Synthesis and Spectral Characterization of Lanthanide Complexes Derived from 2-[(4-Bromo-2,6-Dichloro-Phenylimino)-Methyl]-4,6-Diiodo-Phenol

V. R. Rajewar ¹, M. K. Dharmale² , S. R. Pingalkar¹

¹Department of Chemistry N.E.S.Science College ,Nanded (M.S), India.

²Department of Chemistry Yeshwant Mahavidyalaya ,Nanded (M.S), India.

DOI : http://dx.doi.org/10.13005/ojc/300471

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Article Published : 17 Dec 2014

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ABSTRACT:

The solid complexes of La(III), Pr (III), Tb(III) ,Sm(III) and Nd(III) were prepared from bidentate Schiff base, 2-[(4-bromo-2,6-dichloro-phenylimino)-methyl]-4,6-diiodo-phenol. The Schiff base ligand was synthesized from 3,5 diiodosalicylaldehyde and 4-bromo-2,6-dichlorobenzenamine . These metal complexes were characterized by molar conductivity, magnetic susceptibility, thermal analysis, X-ray diffraction, FTIR, ¹H-NMR and UV-Vis. The analytical data of these metal complexes showed metal:ligand ratio of 1:2 La(III), Pr (III), Tb(III) ,Sm(III) and 1:1 for Nd(III) complexes. The physico-chemical study supports the presence of octahedral geometry around La(III), Pr (III), Tb(III) ,Sm(III) and Nd(III) ions. The IR spectral data reveal that the ligand behaves as bidentate with ON donor atom sequence towards central metal ion. The molar conductance values of metal complexes suggest their electrolyte nature except Nd(III) complex.

The X-ray diffraction data suggest monoclinic crystal system for Pr (III), Nd (III) complexes. Thermal behavior (TG/DTA) shows breakdown of complexes.

KEYWORDS:

Bidentate Schiff base; Metal complexes; Thermal analysis; XRD

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Copy the following to cite this article: Rajewar V. R, Dharmale M. K, Pingalkar S. R. Synthesis and Spectral Characterization of Lanthanide Complexes Derived from 2-[(4-Bromo-2,6-Dichloro-Phenylimino)-Methyl]-4,6-Diiodo-Phenol. Orient J Chem 2014;30(4).

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Introduction

Schiff bases derived from aromatic amines and aldehydes have a wide variety and an important class of ligands in coordination chemistry and find extensive applications in different fields, e.g., biological, inorganic and analytical chemistry ^1.2. Many biologically important Schiff bases have been reported in the literature possessing, antimicrobial, antibacterial, antifungal, anti-inflammatory, antitumor and anti HIV activities ^3.4. Schiff bases play important roles in coordination chemistry as they easily form stable complexes with most transition metal ions ⁵.

The interaction of these donors ligands and metal ions give complexes of different geometries and these complexes are potentially biologically active⁶. Several research papers reported the synthesis and characterization of transition metal complexes of Schiff bases derived from salicylaldehyde^7,8.

Metal complexes with Schiff base ligands containing salicylaldehyde and its derivatives; have been extensively studied. Metal complexes with such ligands are quite common and also reflect their facile synthesis, accessibility of diverse structural modifications and wide applications in different fields, such as catalysis, biological systems and material chemistry^{9, 10}.

Transition metal complexes with Schiff base as ligand have been amongst the widely studied co-ordination compounds in the past few years, since they are found to be widely applicable in many fields such as biochemical, analytical and antimicrobial fields^11-15. It is well known from the literature that much work have been done on the synthesis and characterization of this compounds^16-18 with Schiff base ligand formed from salicylaldehyde or substituted salicylaldehyde and various aromatic amines^19-23.

Salicylic aldehyde is an important intermediate in the manufacture of herbicides  and pesticides.²⁸

Also, salicylaldehyde and its derivatives are used for various reactions for the production of polymers and fibers.

Salicylaldehyde is called 2-hydroxybenzaldehyde and ortho-hydroxy benzaldehyde and is an organic compound with the formula C₇H₆O₂. Part of the class hydroxy aromatic aldehydes, aromatic nucleus contains two functional groups: a hydroxyl and aldehyde one. This colorless liquid has a bitter almond odor at higher concentrations The natural oils found in Spiraea [Filipendula (Spiraea) ulmaria (Rosaceae)].

Sweet-smelling flowers containing salicylaldehyde and methyl salicylate, glycosides form. Was also identified as a component of the characteristic flavor of buckwheat.²⁴ Salicilaldehyde is used as an important intermediate in the chemical industry, in medicine. It is used in perfume, fragrances, dyes, pharmaceuticals, etc.²⁵ Salicylaldehyde and its derivatives can be used as preservatives in cosmetic products, ²⁶ fragrances, essential oils in various biological applications.²⁷  Also get in formulation of perfumes and fragrances.

Experimental

All chemicals and solvents are used AR grade. All the metals were used as their chloride salts. UV spectra recorded on UV-vis spectrophotometer 119. Conductance or metal complex was determined in DMSO on conductivity meter quiptronics model NO-EQ665. Melting points were recorded on in recorded by open capillary method and are uncorreded. H¹-NMR spectra or a Schiff base and its metal complex recorded on Brukcer 300 MHz spectrometer in DMSO. Elemental analysis was carried out on Eager 350 analyser. Magnetic measurement were done on solid complexes using Guoy method. Powder XRD pattern of complexes are recorded Philips Analytical XRD B.V. at CFC Shivaji University Kolhapur.

Synthesis of Ligand

Synthesis of 2-[(4-Bromo-2,6-Dichloro-Phenylimino)-Methyl]-4,6-Diiodo-Phenol (BDPDP) Schiff Base

Schiff base ligand were synthesized by refluxing of 3,5 diiodosalicylaldehyde (0.01M)  and 4-bromo-2,6-dichlorobenzenamine (0.01 M) in 50m1 ethanol on water bath for 4-5 hours in presence of 2-3 drops of glacial acetic acid. The reaction mixture was kept for overnight, where yellow color precipitate was obtained. It was filtered by whatmann paper, washed with distilled water then alcohol, dried in vacuum dessicator. Pure Schiff base was recrystallized from ethanol. The purity of ligand was checked by TLC.

Scheme 1 Click here to View scheme

Synthesis of Metal Complexes

The ethanolic solution of Metal chloride (0.01M) was added to hot ethanolic solution of BDPDP (0.02 M) La(III), Pr (III), Tb(III) ,Sm(III) and (0.01 M) in  Nd(III) complexes drop wise with constant stirring. PH of the reaction mixture was adjusted to 7 -7.2 with alcoholic ammonia solution. Resulting reaction mixture refluxed for 5 to 6 hours on water bath.

Colored complexes was allowed to digest and collected by filtration. Then washed with sufficient quantity of distilled water and little hot ethanol to apparent dryness and dried in vacuum desiccators.

Results and Discussion

Physical and Analytical Parameters

Empirical formulae of the complexes were deduced on the basis of elemental analysis, metal ligand ratio and thermal analysis (table No. 1.1 and 1.2). Complexes possess different colors, metal complexes of ligand BDPDP are insoluble in common organic solvents, dissolve freely in DMSO/DMF High melting points of complexes suggest that complexes are stable at normal temperatures²⁹. Molar conductivity (lm 71 to 82 W^-1cm²mol^-l) reveals electrolytic nature of the complexes³⁰ except Neodymium metal ion complex (lm 14W^-1 cm²mol^-l) reveals   nonelectrolytic nature of the complex.(table 1.1).

Table 1.1: Physical and analytical data of BDPDP metal complexes.

Table 1.2: Percent C, H, N,O and metal ion in BDPDP metal complexes.

Electronic Spectra

Plots of  UV-Visible spectra of ligand BDPDP and its metal complexes were recorded on UV-Visible spectrophotometer 119-Pc based instrument are presented in figure 6.1, 6.2, 6.3 , 6.4,6.5 and 6.6. Ligand (BDPDP) shows strong absorption band at 34160 cm^-1 assigned for  π – π*  transition. Absorption bands and corresponding transition are given in the table No. 1.3.

Table 1.3: Electronic spectral data of BDPDP complexes.

The UV electronic spectra of La(III), Pr (III), Nd(III), Tb(III) and Sm(III)complexes  have indicates absorption bands at 23201 cm^-1, 23201 cm^-1, 23201 cm^-1,23310 cm^-1 and 23310 cm^-1 assigned as charge transfer^31,32.

Infrared Spectra

Determination of coordinating atoms in the complex is made on the basis of comparison of IR spectra of the ligand and their metal complexes. Significant changes in wave numbers of the coordinating atoms involved in coordination are summarized in the table No. 1.4.

IR Spectral Study of BDPDP Ligand 

Ligand BDPDP contains phenolic –OH and azomethine  group. In spectra of ligand exhibits strong n (O-H) stretching at 3447 cm^-1, corresponding to n (OH) of phenol. The band at 1204cm^-1 is due to presence of n (C-O) group. It also indicate n (C=N) stretching frequency at 1616cm^-1. On complexation significant changes in wave numbers are observed.

IR Spectral Study of La(III) Complex

The IR spectra of  Metal complexes   is compared with IR spectra of ligand (BDPDP), there are certain shifts in the bands. In complex deprotonation of —OH in phenolic group and indicating involvement of phenolic group in coordination ³³. The band stretching vibration in ligand due to phenolic n(OH) group observed at 3447cm^-1, Which is disappear in complex.

Besides, ligand exhibits stretching of  n (C=N) stretching at 1616cm^-1 which on complexation  shifted to lower wave number at 1596-1631cm^-1suggesting that azomethine  nitrogen are involved in coordination^{34′ 35} .A new broad  band at 3134-3477cm^-1 suggested  the presence of coordinated water molecule³⁶.

The appearance of new bands in the spectra of metal ion complex at 432-441cm^-1 and 505-520 cm^-1 due to new bonding i.e. n (M-N) and n (M- O)^37,38.

Thus the ligand BDPDP exhibits uninegative bidentate behaviour and coordinates to the metal ion through azomethine  nitrogen and phenoxide oxygen for La(III), Pr (III), Tb(III) and Sm(III)complexes, Nd(III) complex behave neutral in nature.

Table No 1.4  Infrared spectral data of the ligand (DPMDI) and their La(III), Pr (III), Nd(III), Tb(III) and Sm(III) metal complexes

¹HNMR Spectra

¹H NMR spectral studies of ligand BDPDP indicated signals at d 6.9- 7.2 ppm corresponding to aromatic protons (m, 4H, Ar-H) and at d 7.9 ppm due to azomethine group  (CH=N). A strong signal at d 13.3 ppm assignable (S, 1H) due to phenolic OH group (fig. 1.1).

In the metal complex signal corresponding to phenolic OH group at d 13.3 ppm has disappeared^39-41 (fig.1.2) may be attributed to deprotonation of —OH group on involvement of via -OH in bonding. A new peak due to presence of coordinated water at d 2.5 ppm is observed in  metal complex⁴² .The shift in azomethine group from d 7.9 ppm to d 9.6 ppm indicate coordination through water molucule  azomethine group.

Thus, BDPDP.molecule seems to be coordinated to the metal through phenoxide  oxygen  and azomethine group  in  Pr (III) metal  complex.

Figure6.13: 1H NMR ligand BDPDP    Click here to View figure

Figure1.2: 1H NMR Metal complex  Click here to View figure

Thermal Study

Nd(III), Pr(III) and Tb(III) complexes were studied by therrnogravimetric analysis from ambident temperature to 1000°C in nitrogen atomosphere.   The range of temperature, experimental and calculated mass losses of the decomposition reaction are given in the table No. 1.5. TGA/DSC scans are depicted in figures 1.3, 1.4 and 1.5.

Thermal Study of [Tb(L)₂2H₂O]Cl

The thermogram of Tb(III) complex shows weight loss 2.44% corresponding to two coordinated  water molecule in the range from room temperature to 140°C. Decomposition reaction corresponds to an experimental mass  2.42 % occurs in the temperature range 140°C- 280°C attributed loss of  one lattice chlorine ^43. part of the complex.

In the temperature range 280°C-310°C Four iodine part is lost and this loss corresponds to 38.04%. As the temperature increases to 310-600°C there is of 18.16 % indicating loss of four chloride,two bromine , part of metal complex. From 600-800⁰C loss of organic moiety which is 28.12 %.Finally 800°C-1000°C residue is obtained corresponding to Tb₂O₃ as stable residue ⁴⁴ 12.44%.

Thermal Study of [Pr(L)₂2H₂O]Cl

The TGA of Pr(III) complex indicates loss in weight in the range from room temperature to 160°C corresponding to 2.32 % indicates the loss of coordinated water-molecule.

Decomposition beyond this temperature in the range 160°C -390°C corresponds to mass loss of  61.32 % in the TG curve assigned to expulsion of one lattice chloride molecules four iodine, four chloride ,  two bromine   part of the complex. The decomposition occurs in the temperature 390°C -800°C indicates the loss of Organic Moiety  27.68 %. Further at 800°C-1000°C losses of 11.87 % were occurs indicating  presence of thermally stable residual metal oxide⁴⁵.

Thermal Study of [Nd(L)₁2H₂O2Cl]

TGA of Nd (III) complex shows weight loss corresponding to mass loss 4.25 %. This loss corresponds to loss of coordinated water molecule in the range from room temperature to 160°C⁴⁶. Further decomposition at 160°C-430°Closs of 36.71 % was occurs indicating loss of Two iodine, One bromine  of the complex. From 430-800⁰C loss of four chlorine , Organic moiety which is  33.64 %.The end product of decomposition is formation of Nd₂O₃ weight corresponds to 19.58 percent which is equal to theoretical value 20.09.

Table-1.5 Thermal Analysis data for metal complexes

Figure1.3: TG/DSC [Tb(L)22H2O]Cl   Click here to View figure

Figure1.4: TG/DSC [Nd(L)12H2O2Cl]   Click here to View figure

Figure1.5: TG/DSC  [Pr(L)22H2O]Cl     Click here to View figure

Powder X-Ray Studies

X-ray diffractograms of the metal complexes were recorded in the 2q range from 10-90° at a wave length of  1.5405 A°and using Cu Ka radiation source. Results of miller indices, lattice parameters and unit cell volume are computed from programmer. Data has been summarized in the following tables.

[Nd(L)₁2H₂O2Cl]

Crystal system:  Monoclinic  Lattice Type: P

Lattice Parameter:  a= 9.53034  b= 8.00951  c=  7.79302   A⁰

Lattice Parameter: Alpha= 90.000  Beta= 121.572   Gama=90.000

Figure 1 Click here to View figure

The cell data and crystal parameters of [Nd(L)₁2H₂O2Cl]  complex is given in the tables indicates that complex have monoclinic crystal system⁴⁷, with lattice type-P.

[Pr(L)₂2H₂O]Cl

Crystal system:  Monoclinic  Lattice Type: P

Lattice Parameter:  a= 19.06907  b= 4.64343  c=  7.04556 A⁰

Lattice Parameter: Alpha= 90.000  Beta= 108.476   Gama=90.000

Figure 2 Click here to View figure

Cell data and crystal lattice parameters of  [Pr(L)₂2H₂O]Cl  complex attributed to monoclinic crystal system⁴⁸, with lattice type-P.

Proposed Structures of the Chelates

Based on above result probable structure have been proposed

Figure 3 Click here to View figure

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