Preparation of Schiff's base complexes of Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II) and their spectroscopic, magnetic, thermal, and antifungal studies

DOI: 10.1134/S1070328406060066

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Russian Journal of Coordination Chemistry p. 431 - 436 (2006)

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Parekh Parekh

Patel Patel

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Article abstract of DOI:10.1134/S1070328406060066

The potassium salt of salicylidene-DL-alanine (KHL), bis(benzylidene) ethylenediamine (A¹), thiophene-o-carboxaldene-p-toluidine (A ²), and its metal complexes of the formula [(M^II(L)(A) (H₂O)] (M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II); A = A¹ or A²) are prepared. They are characterized by elemental analysis, magnetic susceptibility measurements, thermogravimetric analysis, and infrared and electronic spectral studies. The electronic spectral and magnetic moment data suggest an octahedral geometry for the complexes. All of these complexes, metal nitrates, fungicides (bavistin and emcarb), and ligands are screened for their antifungal activity against Aspergillus niger, Fusarium oxysporum, and Aspergillus flavus using a plate poison technique. The complexes show higher activity than those of the free ligands, metal nitrate, and the control (DMSO) and moderate activity against bavistin and emcarb. Pleiades publishing, Inc. 2006.

Full text of DOI:10.1134/S1070328406060066

ISSN 1070-3284, Russian Journal of Coordination Chemistry, 2006, Vol. 32, No. 6, pp. 431–436. © Pleiades Publishing, Inc., 2006.

Preparation of Schiff’s Base Complexes of Mn(II), Co(II), Ni(II),

Cu(II), Zn(II), and Cd(II) and Their Spectroscopic, Magnetic,

Thermal, and Antifungal Studies¹

H. M. Parekh and M. N. Patel

Department of Chemistry, Sardar Patel University, Vallabh Vidyanagar, 388120, Gujarat, India

e-mail: jeenen@gmail.com, jeenenpatel@yahoo.co.in

Received May 23, 2005

Abstract—The potassium salt of salicylidene-DL-alanine (KHL), bis(benzylidene)ethylenediamine (A¹),

thiophene-o-carboxaldene-p-toluidine (A²), and its metal complexes of the formula [(M^II(L)(A)(H₂O)]

(M = Mn(II), Co(II), Ni(II), Cu(II), Zn(II), and Cd(II); A = A¹or A²) are prepared. They are characterized by

elemental analysis, magnetic susceptibility measurements, thermogravimetric analysis, and infrared and elec-

tronic spectral studies. The electronic spectral and magnetic moment data suggest an octahedral geometry for

the complexes. All of these complexes, metal nitrates, fungicides (bavistin and emcarb), and ligands are

screened for their antifungal activity against Aspergillus niger, Fusarium oxysporum, and Aspergillus flavus

using a plate poison technique. The complexes show higher activity than those of the free ligands, metal nitrate,

and the control (DMSO) and moderate activity against bavistin and emcarb.

DOI: 10.1134/S1070328406060066

INTRODUCTION

aldehyde was purchased from Lancaster (UK). Organic

solvents were puriﬁed by recommended methods [11].

Although numerous transition-metal complexes of

Schiff’s bases have been structurally characterized, rel-

atively few free Schiff’s bases have been similarly char-

acterized [1]. A combination of distinctly different

metal ion binding sites within one ligand can lead to

materials with interesting new properties [2, 3], e.g.,

speciﬁc sensors, molecular wires, and magnetic and

optical devices. Schiff’s bases and their metal com-

plexes have exhibited biological activity as antibiotics,

antivirus, and antitumor agents because of their speciﬁc

structure [4, 5]. Amino acid and sulfur-containing

Schiff’s base complexes derived from aldehyde are

involved in a variety of biological processes, e.g., as

catalysts of transamination, racemization, and carboxy-

lation reactions [6, 7]. In some Schiff’s base com-

plexes, it has been observed that minor changes in the

structure of the ligands containing hard/soft donor

atoms, e.g., nitrogen, sulfur, and/or oxygen markedly

affect the activity of the compounds [8, 9]. In continu-

ation of earlier work [10], we report here the complexes

of transition metal with Schiff’s bases.

Potassium salt of salicylidene-DL-alanine. A

solution of potassium hydroxide (10 mmol, 0.56 g) in

30 ml of absolute alcohol was added to (10 mmol,

0.8909 g) of DL-alanine. The mixture was stirred until

it had completely dissolved in an ethanol–KOH solu-

tion. Then, an ethanolic solution of salicylaldehyde

(10 mmol, 1.22 g) was added quickly. The reaction was

allowed to come to completion by stirring at 60°C for

an hour. The product was crystallized out by diffusion

of excess absolute diethyl ether into the solution. The

product was ﬁltered off and dried in a vacuum desicca-

tor. The yield was 64%; mp 224°C.

Thiophene-o-carboxaldene-p-toluidine. An etha-

nolic solution (100 ml) of thiophene-o-carboxaldehyde

(10 mmol, 1.12 g) and an ethanolic solution (100 ml) of

p-toluidine (10 mmol, 1.07 g) in a mole ratio of 1 : 1

were mixed with constant stirring. Reﬂuxing was car-

ried out for 6 h. The solution was cooled overnight at

room temperature. The formed yellow crystals were

collected and dried in air. The yield was 60%;

mp > 360°C.

EXPERIMENTAL

Bis(benzylidene)ethylenediamine. The prepara-

tion of bis(benzylidene)ethylenediamine was carried

out by reﬂuxing a solution of benzaldehyde (2 mmol,

0.212 g) in 100 ml of ethanol and a solution of ethyl-

enediamine (1 mmol, 0.069 g) in 100 ml of ethanol for

2–3 h. The reaction mixture gave Schiff’s base in the

form of yellow crystals. The product was ﬁltered off,

All the chemicals and solutions used were of analytical

grade. Metal nitrates, salicylaldehyde, benzaldehyde,

DL-alanine, and p-toluidine were purchased from the

E. Meark (India) Limited, Mumbai. Thiophene-o-carbox-

The text was submitted by the authors in English.

431

432

PAREKH, PATEL

Table 1. Analytical data of the ligands and complexes

Content (found/calcd), %

Mp, Yield,

°C

Compound* (empirical formula)

Mol. wt.

metal

KHL (C₁₀H₁₀KNO₃)

A¹(C₁₆H₁₆N₂)

A²(C₁₂H₁₁NS)

231.19 51.99/51.94 4.42/4.32 6.23/6.05

236.16 81.32/81.36 6.78/6.77 11.83/11.85

224 64

235 72

>360 58

201.20 71.66/71.63 5.43/5.46 6.91/6.95 15.92/15.94

[Mn^II(L)(A¹)(H₂O)] (C₂₆H₂₇N₃O₄Mn) 500.20 62.46/62.42 5.33/5.39 8.40/8.39

10.96/10.98 >360 59

11.62/11.68 >360 64

11.61/11.64 >360 53

12.49/12.48 >360 55

12.79/12.80 >360 60

20.20/20.15 >360 61

[Co^II(L)(A¹)(H₂O)] (C₂₆H₂₇N₃O₄Co)

[Ni^II(L)(A¹)(H₂O)] (C₂₆H₂₇N₃O₄Ni)

[Cu^II(L)(A¹)(H₂O)] (C₂₆H₂₇N₃O₄Cu)

[Zn^II(L)(A¹)(H₂O)] (C₂₆H₂₇N₃O₄Zn)

[Cd^II(L)(A¹)(H₂O)] (C₂₆H₂₇N₃O₄Cd)

504.18 61.96/61.93 5.34/5.35 8.36/8.33

503.95 61.93/61.96 5.37/5.35 8.32/8.33

508.80 61.32/61.37 5.36/5.30 8.27/8.25

510.65 61.11/61.14 5.26/5.28 8.26/8.22

557.67 55.91/55.99 4.87/4.84 7.52/7.53

[Mn^II(L)(A²)(H₂O)] (C₂₂H₂₂N₂O₄SMn) 465.22 56.71/56.79 4.76/4.72 6.08/6.01 6.82/6.89 11.76/11.80 >360 54

[Co^II(L)(A²)(H₂O)] (C₂₂H₂₂N₂O₄SCo) 469.21 56.34/56.31 4.62/4.68 5.92/5.96 6.84/6.83 12.59/12.55 >360 61

[Ni^II(L)(A²)(H₂O)] (C₂₂H₂₂N₂O₄SNi) 468.97 56.30/56.34 4.62/4.69 5.99/5.97 6.86/6.83 12.52/12.51 >360 60

[Cu^II(L)(A²)(H₂O)] (C₂₂H₂₂N₂O₄SCu) 473.82 55.78/55.76 4.65/4.64 5.95/5.90 6.74/6.76 13.46/13.41 >360 55

[Zn^II(L)(A²)(H₂O)] (C₂₂H₂₂N₂O₄SZn) 475.67 55.62/55.54 4.60/4.62 5.84/5.88 6.75/6.73 13.77/13.74 >360 59

[Cd^II(L)(A²)(H₂O)] (C₂₂H₂₂N₂O₄SCd) 522.69 50.45/50.55 4.22/4.20 5.33/5.35 6.11/6.13 21.58/21.50 >360 49

* KHL is potassium salt of salicylidene-DL-alanine; A is bis(benzylidene)ethylenediamine; A is thiophene-o-carboxaldene-p-toluidine

(the same in Tables 2–4).

washed with ether, and dried in air. The yield was 72%; method using mercury tetrathiocyanatocobaltate(II) as

mp 235°C.

the calibrant (χ_g= 16.44 × 10^–6cgs units at 20°C). The

diamagnetic correction was made using Pascal’s con-

stant.

Synthesis of the complexes. The preparation of

mixed-ligand complexes was carried out by mixing

aqueous solutions (100 ml) of metal nitrate (10 mmol)

and a hot methanolic solution of the potassium salt of

salicylidene-DL-alanine (10 mmol, 2.31 g) and

bis(benzylidene)ethylenediamine (10 mmol, 2.36 g) or

thiophene-o-carboxaldene-p-toluidine (10 mmol,

2.01 g). The complexes were formed by heating the

mixture in a water bath for 2 h at 60°C. The mixture

was kept overnight at room temperature. Finally, the

obtained colored crystals were collected by ﬁltration,

washed with water and ethanol, and dried in air.

RESULTS AND DISCUSSION

The complexes were synthesized following the gen-

eral procedures outlined by the following equations:

M(NO₃)₂· nH₂O + KHL + A

+ KNO₃+ HNO₃+ (n – 1)H₂O.

[M^II(L)(A)(H₂O)]

The elemental analysis data and some physical

properties of the complexes are listed in Table 1. The

elemental analyses indicate that the complexes have the

general formula [M^II(L)(A)(H₂O)]. All the complexes

are insoluble in methanol, diethyl ether, ethanol, and

DMF but soluble in DMSO.

Physical measurements. Infrared spectra were

recorded on a FT-IR Nicolet 400D spectrophotometer

as KBr pellets in the range 4000–400 cm^–1. Carbon,

hydrogen, nitrogen, and/or sulfur elemental analyses

were performed with a model 240 Perkin-Elmer ele-

IR spectra. The FT-IR spectra of the mixed-ligand

mental analyzer. The metal contents of the complexes complexes are quite complex owing to the presence of

were analyzed by EDTA titration [12] after decompos- numerous bands of varying intensities, making the task

ing the organic matter with a mixture of HClO₄, H₂SO₄, of their assignment quite difﬁcult. However, an attempt

and HNO₃(1 : 1.5 : 2.5). Thermogravimetric analyses has been made to assign some of the important bands.

were obtained with a model 5000/2960 SDTA, TA The presence of coordinated water in the complexes is

Instrument (USA). The reﬂectance spectra of the com- indicated in the range 3300–3450 cm^–1and bands at

plexes were recorded in the range 1700–350 nm (as 690, 680, and 920 cm^–1assigned to the M–OH₂band

MgO discs) on a Beckman DK-2A spectrophotometer. [13]. The strong band at 1635 cm^–1attributable to the

The magnetic moments were measured by Gouy’s C=N stretching vibration of ligands is shifted to a

RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 32 No. 6 2006

PREPARATION OF SCHIFF’S BASE COMPLEXES

Table 2. Electronic parameters of the cobalt(II) and nickel(II) complexes*

433

Observed bands (cm^–1)

Complexes

ν₂/ν₁

β, deg

10Dq

ν₁

ν₂

ν₃

[Co^II(L)(A¹)(H₂O)]

[Ni^II(L)(A¹)(H₂O)]

[Co^II(L)(A²)(H₂O)]

[Ni^II(L)(A²)(H₂O)]

9200

10430

9130

18050

18000

18200

18040

19080

23980

18970

24600

1.96

1.72

1.99

1.75

756

713

754

788

0.77

0.69

0.77

0.76

10665

10430

10603

10270

* The ligand-ﬁeld splitting energy (10Dq), interelectronic repulsion parameter (B), and covalency factor (nephelauxetic ratio) (β) for the

Co(II) and Ni(II) complexes were calculated using the secular equations given by E. König [28]:

for the Co(II) complexes

for the Ni(II) complexes

10Dq = 1/2 [(2ν – ν ) + (v²+ ν ν – v )

]

1/2

10Dq = ν

1 3

15B = ν – 2ν + 10Dq

15B = (ν + ν ) – 3ν

2 3 1

β = B/B (B (free ion) = 971)

β = B/B (B (free ion) = 1030)

0 0

β, deg = (1 – β) × 100

region of 1605–1620 cm^–1in the complexes, indicating appearance of three bands at ~23900, ~18000, and

~10400 cm^–1corresponding to the transitions ³A_2g(F)

the coordination of the azomethine nitrogen [14]. In the

free ligand, a strong band at 1525–1540 cm^–1due to

ν(C–O)(phenolic) shifts to higher energy by 5–10 cm^–1

in the complexes indicating the coordination of the phen-

olic oxygen atom to the metal ion [15]. Two strong and

broad bands in the 1400–1600 cm^–1region in all the

complexes are attributed to the ν_as(COO^–) (~1585 cm^–1)

and ν_s(COO^–) (~1390 cm^–1) stretching vibrations of the

coordinated carboxylate group [16].

³T_1g(P)(ν₃), A_2g(F)

³T_1g(F)(ν₂), and A_2g(F)

³T_2g(F)(ν₁). The magnetic moment values for Ni(II) are

2.91 and 2.88 µ_Band support the hexacoordinate con-

ﬁguration [24]. For the Co(II) complexes, the reﬂec-

tance spectra exhibit the bands of medium intensity at

~19 000, ~18 050, and ~9200 cm^–1, which are assigned

to the transitions T_1g(F)

⁴T_1g(P)(ν₃), T_1g(F)

⁴A_2g(F)(ν₂), and T_1g(F)

⁴T_2g(F)(ν₁), respectively,

The mode of coordination is further supported by

the presence of a new band at ~425 cm^–1due to the

ν(M–O)_carbovibration [17]. The aromatic ν(C–H) and

ν(C=C) bands are observed in a range of 750–780 and

1525–1535 cm^–1, respectively. The band in the range

1370–1380 cm^–1is due to ν(C–CH₃). In all the com-

plexes, a new band is seen in the 460–485 cm^–1region,

which is probably due to the formation of the M–N

bond [18]. In all of the complexes, a medium and/or

weak band observed in the 415–470 cm^–1range can be

attributed to ν(M–O)[19]. The ν(C–S) [20–22] band of

the thiophene-o-carboxaldene-p-toluidine observed at

765 cm^–1is shifted to lower frequency about 750 cm^–1

in the spectra of the mixed-ligand complexes, indicat-

ing the participation of the sulfur atom of the thiophene

ring in coordination. The new band in the region of

430–420 cm^–1can be assigned to the ν(M–S)

mode [23].

of an octahedral cobalt(II) complexes [25] and the mag-

netic moment values are 4.10 and 4.18 µ_B.

The electronic spectra of the Mn(II) complexes

exhibit three weak absorption bands for the transitions

⁶A_1g

⁴T_1g(ν₁) (~14.534 cm^–1), A_1g

⁴T_2g(ν₂)

(~19.600 cm^–1), and A_1g

⁴A_1g, ⁴E_g(ν₃)

(24.471 cm⁻¹). These absorptions are consistent with an

octahedral geometry around Mn(II) in all of the com-

plexes. The magnetic moment values of the Mn(II)

complexes are 6.09 and 6.01 µ_B, suggesting an octahe-

dral geometry [26]. The Cu(II) complexes display a

broad band at ~15520 cm^–1due to the ²E_g

²T_2gtran-

sition. The Cu(II) complexes exhibit magnetic

moments of 1.83 and 1.79 µ_B, respectively. These val-

ues are close to the spin-allowed values expected for a

S = 1/2 system (1.73 µ_B) and may be indicative of an

octahedral geometry around the Cu²⁺ions [27]. The

values of the electronic parameters, such as the ligand-

ﬁeld splitting energy (10Dq), Racah interelectronic

repulsion parameter (B), nephelauxetic ratio (b), and

ratio ν₂/ν₁, are presented in Table 2. The Zn(II) and

Magnetic measurements and electronic spectra.

In order to obtain further structural information, the

magnetic moments and electronic reﬂection spectra of

the complexes were measured. The solid reﬂectance

spectra of the Ni(II) complexes are consistent with the

formation of an octahedral geometry with the Cd(II) complexes are diamagnetic and are likely to be

RUSSIAN JOURNAL OF COORDINATION CHEMISTRY Vol. 32 No. 6 2006

434

PAREKH, PATEL

Table 3. Thermogravimetric data of the complexes

Complexes

TG range, °C Mass loss (found/calcd), %

Assignment

[Mn^II(L)(A¹)(H₂O)]

150–180

180–800

150–180

180–800

150–180

180–800

150–180

180–800

150–180

180–800

150–180

180–800

150–180

180–800

150–180

180–800

150–180

180–800

150–180

180–800

150–180

180–800

150–180

180–800

3.52/3.59

82.27/82.22

3.50/3.57

79.93/79.98

3.59/3.57

81.66/81.60

3.51/3.53

80.83/80.82

3.57/3.52

80.50/80.53

3.26/3.22

73.77/73.74

3.88/3.86

80.85/80.88

3.81/3.83

78.42/78.48

3.84/3.83

80.23/80.23

3.80/3.79

79.46/79.41

3.71/3.78

79.18/79.10

3.47/3.44

71.72/71.78