Synthesis, Characterization and Thermal Decomposition Studies of Cr

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ISSN: 0973-4945; CODEN ECJHAO E-Journal of Chemistry 2009, 6(2), 449-458

Synthesis, Characterization and Thermal Decomposition Studies of Cr(III), Mn(II) and Fe(III) Complexes of N, N'-Bis[1,3-benzodioxol-5ylmethylene]butane-1,4-diamine PRASAD M. ALEX* and K. K. ARAVINDAKSHAN *

Department of Chemistry, Marthoma College, Chungathara, Nilambur, Kerala-679334, India. Department of Chemistry, University of Calicut, Kerala, India. [email protected]

Received 19 September 2008; Accepted 10 October 2008 Abstract: A bidentate Schiff base ligand namely, N,N'-bis-1,3-benzodioxol-5ylmethylene]butane-1,4-diamine was synthesised by condensing piperonal (3,4dioxymethylenebenzaldehyde) with butane-1,4-diamine. Cr(III), Mn(II), Fe(III) complexes of this chelating ligand were synthesised using acetates, chlorides, bromides, nitrates and perchlorates of these metals. The ligand and the complexes were characterised by elemental analysis, 1H NMR, UV-Vis and IR spectra, conductance and magnetic susceptibility measurements and thermogravimetric analysis. The thermograms of three complexes were analysed and the kinetic parameters for the different stages of decompositions were determined. Keywords; Schiff base, Diamine, Piperonal, Transition metal complexes, Thermal decomposition.

Introduction The chelating Schiff base ligands derived from diamines and various carbonyl compounds, encompass a highly remarkable class of compounds having a wide range of applications in catalytic1, synthetic2, analytical3,4, clinical5 and biochemical6 areas and they possess considerable physiological activities7,8. Schiff base derivatives of 1,4-butanediamine and their metal complexes, also find a number of catalytic9, and biological10 applications. A perusal of earlier work revealed that the coordinating possibility of 1,4-butanediamine is enhanced by condensing with a variety of carbonyl compounds11-13. But the literature survey showed that no work has been done on the transition metal complexes of the Schiff base derived from

450

PRASAD M. ALEX et al.

1,4-butanediamine and piperonaldehyde. Therefore, a new Schiff base ligand derived from piperonal and 1,4-butanediamine and its transition metal complexes were synthesised and characterised. The ligand named as N,N'-bis-1,3-benzodioxol-5-ylmethylene]butane-1,4diamine (L) has two donor sites, two nitrogen atoms as azomethine groups (Figure 1). The use of piperonal as the carbonyl compound in these studies owed to the fact that several compounds containing the 3,4-methylenedioxy group possessed various biological activities14-16. Complexes of Cr(III), Mn(II) and Fe(III) were synthesised using acetates, chlorides, bromides, nitrates and perchlorates of these metals. Investigations on thermal decomposition behaviour of some of these complexes were also done. N O

Figure 1.

N O

N,N'-Bis-1,3-benzodioxol-5-ylmethylene]butane-1,4-diamine(L).

Experimental All chemicals viz. piperonaldehyde, butane-1,4-diamine, metal salts, solvents etc., used were of A R grade (E. Merck or B D H). Carbon, hydrogen and nitrogen analyses were carried out by using Hitachi CHN-O rapid analyzer at CDRI, Lucknow. The anions present in complexes were estimated by standard methods17. 1H NMR spectra of the ligand was recorded on a Varien-300 nuclear magnetic resonance instrument using DMSO-d6 as solvent. Infrared spectra were measured in the range 4000-400 cm-1 on a Schimadzu FTIR-8101 spectrophotometer with KBr pellets. The solid state electronic spectra of complexes were recorded using a Schimadzu UV1601 spectrophotometer. The magnetic measurements were made at room temperature by the Gouy method using Hg[Co(NCS)4] as calibrant. The thermal decomposition behaviours of complexes were monitored using a Perkin Elmer TGA-7 Analyser.

Synthesis of the ligand and complexes 1,4-Butanediamine (20 m mol, 176 mg) solution in ethanol (50 mL) was mixed with a solution of piperonaldehyde (40 m mol, 604 mg) in ethanol (50 mL) in 1:2 molar ratio and was refluxed for about 1 h and then cooled. The white precipitate formed was filtered off, washed with water and a few ml of alcohol and then purified by recrystallising from ethanol (yield = 678 mg, 87%). Complexes of Cr(III), Mn(II) and Fe(III) with this ligand were synthesised using acetate, chloride, bromide, nitrate and perchlorate salts of these metals. Solutions of the ligand and metal salts in methanol (10 m mol in 50 mL) (1:1 molar ratio) were refluxed for 2 to 3 h. Metal acetates were dissolved in methanol-water mixture and added to refluxing solutions of the ligand in methanol. The complexes, synthesised using metal chlorides, precipitated during refluxing and were filtered off. In other cases, the reaction mixtures were concentrated and the pasty mass obtained in each case was repeatedly washed with diethyl ether and/or petroleum ether and/or acetone to get the solid complexes separated. The complexes were filtered, washed with suitable solvents and then dried over anhydrous CaCl2.

Results and Discussion Characterisation of ligand In this paper we designed and synthesized a bidentate/tetrdentate Schiff base ligand, N,N'-bis-1,3-benzodioxol-5-ylmethylene]butane-1,4-diamine (L) by the condensation of

Synthesis, Characterisation and Thermal Decomposition Studies

451

1,4-butanediamine with piperonal. The IH NMR spectrum of the ligand, was recorded in DMSO-d6 and it showed a number of characteristic signals of the compound18. The peak observed at a δ value of 8.01 ppm was assigned to the azomethine protons in the molecule. The signals due to the aromatic protons were observed in the range 7.30-6.83 ppm. The singlet peak at 5.96 ppm was assigned to the methylinic protons of the dioxymethylene groups of the piperonal moieties present in the ligand. The inductive effect of the two oxygen atoms deshielded the methylenic protons and this resulted in the higher δ value for these protons. The peaks in the ranges of 3.71-3.65and 1.95-1.91 ppm were assigned to the methylinic protons of the butanediamine moiety of the ligand. The IR spectrum of the ligand showed bands at 3050 and 2983 cm-1 assigned to the C-H stretching of aromatic and methylene groups, respectively. The bands present at 1640 and 1255 cm–1 were assigned to the C=N and C-N stretchings, respectively19. Bands at 1191 and 1099 cm–1 were assigned to the in plane bending of the aromatic C-H and those at 872 and 816 cm–1 to the out of plane bending vibration of the aromatic C-H. The characteristic absorption frequency of the dioxymethylene group of piperonal moiety20 was present at 926 cm–1. The absence of the characteristic stretching frequency of C=O of the aromatic aldehyde group19, indicated that the condensation was complete. The elemental analysis and spectral data for L are consistent with the formula C20H20O4N2 and the structure given in Figure 1.

Formulae and general properties of complexes The reaction of the ligand (L) with different salts of Cr(III), Mn(II) and Fe(III), ions in 1:1 molar ratios gave metal complexes of the given formulae, as evidenced by the micro analytical and spectral data. 1 [MLA3(H2O)], where, M = Cr(III) or Fe(III) and A- = CH3COO-, Cl-, Br-, NO3-or ClO42 [MLA2(H2O)2], where, M = Mn(II) and A- = CH3COO-, Cl-, Br- or ClO43 [ML(H2O)4]( NO3)2 , where, M = Mn(II) The colours, magnetic susceptibilities and molar conductivities and melting points and the micro analytical data of the complexes are listed in Table 1. These air stable metal complexes were non hygroscopic, partially soluble in most organic solvents, but freely soluble in DMF and DMSO. The molar conductivities in DMF (10–3 M) solution showed that all the complexes except one behaved as nonelectrolytes, indicating the coordinated nature of the anions, while the nitrato complex of Mn(II) behaved as a 1:2 electrolyte21.

IR spectra of complexes Table 2 lists the most important IR spectral bands of the ligand and metal complexes. In the spectra of all the complexes the ν(C=N) was shifted to lower frequency, due to its involvement in coordination. Instead of the band at 1640 cm–1 present in the spectrum of the free ligand, new bands appeared in the ranges of 1608-1598, 1604-1591 and 1624-1599 cm–1 in the Cr(III), Mn(II) and Fe(III) complexes, respectively and were assigned to the coordinated azomethine groups22-24. The characteristic absorption frequency of the dioxymethylyne group was found to be present in the spectra of all the complexes at the same frequency as it was observed in the ligand spectrum. This indicated the non-involvement of dioxymethylene groups in coordination in these complexes20.

Pale yellow Pale brown Brown Pale brown Brown Pale brown Pale brown Brown Pale brown Brown Pale brown Orange Orange Orange Orange Orange

87 77 62 69 71 66 75 67 71 68 70 71 65 69 72 73

172 271 278 >300 >300 >300 252 268 272 284 >300 >300 >300 >300 292 >300

µ eff B.M

M.P oC

C20H20O4N2(L) [CrL(AcO)3(H20)]* [CrLCl3(H20)] [CrLBr3(H20)] [CrL(NO3)3(H20)] [CrL(ClO4)3(H2O)] [MnL(AcO)2(H2O)2]* [MnLCl2(H2O)2] [MnLBr2(H2O)2] [MnL(H2O)4](NO3)2 [MnL(ClO4)2(H2O)2] [FeL(AcO)3(H20)]* [FeLCl3(H20)] [FeLBr3(H20)] [FeL(NO3)3(H20)] [FeL(ClO4)3(H20)]

Colour

3.76 3.78 3.79 3.83 3.81 5.79 5.93 6.14 5.98 5.92 6.13 4.98 6.09 6.16 5.98

4.62 14.64 28.24 49.86 48.24 16.32 6.84 15.58 149.86 32.42 11.24 9.78 24.92 31. 86 26.92 *

Microanalytical data, % Found (calculated) Metal

9.12 (8.68) 10.24 (9.84) 8.16 (7.85) 8.82 (8.55) 7.58 (7.22) 10.22 (9.80) 11.1 (10.7) 9.84 (9.12) 9.92 (9.12) 9.06 (8.57) 9.81 (9.26) 10.9 (10.5) 8.71 (8.39) 9.64 (9.13) 8.01 (7.84)

AcO = CH3-COO-

C 68.3 (68.2) 50.8 (52.1) 44.1 (45.4) 35.64 (36.3) 38.4 (39.5) 32.2 (33.3) 50.1 (51.3) 45.5 (46.7) 38.9 (39.8) 38.8 (39.8) 36.6 (37.4) 50.4 (51.8) 43.9 (45.1) 35.1 (36.0) 38.3 (39.2) 32.6 (33.7)

H

N

Anion

5.62 (5.68) 7.89 (7.95) 4.89 (5.18) 4.52 (4.67) 4.02 (4.16) 5.19 (5.30) 20.9 (20.2) 3.16 (3.32) 4.12 (4.23) 37.4 (36.3) 3.48 (3.62) 11.7 (11.5) 2.94 (3.05) 3.76 (3.89) 42.6 (41.4) 4.12 (5.35) 4.74 (4.99) 4.51 (4.67) 5.23 (5.45) 14.1 (13.8) 3.88 (3.98) 4.57 (4.64) 27.1 (26.5) 4.56 (4.64) 9.16 (9.29) 3.52 (3.74) 4.24 (4.36) 31.8 (31.0) 4.99 (5.14) 4.48 (4.65) 4.01 (4.13) 5.18 (5.26) 20.7 (20.0) 2.95 (3.30) 4.13 (4.21) 36.9 (36.0) 3.48 (3.60) 11.12 (11.44) 3.02 (3.09) 3.89 (3.93) 42.98 (42.22)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Compound

Λm ohm-1 cm2mol-1

452

No

Yield, %

Table 1. Formulae, general properties and micro analytical data of ligand and complexes

No.

Compound

3

1 2 3 4

C20H20O4N2(L) [CrL(AcO)3(H20)]* [CrLCl3(H20)] [CrLBr3(H20)]

3429b 3408b 3401b

964m 962m 958m

641w 639w 635w

1640s 1597m 1608m 1599s

5

[CrL(NO3)3(H20)]

3402b

956m

637w

1596m

6

[CrL(ClO4)3(H2O)]

3414b

962m

638w

1605m

*

7 8 9 10

[MnL(AcO)2(H2O)2] [MnLCl2(H2O)2] [MnLBr2(H2O)2] [MnL(H2O)4](NO3)2

3393b 3417b 3403b 3389b

959m 962m 958m 963m

634w 637w 641w 639w

1599m 1601m 1604s 1591w

11

[MnL(ClO4)2(H2O)2] 3419b

961m

634w

1598m

*

12 13 14 15

[FeL(AcO)3(H20)] [FeLCl3(H20)] [FeLBr3(H20)] [FeL(NO3)3(H20)]

3405b 3389b 3411b 3398b

963m 958m 962m 961m

635w 638w 634w 642w

1624m 1599m 1622s 1612m

16

[FeL(ClO4)3(H20)]

3419b

957m

637w

1625m

1588m, 1426w 1432m,1358w 1044sh 1121m,1042w 948w 1592w,1443m 1385s 1115m,1084w 942w 1602m,1439w 1441w,1039w 1117m,1046w 939w

927m 928m 928m 927w

543m 472w 548w 458w 573w 474m

927m

568w 456m

927w

542m 458m

928m 927m 928m 927w

612m 609w 611w 605w

927w

601m 518m

928m 927w 928m 927m

532w 528m 524w 538w

928w

529w 452m

524w 526m 522w 519m

475m 464w 448w 476m


Table 2. Significant IR spectral bands of ligand and Cr(III), Mn(II) and Fe(III) complexes. Assignments and band frequencies* , cm-1 coordinated νNO3ν O-H water ν CO νNO νNO3(coordν νClO4δ ν ν (coord(asy) (coord inated ρKrock (coordinated) O-CH2-O M-N M-O ρwagg C=N inated AcO ) (free inated) H2O) (H2O) (H2O) NO -)

453

454


The IR spectra of all the complexes revealed new bands at 612–524 and 526–448 cm–1, assigned to ν(M–N) and ν(M–O), respectively22,25,26. The M-O band may be either due to coordinated nitrate-, perchlorate- or hydroxyl anion or water molecule. The inclusion of water molecules in the coordination sphere of all the complexes, was supported by the appearance of broad bands in the range 3429-3389 and medium or weak bands at 964-956 and 642-634 cm–1, owing to ν(OH), ρKrock(H2O) and ρwagg (H2O), respectively of coordinated water molecules24, 26.

Coordination of anions The spectra of the acetato complexes of Cr(III), Mn(II) and Fe(III) showed bands in the ranges of 1602-1588 and 1443-1426 cm-1. The separation between these two bands was much larger than the separation for the bands due to asymmetric and symmetric stretchings of free acetate ion. Therefore, the bands were assigned to the C-O stretching vibrations of the unidentately coordinated acetate ions present in them25,27-29. Microanalytical data and the non conducting nature of these complexes further supported this. The IR spectra of nitrato complexes of Mn(II) (No.10) showed sharp band at 1385 cm-1, which corresponded to the νNO(asy) of free nitrate ion25,30,31. The conductance value of the complex confirmed the presence free nitrate ions. But in the IR spectra of nitrato complexes of Cr(III) and Fe(III) such bands were absent and new bands appeared at 1432,1358 and 1044 cm-1 in the Cr(III) complex, at 1441 and 1039cm-1 in the Fe(III) complex and were assigned to νNO3- of unidentate nitrate ions25,31. The non-conducting nature of these complexes also indicated coordinated nature of nitrate ions in them. The spectra of all the perchlorato complexes, investigated here, showed bands corresponding to unidentate perchlorate ions. These bands were found to be present in the ranges 1121-1115, 1084-1042 and 948-939 cm-1 and were assigned to the Cl-O stretchings of the monodentate perchlorate ion of C3v symmetry25,32. The non-conducting nature and the microanalytical data of these complexes also indicated coordinated nature of perchlorate ions.

Magnetic and electronic spectral studies The solid-state electronic spectra of the complexes were recorded by the procedure recommended by Venenzi33. Table 3 lists the important electronic spectral bands of the complexes and their assignments.

Cr(III) complexes In the spectra of all the Cr(III) complexes, two peaks were identified in the ranges 541-519 and 419-398 nm and were assigned to the 4A2g → 4T1g(P) and the 4A2g → 4T2g transitions in an octahedral geometry34,35. The Cr(III) complexes, having d3 configuration, with a ground term 3A2g are expected to show magnetic moments very close to the spin-only value36. All the Cr(III) complexes showed magnetic moments in the range 3.83 to 3.76 B.M. indicating sufficient magnetic dilution36,37.

Mn(II) complexes The electronic spectra of the Mn(II) complexes showed a number of weak bands around 400 nm which were assigned to the spin- and parity forbidden 6A1g(F) → 4T2g(G) transitions in an octahedral field or to the charge-transfer spectra extending to the visible region38,39. The pale-yellow or orange colour of the complexes also supported octahedral geometries. All the complexes of Mn(II), except the chloro complex, which were investigated here, showed magnetic moments in the range of 6.14-5.92 B.M. indicating that they are high-spin with probable octahedral geometry38,40


455

Table 3. Electronic spectral bands of Cr(III), Mn(II) and Fe(III) complexes and their assignments. No. 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

Compound [CrL(AcO)3(H20)]* [CrLCl3(H20)] [CrLBr3(H20)] [CrL(NO3)3(H20)] [CrL(ClO4)3(H2O)] [MnL(AcO)2(H2O)2]* [MnLCl2(H2O)2] [MnLBr2(H2O)2] [MnL(H2O)4](NO3)2 [MnL(ClO4)2(H2O)2] [FeL(AcO)3(H20)]* [FeLCl3(H20)] [FeLBr3(H20)] [FeL(NO3)3(H20)] [FeL(ClO4)3(H20)]

Bands, nm 538, 419 541, 398 519, 417 535, 415 539, 408 404w 397 w 402w 409 w 399w 411, 392 419, 385 402 412 421, 396

Assignment A2g → 4T2g, 4A2g → 4T1g(F) 4 A2g → 4T2g, 4A2g → 4T1g(F) 4 A2g → 4T2g, 4A2g → 4T1g(F) 4 A2g → 4T2g, 4A2g → 4T1g(F) 4 A2g → 4T2g 4A2g → 4T1g(F) 6 A1g(F) → 4Eg or 4A1g (G) 6 A1g(F) → 4Eg or 4A1g (G) 6 A1g(F) → 4Eg or 4A1g (G) 6 A1g(F) → 4Eg or 4A1g (G) 6 A1g(F) → 4Eg or A1g (G) 6 A1g → 4T2g, CT 6 A1g → 4T2g, CT 6 A1g → 4T2g 6 A1g → 4T2g 6 A1g → 4T2g, CT 4

Geometry Octahedral Octahedral Octahedral Octahedral Octahedral Octahedral Octahedral Octahedral Octahedral Octahedral Octahedral Octahedral Octahedral Octahedral Octahedral

Fe(III) complexes The complexes of Fe(III) were orange in colour and gave weak bands in the range 421-402 nm, assigned to the spin- and parity forbidden 6A1g → 4T2g transitions of Fe(III) ion in an octahedral field24,41. The pale yellow or brown colours of the complexes also supported octahedral geometry. All the complexes of Fe(III), except the chloro complex, which were investigated here, showed magnetic moments in the range of 6.16-5.98 B.M. indicating that they are high-spin with probable octahedral geometry23,36.

Thermogravimetric analysis Thermograms of three complexes, viz, [CrLCl3(H20)], [MnLCl2(H2O)2]and [FeLCl3(H20)] were analysed. They underwent dehydration reactions around 150 oC, losing two, four and two molecules of water, respectively, thus confirming the presence of coordinated water molecules and they gave Cr2O3, MnO2 and Fe2O3, respectively, as the end products at temperatures around 600 oC. The decomposition patterns were in good agreement with the suggested formulae. By the analysis of the non-isothermal TG, using the integral method of Coats-Redfern, kinetic parameters, viz, order of reaction(n), activation energy(Ea), frequency factor(A) and entropy of activation(∆S*) were calculated. The enthalpies and free energies of activation for various decomposition stages have also been calculated using the relations, ∆H* ═ Ea – RTs and ∆G* ═ ∆H* – Ts∆S* where Ts is the peak temperature of the decomposition stage investigated42. Figures 2, 3 and 4 give the TG-DTG traces of the complexes, the Table 4 gives the different stages of decomposition and the Table 5 gives the kinetic parameters. Based on inception temperature and activation energy, for the decomposition of complexes excluding the dehydration stage, stabilities of the complexes were found to be in the order, Cr > Mn > Fe.

456

PRASAD M. ALEX et al. Table 4. Thermal decomposition data of Cr(III), Mn(II) and Fe(III) complexes. Loss of mass From Theo- From TG retical Pyrolysis

Temp. Peak Stage range in temp. TG

Complex

[CrLCl3(H20)]

I

100-180 145

3.5

3.4

II

300-580 470

81.3

82.2

84.8

85.6

Total

[MnLCl2(H2O)2]

I

100-180 150

6.9

7.0

II

300-560 440

76.6

77.6

83.5

84.6

Total

[FeLCl3(H20)]

I

120-200 155

3.3

3.4

II

280-580 450

81.0

81.6

84.3

85.0

Total 120

120

100

100

Loss of H2O Loss of the ligand, 3 Clions & subsequent formation of metal oxide [CrLCl(H20)] → ½ Cr2O3 Loss of 2H2O Loss of the ligand, 2 Clions & subsequent formation of metal oxide [MnLCl2(H2O)2]→ MnO2 Loss of H2O Loss of the ligand, 3 Clions & subsequent formation of metal oxide [FeLCl3(H20)] → ½ Fe2O3

84.4

83.7

84.1

Mass%

80

80 Mass%

Assignments

dw dt

60

dw dt

60 40

40

20

20

0

0 0

200

400

600

800

1000

0

1200

200

400

600

Temperature

Figure 2. TG-d TG traces of [CrLCl3(H2 O)]. 100

Mass%

80

dw dt

60 40 20 0 200

400

1000

1200

Figure 3. TG-d TG traces of [M nL Cl3(H2O)2].

120

0

800

Temper ature

600

800

1000

1200

Temper ature

Figure 4. TG-d TG traces of [FeL Cl3(H2O)].


457

Table 5. Kinetic parameters for the decomposition of Co(II), Ni(II) and Cu(II) Complexes. Ea, A ∆S* ∆H* ∆G* γ kJ/mol s-1 J/K/mol kJ/mol kJ/mol I 62.41 3.95 x105 -140.57 58.93 117.69 -0.9822755 [CrLCl3(H20)] II 69.61 1.47 x102 -210.99 63.43 220.20 -0.9998813 I 100.1 2.12 x1010 -50.12 96.59 117.79 -0.9997861 [MnLCl2(H2O)2] II 69.03 1.84 x102 -208.81 63.10 211.98 -0.9999085 7 71.66 120.23 -0.9999177 I 75.22 1.05x10 -130.49 [FeLCl3(H20)] II 67.18 1.41 x102 -211.10 61.17 213.78 -0.9983881 Structures suggested for different complexes are given in Figure 5 and 6. Complex

Stage

n 1 1 1 1 1 1

A

H2O

A

A

M N

N

O

O

Figure 5. Structure suggested for MLA3(H2O)], where M = Cr(III) or Fe(III) and A- = CH3COO-, Cl-, Br-, NO3-or ClO4OH2

H2O

A N O

A

M N

O

Figure 6. Structure suggested for[MLA2(H2O)2], where M = Mn(II) and A- = CH3COO-, Cl-, Br- or ClO4-.

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6. 7. 8. 9.

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