Synthesis, characterization, biological activities, and luminescent properties of lanthanide complexes with N,N′-bis(2-hydroxy-1-naphthylidene)-1,6-hexadiimine

Inorganica Chimica Acta 388 (2012) 120–126

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Synthesis, characterization, biological activities, and luminescent properties of lanthanide complexes with N,N0 -bis(2-hydroxy-1-naphthylidene)-1,6-hexadiimine Abdulaziz M. Ajlouni a,⇑, Ziyad A. Taha a, Waleed Al Momani b, Ahmed K. Hijazi c, Mohammad Ebqa’ai a a

Department of Applied Chemical Sciences, Jordan University of Science and Technology, Irbid 22110, Jordan Department of Allied Medical Sciences, Al Balqa’ Applied University, Jordan c Department of Chemistry, Faculty of Science, Jerash University, Jerash, Jordan b

a r t i c l e

i n f o

Article history: Received 23 January 2012 Received in revised form 12 March 2012 Accepted 14 March 2012 Available online 24 March 2012 Keywords: Schiff base ligand Lanthanides complexes Luminescence properties Antibacterial activity

a b s t r a c t A series of lanthanide complexes with a Schiff base ligand, L (N,N0 -bis(2-hydroxy-1-naphthylidene)-1,6hexadiimine) are presented. The ligand and its complexes were synthesized and characterized based on elemental analyses, molar conductance, IR, 1H and 13C NMR, UV–Vis, and TGA studies. These analytical and spectral data reveal that the ligand L coordinates to the central Ln(III) ion by its two imine nitrogen atoms and two phenolic oxygen atoms and the general formula of the complex is [LnL(NO3)22H2O]NO3, Ln = [Ln = La(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III) and Er(III)] Under the excitation at 396 nm, the luminescence emission properties for Sm, Tb, and Eu complexes are observed. These observations show that the ligand favors energy transfers to the emitting energy level of these lanthanide ions. Furthermore, the antimicrobial activities of all complexes were studied against a number of pathogenic bacteria. The antimicrobial activity results show that most of the synthesized Ln(III) complexes possessed good antibacterial activity and in most cases higher than that of the corresponding ligand L. Ó 2012 Elsevier B.V. All rights reserved.

1. Introduction Lanthanides complexes are very promising for efficient light conversion molecular devices, on account of their potential applications such as luminescent labels for fluoro-immunoassays, light concentrators for photovoltaic devices, antennae in photosensitive bioinorganic compounds and high-technology optics [1–5]. To obtain luminescent lanthanide complexes, the lanthanide ions require a suitable ‘‘antenna’’ ligand as a sensitizer for energy transfer to the metal center, due to the suppression of direct metal excitation by the forbidden f–f transition. The efficiency of the ligand to metal energy transfer is known to affect the luminescence intensity, lifetime, and quantum yield. Thus, energy matching between the Ln(III) emitting levels and the ligand triplet excited state is an important factor for effective emission. Schiff base ligands have been used to optimize the luminescence properties of lanthanide ions [6–8]. Schiff bases containing additional electron-donating groups (azomethines) can trap metal ions with large radii and high coordination numbers. In such a case, the two or more metal atoms are located in one cavity in close proximity to each other and which in turn can be characterized by unusual magnetic properties [9] and catalytic activity [10]. The coordination mode of lanthanide salen-type complexes is usually proposed on the basis of the composition and spectroscopic ⇑ Corresponding author. Tel.: +962 (2) 7201000x23749; fax: +962 (2) 7095014. E-mail address: [email protected] (A.M. Ajlouni). 0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ica.2012.03.029

data. Depending on the preparative procedures, a number of Ln(III)–H2 salen complexes with different compositions have been reported until now, including [LnH2L(NO3)3], [Ln(H2salen)X3 (H2O)n], [Ln2(H2salen)3(NO3)4](NO3)2(H2O)3, [Ln2(salen)3], etc. [11–15]. In addition, Coordination chemistry of lanthanides has become of increasing significance in last few years due to the wide variety of applications of lanthanide complexes in biological and medicinal fields. The object of this study was to seek new fluorescence materials that have strong luminescence, high thermodynamic stability and good solubility, and to study the influence of the Schiff base ligand on the fluorescence properties of rare earth complexes. In our group we have studied many Ln(III) complexes coordinated with different tetradentate ligands [16,17]. In order to make a comparison, we have synthesized synthesis of a series of lanthanide complexes based on tetradentate salen-type ligand L N,N0 -bis(2hydroxy-1-naphthylidene)-1,6-hexadiimine as the sensitizing ligand. These complexes [LnL(NO3)2(H2O)2]NO3, [Ln = La(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III) and Er(III)] were prepared and characterized by elemental analysis, spectral analysis (1H NMR, FT-IR, UV–Vis), molar conductivity measurements, and thermogravimetric studies. The fluorescence properties of the Ln(III) complexes and their fluorescence emission spectra were investigated. In addition, these complexes are evaluated for their antibacterial properties against various pathogenic bacterial strains using agar diffusion method.

A.M. Ajlouni et al. / Inorganica Chimica Acta 388 (2012) 120–126

2. Experimental 2.1. Materials and methods All solvents used were of analytical grade purchased from Aldrich Chemical Company and were used without further purification unless mentioned. [La(NO3)36H2O], [Pr(NO3)36H2O] [Nd(NO3)36H2O], [Sm(NO3)36H2O], [Eu(NO3)35H2O], [Gd(NO3)36H2O], [Tb(NO3)35H2O], [Dy(NO3)3xH2O], and [Er(NO3)36H2O] were purchased from Sigma Aldrich Chemical company and used as received. 2-Hydroxy-1-naphthaldehyde and 1,6-hexyl diamine were purchased from Merck Schuchardt. The metal ions were determined by EDTA titration using xylenol oranges as an indicator [18]. Carbon, nitrogen, and hydrogen analyses were performed using aVario EL elemental analyzer. Infrared spectra (4000–400 cm1) were obtained with KBr discs on a JASCO FT-IR model 470 spectrophotometer. 13C NMR and 1H NMR spectra of H2L ligand and Ln(III)–H2L complexes were recorded on a Bruker AVANCE-400 MHz NMR Spectrometer. Spectra were taken in deuterated DMSO or CDCl3 using TMS as an internal reference. Fluorescence measurements were made on an Edinburgh instrument model FS900SDT spectrometer equipped with quartz cuvettes of 1 cm path length at room temperature. UV–Vis spectra were recorded in DMF solution, concentration of 106 M, at 25 °C, and wavelength was reported in (nm) using a UV-2401 UV–Vis spectrophotometer. The molar conductance measurements were carried out in DMF using WTW LF 318 model conductivity meter equipped with WTW Tetracon 325 conductivity cell. The thermal analysis were performed on a PCT-2A thermo balance analyzer operating at a heating rate of 10 °C/min in the range of ambient temperature up to 900 °C under N2. The clinical isolates used in this study were obtained from the Central Laboratories, Jordan Ministry of Health. These clinical isolates are Salmonella enteritidis, Escherichia coli, Proteus mirabilis, Streptococcus pyogenes, Klebsiella pneumoniae, Pseudomonas aeruginosa, Enterococcus faecalis, and Staphylococcus aureus. 2.2. Synthesis of Schiff base ligand The Schiff base ligand, L, was prepared according to literature method with modification [19]. Briefly, 2.0 mmol (344.4 mg) of the 2-hydroxy-1-naphthaldehyde were condensed with 1.0 mmol (116.2 mg) of 1,6-hexanediamine in refluxing ethanol. Upon cooling a crude yellow product was obtained. The yellow product was collected by filtration, washed with cold ethanol, and airdried. The product was recrystallized from hot ethanol. 1 H NMR (400 MHz, CDCl3) d: 1.45 (quintet, 4H) 1.72 (quintet, 4H), 3.71 (t, 4H), 6.6–8.5 (m, 12 H) 9.11 (s, 2H), 14.6 (s, 2H). 2.3. Synthesis of complexes 1.0 mmol (282.3 mg) Schiff base ligand, L, was dissolved in 15 mL chloroform. To this solution a 15 mL ethyl acetate solution of 1.0 mmol (760.91 mg) Sm(NO3)36H2O was dropwise added. The reaction mixture was stirred for 1 h at room temperature. The precipitated yellow solid complex was separated from the solution by filtration, purified by washing several times with ethyl acetate and chloroform, and then dried for 24 h under vacuum at room temperature. Pr(III), Nd(III), Gd(III), La(III), Er(III), Tb(III), Eu(III), and Dy(III) complexes were prepared by the same way. 2.4. Antimicrobial activity Lanthanides complexes with a tetradentate Schiff base ligand activity was determined initially by using an agar diffusion method

121

[20]. Petri-dishes (90 mm) were prepared containing 20 ml of Mueller–Hinton agar. The inoculum density of all bacterial isolates was standardized with 0.5 McFarland turbidity standards. Once cooled a bacteria lawn was prepared by spreading 100 ll of bacterial culture onto the surface of the dried Mueller–Hinton agar plates using sterile swabs. Wells 6 mm in diameter were punched into the agar and filled with 100 ll of the lanthanides complexes at a concentration of 1 lg/ml [21]. The plates were incubated at 37 °C for 24 h. Zones of inhibition were measured using a caliper. 3. Results and discussions 3.1. Synthesis of the ligand and its complexes The synthetic route for the Schiff base ligand, L, and its new respective Ln complexes are shown in Scheme 1. Schiff base ligand, L, N,N0 -bis(2-hydroxy-1-naphthylidene)-1,6-hexadiimine, was prepared from the condensation of 2-hydroxy-1-naphthaldehyde with 1,6-hexanediamine in 2:1 molar ratio [19]. Nine Schiff base lanthanide complexes were synthesized by treating lanthanide nitrate hydrate with the ligand, L, in ethyl acetate–chloroform solution at room temperature, taken in a 1:1 molar proportion, which yields a series of complexes correspond to the formula of [LnL(NO3)2(H2O)2]NO3, (Scheme 1). 3.2. Characterization of lanthanide complexes 3.2.1. Elemental analysis Table 1 lists the elemental analysis, yields and molar conductivities of the ligand, L, and its complexes. All the Ln(III) complexes are stable in air, non-hygroscopic powder with yellow colors of the Ln(III) ions, soluble in DMSO and DMF, but slightly soluble in methanol, ethanol, ethyl acetate, chloroform, benzene, and insoluble in water and diethyl ether. The elemental contents (C, H, N and Ln) of the ligand, L, and the corresponding Ln(III) complexes are relatively close to those calculated based on molecular formula proposed which indicates the correctness of molecular composition proposed. 3.2.2. Molar conductance Molar conductivity data for all the complexes in DMF solution at room temperature are in the range 117–129 S cm2 mol1 reported for 1:1 electrolytes [22]. The conductivity values Table 1 suggests that two nitrate are coordinated to the Ln ion. 3.2.3. Infrared spectroscopy characterization The chemical shifts of the ligand, L, and its complexes are summarized in Table 2. The IR spectra of the La complexes displayed the ligand characteristic bands with the appropriate shifts due to complex formation (Figs. 1 and 2) and the infrared of the other Ln(III) complexes displays the same manner. It was found that the m(C@N) of the azomethine group occurs at 1627 cm1 in the free Schiff base. After complexation, these bands are shifted to higher wave numbers by 14 cm1 indicates a stronger double bond character of the imine bonds and a coordination of the azomethine nitrogen atoms to the Ln(III) ion [23,24]. This coordination was further supported by the appearance of a medium intensity band around 414 cm1 assigned to m(Ln–N) vibration. In addition, the IR spectrum of the free Schiff base exhibits a broad band between 3100 and 3500 cm1, which is attributed to the stretching frequency of aromatic hydroxyl substituent m(O– H), perturbed by intramolecular hydrogen bonding (O–H  N). The m(O–H) band observed in the spectrum of the free Schiff base is present in the spectra of the Ln(III) complexes, with an increase in the intensity indicating that the hydroxyl oxygen is coordinated

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N (CH2) 6

O

N

HO

+ H2N-CH2) 6-NH2 CH3CH2OH Ref lux OH

OH L

Ln(NO3)3XH2O

CHCl 3 : CH3CO2CH2CH3

[LnL(NO3)2(H2O)2]NO3 Scheme 1. Synthetic route for the Schiff base ligand, L, and its respective Ln complexes, where: Ln is [Ln = La(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III) and Er(III)], L is the Schiff base ligand. x = 0 for Er and, 5 for Tb, Eu, and, 6 for La, Sm, Gd, Pr, Nd, and x for Dy.

Table 1 Analytical data and molar conductance values for the Schiff base ligand, L, and its new lanthanide nitrate complexes. Compound

F.wt.

C (%) found (Calc.)

H (%) found (Calc.)

N (%) found (Calc.)

Ln (%) found (Calc.)

Yield (%)

Km (S cm2 mol1)

Ligand L [NdL(NO3)2(H2O)2](NO3) [SmL(NO3)2(H2O)2](NO3) [DyL(NO3)2(H2O)2](NO3) [LaL(NO3)2(H2O)2](NO3) [ErL(NO3)2(H2O)2](NO3) [PrL(NO3)2(H2O)2](NO3) [TbL(NO3)2(H2O)2](NO3) [GdL(NO3)2(H2O)2](NO3) [EuL(NO3)2(H2O)2](NO3)

424.53 790.82 796.94 809.08 785.48 813.84 787.49 805.5 803.83 798.54

75.31 42.42 42.16 41.61 42.73 41.39 42.74 41.67 41.86 42.21

5.33 4.18 4.21 3.67 4.24 3.82 3.66 4.10 3.99 4.15

9.16 8.79 8.83 8.71 8.70 8.69 8.92 8.76 8.82 8.86

– 18.32 18.45 20.32 17.26 20.76 17.19 19.70 19.67 19.13

90 92 95 90 94 96 93 94 92 94

– 123.98 117.14 119.88 125.54 118.23 128.38 128.98 123.98 121.43

(75.47) (42.53) (42.11) (41.57) (42.81) (41.32) (42.71) (41.75) (41.84) (42.11)

(5.30) (4.08) (4.05) (3.99) (4.11) (3.96) (3.69) (4.00) (4.01) (4.04)

(9.03) (8.86) (8.79) (8.66) (8.92) (8.61) (8.89) (8.69) (8.71) (8.77)

(18.24) (18.87) (20.08) (17.58) (20.55) (17.89) (19.73) (19.56) (19.02)

(Calc.): Calculated.

Table 2 Major infrared spectral data for the Schiff base ligand, L, and [LnL(NO3)2(H2O)2]NO3 complexes (cm1). Compound

Ligand L [NdL(NO3)2(H2O)2]NO3 [SmL(NO3)2(H2O)2]NO3 [DyL(NO3)2(H2O)2]NO3 [LaL(NO3)2(H2O)2]NO3 [ErL(NO3)2(H2O)2]NO3 [PrL(NO3)2(H2O)2]NO3 [TbL(NO3)2(H2O)2]NO3 [GdL(NO3)2(H2O)2]NO3 [EuL(NO3)2(H2O)2]NO3

m(OH) 3440 3444 3449 3444 3445 3444 3443 3444 3449 3444

m(C@N) 1627 1640 1640 1641 1640 1640 1640 1641 1640 1640

m(Ar–O) 1276 1258 1257 1258 1257 1257 1257 1259 1258 1258

m(NO3) m1

m2

m3

m4

m1  m4

mo

– 1476 1477 1476 1476 1477 1476 1477 1477 1477

– 1029 1028 1029 1030 1029 1029 1029 1028 1029

– 817 816 816 818 815 817 816 816 817

– 1286 1286 1286 1286 1286 1286 1286 1286 1286

– 190 191 190 190 191 190 191 191 191

– 1383 1383 1384 1383 1383 1383 1384 1383 1384

to the Ln(III) ion without proton displacement. In addition to that, the m(Ar–O) of the azomethine group occurs at 1276 cm1 in the free Schiff base. After complexation, these bands are shifted to lower wavenumbers by around 18 cm1. This indicates that the coordination to the La(III) ion occurs through the oxygen atoms of aromatic hydroxyl of the ligand, this data was further supported by the appearance of a medium intensity band around 463 cm1 assigned to m(Ln–O) vibration. The characteristic bands that belong to the aromatic rings in the spectra of respective macroacyclic Ln(III) complexes remain almost unshifted. The infrared spectrum of the La(III) complex displays several intense bands at 1476 cm1 (m1), 1030 cm1 (m2), 818 cm1 (m3), and 1286 cm1 (m4) and they are assigned to the coordinated nitrate ion (C2v), these nitrate group can act as unidentate or bidentate coordination. The frequency separation [Dm = m1  m4] between the asymmetric and symmetric stretching of this group can be mode to distinction between these binding states. The difference between m4 and m1 is approximately 191 cm1 which can be suggested that the coordinated NO3 ions in the complexes are bidentate coordination [25,26]. The band at 1383 cm1 in the spec-

m(M–O)

m(M–N)

– 468 470 475 463 475 460 471 471 471

– 411 415 415 414 411 415 415 413 415

trum of the complex indicates that free nitrate groups (D3h) in the coordinating sphere are exist, in agreement with the results of the conductivity experiments discussed in the previous section. 3.2.4. Thermogravimetric (TG) analysis Thermogravimetric (TG) and differential thermogravimetric (DrTG) analysis were carried out for the ligand, L, and its corresponding Ln(III) complexes within the temperature range from ambient temperature up to 900 °C under a N2 flow. The correlation between the different decomposition steps of Ln(III) complexes with the corresponding weight losses are discussed in terms of the proposed formula of the Ln(III) complexes. All the Ln(III) complexes showed similar thermal decompositions (Fig. 3). The TGA curve of Sm(III) complex shows that the Sm(III) complex undergoes multi-stage changes. The first stage, mass loss percentage was 4.45% is consistent with the theoretical value (3.81%) of complex that loss two water molecules. The decomposition temperatures of these hydrates from around 113 to 269 °C suggests that the water molecules present in the Sm(III) complex bonded in the inner coordination sphere.

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123

to give the Sm(III) oxide [27]. The residue reached constant mass at 600 °C. 3.3. Electronic spectroscopy

414

816

463

1028

Absorbance

a

b 1100

1000

900

800

700

600

500

400

-1

Wave Number / cm

Fig. 1. Infrared spectra of: (a) Schiff base ligand L; (b) [SmL(NO3)2(H2O)2](NO3) in the region 1100–400 cm1.

Absorbance

1627

2

1286

1257

1383

1476

1640

a

b

0

1700

1600

1500

1400

1300

1200

1100

-1

Wave Number / cm

Fig. 2. Infrared spectra of: (a) Schiff base ligand L; (b) [SmL(NO3)2(H2O)2](NO3) in the region 1700–1100 cm1.

4

0.5

DrTG 0

3

-0.5

2.5

-1

2

-1.5

1.5

-2

TGA

1

-2.5

0.5 0

mg/ minute

Weight Loss/ mg

3.5

-3 0

200

400

600

800

1000

o

Temperature/ C Fig. 3. TGA–DrTGA curves of [Sm (L) (NO3)2(H2O)2]NO3.

The second stage of decomposition in the range 269–330 °C due to loss of three nitrate ions with a weight loss of 23.70% is consist with theoretical value (23.34%). Third stage occurs at 333–580 °C with a weight loss of 52.72% due to loss of the organic moiety is consisting with theoretical value (53.23%). The last step which is the oxidation of Sm(III) residue

3.3.1. UV–Vis spectroscopy of complexes UV–Vis absorption spectra of the ligand, L, and its lanthanide complexes were carried out in 7.9  107 M in methanol solvent at room temperature. The UV–Vis spectra values of the maximum absorption wavelength (kmax) and absorbance for the ligand, L, and its Ln(III) complexes {Ln = La, Gd, Tb, Er, Sm, Dy, Nd, Eu and Pr} are listed in Table 3. The absorption spectrum of the ligand, L, shows four maxima at 306, 328, 397, and 415 nm, Fig. 4. The intensity bands that observed at kmax = 306 nm and kmax = 328 nm are attributed to the p ? p⁄ transitions of the aromatic ring. The absorption band at kmax = 397 nm corresponds to the p ? p⁄ transition of the azomethine group C@N and the last band appearing at low energy (kmax = 415 nm) corresponds to the n ? p⁄ transitions of conjugation between the lone pair of electrons of p-orbital of N-atom in C@N [28]. UV–Vis spectra show that the intensities of kmax for lanthanide complexes are higher than those of the ligand, L, with a slight change in the wave number. 3.3.2. Luminescence spectroscopy of complexes The fluorescence characteristic of the ligand, L, and its lanthanide complexes are listed in Table 4. The compounds were excited by absorption band at 396 nm. The free ligand, L, exhibits a broad emission band centered at 466 nm in methanol solution, Fig. 5. This emission is attributed to p ? p⁄ electron transitions of the ligand, it was found blue shift after complexation. The efficient intramolecular energy transfer from the lowest triplet state energy level of organic ligands to the resonance energy level of the central Ln(III) (antenna effect) is one of the key factors influencing the luminescence properties of lanthanide metal complexes [29,30]. The most important observation, [SmL(NO3)2(H2O)2]NO3, [TbL(NO3)2(H2O)2]NO3, and [EuL(NO3)2(H2O)2]NO3 complexes exhibit the characteristic emission spectra of the Sm(III), Tb(III), and Eu(III) ions at room temperature, excitation at 396 nm, as shown in Figs. 6–8. These indicate that the Schiff base ligand, L, is a good organic chelator to absorb and transfer energy to the Ln(III) ions. Fig. 6 showed the sensitized emission spectrum of the [EuL(NO3)2(H2O)2]NO3 complex displays three main bands at 548, 593, and 619 nm corresponding to the 5D0 ? 7F0, 5D0 ? 7F1, and 5D0 ? 7F2 transitions, respectively. Where, the term symbols (2S+1FJ) refer to be atomic spectral term of lanthanide ions, among the seventh state (7) is the spin multiplicity which equal to 2S + 1 (S = the total spin quantum number, for Eu+3 = 6/2), F represents the total orbital quantum number (L) in spectroscopic notation, and J is the total angular momentum quantum number, J = L ± S. The sensitized emission spectrum of the [SmL(NO3)2(H2O)2]NO3 complex displays three main bands at 546, 565, 600, and 647 nm corresponding to the 4G5/2 ? 6H3/2, 4G5/2 ? 6H5/2, 4G5/2 ? 6H7/2, and 4G5/2 ? 6H9/2 transitions, respectively (Fig. 7). The emission spectrum of [TbL(NO3)2(H2O)2]NO3 complex, showed five emission bands at 490, 546, 587, 622, and 647 nm corresponding to the 5 D4 ? 7F6, 5D4 ? 7F5, 5D4 ? 7F4, 5D4 ? 7F3, 5D4 ? 7F2 transitions, respectively (Fig. 8) [31]. Among these transitions, the 5D4 ? 7F5 transition exhibits the strongest green emission and 5D4 ? 7F6 transition shows the second strongest blue emission. Although different paths have been suggested for the energy transfer from the ligand, L, excited states to the resonance state of Ln(III) in lanthanide complexes, the favorite mechanism involves strong absorption of ultraviolet energy that excites electrons from the ligand, L, to the excited singlet (SL) state, followed by an energy migration via nonradiative intersystem crossing to the ligand, L,

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Table 3 The UV–Vis absorption bands (kmax) and absorbance (Abs.) of the Schiff base ligand, L, and its lanthanide metal complexes in methanol (7.9  107 M) solution at room temperature.

Table 4 Luminescence spectra data of the Schiff base ligand, L, and its respective lanthanide complexes in methanol solution (6.6  105 M) at room temperature with kexc = 396 (nm).

Compound

kmax (nm)

Abs.

Band assignments

Compound

kem (nm)

Assignment

Ligand L

306 328 397 415

0.211 0.117 0.238 0.248

p ? p⁄ p ? p⁄ p ? p⁄ n ? p⁄

[ErL(NO3)2(H2O)2]NO3

307 328 396 415

0.235 0.163 0.275 0.258

p ? p⁄ p ? p⁄ p ? p⁄ n ? p⁄

Ligand L [LaL(NO3)2(H2O)2]NO3 [GdL(NO3)2(H2O)2]NO3 [NdL(NO3)2(H2O)2]NO3 [PrL(NO3)2(H2O)2]NO3 [DyL(NO3)2(H2O)2]NO3 [ErL(NO3)2(H2O)2]NO3 [SmL(NO3)2(H2O)2]NO3

p⁄ ? p p⁄ ? p p⁄ ? p p⁄ ? p p⁄ ? p p⁄ ? p p⁄ ? p p⁄ ? p

[GdL(NO3)2(H2O)2]NO3

307 329 399 415

0.245 0.138 0.282 0.289

p ? p⁄ p ? p⁄ p ? p⁄ n ? p⁄

[NdL(NO3)2(H2O)2]NO3

307 328 396 415

0.222 0.169 0.283 0.258

p ? p⁄ p ? p⁄ p ? p⁄ n ? p⁄

[PrL(NO3)2(H2O)2]NO3

307 329 399 417

0.245 0.135 0.282 0.294

p ? p⁄ p ? p⁄ p ? p⁄ n ? p⁄

466 461 454 454 458 455 453 450 546 565 600 647 448 490 546 587 622 647 453 543 547 619

[SmL(NO3)2(H2O)2]NO3

307 328 398 416

0.244 0.146 0.283 0.289

p ? p⁄ p ? p⁄ p ? p⁄ n ? p⁄

[TbL(NO3)2(H2O)2]NO3

307 328 396 415

0.218 0.166 0.278 0.255

p ? p⁄ p ? p⁄ p ? p⁄ n ? p⁄

307 328 399 417

0.232 0.121 0.264 0.278

p ? p⁄ p ? p⁄ p ? p⁄ n ? p⁄

[EuL(NO3)2(H2O)2]NO3

307 328 396 415

0.218 0.166 0.277 0.254

p ? p⁄ p ? p⁄ p ? p⁄ n ? p⁄

[DyL(NO3)2(H2O)2]NO3

307 329 395 415

0.229 0.177 0.283 0.251

p ? p⁄ p ? p⁄ p ? p⁄ n ? p⁄

[EuL(NO3)2(H2O)2]NO3

4

G5/2 ? 6H3/2 G5/2 ? 6H5/2 4 G5/2 ? 6H7/2 4 G5/2 ? 6H9/2 p⁄ ? p 5 D4 ? 7F6 5 D4 ? 7F5 5 D4 ? 7F4 5 D4 ? 7F3 5 D4 ? 7F2 p⁄ ? p 5 D0 ? 7F0 5 D0 ? 7F1 5 D0 ? 7F2 4

a b c d

Fluorescence Intensity

[LaL(NO3)2(H2O)2]NO3

[TbL(NO3)2(H2O)2]NO3

(broad) (broad) (broad) (broad) (broad) (broad) (broad) (broad) (sharp) (sharp) (sharp) (sharp) (broad) (sharp) (sharp) (sharp) (sharp) (sharp) (broad) (sharp) (sharp) (sharp)

e f g

450

500 550 600 Emission Wavelength (nm)

650

Fig. 5. The fluorescence spectra of; (a) ligand, L, (b) [ErL(NO3)2)H2O)2]NO3, (c) [NdL(NO3)2)H2O)2]NO3, (d) [LaL(NO3)2)H2O)2]NO3, (e) [GdL((NO3)2)H2O)2]NO3, (f) [PrL(NO3)2)H2O)2]NO3, and (g) [DyL((NO3)2)H2O)2]NO3, in methanol solution at room temperature. Fluorescence spectrum is obtained with kexc = 396 nm.

0.3

Absorbance

0.2

0.1

b e d

a

c 0 270

360

450

540

Wavelength (nm) Fig. 4. The UV–Vis absorption spectra of; (a) ligand, L, (b) [DyL(NO3)2(H2O)2]NO3, (c) [LaL(NO3)2(H2O)2]NO3, (d) [SmL(NO3)2(H2O)2]NO3, and (e) [TbL(NO3)2(H2O)2]NO3 in methanol solution at room temperature.

triplet excited (TL) state energy. The energy is then transferred intramolecularly from the lowest triplet excited sate TL of the Schiff

Fig. 6. The fluorescence spectrum of [EuL(NO3)2(H2O)2]NO3. Fluorescence spectrum is obtained with kexc = 396 nm.

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Fig. 7. The fluorescence spectrum of [SmL(NO3)2(H2O)2]NO3. Fluorescence spectrum is obtained with kexc = 396 nm.

low, back energy transfer from the lanthanide ion to the ligand, L, occurs which reduces the efficiency of the sensitized emission. The result of our luminescence experiments are in consistence with this mechanism for intramolecular energy transfer [16]. La(III) and Gd(III) complexes exhibit single main band at 461 and 454 nm, respectively attributed to p ? p⁄ electron transitions of the Schiff base ligand, L (Fig. 5). La(III) has no 4f electron and has no excited states below the triplet state of the ligand, L, Gd(III) possess a relatively stable 4f shell and the lowest-lying excited state 6P7/2, located at about 311 nm, is expected to be much higher than the energy singlet and triplet state of the ligand, L [32]. Therefore, the energy absorbed by the ligand, L, cannot be transferred to the La(III) or Gd(III) ions by an intramolecular energy transfer process but relaxes through its own lower energy levels. The fluorescence spectra of the La(III) or Gd(III) ions are due to the emission of the ligand, L, and the emission band at the shortest wavelength is assumed to be a 0–0 transition (from the lowest triplet energy state to the ground state of the ligand, L. The emission spectra of the Er(III), exhibits single broad emission band at 453 nm attributed to p ? p⁄ electron transitions of the ligand, L. Therefore, Er(III) complex emits strong fluorescence characteristic of the ligand, L, and the characteristic band of Er(III) did not appear may be due to that the energy levels of the Er(III) are often intermixed and provide paths for efficient quenching of the excited state of the ligand, L. Nd(III), Dy(III), and Pr(III) complexes exhibit single main band at 454, 455, and 458 nm, respectively attributed to p ? p⁄ electron transitions of the Schiff base ligand, L (Fig. 5). The characteristic band of Nd(III), Dy(III) and Pr(III) did not appear, the reason is probably the large energy gap between the triplet state levels of the ligand, L, and the lowest resonance levels of Nd(III), Dy(III) and Pr(III), thus no energy transfer takes place in these complexes [33]. 3.4. Antimicrobial activity

Fig. 8. The fluorescence spectrum of [TbL(NO3)2(H2O)2]NO3. Fluorescence spectrum is obtained with kexc = 396 nm.

base ligand, L, not via the singlet state since it has short-life, to a resonance state of the Ln(III), from which the emission in the visible region occurs. To obtain luminescence, the lowest triplet state energy level of the Ligand, L, must be nearly equal or lie above the resonance energy level of the lanthanide ion. If the triplet energy is

The results of antibacterial activity are presented in Table 5. The ligand was found to be of low activity against two of the four Gram negative bacterial species used in this study with inhibitory zones within 1–5 mm, namely P. mirabilis and S. enteritidis and the other two, K. pneumonia, and E. coli were resistant. All Gram positive bacteria, S.aureus, S. pyogenes and E. faecalis were found to be resistant to the same ligand. All the metal complexes exhibited prominant activity in the range 5–15 mm inhibition zones to the Gram negative bacterial species except for K. pneumonia which was found to

Table 5 Antibacterial activity of the Schiff base ligand L and its Ln(III) complexes against test bacteria using agar well diffusion. Tested compounds

Ligand L [DyL(NO3)2(H2O)2]NO3 [ErL(NO3)2(H2O)2]NO3 [GdL(NO3)2(H2O)2]NO3 [LaL(NO3)2(H2O)2]NO3 [NdL(NO3)2(H2O)2]NO3 [PrL(NO3)2(H2O)2]NO3 [SmL(NO3)2(H2O)2]NO3 [TbL(NO3)2(H2O)2]NO3 [EuL(NO3)2(H2O)2]NO3 DMSO (ve control) Oxytetracycline (+ve control)

Gram () bacteria

Gram (+) bacteria

Ec

Kp

Pm

Se

Pa

Sa

Sp

En

  +++ +++ ++ +++ ++ ++ +   +++

        +++ ++  +++

+ + + +++ ++ +++ ++ ++    +++

+ ++ +  ++ +++ +++ +++  ++  +++

           ++

           +++

   + +   + + +  +++

        + ++  ++

Ec: Eschereshia coli; Kp: Klebsiella pneumonia; Pm: Proteus mirabilis; Se: Salmonella enteritidis; Pa: Pseudomonas aeruginosa; Sa: Staphylococcus aureus; Sp: Streptococcus pyogenes; En: Enterococcus faecalis. Key to interpretation: () = no inhibition zone = inactive; 1–5 mm (+) = less active; 6–10 mm (++) = moderately active; 10–15 mm (+++) = highly active.

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be resistant to all complexes. The higher activity of the complexes compared to free ligand may be attributed to chelation which reduces polarity of the metal ion by partial sharing of the positive charge with donor atoms of the ligand [34]. This increases the lipophilic character, favoring the permeation through lipid layers of the bacterial membrane. Higher activity observed against the Gram negative bacteria can be explained by considering the effect on lipopolysaccharide (LPS), a major component of the surface of Gram negative bacteria [35]. LPS is an important entity in determining the outer membrane barrier function and the virulence of Gram negative pathogens. The Schiff base can penetrate the bacterial cell membrane by coordination of metal ion through oxygen or nitrogen donor atom to LPS which leads to the damage of outer cell membrane and consequently inhibits growth of the bacteria. 4. Conclusion A tetradentate Schiff base ligand, L and its corresponding lanthanide complexes [LnL(NO3)2(H2O)2]NO3, Ln =[Ln = La(III), Pr(III), Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III) and Er(III)] were synthesized and characterized. Under UV light excitation, the Sm, Tb, and Eu complexes exhibited characteristic luminescence of Sm, Tb, and Eu ions, which indicates that the ligand, L, is a good organic chelator to absorb and transfer energy to metal ions. The energy gap between the lowest triplet state level of the Schiff base and the lowest excited state level of Sm(III), Tb(III), and Eu(III) favor to the energy transfer process for Sm, Tb, and Eu. Thus, the present results demonstrate that the Schiff base ligand complexes of lanthanides nitrate can be a candidate as a luminescent in supramolecular nanodevice and laser materials. The antimicrobial activity of all complexes was studied against P. aeruginosa, Klebsiella, and E. coli bacteria. It was observed from the result that most of the synthesized complexes of the tested series possessed good antibacterial activity against bacteria and the microbial activity of the complexes in most cases is higher than that of the corresponding ligand. Acknowledgments The authors are grateful to the Deanship of Scientific Research at Jordan University of Science and Technology for the financial support of this work.

References [1] J.C.G. Bünzli, C. Piguet, Chem. Soc. Rev. 34 (2005) 1048. [2] L.D. Carlos, R.A. Sá Ferreira, V. de Zea Bermudez, S.J.L. Ribeiro, Adv. Mater. 21 (2009) 509. [3] K. Binnemans, Chem. Rev. 109 (2009) 4283. [4] N. Sabbatini, M. Guardigli, J.M. Lehn, Coord. Chem. Rev. 123 (1993) 201. [5] F.J. Steemers, W. Verboom, D.N. Reinhoudt, E.B. Vandertol, J.W. Verhoeven, J. Am. Chem. Soc. 117 (1995) 9408. [6] R.E. Whan, G.A. Crosby, J. Mol. Spectrosc. 8 (1962) 315. [7] F.J. Steemers, W. Verboom, T.D.N. Reinhoud, E.B. Vandertol, J.W. Verhoeven, J. Am. Chem. Soc. 17 (1995) 9408. [8] S.E. Brooker, Eur. J. Inorg. Chem. (2002) 2535. [9] A.E. Martell, J. Perutka, D. Kong, Coord. Chem. Rev. 55 (2001) 216. [10] D. Wei, Y. Jun-Na, L. Wei-Sheng, W. Ya-Wen, Z. Jiang-Rong, W. Da-Qi, Inorg. Chem. 10 (2007) 105. [11] C. Joy, T. Santarupa, P. Guillaume, Z.F. Raymond, C.J. Loïc, M. Samiran, Eur. J. Inorg. Chem. (2009) 3993. [12] T. Małgorzata, Kaczmarek, P.-M. Izabela, K. Maciej, R.-P. Wanda, Inorg. Chem. Commun. 7 (2004) 1247. [13] N.F. Choundhary, N.G. Connelly, P.B. Hitchcock, G.J. Leigh, J. Chem. Soc., Dalton Trans. (1999) 443. [14] Z.L. You, L.L. Tang, H.L. Zhu, Acta Crystallogr., Sect. E 61 (2005) m36. [15] P.A. Vigato, T. Zhang, H. Sun, Coord. Chem. Rev. 248 (2004) 1717. [16] Z.A. Taha, A.M. Ajlouni, K.A. Al-Hassan, A.K. Hijazi, A.B. Faig, Spectrochim. Acta, Part A 81 (2011) 317. [17] Z.A. Taha, A.M. Ajlouni, W.A. Al Momani, A.A. Al-Ghzawia, Spectrochim. Acta, Part A 81 (2011) 570. [18] F.J. Welcher, The Analytical Uses of EDTA, Van Nostrand, New York, 1995. p. 50. [19] T. Friscic, B. Kaitner, E. Mestrovic, Croat. Chem. Acta 71 (1998) 87. [20] C. Perez, M. Pauli, P. Bazerque, Acta Biol. Med. Exp. 15 (1990) 113. [21] E.A. Ter Laak, J.H. Noordergraaf, M.H. Verschure, Antimicrob. Agents Chemother. 37 (1993) 317. [22] W. Geary, Coord. Chem. Rev. 7 (1971) 81. [23] G. Leniec, S.M. Kaczmarek, J. Typek, B. Kołodziej, E. Grech, W. Schilf, J. Phys.: Condens. Matter 18 (2006) 9871. [24] S.M. Kaczmarek, G. Leniec, J. Non-Cryst. Solids (2009) 355. [25] P. Yan, W. Sun, G. Li, C. Nei, T. Gao, Z. Yue, J. Coord. Chem. 60 (2007) 1973. [26] W. Wang, Y. Huang, N. Tang, Spectrochim. Acta 66 (2007) 1058. [27] M.C.C. Cardoso, D.M. Arau´jo Melo, J. Zukerman-Schpector, L.B. Zinnera, G. Vicentini, J. Alloys Compd. 344 (2002) 83. [28] O.A. Gansow, P.A. Loeffler, R.E. Davis, R.E. Lenkinski, M.R. Wilcott, J. Am. Chem. Soc. 14 (1976) 4250. [29] M. Kaczmarek, I. Markiewicz, M. Kubicki, Inorg. Chem. Commun. 7 (2004) 1247. [30] M.K. Taylor, J. Reglinski, L. Berlouis, A.R. Kennedy, Inorg. Chim. Acta 359 (2006) 2455. [31] T. Yang, W. Qin, Spectrochim. Acta, Part A 67 (2007) 568. [32] F. Gutierrez, C. Tedeschi, L. Maron, J.P. Daudey, R. Poteau, J. Azema, P. Tisnès, C. Picard, J. Chem. Soc., Dalton Trans. (2004) 1334. [33] H.Y. Lia, J. Wua, W. Huanga, H.Y. Zhoua, H.R. Lib, Y.X. Zheng, J.L. Zuo, J. Photochem. Photobiol. A: Chem. 208 (2009) 110. [34] A.A. Osowole, G.A. Kolawole, O.J. Fagade, Coord. Chem. 61 (2008) 1046. [35] M.S. Islam, M.A. Farooq, J. Biol. Sci. (Online) 2 (2002) 797.