Bioinorganic Chemistry and ApplicationsVolume 2011 (2011), Article ID 531946, 10 pagesdoi:10.1155/2011/531946

Research Article

Lanthanide Complexes of Substituted -Diketone Hydrazone Derivatives: Synthesis, Characterization, and Biological Activities

W. H. Hegazy1,2 and I. H. Al-Motawaa¹

¹Chemistry Department, College of Science, King Faisal University, Al-Ahsa 31982, Saudi Arabia²College of Science, Suez Canal University, Suez, Egypt

Received 11 March 2011; Accepted 26 April 2011

Academic Editor: Lorenzo Pellerito

Copyright © 2011 W. H. Hegazy and I. H. Al-Motawaa. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Abstract.

A series of β-diketone hydrazone derivatives have been synthesized through condensation of β-diketone with aromatic aldehydes followed by reaction with phenylhydrazine. The structure of the ligands and intermediates are well defined through elemental and spectroscopic analyses. These hydrazones are potential ligands toward lanthanide metal ions. New complexes of trivalent Scandium, Yttrium, Lanthanum, and Cerium have been synthesized. The composition of these complexes is discussed on the basis of elemental analyses, IR, magnetic moments, and thermal analyses. The prepared complexes were screened for antibacterial and antifungal properties and have exhibited potential activity.

1. Introduction

Metal complexes of Schiff bases occupy a central role in coordination chemistry for analytical, physical, and biochemical purposes [1–19]. Many complexation process of β-diketones Schiff bases and/or hydrazones with lanthanide metal ions have been synthesized and characterized by elemental analysis, DTA-TG,X-ray, IR, fluorescence, UV spectra,and molar conductance [20–31].Biochemical activities of some complexes were reported [15].

The present investigation deals with the preparation of some new β-diketone dihydrazone derivatives (L¹–L¹²) and their mononuclear Sc(III), Y(III), La(III), and Ce(III) complexes. The prepared ligands were characterized by elemental analysis, IR, ¹H NMR, and mass spectra. Elemental analysis, IR, magnetic susceptibility measurements, TG, and conductivity measurements characterize the prepared complexes. The antibacterial activities of the prepared complexes were assessed against Gram-positive bacteria B. subtilis and S. aureus and Gram-negative bacteria E. coli and S. typhi. Prepared complexes were also screened for their antifungal activities against two fungi (A. niger and C. albicans).

2. Results and Discussion

The synthesized ligands L¹–L¹² were characterized by their physical properties, elemental analyses, IR Spectra, ¹H NMR, and mass spectra. The data are given in Tables 1–4, respectively. Figure 1 represents tautomerization of the ligands.

Table 1: Physical properties and elemental analyses of the ligands.

Color
Yield%
MP/°C
Elemental analyses found (calc.)

%C
%H
%N

L₁·4H₂OC₂₄H₂₃N₄F460.46
Yellow
81
213
62.88 (61.65)
6.95 (6.75)
12.23 (12.36)

L₂·7H₂OC₂₄H₂₃N₄Cl530.8
Yellow
83
238
54.49 (54.40)
7.00 (6.74)
10.60 (11.36)

L₃ C₂₄H₂₃N₄Br447.36
Yellow
80
188
64.43 (63.69)
5.14 (500)
12.51 (11.37)

L₄ C₂₄H₂₃N₅O397.41
Orange-red
79
163
69.60 (69.73)
5.30 (5.57)
16.50 (16.95)

L₅·3H₂OC₂₉H₂₃N₄F502
Dark-green
88
225
69.31 (68.87)
6.17 (6.17)
11.15 (10.67)

L₆·3H₂OC₂₉H₂₅N₄Cl518.88
Light-pink
74
216
67.18 (66.64)
5.97 (5.22)
10.81 (10.41)

L₇ C₂₉H₂₃N₄Br509.43
Light-pink
74
20
68.42 (69.13)
4.95 (5.26)
10.99 (10.17)

L₈·3H₂OC₂₉H₂₅N₅O₂530
Orange
67
231
65.78 (65.05)
5.86 (5.25)
13.23 (13.31)

L₉ C₃₄H₂₇N₄F510.59
Pale-beige
70
138
80.00 (80.90)
5.32 (5.32)
10.97 (10.95)

L₁₀ C₃₄H₂₇N₄Cl527.04
Beige
88
143
77.48 (76.61)
5.15 (4.82)
10.63 (9.99)

L₁₁ C₃₄H₂₇N₄Br571.47
Beige
65
173
71.46 (71.46)
4.75 (5.31)
9.80 (9.72)

L₁₂ C₃₄H₂₇N₅O₂537.58
Orange
70
190
75.00 (74.25)
5.03 (5.22)
13.03 (12.65)

Table 2: Selected infrared data of the ligands (cm⁻¹).

υ(N–H)
υ(C=N)
υ(C–N)δ(N–H)
υ(N=N)
δ(N–H)
υ(N–N)

L₁
3431
1600
1456
1373
1222
1072

L₂
3430
1598
1443
1376
1249
1071

L₃
3421
1598
1487
1375
1247
1072

L₄
3433
1601
1442
1375
1192
1080

L₅
3447
1598
1502
1365
1226
1098

L₆
3429
1596
1497
1364
1221
1070

L₇
3449
1594
1454
1359
1211
1066

L₈
3346
1597
1444
1346
1240
1060

L₉
3430
1595
1446
1346
1182
1109

L₁₀
3448
1594
1445
1320
1260
1089

L₁₁
3441
1595
1446
1359
1251
1072

L₁₂
3408
1594
1451
1360
1281
1067

Table 3: ¹HNMR spectroscopic data of the ligands (δ/ppm).

2 CH₃ groups of azoform (d, 3H)
2 CH₃ groups of hydrazoform (d, 3H)
2 CH groups of azoform (d, 2H)
NH groups of hydrazoform (D₂O exchangeable, s, 1H)
Aromatic + methylenic protons (m)

L₁
1.588
2.50
3.41
broad
7.12–7.50

L₂
1.61
2.50
3.36
broad
6.85–7.75

L₃
1.60
2.495
3.39
broad
6.70–7.60

L₄
2.00
2.44
3.52
broad
6.71–7.54

L₅
2.24
2.49
3.85
broad
6.56–7.63

L₆
1.37
2.50
4.00
4.80, 7.77
6.91–7.25

L₇
1.436
2.50
3.34
4.83, 7.98
6.83–7.68

L₈
1.45
2.50
3.34
4.79, 8.21
7.06–7.77

L₉
—
—
3.45
—
6.42–7.97

L₁₀
—
—
3.40
—
6.62–7.95

L₁₁
—
—
3.50
—
6.50–7.12

L₁₂
—
—
3.38
—
7.39–8.23

Table 4: m/z values (relative intensities) of the main fragments of the ligands.

[M]⁺
[A]⁺
[B]⁺
[C]⁺
[D]⁺
[E]⁺
[F]⁺
[G]⁺

L₁
386 (11)
281 (20)
263 (19.0)
173 (18.1)
131 (10.40)
118 (31)
92 (12.6)
77 (100)

L₂
402 (0.28)
297 (4.12)
263 (1.01)
173 (6.07)
131 (3.74)
118 (40)
92 (15.54)
77 (100)

L₃
447 (0.12)
342 (1.34)
263 (0.79)
173 (8.90)
131 (2.61)
118 (29.64)
92 (23.06)
77 (100)

L₄
413 (8)
308 (12.7)
263 (41.1)
173 (11.3)
131 (12.7)
118 (28)
92 (53)
77 (100)

L₅
448 (1.11)
343 (6.1)
325 (13.1)
234 (16.2)
131 (4.4)
118 (13.5)
92 (7.7)
77 (97)

L₆
464 (26.0)
359 (22.27)
324 (0.19)
233 (4.64)
131 (0.82)
118 (2.57)
92 (3.67)
77 (100)

L₇
50918.9
404 —
325 13.1
234 12.5
131 1.0
118 13.5
92 7.7
77 97.3

L₈
475 (8.6)
370 (2.4)
324 (25.9)
233 (4.4)
131 (1.3)
118 (1.0)
92 —
77 (62)

L₉
510 (8)
405 —
386 —
295 (40.2)
193 (11.6)
180 (4.2)
154 (1.1)
77 (72.6)

L₁₀
527 (3.24)
422 —
387 (2.8)
296 —
194 (12.3)
181 —
155 (2.03)
78 (84)

L₁₁
571 (7.11)
466 —
386 —
295 32.9
193 8.6
180 25.7
154 —
77 81.4

L₁₂
537 [M+1]⁺ (10)
432 (8)
386 —
297 (90)
193 (28)
180 (4)
154 (29)
77 (31)

Figure 1: Tautomerization of the ligands.

The elemental analyses of the ligands, Table 1, were found in good agreement with the calculated data (±0.9%).

The infrared spectra of the ligands show broad bands in the region 3449.46–3208.93 cm⁻¹ assigned to N–H stretching vibrations, strong-intensity bands in the region 1601.2–1594.04 cm⁻¹ assigned to C=N stretching vibrations, strong-intensity bands in the region 1502.21–1442.31 cm⁻¹ assigned to interaction (coupling) between C–N stretching and N–H bending vibrations of the C–H–N group, and medium-intensity bands in the region 1376.13–1320.88 cm⁻¹ assigned to N=N asymmetric stretching vibrations of the azoform of the ligands which formed as a result of the azo-hydrazo tautomerism [21]. Substitutions at the ortho- and parapositions enhance the mesomeric effect, which activate azo-hydrazo tautomerism. Weak intensity bands in the region 1281.66–1182.83 cm⁻¹ are assigned to N–H inplane bending vibrations. Medium intensity bands in the region 1109.24–1060.85 cm⁻¹ are assigned to N–N stretching vibrations. It is notable that no bands around 1700 cm⁻¹ are observed which confirms the condensation of C=O groups of the Knövenagel condensation with phenylhydrazine [31, 32]. Two medium-intensity bands corresponding to C=C stretching vibrations of the aromatic rings are shown around 1600 and 1500 cm⁻¹. Selected infrared data of the new ligands are listed in Table 2.

The ¹H NMR chemical shifts and coupling constants of DMSO-d₆ are given in Table 3 suggesting the existence of two tautomeric forms except for ligands L₉–L₁₂. Two sets of signals are observed for the methyl group for ligands L₁–L₈. The resonance of the CH groups of the azoform is readily detectable for all ligands, whereas the peaks of the two NH groups of the hydrazoform (L₁–L₈) are broad in the case of L₁–L₅. The above IR and NMR spectroscopic features point to an azo-hydrazo tautomerism for ligands L₁–L₈ as shown below. Steric hindrance as well as electrondonating properties of the two phenyl groups prevent hydrazoform.

The mass spectroscopic fragmentation pathway of the ligands is shown in Scheme 1. The molecular ions in the mass spectra and their relative abundances are given in Table 4.

(a)

(b)

(c)

Figure 2: Representative structures of the complexes.

3. Methodology

3.1. Chemicals and Equipments

The required 3-benzylidene-2,4-pentanedione, 3-benzylidene-1-phenyl-1,3-butandione, and 3-benzyllidene-1,3-diphenyl-1,3-propanedione were synthesized as described previously [32]. The Schiff bases were prepared by condensation with phenylhydrazine (BDH, England) in dry absolute ethanol(Riedel-de Han) in presence of HCl (Riedel-de Han) as a catalyst [31]. Sc(NO₃)₃·H₂O 99%, Y(NO₃)₃·6H₂O 99%, Ce(NO₃)₃·6H₂O 99%, and La(NO₃)₃·6H₂O 97% were purchased from BDH. 4-chloro-benzaldehyde 97% (Fluka), 4-fluorobenzaldehyde 98% (BDH), 4-nitrobenzaldehyde 98% (BDH), 4-bromobenzaldehyde 99% (BDH), 1,3-diphenyl-1,3-propandion 98% (BDH), phenyl-1,3-butanedion 99% (BDH), and acetylacetone 99% (WINLAB) were also used. All other solvents used were of the ANALAR grade. Elemental analyses were performed at King Saud University, Saudi Arabia. Melting points were recorded on a Gallenkamp melting point apparatus. IR spectra were recorded on Perkin Elmer (spectrum 1000) FT-IR spectrometer using KBr pellets at the chemistry department, College of Science, King Fahd University for Petroleum and Minerals Saudi Arabia. Proton NMR spectra were recorded using JEOl EX-270 MHz (DMSO-d₆) with TMS as an internal reference. Mass spectra were recorded with the aid of GCMS-QP 1000 EX Shimadzu spectrophotometer at 70 eV using a direct insertion probe at 25–300°C at the Microanalytical Centre, Cairo University, Egypt. Thermogravimetric analyses were measured under nitrogen flow rate: 30 cm³ min⁻¹ using a Shimadzu TGA-60H thermobalance from room temperature up to 1000°C at the chemistry department, college of Science, King Faisal University Saudi Arabia. The magnetic susceptibilities were measured using a Sherwood Scientific Ltd. Magnetic susceptibility balance (England).

3.2. Preparation of the Ligands

Condensation of substituted {p-F(1), p-Cl(2), p-Br(3), and p-NO₂(4)} 3-benzylidene-2, 4-pentanedione (I), 3-benzylidene-1-phenyl-1,3-butandione (II), and 3-benzyllidene-1,3-diphenyl-1,3-propanedione (III) with phenylhydrazine (see equation below) was performed by refluxing 20 mmol solution of the carbonyl compounds ( 4.124, 4.453, 5.342, 4.662 g), ( 5.363, 5.690, 6.581, 5.903 g), and ( 6.604, 6.932, 7.822, 7.140 g) with 40 mmol phenylhydrazine (3.93 cm³) in 30 cm³ absolute ethanol in presence of 5 cm³ concentrated HCl as a catalyst for 18–24 h. The solution was then cooled to room temperature and added in portions with continuous stirring to crushed ice prepared from bidistilled water. The resulting yield was filtered, washed with water, and recrystallized from ethanol until constant melting point. Color, MP., yield, and elemental analyses are given in Table 1.

3.3. General Procedure for the Complexes

A solution containing 5 mmol of ligand in 40 cm³ ethanol was refluxed with a solution of 7 mmol of Sc(III), Y(III), La(III), and Ce(III) nitrates for about 12 h after adjusting the pH using ammonia (1 : 1) or Thiel Buffer [38] solution, cooled to room temperature, filtered, washed with ethanol and water, recrystallized from ethanol, and dried on air. The physical properties of the prepared complexes were very stable under ordinary conditions.

3.4. Antimicrobial Studies

3.4.1. Preparation of the Discs

The complex (60 μg) in DMF (0.01 cm³) was mounted on a paper disc (prepared from blotting paper (5 mm diameter)) with the help of micropipette. The discs were left at room temperature till dryness and then applied on the microorganism-grown agar plates.

3.4.2. Preparation of Agar Plates

Minimal agar was used for the growth of specific microbial species. The preparation of agar plates for B. subtilis, S. aureus, E. coli, and S. typhi (bacteria) utilized nutrient agar (2.30 g; obtained from Panreac Quimica SA, Spain) suspended in freshly distilled water (100 cm³) and potato dextrose agar medium (3.9 g/100 cm³; obtained from Merck) for A. niger and C. albicans (fungi). This was allowed to soak for 15 min and then boiled on a water bath until the agar was completely dissolved. The mixture was autoclaved for 15 min at 120°C, then poured into previously washed and sterilized Petri dishes, and stored at 30°C for inoculation.

3.4.3. Procedure of Inoculation

Inoculation was done with the help of platinum wire loop, which was heated to red-hot in a flame, cooled and then used for the application of the microbial strains.

3.4.4. Application of the Discs

Sterilized forceps were used for the application of the paper disc on previously inoculated agar plates. When the discs were applied, they were incubated at 37°C for 24 h for bacteria and yeast and at 28°C for 48 h for fungi. The zone of inhibition around the disc was then measured in millimeters [35].

Acknowledgment

The authors wish to express their deep thanks to the King Abdul-Aziz City for Science and Technology (KACST), Riyadh, Saudi Arabia for providing support to this scientific research.

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