View of METAL COMPLEXES OF 1-BENZOYL-1-CYANOETHYLENE-2, 2-DITHIOLATE LIGAND – SYNTHESIS AND CHARACTERIZATION

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ACCENT JOURNAL OF ECONOMICS ECOLOGY & ENGINEERING

Peer Reviewed and Refereed Journal IMPACT FACTOR: 2.104 (INTERNATIONAL JOURNAL) UGC APPROVED NO. 48767, (ISSN NO. 2456-1037)

Vol. 03, Issue 07,July2018 Available Online: www.ajeee.co.in/index.php/AJEEE

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METAL COMPLEXES OF 1-BENZOYL-1-CYANOETHYLENE-2, 2-DITHIOLATE LIGAND – SYNTHESIS AND CHARACTERIZATION

Akhilesh Prasad

Department of Chemistry, Faculty of Science, Shri Murli Manohar Town PG College, Ballia – 277001(UP)

Abstract - Bimetallic complexes [MM´(bcd)2] [M = Cu⁺; M´ = Ni²⁺; M = Fe³⁺; M´ = Cu⁺; bcd^2- = 1-benzoyl-1-cyanoethylene-2,dithiolate^2- and their I2-doped products have been synthesized and characterized using various spectroscopic techniques, magnetic and solid-state electrical conductivity technique. Their I2-doped products show behavior of semi- conductivity in the 303-523 K temperature range.

1 INTRODUCTION

A bimetallic coordination polymers of the type [MM΄(bcd)2] [M = Cu⁺; M´ = Ni²⁺; M = Fe³⁺; M´ = Cu; 1-benzoyl-1- cyanoethylene-2,dithiolate^2- (bcd^2-)have been synthesized and have been characterized by elemental analyses,

magnetic susceptibility, IR and UV-visible spectroscopies and the solid-

state electrical conductivity technique.

The solid-state electrical conductivities, σrt, ~ 10^-12S cm^-1is measured at room temperature and increase in conductivity with increase in temperature in the 303 – 523 K range with activation energies, Ea

= 0.20 – 0.68 eV show semiconducting properties of [FeCu(bcd)2]. The conductivity of I2-doped products of the complexes are increased in 10-10² order of magnitude and show the behavior of semiconductors over the given temperature range.

The coordination polymers involving heterometals with different electronic properties and with N, S based ligands have attracted considerable attention not because of their structural diversities but also for their interesting electrical and magnetic properties.^1-7This ligand has a potential as a rubber vulcanization accelerator.⁸The literature^{5, 10-14} contains limited examples of the heterobimetallic complexes of the ligand bcd^2-, which show diversified coordination patterns with transition metal ions.

Keeping this pointin mind, the interesting molecular conducting and magnetic^15, ¹⁶ properties of the monometallic and bimetallic complexes of sulfur and nitrogen containing ligands such as thiocyanate (SCN^-)^{17, 18} and 1,1- as well as 1,2- dithioligands,^19-21 herein we report the synthesis, characterization and electrical properties of the heterobimetallic complexes formed with

the ligand 1-benzoyl-1-cyanoethylene- 2,dithiolate^2- and the metal ions Ni²⁺,Fe³⁺, and Cu⁺. An important aspect of undertaking the present work is that the ligand bcd^2- having an additional sulfur atom in the heterocyclic ring which is normally not associated in bonding with the metal ions may induce substantial S…S/M…S intermolecular stacking, an important prerequisite for the higher conductivities of the complexes.

2 EXPERIMENTAL SECTION

2.1 Materials and General Procedures All the experiments were carried out in open atmosphere without eliminating moisture and oxygen from the reaction chamber because the ligand and the starting metal salts are stable in aqueous medium. All the reagents used were commercially available and used without further purification. Sodium benzoylacetonitrile was prepared according to reported literature¹⁵ by treating an ethanolic solution of benzoylacetonitrile with stoichiometric amount of sodium hydroxide in absolute ethanol. The sodium 1-benzoyl-1- cyanoethylene-2,2-dithiolate (Na2bcd) was preparedin situ by adding CS2 (1.5 mL, ~ 2 mmol) to a stirring solution of sodium benzoylacetonitrile (0.38 g, 2 mmol) in 20 mL DMSO. The colour of the reaction mixture rapidly changed from yellow to red. Red solution of Na2bcd thus obtained was used for the preparation of the complexes.Elemental analysis (C H N) was performed on a Carlo Erba 1108 element analyzer at CDRI, Lucknow. The compounds were decomposed by aqua- regia and the metals, nickel as dimethylglyoximate, copper as cuprous thiocyanate and iron as oxinate were determined gravimetrically following

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2 standard procedures.²² Sulfur was determined as BaSO4. The experimental details dealing with the magnetic susceptibility and pressed pellet electrical conductivity measurements and recording of IR spectra (4000-400 cm^-1) as KBr disc were the same as described earlier. The FAR-IR spectra were obtained with a Varian 3500 FT IR, the sample was grounded and compacted as polyethylene disc. The electronic spectra of the complexes in Nujol mulls spread on the filter paper strip were recorded on a

Shimadzu 1700 UV-Visible

spectrophotometer.^12-13

2.2 Preparation of Heterobimetallic Complexes [MM΄(bcd)2] [M = Ni²⁺, Fe³⁺; M΄ = Cu⁺ ]

The heterobimetallic complexes were prepared according to the following general procedures by a single-pot reaction at room temperature. To a 25 mL ethanol-water (90:10, v/v) stirring solution containing a mixture of two different metal salts i.e. Ni(NO3)2.6H2O (0.29 g, 1.0 mmol); Cu(NO3)2.3H2O (0.48 g, 2.0 mmol) and Cu(NO3)2.3H2O (0.24 g, 1.0 mmol) and (NH4)2Fe(SO4)2.6H2O (0.39 g, 1.0 mmol) was added gradually a 25 mL solution of Na2bcd (1.08g, 2.0 mmol) in the same solvent mixture. In each case, colored precipitate immediately formed and the mixture was left to stir for 4 days.

The resulting precipitates were suction filtered and washed two times with 5 mL portion of ethanol-water mixture followed by two times with 2.5 mL portion of diethyl ether and driedinvacuo over CaCl2. Analytical data and general properties of complexes are listed in table 1.

2.3 Techniques of I2-doping of the Complexes

I2-doped products of the bimetallic complexes were isolated by placing 1 g iodine and about 200 mg of each complex separately in the petridishes in a closed chamber/desiccator. The I2 vapor was exposed for 7 days and the dark brown I2- doped products obtained were dried in vacuo. Elemental analyses of the I2-doped products do not correspond to any definite stoichiometry of the complexes but are reproducible. The IR and UV- visible spectra of the I2-doped products feature almost similar to the parent mixed-ligand heterobimetallic complexes

suggesting that the complexes do not decomposed on exposure of iodine vapors instead a little chemical reactions occurred rather than the absorption of iodine.

3 RESULTS AND DISCUSSION

The reaction is carried out by the reaction between metal salt and sodium salt of the ligand in 1:2 molar equivalent in EtOH- H2O heterobimetallic complexes [MM(bcd)2] were obtained in high yield according to the following equations:

1. C6H5COCH2CN + 2NaOH

 

^Ethanol

  

Na2C6H5COCCN + 2H2O

2. Na2C6H5COCCN + CS2

 

^Ethanol

  

Na2C6H5CO(CN)C2S2 (Na2bcd)

3. 2Na2bcd +M′X2

 

^Ethanol

  

Na2

[M′(bcd)2] + 2NaX

4. Na2[M′(bcd)2] +MX2

 

^Ethanol

  

[MM′(bcd)2] + 2NaX

M = Ni(II), Fe(III); M′ = Cu(II);

bcd^2-= 1-benzoyl-1-cyanoethylene-2,2- dithiolate.

All the complexes are stable in air and decompose in the 180 - 300 ^oC temperature range. Elemental analyses for all the complexes are in good agreement with the calculated values of their assigned formulae. These are insoluble in water, ethanol, methanol, dichloromethane, benzene, DMSO and DMF indicating their polymeric nature.

Insolubility prevented their solution conductivity measurements, recording of UV spectra in solution and growing of the single crystals for structural elucidation.

3.1 IR, Magnetic Moment, and Electronic Absorption Spectra

The IR spectra of the complexes show intense IR absorptions characteristic of the ligand bcd^2- and NBu4n group near 2900, 2200,1600, 1450 and 1000 cm^-1 assigned to (C-H), (C≡N), (C=O),

(C=CS2) and (C-S) consistent with (S, S) bidentate/ binucleating-bridging behavior of ligand bcd^2- in the complex salt (NBu4n)2[Cu(bcd)2] and heterobimetallic complexes [MM′(bcd)2] (Fig. 3). The occurrence of strong bands near 2200 and 1600 cm^-1 invariably in all the complexes clearly suggests non- involvement of (C≡N) and C═O groups in coordination.

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3

N C C C O Ph

C S

S C N

C C O

Ph C

S S M^'

2-

[M'(bcd)]^2-

Fig. 1 Bonding behavior of the ligand bcd^2- in the complexes

Theeff= 2.23 µB is indicative of low spin diamagnetic square planar environment²⁵ about nickel(II) in the bimetallic complex [CuNi(bcd)2. The UV- visible spectrum of this complex shows three absorption bands at 450, 620 and 740 nm which may be arising from MLCT and d-d transitions for the square planar coordination about Ni(II)²⁶. Its electronic absorption spectrum displays medium absorption bands at 420, 600 and 720 nm. Since all ligands are similar, there is no change in the ligand field strength. The low energy bands may be ascribed for the higher energy band for the tetrahedral coordination about copper(I).²⁶ Diamagnetism together with the electronic absorption bands at 350, 400, 460, 500 and 660 nm show square planar coordination geometry about Ni(II) in [NiCu2(bcd)2] and tetrahedral geometry around copper(I). The μeff= 4.71 µBfor [FeCu(bcd)2] is in between the spin only value for S = 3/2and S = 5/2 (Fe(III), 3d⁵) suggesting coupling between spin and orbital angular momentum for the d electrons. Departures from the spin only magnetic moment are expected for 3d⁵ complexes. All transitions in the high spin Fe(III), complexes are spin forbidden which results generally weak bands.

Somewhat larger band intensity of this acentric complex may be the result of larger metal-lig and bond covalency. UV- visible spectrum of this complex shows two absorptions at 440 nm and 850 nm assignable to spin forbidden transition following high spin distorted octahedral coordination^26-28, about Fe(III). Very low intensity d-d absorptions are often obscured by the strong lig and to metal charge transfer bands because of the high oxidizing power of Fe(III) complexes.

In the light of above studies and based on the known structures,^10,11 the polymeric structures for the

heterobimetallic complexes where metal ions Ni(II)possess square planar, Fe(III) octahedral and Cu(I) tetrahedral geometries in these complexes (Fig. 3).

3.2 Electrical Conductivity

Metal chalcogen rich complexes exhibit higher electrical conductivities because of the dominant S…S / M…S intermolecular stacking and extended delocalized networks as well as partial oxidation- reduction of the complexes. The oxidized species exhibit appreciably increased electrical conductivities which are due to the formation of electron conduction pathways through more extended S…S molecular contacts caused by the ligand centered oxidation. All complexes exhibit room temperature conductivity,



rt(303 K)

~ 10^-12 S cm^-1.[FeCu(bcd)2] show the behavior of semiconductors as their conductivity increase progressively with increasing temperature. The activation energies of the order ~ 0.20 eV obtained from the slopes indicate small band gaps for these compounds. A remarkable increase in the conductivity i.e. 3 orders of magnitude at higher temperature for [FeCu(bcd)2] may be ascribed to its having different packing/stacking arrangement of the molecules where charge carriers have increasing difficulties at lower temperature to cross the non-conducting barriers. The thermal energy activates the charge-carriers and increases their nobilities. Somewhat higher activation energy ~ 0.68 eV with larger slope for this complex may be attributed to the preferred octahedral and tetrahedral environment about Fe(III) and Cu(I).

[NiCu2(bcd)2] insulator in the considered temperature range. In the case of paramagnetic complex [FeCu(bcd)2] the unpaired electrons seem not to exhibit important role in the conduction mechanism All of the I2-doped products exhibit semiconducting behavior in the considered temperature range.

4 CONCLUSIONS

The ligand 1-benzoyl-1-cyanoethylene-2, dithiolate^2- bridged heterometallic coordination polymers [MM(bcd)4] have been synthesized and their electrical, magnetic and spectral properties studied.

The electrical conductivities study show that the bimetallic complexes

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4 [FeCu(bzta)4] exhibit semiconducting behavior.

C C S C S C N

O Ph C C

S C S C N

O Ph

C C S S

C C N

O Ph Ni

C C S C S C N

O Ph

C C S S

C C N

O Ph Ni

Cu

_C _C

S

S C

C N O

Ph

Fe

S

Cu

S

[CuNi(bcd)

₂

] [FeCu(bcd)

₂

]

Fig. 2 Proposed structure of the complexes

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