Crystal Structures and Luminescent and Thermal Properties of

Article pubs.acs.org/jced

Crystal Structures and Luminescent and Thermal Properties of Lanthanide Complexes with 3,5-Diisopropylsalicylic Acid and 1,10Phenanthroline Jun-Ru Zheng,†,‡ Ning Ren,§ Jian-Jun Zhang,*,†,‡ Da-Hai Zhang,§ Li-Zhen Yan,† and Yuan Li‡ †

Testing and Analysis Center, Hebei Normal University, Shijiazhuang 050024, P. R. China College of Chemistry and Material Science, Hebei Normal University, Shijiazhuang 050024, P. R. China § Department of Chemistry, Handan College, Handan 056005, P. R. China ‡

ABSTRACT: Two novel complexes ([Ln(3,5-Dipr-2-OHBA)3(phen)]2 (Ln = Dy(1), Yb(2); 3,5-Dipr-2-OHBA = 3,5-diisopropylsalicylic acid; phen = 1,10phenanthroline)) were synthesized and characterized by elemental analysis, conductivity measurements, IR spectra, single crystal X-ray diffraction, and thermogravimetric differential scanning calorimetry/Fourier transform infrared (TG/DSC-FTIR) technology. The fluorescent property of complex 1 was also studied. The two binuclear complexes are isostructural. Each Ln3+ ion is octacoordinated, yielding a trigondodecahedron conformation. The thermal properties of the title complexes were investigated by simultaneous TG/DSC-FTIR techniques. The kinetic parameters of the first decomposition stage for the complexes were calculated by the integral isoconversional nonlinear method (NL-INT method), Starink method, Kissinger’s method, and Ozawa−Doyle’s method. The thermodynamic parameters (ΔH≠, ΔG≠, and ΔS≠) at the peak temperatures of the DTG curves were also calculated. Heat capacities of the two complexes were measured by DSC. The values of the experimental heat capacities were fitted to a polynomial equation with the least-squares method. Besides, the smoothed heat capacities and thermodynamic functions (HT − H298.15K), (ST − S298.15K), and (GT − G298.15K) were calculated.

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INTRODUCTION

heat capacities is crucial for designing chemical processes as well as for the progress of thermodynamic theories.26 In this work, we synthesized two novel complexes ([Ln(3,5Dipr-2-OHBA)3(phen)]2 (Ln = Dy, Yb) and determined their crystal structures. The photoluminescence behavior of [Dy(3,5Dipr-2-OHBA)3(phen)]2 was also studied. The thermodynamics and kinetics of the thermal decomposition of the title compounds were studied using the TG/DSC-FTIR coupling techniques. The FTIR absorption spectra of the products formed during thermal decomposition were obtained. The nonisothermal multiple scan method, which does not involve the kinetic model function, has been widely recognized in dealing with the thermal analysis data. Here, the kinetic parameters of the first decomposition stage for the complexes were calculated by the integral isoconversional nonlinear method (NL-INT method), Starink method, Kissinger’s method, and Ozawa−Doyle’s method. The thermodynamic parameters (ΔH≠, ΔG≠, and ΔS≠) at the peak temperatures of the DTG curves were also calculated. Heat capacities of the two complexes were measured by differential scanning calorimetry (DSC). The values of the experimental heat capacities were fitted to a polynomial equation with the least-squares method.

Very young children are fascinated with building blocks because elaborate structures may be created from far simpler objects. It is with the same enthusiasm that chemists have much interest in coordination chemistry due to the versatile coordination modes of complexes.1−3 There is a continued interest in synthesizing macrocyclic complexes of lanthanides,4−6 because they have potential value in basic and applied research.7 Lanthanide complexes have been widely used in biochemistry, magnetic materials, catalysts, photoelectric conversion material, and so on,8−18 due to the specific structure of f-electronic shells of lanthanides19 and the structural diversity of lanthanide complexes. Thermal analyses of solid materials are very important in understanding their thermal behavior, for example, estimation of the decomposition temperature of devices, prediction of the aging of concretes, determination of the safety conditions of explosive materials, and so on.20 Kinetic analyses of thermal decomposition processes have attracted the interest of researchers all along.21−25 Kinetic data are also important in the development of theoretical models that aim to postulate mechanisms for thermal decomposition. As we know, heat capacities of substances are necessary for thermodynamic calculations, such as the determination of enthalpy, entropy, and Gibbs free energy. The knowledge of the © 2012 American Chemical Society

Received: May 8, 2012 Accepted: July 31, 2012 Published: August 9, 2012 2503

dx.doi.org/10.1021/je3005134 | J. Chem. Eng. Data 2012, 57, 2503−2512

Journal of Chemical & Engineering Data

Article

Based on the fitted polynomial and thermodynamic equations, the smoothed heat capacities and thermodynamic functions (HT − H298.15K), (ST − S298.15K), and (GT − G298.15K) were calculated.

structures were resolved by direct methods using the SHELXS97 program and refined by full-matrix least squares on F2 using the SHELXL-97 program. The thermogravimetric (TG), differential thermogravimetric (DTG), differential scanning calorimetric (DSC), and Fourier transform infrared (FTIR) analyses were conducted using a TG/DSC-FTIR system, which was a Netzsch STA 449 F3 Instrument with a Bruker TENSOR27 FTIR spectrometer, under a simulated air atmosphere, with the rate of 10 K·min−1 from (300.15 to 1273.15) K. The Netzsch STA 449 F3 instrument was linked to the heated gas cell of the FTIR instrument by means of a heated transfer line, and the temperatures of the cell and the transfer line were kept at 473 K. The sample masses were about 6 mg. The heat capacities of the complexes were determined using a Netzsch DSC 200 F3 in the temperature range of (273.15 to 485.15) K under the linear heating rate of 10 K·min−1 using an indirect measurement method. The atmosphere was nitrogen gas, and the flow rate was 20 mL·min−1. To verify the reliability of the heat capacity measurement method by DSC, the heat capacity of the reference standard material sapphire was measured, and the relative deviations of our experimental results were within 0.50 % compared with the recommended values by the National Institute of Standards and Technology (NIST).27 The baseline, reference, and sample measurements were carried out under the same conditions. The sample masses were about 10 mg, and the reference standard substance sapphire mass used was 12.74 mg. The apparatus has an automatic data processing program from which we can obtain the Cp,m curves of the sample by an indirect measurement method.

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EXPERIMENTAL SECTION Synthesis of Complexes 1 and 2. A mixture of 3,5-Dipr2-OHBA (0.6 mmol) and phen (0.2 mmol) was dissolved in ethanol (95 %), and the pH of the solution was adjusted between 5 to 7 using 1 mol·L−1 NaOH solution. Then the mixture ligands was added dropwise into the LnCl3·6H2O (Ln = Dy(1), Yb(2); 0.2 mmol) aqueous solution under stirring. The stirring was maintained for 8 h and left standing for 12 h. Subsequently, the precipitates were filtered out and dried. After the volatilization of the mother liquor, the cuboid crystals of the title complexes were obtained in two weeks at room temperature. Calcd for 1: C, 60.86; H, 5.91; N, 2.78; Dy, 16.14 %. Found: C, 60.53; H, 5.94; N, 2.85; Dy, 15.78 %. Calcd for 2: C, 60.23; H, 5.85; N, 2.75; Yb, 17.01 %. Found: C, 60.82; H, 5.91; N, 2.75; Yb, 16.70 %. Materials. All of the reagents were of analytical grade and used without further purification as commercially obtained. Table 1 summarizes relevant information on sample material Table 1. Chemical Samples Used in this Study source

state

initial mole fraction

Beijing Lanthanide Innovation Technology Co., Ltd. Alfa Aesar

solid

0.999

solid

≥0.98

Kerme Tianjin Yongda Chemical Reagent Co., Ltd. Tianjin Senchang Industrial Co., Ltd.

solid liquid

≥0.99 ≥0.95

solid

≥0.96

chemical name Ln2O3 3,5diisopropylsalicylic acid 1,10-phenanthroline 95 % ethanol NaOH

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RESULTS AND DISCUSSION Molar Conductance. The molar conductance of title complexes was detected using 1.0·10−3 mol·L−1 solutions in N,N-dimethylformamide (DMF). The values of the two complexes are 12.40 s·cm2·mol−1 and 15.16 s·cm2·mol−1, respectively, indicating that the two complexes are both nonelectrolyte.28 Infrared Spectra. IR spectra data of the organic ligands and the complexes are listed in Table 2. In the IR spectra of the complexes, the characteristic peaks of νas(COO−) and νs(COO−) of the ligand 3,5-Dipr-2-OHBA are observed at (1624 and 1385) cm−1, and the νCO (−COOH) of the free ligand at 1691 cm−1 completely disappears. Meanwhile, the band at (419 to 420) cm−1 in the complexes is assigned to ν(Ln−O). These facts indicate that the oxygen atoms from the carboxylate group are coordinated to the Ln3+ ion.29 The bands of νCN (1560 cm−1) and δC−H ((853 and 735) cm−1) in the spectra of the free phen ligand are observed to move to lower wavenumbers in complexes, suggesting the coordination of the two nitrogen atoms of the neutral ligand to the Ln3+ ion.30,31

purities. LnCl3·6H2O (Ln = Dy, Yb) were prepared by dissolving Ln2O3 in hydrochloric acid and then by evaporating the liquid with water-bath heating. Apparatus and Conditions of the Experiment. The Ln content was determined by ethylenediaminetetraacetic acid (EDTA) titration using xylenol orange as an indicator. Elemental analyses of C, H, and N were determined using a Vario-EL III elemental analyzer. Conductivity measurements were carried out with a Shanghai DDS-307 conductometer. IR spectra of the compounds were obtained on a Bruker TENSOR27 spectrometer in the range of (4000 to 400) cm−1 using the conventional KBr discs technique at room temperature. The single crystal X-ray diffraction data were obtained by a Saturn724+ diffractometer with graphitemonochromated Mo Kα radiation (λ = 0.71073 Å). The

Table 2. Frequencies (cm−1) of the Absorption Bands for the Ligands and Complexesa

a

ligands and complex

νCN

phen 3,5-Dipr-2-OHBA [Dy(3,5-Dipr-2-OHBA)3(phen)]2 [Yb(3,5-Dipr-2-OHBA)3(phen)]2

1560

ν(CO)

νas(COO−)

νs(COO−)

δC−H

νLn−O

853

735

844 850

730 729

1691 1549 1553

1624 1624

1385 1385

419 420

Standard uncertainties u( f) = 1 cm−1 ( f is frequency). 2504



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Single-Crystal X-ray Diffraction Studies. The crystal structure data and refinement details for complexes 1 and 2 are listed in Table 3. Selected bond lengths are given in Table 4.

Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_ request/cif. Here complex 1 is chosen as a representative. [Dy(3,5-Dipr2-OHBA)3(phen)]2 is a centrosymmetric binuclear complex. Each Dy3+ ion is octa-coordinated by four oxygen atoms from two chelating 3,5-Dipr-2-OHBA groups, two oxygen atoms from two bridging 3,5-Dipr-4-OHBA ligands and two nitrogen atoms from one chelating phen molecule (Figure 1a). The coordination polyhedron is a trigondodecahedron (Figure 1b).

Table 3. Crystal Data and Structure Refinement for Complexes 1 and 2 parameter empirical formula formula weight temperature (K) wavelength crystal system, space group unit cell dimensions a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) volume Z, ρcalc. (Mg·m−3) absorption coefficient (mm−1) F(000) crystal size (mm) θ range (deg) limiting indices

collected/unique

complex 1 C102H118N4O18Dy2 2013.00 185(2) 0.71073 Å triclinic, P-1

2 C102H118N4O18Yb2 2034.08 293(2) 0.71073 Å triclinic, P-1

11.8019(19) 13.618(2) 17.201(3) 101.0250(10) 100.7720(10) 112.7000(10) 2397.3(7) Å3 1, 1.394 1.615

12.0520(11) 13.5729(13) 17.1721(18) 100.2130(10) 100.9300(10) 113.406(2) 2429.6(4) Å3 1, 1.390 1.980

1034 0.26 × 0.16 × 0.10 3.08−27.49 −15 ≤ h ≤ 15 −17 ≤ k ≤ 17 −22 ≤ l ≤ 22 23359/10798 [R(int) = 0.0278] 0.8552 and 0.6779

1042 0.19 × 0.13 × 0.10 2.34−25.02 −9 ≤ h ≤ 14 −16 ≤ k ≤ 12 −20 ≤ l ≤ 20 12725/8460 [R(int) = 0.0333] 0.8266 and 0.7048

max. and min. transmission data/restraints/ 10798/0/544 parameters 2 goodness of fit on F 0.999 final R indices [I > 2σ(I)] R1 = 0.0508, wR2 = 0.1206 R indices (all data) R1 = 0.0578, wR2 = 0.1256 largest diff. peak and hole 3.368 and −3.227 (e·Å−3)

8460/0/591 0.996 R1 = 0.0509, wR2 = 0.1011 R1 = 0.0822, wR2 = 0.1138 1.385 and −0.826

Table 4. Selected Bond Lengths (Å) for Complexes 1 and 2a complex 1 Dy(1)−O(9)#1 Dy(1)−O(5) Dy(1)−O(6) Dy(1)−N(1) complex 2

2.240(3) 2.369(3) 2.404(4) 2.498(4)

Dy(1)−O(8) Dy(1)−O(3) Dy(1)−O(2) Dy(1)−N(2)

2.312(3) 2.369(3) 2.428(3) 2.535(4)

Yb(1)−O(2)#1 Yb(1)−O(4) Yb(1)−O(7) Yb(1)−N(2)

2.200(4) 2.325(5) 2.369(5) 2.460(5)

Yb(1)−O(1) Yb(1)−O(8) Yb(1)−O(5) Yb(1)−N(1)

2.264(4) 2.331(4) 2.400(4) 2.489(6)

Figure 1. (a) Molecular structure of complex 1. (b) Coordination geometry of the Dy3+ ion.

The average distance between the Dy3+ ion and the coordination oxygen atoms is 2.354 Å. The Dy−O bond lengths of chelating carboxyl groups are longer than those of the bidentate bridging carboxyl groups, probably owing to the stronger strain in the four-membered ring of chelating coordination.32 The mean length of Dy−N bonds is 2.517 Å, which is longer than the Dy−O average distance. Just for these reasons, the neutral ligand phen and part of the carboxyl groups were decomposed in the first stage of the thermal decomposition process.

Symmetry transformations used to generate equivalent atoms: #1 −x + 1, −y + 1, −z + 1. a

On the basis of single-crystal X-ray diffraction studies, complexes 1 and 2 are isostructural. CCDC 846564 and 846563 contain the crystallographic data for complexes 1 and 2. These data can be obtained free of charge from The Cambridge 2505



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stronger, that is possibly due to the coordination environment.34 Thermal Decomposition Process of the Title Complexes. TG, DTG, and DSC curves were obtained with the rate of 10 K·min−1 from (300.15 to 1273.15) K, which are shown in Figure 4, respectively. The thermal analytical data of

The mean Yb−O and Yb−N bond lengths of the complex 2 are 2.315 Å and 2.475 Å (Figure 2), which are slightly shorter

Figure 2. (a) Molecular structure of complex 2. (b) Coordination geometry of the Yb3+ ion. Figure 4. TG-DTG and DSC curves of complexes 1 (a) and 2 (b) at a heating rate of 10 K·min−1.

than the corresponding average distances of the complex 1. This can be explained by the fact that the radius of the Dy3+ ion is larger than that of the Yb3+ ion.33 Fluorescence Spectra. The emission spectrum of complex 1 (Figure 3) was recorded upon the excitation wavelength at

the two complexes are listed in Table 5. The enthalpies and peak temperatures for the two complexes from DSC analysis are listed in Table 6. Complex 1 will be described in detail. According to the DTG curve, the thermal decomposition process of the complex 1 presents two main stages. In the first stage, the corresponding weight loss on TG curve is 32.74 % due to the release of all phen molecules and part of (3,5-Dipr-2-OHBA) ligands. A further increase of the temperature leads to the completed decomposition of the organic ligands. The total weight loss is 81.04 %, indicating that the residues are Dy2O3 (calculated, 81.47 %). Moreover, in the first stage, there appears a small endothermic peak (Tp = 548.25 K, ΔHm = 232 J·g−1) on the DSC curve, corresponding to release the two phen molecules and part of (3,5-Dipr-2-OHBA) ligands. In the second stage, a strong exothermic peak (Tp = 725.35 K, ΔHm = −5097 J·g−1) corresponding to the loss of the remaining organic ligands can be observed on the DSC curve. The decomposition stages of complex 2 are similar to complex 1. Based on the above analysis, the thermal decomposition of the title complexes can be described as the following process:

Figure 3. Emission spectrum of complex 1 (λex = 345 nm).

345 nm. Obviously, the Dy3+ ion gives rise to the typical emission bands at 482 and 575 nm corresponding to the characteristic emission 4 F 9/2 → 6 H 15/2 and 4 F 9/2 → 6 H13/2 transitions. The second emission peak corresponding to the hypersensitive transition 4F9/2−6H13/2 (ΔL = 2, ΔJ = 2) is 2506



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Table 5. Thermal Decomposition Data for Complexes 1 and 2 (β = 10 K·min−1) mass loss rate/% complexes

stage

temperature range (K) DTG peak temperature (K)

1

I II

507.82−587.25 587.25−1232.15

546.82 722.82

2

I II

505.89−578.35 578.35−1201.45

549.89 752.89

found 32.74 48.30 81.04a 33.69 46.44 80.13a

calcd b

17.90 63.57 81.47a 17.72b 62.91 80.63a

probable removed groups

residue

−2phen-x(3,5-Dipr-4-OHBA) −(6−x) (3,5-Dipr-4-OHBA)+3O

Dy2(3,5-Dipr-4-OHBA)6−x Dy2O3

−2phen-x(3,5-Dipr-4-OHBA) −(6−x) (3,5-Dipr-4-OHBA)+3O

Yb2(3,5-Dipr-4-OHBA)6‑x Yb2O3

The total loss rate. bTheoretical value of the loss of two phen molecules. In column 7 assign + for including oxygen atoms and − for leaving groups. Standard uncertainties u are u(T) = 0.01 K, u(w) = 0.0001 (w is the mass loss rate). a

Table 6. Enthalpies and Peak Temperatures for Complexes 1 and 2 from DSC Analysisa ΔHm complexes

stage

temperature range (K)

DSC peak temperature (K)

1

I

536.3−562.65

548.25

II

709.55−741.65

725.35

I

540.15−558.35

548.45

II

628.15−777.95

756.15

2

a

(J·g−1) 232 (endo) 5097 (exo) 136 (endo) 4846 (exo)

Standard uncertainties u are u(T) = 0.01 K, u(ΔHm) = 1 (J·g−1).

[Ln(3,5‐Dipr‐2‐OHBA)3 (phen)]2 → Ln2(3,5‐Dipr‐2‐OHBA)6 − x → Ln2O3(Ln = Dy, Yb)

TG-FTIR Spectra of Gaseous Products. Stacked plots of the FTIR spectra of the evolved gases for the two complexes (Figure 5) were observed in the online (TG-FTIR) system at the heating rate of 10 K·min−1. The complex 1 was chosen as a representative due to the same thermal decomposition processes and IR spectra of gaseous products. According to Figure 5a, the FTIR spectrum of the evolved gas for the complex 1 presents two main stages, which is consistent with the thermal decomposition processes. Furthermore, the strongest signals of the two main stages in the FTIR spectrum, corresponding to the DTG peak, are at 547.35 K and 731.79 K, respectively. Two IR spectra at T = (547.35 and 731.79) K are shown in Figure 6. The evolved gases in the first stage of thermal decomposition process are more complicated according to Figure 6a. The characteristic bands of CO2 (2359 to 2310 cm−1)35 and H2O (3566 to 3737 cm−1) can be observed. Besides in the FTIR spectra some gaseous organics are detected. The absorption peak at 2969 cm−1 is attributed to the νC−H from evolved aliphatic or aromatic hydrocarbons. The bonds (1609 and 1500 cm−1) are attributed to the νCC of the benzene ring. Simultaneously, the bands of (1609 and 1500) cm−1 can also be considered as the νCN, which overlap with other evolved gases in the FTIR spectra. There is a characteristic peak at 1429 cm−1 attributed to the stretching of the carbonyl group, νC−O. The bands at (1389 and 1369) cm−1 can be attributed to deformation symmetric vibrations of −CH3 groups. Bands in the wavenumbers (1315 and 1169) cm−1 are considered as the νC−O and the βO−H of phenolichydroxyl, respectively. From the

Figure 5. Stacked plots of the FTIR spectra of the evolved gases for the complexes 1 and 2 as observed in the online (TG-FTIR) system at the heating rate of 10 K·min−1 (a = complex 1, b = complex 2).

above, it can be concluded that the gaseous products contain broken and not broken carboxylic ligands and phen ligands. According to Figure 6b, in the second stage, the main characteristic bands of CO2 (2359 to 2310 cm−1), H2O (3566 to 3737 cm−1), and CO (2182, 2114 cm−1)36 are only detected. The organic ligands are probablely decomposed at 731.79 K under air atmosphere. Kinetics of the First Decomposition Stage. The activation energies E of the first decomposition stage were obtained by the integral isoconversional nonlinear method 2507



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Figure 7. Relationship between E and a by the NL-INT method (a = complex 1, b = complex 2).

Figure 8. Relationship between E and a by the Starink method (a = complex 1, b = complex 2). Figure 6. FTIR spectra of the evolved gases for the complex 1 at T = (547.35 (a) and 731.79 (b)) K.

indicating that the first decomposition stage is a multiple-step reaction.39−41 In the present work, the values of the apparent activation energy E and the pre-exponential factor A at the peak temperatures of DTG curves were calculated using Kissinger’s method42 and Ozawa−Doyle’s method.43 The Kissinger eq 4 and Ozawa−Doyle eq 5 are as follows, respectively:

(NL-INT method)37 and the Starink method38 in the condition of not involving the kinetic function. The equations are as follows: NL-INT method: n

Ω1I(Eα) = min

n

∑∑ i=1 j≠i

βj ·I(Eα , Tα , i) βi ·I(Eα , Tα , j)

⎛ β⎞ E 1 AR − a ln⎜⎜ 2 ⎟⎟ = ln E R Tp a ⎝ Tp ⎠

− n(n − 1) (1)

log β +

where the integral form of I(E,T) is the Senum−Yang approximate calculation ⎡ ⎞⎤ ⎛ u 2 + 10u + 18 ISY‐3(E , T ) = ⎢Te−u⎜ 3 ⎟⎥ ⎝ u + 12u 2 + 36u + 24 ⎠⎦ ⎣

β Tf

1.92

= −1.0008

E +C RTf

(5)

where Tp is the peak temperature, K; R is the gas constant, 8.314 J·mol−1·K−1; β is the linear heating rate, K·min−1; C is a constant. Based on the first peak temperatures measured with four different heating rates of (5, 10, 15, and 20) K·min−1, the kinetic parameters were obtained and are listed in Table 7. The calculated results using the four methods were similar. By substituting the average values of activation energy E and preexponential factor A into eqs 6 to 8,44,45 thermodynamic parameters of the complexes at the peak temperatures were evaluated.

(2)

Starink method: ln

0.4567Ea =C RTp

(4)

(3)

where Tf is the absolute temperature, β is the linear heating rate, R is the gas constant, E is the activation energy, and C is a constant. The relationship between E and a (conversion) using the two methods are shown in Figures 7 and 8. By comparison and analysis, the values of E corresponding to a obtained using the two methods are very consistent with each other. Besides, the activation energy E change obviously with the values of α, 2508

A exp( −E /RT ) = ν exp(−ΔG≠/RT )

(6)

ΔH ≠ = E − RT

(7)

ΔG≠ = ΔH ≠ − T ΔS ≠

(8)



Article

Table 7. Kinetic Parameters of the Complexes complex 1

E

ln A

kinetic method

kJ·mol−1

s−1

NL-INT Starink Kissinger Ozawa−Doyle average value complex 2

194.35 194.36 194.2 193.2 194.03 E

38.361

ln A

−1

kinetic method

s−1

kJ·mol

NL-INT Starink Kissinger Ozawa−Doyle average value

Table 9. Experimental Molar Heat Capacities of Complexes 1 and 2a

210.02 210.03 209.8 208.2 209.51

41.815

where ν is the Einstein vibration frequency, ν = kB T/h (kB and h are Boltzmann and Planck constants, respectively), ΔG≠ the Gibbs energy of activation, ΔH≠ the enthalpy of activation, and ΔS≠ the entropy of activation. The values of entropy, enthalpy, and the Gibbs free energy of activation at the considered peak temperature are shown in Table 8. The values of ΔG≠ are more than 0, indicating that the Table 8. Thermodynamic Parameters of the Complexes ΔG≠

β complexes 1

2

K·min

−1

−1

kJ·mol

ΔH≠ −1

kJ·mol

ΔS≠

Tp

J·mol−1·K−1

K

5 7 10 15 average value

156.83 156.53 156.33 156.01 156.43

189.56 189.51 189.48 189.44 189.50

60.80 60.73 60.68 60.60 60.70

538.15 543.15 546.45 551.75

5 7 10 15 average value

156.72 156.32 155.98 155.60 156.16

205.02 204.99 204.95 204.92 204.97

89.50 89.43 89.37 89.31 89.40

539.75 544.15 547.95 552.25

decomposition reactions for the two complexes are not spontaneous reaction. The values of ΔH≠ are more than 0, suggesting that the reactions are endothermic. Heat Capacity of the Title Complexes. The molar heat capacities of the two complexes were measured by DSC from (263.15 to 485.15) K. The average molar heat capacities of four parallel experiments are listed in Table 9 and plotted in Figure 9. The average values of the molar heat capacities were fitted to the following polynomial equation at reduced temperature (x) by means of the least-squares method.46,47 The equation is the following: Complex 1:

complex 1

complex 2

T

Cp,m

Cp,m

T

complex 1 Cp,m

complex 2 Cp,m

K

J·K−1·mol−1

J·K−1·mol−1

K

J·K−1·mol−1

J·K−1·mol−1

263.15 266.15 269.15 272.15 275.15 278.15 281.15 284.15 287.15 290.15 293.15 296.15 299.15 302.15 305.15 308.15 311.15 314.15 317.15 320.15 323.15 326.15 329.15 332.15 335.15 338.15 341.15 344.15 347.15 350.15 353.15 356.15 359.15 362.15 365.15 368.15 371.15 374.15

2328.3 2350.0 2371.2 2394.1 2417.4 2443.0 2469.7 2497.0 2524.4 2553.3 2583.7 2615.8 2649.2 2683.0 2718.0 2750.8 2782.2 2813.2 2843.8 2874.3 2899.2 2923.6 2945.7 2965.3 2984.5 3007.3 3035.3 3063.0 3086.9 3104.7 3119.7 3134.3 3149.5 3161.5 3170.6 3178.5 3183.3 3184.0

2302.7 2325.5 2348.4 2373.8 2401.7 2429.0 2456.9 2487.3 2518.0 2551.8 2586.3 2624.7 2664.2 2702.9 2743.1 2782.8 2820.3 2858.6 2895.4 2928.4 2959.6 2989.1 3014.21 3036.8 3059.9 3080.7 3094.5 3105.1 3114.6 3126.8 3139.1 3150.1 3162.8 3183.4 3203.3 3221.4 3240.0 3258.7

377.15 380.15 383.15 386.15 389.15 392.15 395.15 398.15 401.15 404.15 407.15 410.15 413.15 416.15 419.15 422.15 425.15 428.15 431.15 434.15 437.15 440.15 443.15 446.15 449.15 452.15 455.15 458.15 461.15 464.15 467.15 470.15 473.15 476.15 479.15 482.15 485.15

3187.7 3195. 9 3208.7 3223.4 3235.9 3253.3 3270.5 3286.8 3303.8 3320.0 3336.5 3352.7 3367.4 3382.4 3400.4 3416.2 3430.5 3443.3 3456.8 3471.7 3486.0 3499.8 3512.8 3523.3 3532.4 3539.1 3542.3 3544.0 3544.5 3545.4 3547.7 3550.0 3556.7 3565.8 3577.8 3591.6 3601.0

3276.3 3290.3 3302.6 3312.2 3320.4 3328.8 3339.1 3352.5 3367.4 3382.1 3399.0 3417.4 3435.3 3450.4 3466.0 3479.7 3492.8 3507.2 3521.7 3536.2 3550.9 3563.2 3574.9 3585.3 3597.7 3611.3 3623.2 3632.9 3644.5 3661.7 3679.2 3697.8 3717.4 3736.3 3753.0 3770.2 3789.3

a Standard uncertainties u are u(T) = 0.01 K, u(Cp,m) = 0.1 (J·K−1·mol−1).

Cp,m/J·mol−1· K−1 = 3191.64 + 383.3x + 23.25x 2 + 1299.57x 3 − 806.95x 4 − 1989.93x 5 + 611.77x 6 + 952.98x 7 − 48.62x 8

R2 = 0.9997

Figure 9. Relationship of molar heat capacities varying with temperature (a = complex 1, b = complex 2).

Complex 2: 2509



Article

Cp,m/J·mol−1· K−1 = 3246.51 + 478.44x + 190.24x 2

Table 11. Smoothed Molar Heat Capacities and Thermodynamic Functions of Complex 2

+ 619.62x 3 − 1851.34x 4 − 373.78x 5 + 2380.9x 6 + 14.91x 7 − 917.03x 8

where x is the reduced temperature, x = [T − (Tmax + Tmin)/ 2]/[(Tmax − Tmin)/2], T is the experimental temperature, Tmax and Tmin are the respective upper limit (485.15 K) and lower limit (236.15 K) in the above measured temperature region, and R2 is the correlation coefficient. Thermodynamic Functions of the Title Complexes. The smoothed heat capacities and thermodynamic functions of the two complexes were calculated on the basis of each fitted polynomial and the following thermodynamic equations:31 T

HT − H298.15K =

∫298.15K Cp,mdT

(9)

T

∫298.15K Cp,mT −1dT

ST − S298.15K =

(10)

T

GT − G298.15 K =

T

∫298.15K Cp,mdT − T ∫298.15K Cp,mT −1dT (11)

The smoothed values of Cp,m and thermodynamic functions relative to the standard reference temperature 298.15 K with an interval of 10 K are shown in Tables 10 and 11, respectively.

■

CONCLUSION Two new coordination compounds of [Ln(3,5-Dipr-2-OHBA)3(phen)]2 were synthesized and characterized. The crystal structures showed that the central Ln3+ ions of the dinuclear complexes were octa-coordinated into a trigondodecahedron

K 263.15 273.15 283.15 293.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15 383.15 393.15 403.15 413.15 423.15 433.15 443.15 453.15 463.15 473.15 483.15

HT − H298.15K

Cp,m −1

−1

J·K ·mol

2325.17 2403.34 2487.99 2585.72 2692.66 2800.5 2900.71 2987.05 3056.73 3110.62 3152.56 3188.19 3223.52 3263.48 3310.63 3364.37 3420.74 3473.17 3514.25 3538.75 3548.13 3556.64 3599.28

Cp,m

HT − H298.15K

ST − S298.15K

GT − G298.15K

J·K−1·mol−1

kJ·mol−1

J·K−1·mol−1

kJ·mol−1

263.15 273.15 283.15 293.15 303.15 313.15 323.15 333.15 343.15 353.15 363.15 373.15 383.15 393.15 403.15 413.15 423.15 433.15 443.15 453.15 463.15 473.15 483.15

2310.09 2378.62 2474.87 2594.41 2722.99 2845.81 2952.41 3038.34 3104.7 3156.43 3200.19 3242.21 3286.8 3335.5 3387.2 3439.03 3487.86 3532.01 3572.6 3613.94 3661.94 3719.68 3778.8

−86.156 −62.733 −38.49 −13.158 13.481 41.336 70.344 100.315 131.046 162.361 194.148 226.36 259.002 292.11 325.722 359.855 394.493 429.597 465.122 501.052 537.423 574.325 611.825

−306.93 −219.57 −132.42 −44.51 44.84 135.23 226.4 317.74 408.61 498.56 587.32 674.82 761.14 846.44 930.86 1014.49 1097.33 1179.31 1260.39 1340.57 1419.96 1498.78 1577.21

−5.388 −2.756 −0.996 −0.111 −0.112 −1.011 −2.818 −5.539 −9.171 −13.707 −19.137 −25.448 −32.628 −40.667 −49.553 −59.28 −69.84 −81.223 −93.422 −106.427 −120.23 −134.824 −150.204

geometry. Under the UV light excitation, the complex 1 exhibited characteristic luminescence of the dysprosium ion. A thermal analysis of the title complexes was investigated by simultaneous TG/DSC-FTIR techniques. The relationship between E and a were calculated by the NL-INT method and the Starink method, indicating the first decomposition stage was a multiple-step reaction. The thermodynamic parameters (ΔH≠, ΔG≠, and ΔS≠) at the peak temperatures of the DTG curves were also calculated. The heat capacities of the two complexes were measured by DSC. The smoothed heat capacities and thermodynamic functions (HT − H298.15K), (ST − S298.15K), and (GT − G298.15K) were also calculated.

Table 10. Smoothed Molar Heat Capacities and Thermodynamic Functions of Complex 1 T

T K

R2 = 0.9997

ST − S298.15K J·K ·mol

kJ·mol−1

−86.533 −62.89 −38.444 −13.086 13.354 40.824 69.34 98.792 129.025 159.874 191.198 222.905 254.961 287.391 320.256 353.627 387.553 422.029 456.979 492.259 527.702 563.216 598.946

−308.33 −220.15 −132.26 −44.26 44.42 133.56 223.19 312.94 402.35 490.96 578.42 664.54 749.32 832.87 915.41 997.17 1078.31 1158.83 1238.6 1317.32 1394.69 1470.55 1545.28

−5.396 −2.755 −0.993 −0.111 −0.111 −1 −2.783 −5.463 −9.04 −13.506 −18.854 −25.069 −32.139 −40.051 −48.793 −58.356 −68.733 −79.919 −91.907 −104.687 −118.248 −132.575 −147.654

kJ·mol

−1

−1

GT − G298.15K

−1

■

AUTHOR INFORMATION

Corresponding Author

*Tel.: +86-31180786457. Fax: +86-31180786312. E-mail address: [email protected]. Funding

This project was supported by the National Natural Science Foundation of China (Nos. 21073053 and 20773034) and the Natural Science Foundation of Hebei Province (No. B2012205022). Notes

The authors declare no competing financial interest.

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NOTE ADDED AFTER ASAP PUBLICATION This paper was published on the Web on August 9, 2012 with an incorrect version of equation 4 and incorrect title for Table 7. The corrected version was reposted on August 16, 2012.

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Crystal Structures and Luminescent and Thermal Properties of

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