT MLCT

345

MLCT MLCT

H−1 = HOMO−1, H = HOMO, L = LUMO, L+1 = LUMO +1 etc., Sb = Schiff base, Ph = Phenyl, ILCT= inter-ligand charge transfer; MLCT= metal to ligand charge transfer; LMCT= ligand to metal charge transfer, Exc. = excitation, Ass. = assignment;

38

Immobilization

of

Montmorilonite-K10:

cobalt(III)

Schiff

base

Synthesis,

experimental

complexes and

onto

theoretical

structural determination

Ali Hossein Kianfar2a, Wan Ahmad Kamil Mahmoodb, Mohammad Dinaria, , Hossein Farrokhpoura, Majid Enteshria and Mohammad Hossein Azarianb

a

Department of Chemistry, Isfahan University of Technology, Isfahan, Iran, 84156-83111

b

School of Chemical Sciences, Universiti Sains Malaysia,11800 Minden, Penang, Malaysia

The [Co(naphophen)(PPh3)(OH2)]ClO4 and [Co(naphophen)(PBu3)(OH2)]BF4 complexes were synthesiszed and chracterized by FT-IR, UV-Vis, 1H NMR, 13C NMR spectroscopy and elemental analysis techniques. The coordination geometry of synthezised complexes were determined by X-ray crystallography. The theoretical calculations were also performed to optimize the structure of complexes in the gas phase. The UV-Visible and IR spectra of complexes were calculated. The obtained complexes were incoporated into Montmorillonite-K10 nanoclay via

2

Ali Hossein Kianfar, E-mail: [email protected] ; [email protected]

Tel : +98-31-33913251 Fax : +98-31-33912350

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simple ion-exchange reaction and were identified by FT-IR, XRD, TGA/DTA, SEM and TEM techniques.

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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 and TEM were used for the characterization of these materials
SEM and TEM show the resulting hybrid nanomaterials have layer structures
DFT calculation of the UV-Visible of the complexes

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