Crystal Structures, Thermal Properties, and Biological Activities of a

Apr 8, 2013 - only by two bidentate-bridging 4-eba ligands, and another two. 4-eba ligands coordinate to one Dy3+ ion in a chelating mode. The coordin...
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Crystal Structures, Thermal Properties, and Biological Activities of a Series of Lanthanide Compounds with 2,4-Dichlorobenzoic Acid and 1,10-Phenanthroline Jing-Yu Liu,†,‡ Ning Ren,§ Jian-Jun Zhang,*,†,‡ Shu-Mei He,† and Shu-Ping Wang‡ †

Testing and Analysis Center, and ‡College of Chemistry & Material Science, Hebei Normal University, Shijiazhuang 050024, People’s Republic of China § Department of Chemistry, Handan Key Laboratory of Organic Small Molecule Materials, Handan College, Handan 056005, People’s Republic of China S Supporting Information *

ABSTRACT: A new family of binuclear lanthanide compounds of general formula [Ln(2,4-DClBA)3phen]2 (Ln(III) = Nd (1), Sm (2), Dy (3), Yb (4); 2,4-DClBA = 2,4-dichlorobenzoate; phen = 1,10-phenanthroline) have been synthesized and characterized by elemental analysis, molar conductance, infrared spectroscopy, ultraviolet spectra, thermogravimetric analysis, and single-crystal X-ray diffraction. On the basis of X-ray crystallography, compounds 2−4 belong to the triclinic crystal system, PI ̅ space group. In compound 2, the Sm3+ ion adopted a distorted monocapped square-antiprism coordination geometry. Compounds 3 and 4 are isomorphous whose central ions (Dy3+ and Yb3+) formed a distorted square-antiprism geometry. The heat capacities of compounds 1−4 are measured using DSC technology and fitted to a polynomial equation by the least-squares method. The smoothed molar heat capacities and thermodynamic function data of compounds 1−4 relative to the reference temperature 298.15 K are then calculated. Meanwhile, these compounds exhibit in good antifungal activity against C. albicans, good antibacterial activity against S. aureus, and better antibacterial activity against E. coli. The fluorescence spectra of the samarium and dysprosium compounds behave as characteristic transitions of Sm(III) and Dy(III) ions.

1. INTRODUCTION In recent years, the design and synthesis of lanthanide aromatic carboxylic acid compounds have continued to be an active area of research of their various structures1−6 and potential application in many areas such as extraction and separation, catalysts, luminescent probes, nonlinear optics (NLO), magnetism, and so on.7−12 The introduction of nitrogen-containing ligands may strengthen conjugate function, enhance rigidity and stability, and reinforce fluorescence ability of the compounds.13−15 As we know, certain lanthanide aromatic carboxylic acid compounds possess anti inflammation, sterilization, and antitumor activities,16,17 which is significant as biological pharmaceutical. Therefore, a need is appearing to synthesize compounds that have better biological activity than that of the ligands. Moreover, the heat capacity, Cp, is a key thermophysical quality. It is significant in designing chemical processes as well as in the progress of thermodynamic theories. The thermodynamic function enthalpy, entropy, and Gibbs energy data obtained at certain temperatures are important for both theoretical and practical purposes. In this Article, four new lanthanide compounds were prepared and characterized by single-crystal X-ray diffraction, elemental analysis, molar conductivity, thermogravimetric analysis, infrared, and ultraviolet spectroscopy. The luminescent properties of the samarium and dysprosium compounds were also studied. The ligands and the title compounds were tested in vitro to evaluate their antimicrobial activities against Escherichia coli, Staphylococcus aureus, and Candida albicans. In addition, the heat capacities Cp,m of compounds 1−4 were © 2013 American Chemical Society

measured between 263.15 and 485.55 K by means of differential scanning calorimeter, and the thermodynamic function, the enthalpy, entropy, and Gibbs free energy of the compounds relative to the standard reference temperature 298.15 K were also calculated.

2. EXPERIMENTAL SECTION 2.1. Materials. LnCl3·6H2O [Ln(III) = Nd (1), Sm (2), Dy (3), Yb (4)] were prepared by dissolving Ln2O3 (99.99%) in 6 N HCl and afterward evaporation at 80 °C until the crystal film formed. All other chemicals were of analytical grade, which were achieved from commercial sources and used without further purification. 2.2. Syntheses of the Compounds. LnCl3·6H2O [Ln(III) = Nd (1), Sm (2), Dy (3), Yb (4)] (0.5 mmol) was dissolved in 5 mL deionized water, and the first ligand 2,4dichlorobenzoic acid (1.5 mmol) and the second ligand 1,10phenanthroline (0.5 mmol) were dissolved together in 10 mL 95% ethanol solution. The pH of the two ligands ethanol solution was adjusted to 5−7 with 1 mol L−1 NaOH solution by adding dropwise the LnCl3 aqueous solution under stirring. The mixture was stirred at room temperature for 6 h and then deposited for 12 h. The resulting precipitate was filtered off, washed with 95% alcohol, and dried in a far-infrared dryer at 50 Received: Revised: Accepted: Published: 6156

January 21, 2013 March 31, 2013 April 8, 2013 April 8, 2013 dx.doi.org/10.1021/ie400228j | Ind. Eng. Chem. Res. 2013, 52, 6156−6163

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Figure 1. (a) Molecular structure of compound 2 at the 30% probability displacement ellipsoids. All hydrogen atoms are omitted for clarity. (b) Coordination geometry of the Sm(III) ion.

Figure 2. (a) Molecular structure of compound 3 at the 30% probability displacement ellipsoids. All hydrogen atoms are omitted for clarity. (b) Coordination geometry of the Dy(III) ion.

°C for 3−4 h. The single crystals of compounds 2−4 were collected from the mother liquor after 2 weeks at room temperature. Anal. Calcd for [Nd(2,4-DClBA)3phen]2: C, 44.31; H, 1.92; N, 3.13; Nd, 16.13. Found: C, 44.03; H, 1.99; N, 3.05; Nd, 16.01. Anal. Calcd for [Sm(2,4DClBA)3phen]2: C, 44.01; H, 1.90; N, 3.11; Sm, 16.70. Found: C, 43.53; H, 1.94; N, 2.83; Sm, 16.43. Anal. Calcd for [Dy(2,4-DClBA)3phen]2: C, 43.43; H, 1.88; N, 3.07; Dy, 17.80. Found: C, 42.69; H, 1.99; N, 3.03; Dy, 18.02. Anal. Calcd for [Yb(2,4-DClBA)3phen]2: C, 42.93; H, 1.86; N, 3.03; Yb, 18.74. Found: C, 42.61; H, 1.90; N, 2.97; Yb, 18.43. 2.3. Characterization. Elemental analysis was measured by a Vario-EL III elemental analyzer, and the metal content was

assayed using an EDTA titration method. FTIR spectra were recorded with a Bruker TENSOR27 spectrometer with KBr pellets in the spectral range of 4000−400 cm−1. Ultraviolet spectra were obtained in DMSO solvent (c = 1 × 10−5 mol L−1) with a Shimadzu 2501 spectrometer. Thermogravimetric analyses (TGA) was performed under nitrogen atmosphere with a Perkin-Elmer TGA7 thermogravimetric analyzer in the range from 298 to 1223 K at a heating rate of 10 K min−1. Molar conductivity was measured by DDS-307 conductometer (Shanghai Precision & Scientific Instrument CO.LED). The single-crystal X-ray data were collected for compounds 2−4 on a Smart-1000 (Bruker AXS) diffractometer with monochromated Mo Kα radiation (λ = 0.071073 Å) at 298(2) K. All 6157

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Figure 3. (a) Molecular structure of compound 4 at the 30% probability displacement ellipsoids. All hydrogen atoms are omitted for clarity. (b) Coordination geometry of the Yb(III) ion.

3. RESULTS AND DISCUSSION 3.1. Molar Conductance. Molar conductivity of the prepared compounds was determined in DMSO with DMSO as a reference. The values of molar conductance for compounds 1−4 are 35.5, 34.0, 33.2, and 36.7 S cm2 mol−1, respectively. Therefore, we can conclude that these compounds are nonelectrolyte in DMSO.18 3.2. Descriptions of the Structures. Figures 1, 2, and 3 showed the molecular structures of compounds 2−4 and coordination geometry of the Sm(III), Dy(III), and Yb(III) ions. Selected bond lengths and bond angles were listed in S2, 3, and 4 (see the Supporting Information), respectively. Singlecrystal X-ray diffraction studies revealed that compound 2 is a binuclear molecule with an inversion center and crystallizes in the triclinic space group PI.̅ The moleculare structure of compound 2 is composed of two Sm(2,4-DClBA)3phen units including three carboxylic ligands and one 1,10-phentermine ligand. In the compound, carboxylic ligands act in three coordination modes, which are μ2-η1:η1, η2, and μ2-η2:η1. As seen in Figure 1a, each Sm3+ ion is coordinated to nine atoms: three oxygen atoms from the two bridging-chelating carboxylic group, two oxygen atoms deriving from one chelating bidentate carboxylic group, the other two from two bridging bidentate carboxylic groups, and two nitrogen atoms from bidentate phen groups. The coordination environment of Sm(III) ion can be described as a distorted monocapped square-antiprism (Figure 1b), in which the top square upper face and the bottom are constructed by atoms O1A, O2, O3, O4A and O5, O6, N1, N2, respectively. Atom O1 occupies the capping vertex of the polyhedron. In compound 2, the bond distance of two Sm(III) ions is 4.0587(8) Å. The bond lengths of Sm1−O are in the range from 2.365(5) to 2.686(5) Å, with the average bond length of 2.457 Å, and the bond angles of O−Sm1−O in the range from 52.43(19)° to 148.76(18)°. The bond distances of Sm1−N are 2.632(6) and 2.593(6) Å with an average bond distance of 2.612 Å, and the N−Sm1−N bond angle is 62.9(2)°. In addition, the average bond length of Sm1−O is longer than that of Sm1−N, which indicates that the bond

calculations were performed on a computer using SHELXS-97 and SHELXL-97 programs. A summary of the crystallographic data and details of the structure refinements are listed in S1 (see the Supporting Information). The fluorescent spectra of compounds 2 and 3 were described on an F-4500 Hitachi spectrophotometer in the solid state at room temperature with slit width of 5 nm. 2.4. Heat Capacity Measurements. Heat capacities of compounds 1−4 were carried out with a NETZSCH DSC 200 F3 in the temperature range from 263.15 to 485.55 K under nitrogen atmosphere at a heating rate of 10 K min−1 by an indirect measurement method. The mass of the reference standard substance sapphire (12.75 mg) loaded in an aluminum crucible sealed with a pierced lid was accurately weighted on heating. The samples were performed three times with similar weight (11.78 mg) almost under the same conditions. The Cp curves of the samples were obtained by the apparatus with an automatic data processing program. In addition, the heat capacity of the reference standard sapphire (12.75 mg) was measured to determine the reliability for this method by DSC. The relative deviations of our experimental results were within ±0.50%, which compared to the recommended values by the National Institute of Standards and Technology (NIST). 2.5. Test of Biological Activity. The lanthanide chlorides, ligands, and their compounds were tested for biological activity using the filter paper disc diffusion method. Mueller−Hinton agar medium was used as the microorganic medium, and Escherichia coli, Staphylococcus aureu, and Candida albicans were the microorganisms. Sterile filter paper discs of diameter 5 mm were prepared for the purpose of antimicrobial slices. The sterile filter paper discs were soaked in 5 μL of ligands, and compound solutions were prepared in sterile DMSO with concentrations of 0.008, 0.016, and 0.032 mol L−1. The antimicrobial activity was estimated by the size of the zone of inhibition formed around the paper disks on the seeded agar plates. The antibacterial effects against Escherichia coli and Staphylococcus aureus were investigated after 24−38 h incubation at 37 °C, and the antifungal effect against Candida albicans is recorded after 48 h incubation at 30 °C. 6158

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Table 1. Significant IR Spectra Data of the Ligands and Compounds (cm−1) compounds

νCN

δC−H

Phen 2,4-DClHBA 1 2 3 4

1560

739,854

1519 1519 1519 1519

730,844 730,842 729,844 729,844

νCO

νas(COO−)

νs(COO−)

ν(Ln−O)

1606 1613 1649 1650

1428 1426 1426 1427

418 419 418 419

1699

compounds are similar, but different from that of the two free ligands. The absence of strong carboxyl characteristic absorption band ν(COOH) at about 1699 cm−1 in all spectra of the compounds indicates complete deprotonation of 2,4DClHBA. Meanwhile, the new bands occurring in the region 419−418 cm−1 (νLn−O) for the compounds indicate that oxygen atoms of the carboxyl groups participate in coordination with the Ln(III) ion.23 The bands appearing in the spectra of the compounds at about 1650−1606 cm−1 belong to the asymmetric vibrations of carboxyl groups, while those at about 1428−1426 cm−1 correspond to their symmetric vibrations.24 Furthermore, there are characteristic bands at 1560 cm−1 for νCN, 739 and 854 cm−1 for δC−H of the 1,10phenanthroline group, which shifted to lower wavenumber 1519, 730−729, and 844−842 cm−1, respectively, indicating the nitrogen atoms of phen are coordinated to rare earth ion, which was confirmed by structural analyses.25 3.4. Ultraviolet Spectra. UV spectra of the two ligands and the title compounds are depicted in DMSO solution with DMSO solution as a reference. The compounds and the ligands all have the strong π−π transition absorption. In the UV absorption spectra of the compounds, the maximum absorption peak of the free carboxylic ligand is at 270 nm, which shifts to longer wavelengths in the compounds at 285−286 nm. This phenomenon may be duo to the expansion of the π-conjugated system caused by the metal coordination.26 Furthermore, the maximum absorption band at 285 nm for the compounds is similar to that in the phen, which indicates that the formation of Ln−N has no conspicuous influence on the UV absorption of the phen. However, compared to the two ligands, the absorbency absorption of the compounds is greatly enhanced, suggesting that there is a bigger chelating ring formed.27 3.5. Luminescence Properties. The solid-state fluorescence property of the Sm3+ (1) and Dy3+ (3) compounds were recorded in the range from 400 to 800 nm at room temperature. The fluorescence spectra were obtained while monitoring excitation wavelength at 345 nm for compound 1 and 340 nm for 3 as shown in Figures 4 and 5. The emission spectrum of compound 1 (Figure 4) consists of three bands at 560, 603, and 650 nm, which give rise to the 4G5/2→6F5/2, 4 G5/2→6F7/2, and 4G5/2→6F9/2 transitions of Sm3+ ion,28,29 respectively. From Figure 5, two peaks at 482 and 576 nm in the visible light region corresponding to the 4F9/2→6H15/2 and 4F9/2 →6H13/2 transition of Dy3+ ion were observed.30 The second emission peak corresponding to the hypersensitive transition 4 F9/2→6H13/2 (ΔL = 2, ΔJ =2) is stronger, which is possibly ascribed to coordination environment.31 Moreover, compared to [Eu(2,4-DClBA)(bipy)]224 (2,4DClBA = 2,4-dichlorobenzoate; bipy = 2,2-bipyridine), the luminescence of compounds 1 and 3 is weaker due to the difference in energy between the excited energy level of the ligands and Ln3+ ions.

energy for Sm1−N is weaker than that of the Sm1−O. Therefore, the Sm1−N bond is broken first in the thermal decomposition process, which is demonstrated by the thermogravimetric experiment. Compounds 3 and 4 are isomorphous, which were established by X-ray crystallography; hence compound 3 is used as a representative to describe in detail. Compound 3 crystallizes in the triclinic PI ̅ space. Two Dy(III) ions are connected together by four carboxylic groups adopting μ2-η1:η1 coordination mode to form a dimer with a crystallographic inversion center. Each Dy(III) ion is surrounded by eight atoms, in which four oxygen atoms belong to bidentatebridging carboxylic ligands, two oxygen atoms belong to bidentate-chelating carboxylic ligand, and two nitrogen atoms belong to one 1,10-phenanthroline ligand. The coordination sphere of each Dy(III) ion can be described as a distorted square-antiprism (Figure 2b), and the upper and lower planes are structured by O1, O2A, O3, O4A and O5, O6, N2, N1, respectively. The Dy1−O bond lengths vary from 2.254(6) to 2.434(6) Å with the average distance of 2.332 Å. The O−Dy1− O bond angles in the range from 53.6(2)° to 145.3(2)°, and the average O−Dy1−O bond angles is 79.8(3)°. The Dy1−N1 bond distance is 2.553(7) Å and Dy1−N2 is 2.538(7) Å with average bond lengths of 2.5456 Å, and the N−Dy1−N bond angle is 63.9(2)°. Moreover, the Dy1−O distance of the chelating carboxyl group [2.434(6)−2.402(6) Å] is larger than that of the bridging carboxyl group [2.254(6)−2.361(6) Å], which is attributed to chelating carboxyl group O5−C15−O6 with Dy(III) ion to form an unstable four-membered ring.19 Several lanthanide ternary compounds with benzoic acid and its derivatives have been synthesized and studied for various crystal structures, such as [Ln(4-eba)3(phen)]2 (Ln = Nd (1), Sm (2), Eu (3), Tb (4), Dy (5), and Ho (6); 4-eba = 4ethylbenzoate).14 Among them, compounds 1−4 are isostructural, and have the same structures as [Sm(2,4DClBA)3phen]2 (2), while the structure of compound 6 is similar to [Dy(2,4-DClBA)3phen]2 (3). However, in compound 5, two eight-coordinated Dy3+ ions are held together only by two bidentate-bridging 4-eba ligands, and another two 4-eba ligands coordinate to one Dy3+ ion in a chelating mode. The coordination polyhedron around Dy3+ is a trigondodecahedron. Such a structure is seldom reported and is interesting in lanthanide carboxylate compounds. The lanthanide ternary compounds with methyl or methoxy substituted benzoic acid benzoic acid are typical binuclear molecules, which have two types of Ln(III) ion coordination environments, for instance, Ln2(o-MBA)6(Phen)2·nH2O (n = 0,1) (Ln = La, Pr, Y, Yb; oMBA = o-methylbenzoate),20 [Ln(3,4,5-tmoba)3phen]2 (Ln = Pr, Nd, and Ho; 3,4,5-tmoba = 3,4,5-trimethoxybenzoate),21 and [Ln(2,3,4-tmoba)3phen]2 (Ln = Dy, Eu, Tb; 2,3,4-tmoba = 2,3,4-trimethoxybenzoate).22 3.3. IR Spectra. The IR spectra data of the ligands and title compounds 1−4 are shown in Table 1. The IR spectra of the 6159

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Figure 4. Fluorescence spectrum of compound 2 (λ = 345 nm).

Figure 5. Fluorescence spectrum of compound 3 (λ = 340 nm). Figure 6. TG-DTG curves of compounds 1 (a) and 4 (b).

3.6. Thermogravimetric Analysis. Thermogravimetric analysis of the title compounds 1−4 was carried out from 298 to 1223 K at a heating rate of 10 K min−1 under nitrogen atmosphere to study the thermal stability. The TG-DTG curves of compounds 1−4 show that there are three stages of weight loss. Yet the decomposition patterns of compounds 1 and 2 are very similar; hence only compound 1 is presented as an example. As seen in Figure 6a, the first and second steps have been assigned to the removal of two phen molecules and partial 2,4-DClBA ligands in the temperature range of 526.37−913.63 K. The third step is between 913.63 and 1223 K corresponding to decomposition of the remaining 2,4-DClBA ligands. The final residue of neodymium oxide (Nd2O3) was obtained with a final weight of 18.84% (calcd 18.81%). For compound 4 (Figure 6b), the first weight loss is in the range of 545.42− 719.97 K with the decomposition of two phen molecules and partial 24-DClBA ligands. The second and third stages begin at 667.15 K and end at 1223 K, in which the rest of the 2,4DClBA ligands are removed and the compound decomposed completely into Yb2O3 with a total loss of 78.90% (calcd 78.66%). TG curves of compound 3 is similar to compound 4; therefore, from the above analyses, the thermal decomposition processes of compounds 1−4 are presented as follows:

where Ln = Dy3+ and Yb3+. Besides, it can be seen that compounds 1−4 all have good thermostability because of the stable structures of these compounds, and the fact that Ln−N bonds of the compounds break first in the TG experiments due to the weaker bond energy of Ln−N than that of Ln−O. 3.7. Heat Capacities. The experimental molar heat capacities of compounds 1−4 were measured by DSC technology over the temperature in the range from 263.15 to 485.55 K, because there is no weight loss up to T = 500 K in the TG curves. The average results of molar heat capacities by carrying out three parallel experiments are shown S5 (see the Supporting Information), and the curves are depicted in Figure 7. From Figure7, it can be seen that there is no obvious endothermic or exothermic peak in the curves of molar heat capacities Cp,m over the measured temperature range. Yet they are not smooth curves in the temperature range between 315 and 350 K, which is similar to [Ln(2,3-DClBA)3phen]2 (Ln(III) = Eu (1), Tb (2), Ho (3); 2,3-DClBA = 2,3dichlorobenzoate),32 and the reasons need further research. Moreover, the curve of Cp,m for compound 3 has a similar trend in the measured temperature range as compound 4, and little difference from compounds 1 and 2, which possibly is due to the different structures.33 The molar heat capacities for compounds 1−4 are fitted to the following polynomial equation of heat capacities (Cp,m) with reduced temperature (x) by means of least-squares fitting. Compound 1 [Nd(2,4-DClBA)3phen]2:

[Ln(2, 4‐DClBA)3 phen]2 → Ln2(2, 4‐DClBA)6 phen2 − x → Ln2(2, 4‐DClBA)6 − x → Ln2O3

where Ln = Nd3+ and Sm3+. [Ln(2, 4‐DClBA)3 phen]2 → Ln2(2, 4‐DClBA)6 − x → → Ln2O3 6160

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Figure 7. Molar heat capacities of compounds 1−4 with temperature/K by DSC (△, compound 1; ○, compound 2; ▽, compound 3; ◇, compound 4).

where x is the reduced temperature, x = [T − (Tmax + Tmin)/ 2]/[(Tmax − Tmin)/2], x = (T − 374.35)/111.2, T is the experimental temperature, Tmax(485.55 K) is the upper limit, Tmin(263.15 K) is the lower limit in the temperature range, R2 is correlation coefficient, and SD is the standard deviation of the fitted curves for the compounds. 3.8. Thermodynamic Functions. On the basis of the polynomial equation of heat capacity and thermodynamic relationship as follows, the thermodynamic function data of compounds 1−4 relative to the reference temperature 298.15 K are tabulated with an interval of 10 K in the temperature range from 263.15 to 485.55 K.

Cp,m/(J·K−1·mol−1) = 1862.69998 + 336.39607x + 391.24825x 2 + 227.92208x 3 − 1610.69455x 4 + 1178.77207x 5 + 1792.56385x 6 − 2521.11816x 7 − 639.57612x 8 + 1305.11529x 9 R2 = 0.9997

SD = 4.83656

Compound 2 [Sm(2,4-DClBA)3phen]2: Cp,m/(J·K−1·mol−1) = 1818.82099 + 510.43329x + 427.71349x 2 − 1040.4552x 3 − 597.15414x 4 5

6

+ 4105.28417x − 362.52595x − 5198.38423x

T

HT − H298.15 =

7

+ 548.85827x 8 + 2177.23544x 9 2

R = 0.9995

SD = 6.50582

∫298.15 Cp,mT −1 dT T

GT − G298.15 =

Cp,m/(J·K−1·mol−1) = 2016.34422 + 406.82282x

(2) T

∫298.15 Cp,m dT − T ∫298.15 Cp,mT −1 dT (3)

+ 428.8973x 2 + 133.24913x 3 − 1182.87342x 4

The smoothed values of Cp,m and the thermodynamic functions HT − H298.15, ST − S298.15, GT − T298.15 of compounds 1−4 are listed in S6−S9 (see the Supporting Information), respectively. 3.9. Biological Activity. The antimicrobial activities of the compounds, LnC13·6H2O, and the ligands were tested using the filter paper disc diffusion technique. The diameters of the zones where the growth of the microorganic strains Escherichia coli, Staphylococcus aureu, and Candida albicans was inhibited were measured to evaluate the antimicrobial activity of these compounds. The results of diameter of inhibition zone expressed as average value and standard deviation by carrying out three parallel tests were presented in S10 (see the Supporting Information). From the results, it is clear that the pure ligands and LnCl3·6H2O have no inhibiting effect, while their compounds

+ 1393.25179x 5 + 973.18118x 6 − 2681.7906x 7 − 241.79336x 8 + 1296.78066x 9 SD = 3.83122

Compound 4 [Yb(2,4-DClBA)3phen]2: Cp,m/(J·K−1·mol−1) = 2053.19391 + 431.61311x + 417.48786x 2 − 197.06637x 3 − 1308.69354x 4 + 2718.01983x 5 + 1446.82839x 6 − 4488.23482x 7 − 573.97905x 8 + 2110.97312x 9 R2 = 0.9998

(1)

T

ST − S298.15 =

Compound 3 [Dy(2,4-DClBA)3phen]2:

R2 = 0.9999

∫298.15 Cp,m dT

SD = 4.37436 6161

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Industrial & Engineering Chemistry Research exhibit certain inhibitory activity against the chosen microorganisms. The diameter of inhibition zone of these compounds increased along with the rise of their concentration in the range of 0.008−0.032 mol L−1. There was no significant difference for inhibitory activity of compounds 1−4 under the same concentration. These compounds exhibited good antimicrobial activity against Staphylococcus aureu and Candida albicans, excellent antibacterial activity toward Escherichia coli under the concentration of 0.032 mol L−1, so they have potential medicinal value worthy of further investigation. Furthermore, the antibacterial activities for the compounds against Escherichia coli and Staphylococcus aureus are a little better than the previously reported Ln2(oMBA)6(Phen)2·nH2O (n = 0,1) (Ln = La, Pr, Y, Yb; o-MBA = o-methylbenzoate).20 The antibacterial activity was similar to the lanthanide ternary compounds with benzoic acid and 2,4,6tri(2-pyridyl)-s-triazine, which exhibited superior antibacterial activity against Escherichia coli.34 The antimicrobial activity for the compounds may be due to the π-electron delocalization over the chelate ring.35,36 This effect increases the lipophilic character of the metal ion, which favors permeation through the lipoid layers of the microorganic membranes and impairs normal cell processes.34

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REFERENCES

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ASSOCIATED CONTENT

S Supporting Information *

CCDC 883848, CCDC 883844, and CCDC 883846 contain the supplementary crystallographic data for [Sm(2,4DClBA)3phen]2 (2), [Dy(2,4-DClBA)3phen]2 (3), and [Yb(2,4-DClBA)3phen]2 (4). These data can be obtained free of charge from The Cambridge Crystallographic Data Centre at www.ccdc.cam.ac.uk/data_request/cif. This material is available free of charge via the Internet at http://pubs.acs.org.

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ACKNOWLEDGMENTS

This research work is supported by the National Natural Science Foundation of China (nos. 21073053, 21141002, and 20773034) and the Natural Science Foundation of Hebei Province (no. B2012205022).

4. CONCLUSION A new series of binuclear lanthanide compounds with 2,4dichlorobenzoate and 1,10-phenanthroline were successfully synthesized and characterized. The two kinds of crystal structures were obtained due to the different coordination mode of carboxyl in compounds 2−4 based on the X-ray crystallography. The Sm3+ ions formed a distorted monocapped square-antiprism with a typical coordination number of nine in compound 2, while in compounds 3 and 4, the Dy3+ and Yb3+ ions had a coordination number of eight with a distorted square-antiprism coordination polyhedron. The heat capacities of compounds 1−4 were measured between 263.15 and 485.55 K by means of differential scanning calorimetry, and the derived thermodynamic functions (HT − H298.15), (ST − S298.15), and (GT − G298.15) of compounds 1−4 relative to the standard reference temperature 298.15 K were also calculated. Moreover, according to the antimicrobial testing results, these compounds exhibit good antimicrobial effects toward C. albicans and S. aureus, and better antibacterial effect toward E. coli. The fluorescence spectra of compounds 2 and 3 show the characteristic transitions of Sm3+ and Dy3+ ions.

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