Crystal structures and thermodynamic properties of lanthanide complexes with 2-chloro-4,5-difluorobenzoate and 1,10-phenanthroline

J. Chem. Thermodynamics 56 (2013) 38–48

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Crystal structures and thermodynamic properties of lanthanide complexes with 2-chloro-4,5-difluorobenzoate and 1,10-phenanthroline Kun Tang a,b, Jian-Jun Zhang a,b,⇑, Da-Hai Zhang c, Ning Ren c, Li-Zhen Yan a, Yuan Li b,⇑ a

Testing and Aanlysis Center, Hebei Normal University, Shijiazhuang 050024, PR China College of Chemistry & Material Science, Hebei Normal University, Shijiazhuang 050024, PR China c Department of Chemistry, Handan College, Handan 056005, PR China b

a r t i c l e

i n f o

Article history: Received 11 May 2012 Received in revised form 5 June 2012 Accepted 30 June 2012 Available online 14 July 2012 Keywords: Rare earth Crystal structure Thermogravimetric analysis Infrared (IR) spectroscopy Thermodynamics

a b s t r a c t A series of lanthanide complexes with the 2-chloro-4,5-difluorobenzoate (2-cl-4,5-dfba) and 1,10-phenanthroline (phen), have been synthesized with the formulae of [La(2-cl-4,5-dfba)3phen]nnH2O (1), [Nd(2-cl-4,5-dfba)3phenH2O]2 (2), [Ln(2-cl-4,5-dfba)3phen]2 (Ln = Eu (3), Ho (4)). The complexes are characterized by elemental analysis, infrared and fluorescent spectra and X-ray single-crystal diffraction. The structures of the four complexes are very different. Complex 1 is an infinite 1D chain polymeric structure formed by the asymmetric units with the mirror growth pattern. Each La3+ ion is coordinated to four bridging carboxylic groups, two tridentate chelating–bridging carboxylic groups, simultaneous with one phen molecule, giving the coordination number of nine. In the molecular structures of complexes 2 and 3, two Ln3+ ions are linked by four carboxyl groups, forming two binuclear molecules. In addition, each Nd3+ ion in complex 2 is bonded to one H2O molecule and one carboxyl group by monodentate mode, one phen molecule by bidentate chelating, and each Eu3+ ion is also chelated to one phen molecule and one carboxyl group in complex 3. And in complex 4, the Ho3+ ion yields a eight-coordinated distorted square anti-prism coordination geometry. The three-dimensional IR accumulation spectra of gaseous products for complexes 1 to 4 are analyzed and further authenticated the thermal decomposition processes with TG-DTG curves. The heat capacities of complexes 2 to 4 are measured and fitted to a polynomial equation by the least squares method on the basis of the reduced temperature x (x = [T(Tmax + Tmin)/2]/[(Tmax  Tmin)/2]). Then the smoothed molar heat capacities and thermodynamic functions of complexes 2 to 4 are calculated. The fluorescence intensity of complex 3 is markedly improved as well. Ó 2012 Elsevier Ltd. All rights reserved.

1. Introduction It is undeniable that lanthanide is a valuable natural resource. Due to its high coordination number and flexible coordination modes [1], more and more lanthanide complexes are obtained. The unique and various structures are also observed, in which the one-dimensional chain structure of ternary complexes are rare [2]. Simultaneously, the expanding application values, such as activator [3], luminescent material [4] and bacteriostatic agents [5], have drawn public attention. In addition, the knowledge of the thermodynamic properties, e.g. heat capacity [6], phase transition [7], and thermal decomposition processes [8], is an important requirement for the basic data collection and their applications. The differential scanning calorimetry and the (TG/DSC + FTIR) system are the advanced science and technology to obtain valid data. As a part of our series of study, we successfully synthesized four ⇑ Corresponding authors. Address: Testing and Aanlysis Center, Hebei Normal University, Shijiazhuang 050024, PR China. Tel.: +86 31180786457; fax: +86 31180786312 (J.-J. Zhang). E-mail addresses: [email protected] (J.-J. Zhang), [email protected] (Y. Li). 0021-9614/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.jct.2012.06.032

complexes [La(2-cl-4,5-dfba)3phen]nnH2O (1), [Nd(2-cl-4,5-dfba)3phenH2O]2 (2), [Ln(2-cl-4,5-dfba)3phen]2 (Ln = Eu (3), Ho (4)). Here we report the synthesis, structures, fluorescence, and thermal properties of new lanthanide complexes. The results show that the structure of complex 1 is a one-dimensional chain structure formed by the asymmetric units with the mirror image growth pattern. And the thermal decomposition processes and heat capacity curves also show subtle differences. In addition, complex 3 exhibits intense fluorescence property.

2. Experimental 2.1. Material, experimental equipment, and conditions The Ln2O3, 2-chloro-4,5-difluorobenzoic acid, and 1,10-phenanthroline were acquired from commercial sources at analytical grade and used without further purification. Table 1 summarizes relevant information on sample material purities. Elemental analyses of C, H, and N were carried out on a Vario-EL III elemental analyzer and the metal content was determined by

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K. Tang et al. / J. Chem. Thermodynamics 56 (2013) 38–48 TABLE 1 Chemical samples used in this study. Chemical name

Source

State

Initial mole fraction

Ln2O3 2-Chloro-4,5-difluorobenzoic acid 1,10-Phenanthroline 95% Ethanol NaOH

Beijing Lanthanide Innovation Technology Co., Ltd. Alfa Aesar Kermel Tianjin Yongda Chemical Reagent Co., Ltd. Tianjin Senchang Industrial Co., Ltd.

Solid Solid Solid Liquid Solid

0.999 P0.98 P0.99 P0.95 P0.96

EDTA chelatometric titration. The IR spectra were recorded in the range of (4000 to 400) cm1 at room temperature using the Bruker TENSOR27 spectrometer with conventional KBr discs technique. The single crystal X-ray diffraction data were obtained by Saturn724+ diffractometer with graphite-monochromated Mo Ka radiation (k = 0.071073 nm) at T = 153 (2) K and 133 (2) K. The structure was solved by direct methods using the SHELXS-97 program and refined by full-matrix least squares on F2 using the SHELXL-97 program [9]. Table 2 gives the summary of the crystallographic data and details of the structure refinements for the complexes 1 to 4. The numbers of the four complexes (CCDC 804517 (1), 804521 (2), 804522 (3), 804520 (4)) contain the supplementary crystallographic data for this paper, which can be obtained free of charge from the Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Excitation and emission spectra were performed on an F-4600 Hitachi spectrophotometer. The thermogravimetric (TG), differential thermogravimetric (DTG), differential scanning calorimetric (DSC) of the complexes were conducted using a (TG/DSC + FTIR) system, which was a NETZSCH STA 449 F3 Instrument with a Bruker TENSOR27 Fourier transform infrared spectrometer, under a nitrogen atmosphere at a flow rate of 40 cm3  min1 with the heating rate of 10 K  min1 from T = 299.15 K to 1375.15 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 T = 473 K and 483 K. Heat capacities of the prepared complexes were determined using a NETZSCH DSC 200 F3 with the nitrogen atmosphere and the flow rate of 40 cm3  min1 over the temperature range of 258.15 K to 493.15 K at a heating rate of 10 K  min1. The heat capacity of the reference standard material sapphire (25.14 mg) was measured to verify the reliability of the heat capacity measurement method by DSC. Compared with the recommended values by the National Institute of Standards and Technology (NIST) [10], the relative deviations of our experimental results were within ±0.50%. The mass of the reference standard substance sapphire (25.14 mg) or a sample (6 mg) loaded in an aluminum crucible sealed with a pierced lid was accurately weighed on heating. The baseline, reference, and sample measurements were carried out under the same conditions. The apparatus has an automatic data processing program from which we can obtain the heat capacity curves of the sample by an indirect measurement method. 2.2. Preparation of complexes 1 to 4 The ligands of 2-chloro-4,5-difluorobenzoic acid (1.5 mmol) and 1,10-phenanthroline (0.5 mmol) were mixed together using the 95% ethanol and afterwards adjusted pH to 6 to 7 by adding

TABLE 2 Crystal data and structure refinement for complexes 1 to 4. Complex

1

2

3

4

Empirical formula Formula weight temperature/K Wavelength/nm Crystal system Space group Unit cell dimensions a/nm b/nm c/nm a/° b/° c/° Volume/nm3 Z, calculated Density/(mg  cm3) Absorption coefficient/mm F/000 Crystal size/mm h range for data collection/deg Limiting indices

C33H16Cl3F6LaN2O7 911.74 153(2) 0.071073 Triclinic  P1

C66H32Cl6F12N4Nd2O14 1834.14 153(2) 0.071073 Triclinic  P1

C66H28Cl6F12N4Eu2O12 1813.54 133(2) 0.071073 Monoclinic P2(1)/c

C66H28Cl6F12N4Ho2O12 1839.48 133(2) 0.071073 Monoclinic P2(1)/c

1.01057(12) 1.30171(15) 1.31887(15) 72.717(3 83.335(4) 85.693(4) 1.6439(3) 2, 1.842 1.630 892 0.32  0.32  0.27 2.56 to 29.12 13 6 h 6 3 17 6 k 6 17 17 6 l 6 17 17,332/8526 [R(int) = 0.0211] 96.5% 0.6673 and 0.6235 8526/3/477 1.000 R1 = 0.0236 wR2 = 0.0526 R1 = 0.0280 wR2 = 0.0543 463 and 418

1.0869(2) 1.1615(2) 1.4342(3) 104.307(2) 103.338(2) 102.2390(10) 1.6361(6) 1, 1.862 1.919 898 0.25  0.22  0.21 2.33 to 29.12 14 6 h 6 14 15 6 k 6 15 18 6 l 6 19 17,489/8512 [R(int) = 0.0295] 96.7% 0.6887 and 0.6455 8512/0/477 0.999 R1 = 0.0325 wR2 = 0.0666 R1 = 0.0384 wR2 = 0.0694 476 and 646

1.22678(18) 2.6455(4) 0.99496(15) 90 98.544(2)) 90 3.1932(8)) 2, 1.886 2.301 1768 0.32  0.25  0.15 2.28 to 29.12 16 6 h 6 15 36 6 k 6 36 13 6 l 6 13 33,094/8535 [R(int) = 0.0489] 99.4% 0.7300 and 0.5264 8535/0/460 0.957 R1 = 0.0433 wR2 = 0.1283 R1 = 0.0514 wR2 = 0.1366 993 and 1095

1.21768(14) 2.6624(3) 0.98983(11) 90 98.278(2) 90 3.1755(6) 2, 1.924 2.830 1784 0.25  0.22  0.08 2.85 to 29.14 16 6 h 6 16 36 6 k 6 36 12 6 l 6 13 31,401/8476 [R(int) = 0.0405] 99.1% 0.8116 and 0.5357 8476/0/460 0.998 R1 = 0.0346 wR2 = 0.0734 R1 = 0.0434 wR2 = 0.0780 1487 and 629

Reflections collected/unique Completeness to h = 29.15 Max. and min. transmission Data/restraints/parameters Goodness-of-fit on F2 Final R indices [I > 2r(I)] R indices (all data) Largest diff. peak and hole/(e  nm3)

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1.0 mol  dm3 NaOH solution. LnCl36H2O was obtained by a reaction of Ln2O3 and HCl (6.0 mol  dm3) and then drying to the solid. The LnCl36H2O (0.5 mmol) was dissolved in distilled water and then adding the mixture of ligands slowly. The mixture solution was stirred for 8 h at room temperature and then deposited for 12 h. Subsequently, the precipitates were filtered out, washed with 95% ethanol and dried in a far infrared dryer until powder. The single crystals were collected from the mother liquor after three weeks at room temperature. Elemental analyses for C33H16Cl3F6LaN2O7 (%): Calcd: C 43.47, H 1.77, N 3.07, La 15.24; Found: C 43.55, H 1.81, N 3.11, La 15.28; for C66H32Cl6F12N4Nd2O14 (%): Calcd: C 43.22, H 1.76, N 3.05, Nd 15.73; Found: C 43.69, H 1.64, N 3.11, Nd 16.04; for C66H28Cl6F12N4Eu2O12 (%): Calcd: C 43.71, H 1.56, N 3.09, Eu 16.76; Found: C 43.97, H 1.66, N 3.19, Eu 16.46; for C66H28Cl6F12N4Ho2O12 (%): Calcd: C 43.09, H 1.53, N 3.05, Ho 17.93; Found: C 43.24, H 1.70, N 3.06, Ho 18.24. 3. Results and discussion 3.1. Infrared spectra The values of the characteristic absorption of ligands and complexes in IR spectra are listed in table 3. The bonds of the organic carboxylate ligand mC@O completely disappear in the spectra of the complexes. However, the peaks appear arising from asymmetric and symmetric vibrations of the COO group at 1518 cm1, 1426 cm1 for complex 1, 1519 cm1, 1426 cm1 for complex 2, 1520 cm1, 1427 cm1 for complex 3, and 1521 cm1, 1428 cm1 for complex 4, respectively. Meantime the characteristic absorption bond of Ln–O (Ln = La, Nd, Eu, Ho) all occur at 417 cm1 or 416 cm1. These facts indicate that the oxygen atoms of the carboxylate ligands coordinate to the central Ln3+ ion. In addition, the absorption peaks of mC@N and dC–H of the phen ligand have downshifted to (1604 to 1628) cm1, (843 to 844) cm1, and (729 to 731) cm1 for complexes 1 to 4, suggesting that the coordination of the nitrogen atoms of the phen ligand to the Ln3+ ion [11]. 3.2. Structural description of complexes 1 to 4 The structures and coordination geometry of the four complexes are shown in figures 1a and 1b to 4a and 4b, respectively. Selected bond lengths for the complexes 1 to 4 are listed in table 4. As shown in the figures, they have different structures. So the structures of these complexes will be discussed separately in the following. 3.2.1. Structure of complex 1 As shown in figure 1b, complex 1 has an infinite 1D chain polymeric structure which is interesting in lanthanide carboxylate complexes. The chain is formed by the asymmetric units with the mirror growth pattern, namely, the asymmetric units of the 1D chain are equivalent. The crystal water molecule exists around the 1D chain with a proportion (La3+:H2O = 1:1). Each center of the

Fig. 1a. Asymmetric unit structure of complex 1 (A: 1  x, 1  y, 1  z, B: x, 1  y, 1  z). All hydrogen atoms and crystal water molecules are omitted for clarity, and thermal ellipsoids are drawn at the 30% probability level.

asymmetric unit, La3+ ion, is coordinated by four oxygen atoms from four bridging carboxylic groups, three oxygen atoms from two tridentate chelating–bridging carboxylic groups, simultaneous with two nitrogen atoms from one phen molecule, giving the coordination number of nine. The length of the La–O bonds is in the range of 0.24588 nm to 0.28391 nm, with an average length of 0.25458 nm. Wherein, the length of bond La(1)–O(6) is the longest due to the instability of four-member ring formed by the bidentate chelating–bridging carboxylates. The mean bond distance of La–N is 0.27095 nm. 3.2.2. Structure of complex 2 As shown in figure 2a, complex 2 has an inversion center. The central Nd3+ ion has a distorted mono-capped square-antiprism coordination geometry (figure 2b). The upper square face is formed by O1, O3, O2A, O4 and the lower is O5, O7, N1, N2. The atom O2 caps the upper plane. The molecular structure of complex 2 is a dual-core structure. The two Nd3+ ions are connected together by four 2-cl-4,5-dfba groups, with two of them in a bridging bidentate mode and the other two a bridging–chelating tridentate mode. In addition, each Nd3+ ion is further coordinated by one 2-cl-4,5-dfba group and one H2O molecule with monodentate mode, simultaneous with two nitrogen atoms from one phen molecule, giving the coordination number of nine. It is surprise that the solvents water, involved in the coordination, though the halogen–benzoic

TABLE 3 IR absorption data of the ligands and complexes 1 to 4/cm1. Complex

m C@ N

dC–H

phen 2-cl-4,5-dfhba [La(2-cl-4,5-dfba)3Phen]nnH2O [Nd(2-cl-4,5-dfba)3phenH2O]2 [Eu(2-cl-4,5-dfba)3phen]2 [Ho(2-cl-4,5-dfba)3phen]2

1645

864,738

1604 1627 1628 1612

843,731 844,731 843,730 843,729

m C@ O

mas(COO)

ms(COO)

m(Ln–O)

1518 1519 1520 1521

1426 1426 1427 1428

417 417 417 416

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K. Tang et al. / J. Chem. Thermodynamics 56 (2013) 38–48

41

Fig. 1b. 1D chain polymeric structure of complex 1.

Fig. 2b. Coordination geometry of the Nd3+ ion.

acid and phen are good chelating ligands. The probable reason may be the larger spatial effects of the three halogen substituents on the benzene ring. The distance of Nd–O varies from 0.23985 nm to 0.27362 nm, with an average value of 0.24949 nm. The mean length of the bond Nd–N is 0.2635 nm.

prismatic conformation (figure 3b), in which atom O3 locates at the capped position, atoms O1, O4, O2, and O3A form the top-side plane and the atoms O6, O5, N1, and N2 form the under-side plane. The distances of the bond Eu–O are from 0.2350 nm to 0.3014 nm, with an average value of 0.24874 nm. The lengths of Eu–N bonds are 0.2558 nm and 0.2595 nm with a mean bond length 0.25765 nm. The atom O3 occupied the capped place in the distorted mono-capped square anti-prism form the longest bond, which is because of the oxygen atom both being a member of the unstable four-membered ring linked with the other Eu3+ ion. This phenomenon also occurs in complexes 1 to 2.

3.2.3. Structure of complex 3 As seen from figure 3a, two Eu3+ ions, six 2-cl-4,5-dfba groups and two phen molecules are contained within a centro-symmetric unit. The two center Eu3+ ions are connected together by four 2-cl-4,5-dfba groups, with two of them in a bridging bidentate mode and the other two in a bridging–chelating tridentate mode, which is similar to complex 2. In addition, each Eu3+ ion is further chelated by one 2-cl-4,5-dfba group and one phen molecule, yielding a nine-coordinated distorted mono-capped square anti-

3.2.4. Structure of complex 4 As shown in figure 4a, the molecular structure of complex 4 is a dual-core structure. The two Ho3+ ions are connected together by four 2-cl-4,5-dfba groups, with a bridging bidentate mode. In addition, each Ho3+ ion is further coordinated by one 2-cl-4,5dfba group and one phen molecule, yielding a eight-coordinated distorted square anti-prism coordination geometry (figure 4b). One square face is formed by atoms O1, O4, O2A, O3A and the other is formed by O6, O5, N1, N2. In table 2, the average bond

Fig. 2a. Molecular structure of complex 2 (A: 2  x, 2  y, z). All hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at the 30% probability level.

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K. Tang et al. / J. Chem. Thermodynamics 56 (2013) 38–48

Fig. 3a. Molecular structure of complex 3 (A: 1  x, 1  y, 1  z). All hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at the 30% probability level.

Fig. 3b. Coordination geometry of the Eu3+ ion. Fig. 4a. Molecular structure of complex 4 (A: 1  x, 1  y, 1  z). All hydrogen atoms are omitted for clarity, and thermal ellipsoids are drawn at the 30% probability level.

length of Ho–O (0.24155 nm) formed by the chelating carboxylic groups is longer markedly than the average (0.23208 nm) formed by the bridging carboxylic groups, which may be caused by the instability of the four-membered ring in the chelating mode [12]. The average Ho–O distance is 0.23523 nm and the average Ho–N distance is 0.25295 nm. By comparing the two mean bond distances, the bond energy of Ln–O (Ln = La, Nd, Eu, and Ho) is greater than that of the Ln–N bonds, hence the neutral ligand phen should be decomposed first, which can be proved by the thermal decomposition process.

3.3. Luminescence spectra of complex 3 Because the luminescent intensity of the other three complexes is very weak, here only the fluorescence property of complex 3 is studied in the article. The excitation spectra of complex 3 in the solid state were performed over the range of 200 nm to 500 nm, selected 395.6 nm. The fluorescence spectra are shown in figure 5, which are observed over the range of 400 nm to 700 nm at room

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K. Tang et al. / J. Chem. Thermodynamics 56 (2013) 38–48

Fig. 4b. Coordination geometry of the Ho3+ ion.

temperature. Complex 3 exhibits red luminescence and strong characteristic luminescence of europium ion under the radiation of UV light. For complex 3, three significant emission peaks of Eu3+ ion occur at (580, 592, and 614.8) nm, corresponding to the 5 D0 ? 7F0, 5D0 ? 7F1, and 5D0 ? 7F2 transitions, respectively. The intensity of the 5D0 ? 7F2 at 614.8 nm is much stronger than the others, indicating that there is no inversion center in the site of the Eu3+ ion. The fact that the Eu3+ ion having no inversion deepens the degree of asymmetry in the Eu3+ environment, which raises the electric dipole transition [13]. But the magnetic dipole transition (5D0 ? 7F1) is unrelated to the site asymmetry. Compared with the foregone luminescence intensity of solid Eu chlorides, the luminescence intensity of complex 3 is markedly improved. 3.4. Thermal analysis The TG/DTG–DSC curves of complexes 1 to 4 with a heating rate of 10 K  min1 are shown in figure 6a to d, respectively. The thermal analytical data for those complexes are listed in table 5. As shown in figure 6a, complex 1 has three main mass loss stages. The first stage takes place from T = 305.15 K to 392.15 K with a mass loss of 1.67% (the theoretical mass loss is 1.97%), which is equivalent to the loss of nH2O. This process is accompanied by one endothermic peak within the range of 333.15 K to 379.15 K, absorbing 19.99 J  g1 of heat. The second degradation region occurs over the temperature range of 507.15 K to 736.15 K, with a mass loss of 46.61%, which corresponds to the loss

FIGURE 5. Emission spectrum of complex 3 (kex = 395.6 nm).

of nphen and partial 2-cl-4,5dfba molecules. This stage is accompanied by one endothermic peak from 531.15 K to 576.15 K and one exothermic peak from 603.15 K to 774.15 K, which corresponds to the loss of phen molecules and a fraction of 2-cl-4,5-dfba. We can see obviously there is a endothermic peak from 470.15 K to 500.15 K, while no mass loss in this temperature range, indicating that the second endothermic peak may be a solid-solid phase transition for the complex 1. Up to T = 1362.15 K, the complex is still not completely oxidized, with a total mass loss of 60.97%. The residue may include the La2O3 and undecomposed 2cl-4,5dfba mainly for carbon debris, which are confirmed by the similar characteristic absorption in IR spectrum of La2O3. Based on the analysis above, the thermal decomposition process of the complex 1 is:

½Lað2-cl-4; 5-dfbaÞ3 Phenn  nH2 O ! ½Lað2-cl-4; 5-dfbaÞ3 Phenn ! ½Lað2-cl-4; 5-dfbaÞ3x n ! nLa2 O3 þ C: As shown in figure 6b, there are two main mass loss stages of complex 2. The first stage occurs at T = 504.15 K and ends at 773.15 K, with a mass loss of 52.78%, which attributed to the loss of two phen (theoretical mass loss of 19.65%) and part of 2-cl4,5dfba ligands. During the decomposition process, the DSC curve shows the corresponding single endothermic peak with the heat

TABLE 4 The bond lengths of complexes 1 to 4/nm. Complex 1 La(1)–O(1) La(1)–O(6)#1a La(1)–N(2)

0.24588(13) 0.24942(13) 0.27056(16)

La(1)–O(3) La(1)–O(2)#2b La(1)–N(1)

Nd(1)–O(2)#3c Nd(1)–O(3) Nd(1)–N(2)

0.23985(18) 0.24384(19) 0.2602(2)

Nd(1)–O(5) Nd(1)–O(7) Nd(1)–N(1)

Eu(1)–O(3)#1a Eu(1)–O(2)#1a Eu(1)–N(1)

0.2350(3) 0.2397(3) 0.2558(3)

Eu(1)–O(1) Eu(1)–O(6) Eu(1)–N(2)

Ho(1)–O(3)#1a Ho(1)–O(2)#1a Ho(1)–N(1)

0.2288(2) 0.2340(2) 0.2501(3)

Ho(1)–O(1) Ho(1)–O(6) Ho(1)–N(2)

0.24763(13) 0.25067(13) 0.27134(17)

La(1)–O(4)#1a La(1)–O(5) La(1)–O(6)

0.24835(13) 0.25623(14) 0.28391(14)

0.24060(19) 0.2504(2) 0.2668(2)

Nd(1)–O(4)#3c Nd(1)–O(1) Nd(1)–O(2)

0.24264(19) 0.25341(19) 0.27362(19)

0.2365(3) 0.2420(3) 0.2595(3)

Eu(1)–O(4) Eu(1)–O(5) Eu(1)–O(3)

0.2381(3) 0.2485(3) 0.3014(3)

0.2319(2) 0.2372(2) 0.2558(3)

Ho(1)–O(4) Ho(1)–O(5)

02336(2) 0.2459(2)

Complex 2

Complex 3

Complex 4

Symmetry transformations used to generate equivalent atoms: ax + 1, y + 1,z + 1; bx, y + 1, z + 1; cx + 2, i + 2, z.

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K. Tang et al. / J. Chem. Thermodynamics 56 (2013) 38–48

FIGURE 6. TG, DTG, and DSC curves of complexes 1 to 4 (a = complex 1, b = complex 2, c = complex 3, d = complex 4). TABLE 5 Thermal analytical data of complexes 1 to 4. Complex

1

2

a b c

Step

I II III I II

Temperature range/K

305.15 to 392.15 507.15 to 736.15 736.15 to 1362.05 504.15 to 773.15 773.15 to 1359.15

DTG Tpa/K

356.15 671.15

679.15

Mass loss rate/% Found

Cal.

1.67 46.61 12.69 60.97

1.97 19.77b

52.78 10.03 62.81

Probable expelled groups

nH2O iphen + x(2-cl-4,5-dfba) y(2-cl-4,5-dfba)

82.13c 19.65b

La2O3 + C 2H2O + 2phen + x(2-cl-4,5-dfba) y(2-cl-4,5-dfba)

81.65c

3

I II

501.15 to 779.15 779.15 to 1362.05

691.15

50.92 11.74 62.66

19.87b

4

I II

501.15 to 785.15 785.15 to 1303.15

694.15

51.64 9.55 61.19

19.59b

Residue

Nd2O3+C 2phen + x(2-cl-4,5-dfba) y(2-cl-4,5-dfba)

80.60c

Eu2O3+C 2phen + x(2-cl-4,5-dfba) y(2-cl-4,5-dfba)

79.46c

Ho2O3+C

The peak temperature of DTG. The theoretical value of the loss of phen. The theoretical total mass loss.

of 57.77 J  g1 from T = 509.15 K to 569.15 K, and one exothermic peak with the heat of 130.6 J  g1 from T = 621.15 K to 740.15 K. The second stage takes place from T = 773.15 K to 1359.15 K, with a total mass loss of 62.81%. The complex is still not fully decomposed into oxide, with carbon debris in the residue. So the thermal decomposition process of complex 2 is:

½Ndð2-cl-4; 5-dfbaÞ3 phenH2 O2 ! Nd2 ð2-cl-4; 5-dfbaÞ6x

The first stage arises from T = 501.15 K to 779.15 K, in which the DSC curve shows one endothermic (64.3 J  g1) and one exothermic (186.8 J  g1) peaks. Two phen and part of the 2-cl-4,5dfba ligands decomposed together, with a mass loss of 50.92%. The second stage occurs from T = 779.15 K to 1362.05 K, with a total mass loss of 62.66%. The residues are the Eu2O3 and carbon debris of carboxylic acid ligand. The thermal decomposition processes of complexes 3 and 4 are:

! Nd2 O3 þ C: On the grounds of the figure 6c and d, complexes 3 and 4 undergo the same decomposition processes. So we chose complex 3 as a representative. For complex 3, there are two main mass loss stages.

½Lnð2-cl-4; 5-dfbaÞ3 phen2 ! Ln2 ð2-cl-4; 5-dfbaÞ6x ! Ln2 O3 þ C ðLn ¼ Eu; HoÞ:

K. Tang et al. / J. Chem. Thermodynamics 56 (2013) 38–48

3.5. TG-FTIR spectra of gaseous products The TG-FTIR spectra of gaseous products of thermal decomposition processes for complexes 1 to 4 are acquired through (TG/ DSC + FTIR) system. Figure 7(a) to (d) show the three-dimensional IR accumulation spectra of gaseous products from T = 299.15 K to 1373.15 K. From figure 7 we can observe that the escape of gaseous products mainly occurs in one step apart from complex 1, which we will illustrate separately. The two IR spectra at T = 359.96 K and 691.04 K selected from the maximum peaks of the 3D spectra for complex 1 are shown in figure 8, viz. at the two specific temperatures, complex 1 products the mixed gases. In figure 8a, there are only the characteristic peaks of water molecules in the range of (3750 to 3500) cm1 and (1900 to 1300) cm1. This fact indicates that the crystal water molecules of complex 1 are decomposed, which is consistent with the TG experiments. In figure 8b, the absorption peaks attributed to carbon dioxide molecules are situated around (2359 to 2311 and 669) cm1, with the (2359 to 2311) cm1 corresponding to the stretching asymmetric vibration and the 669 cm1 presenting the deformation vibration of CO2 molecules [14]. The characteristic peaks of water molecules also exist in figure 8b. The existence of these two small molecules (CO2, H2O) demonstrates that parts of the ligands have been completely oxidized at T = 691.04 K. The absorption peaks at (904, 861, and 779) cm1 are ascribed to the plane bending vibration of C–H with the isolated H on the benzene ring or aromatic hydrocarbons [15]. But the peaks at 904 cm1 and 779 cm1 may represent the stretching vibration of the bonds’ (C–F and C–Cl). A series of absorption peaks at (1409, 1282, and 1211) cm1 may be the char-

45

acteristic peaks of the stretching vibration (C–O) and plane bending vibration (O–H) of carboxyl. At the same time, the peaks (1282 cm1, 1211 cm1) may also be the characteristic absorption of stretching vibration (C–N). The absorption peak at 3076 cm1 is attributed to stretching vibrations of C–H from evolved aliphatic or aromatic hydrocarbons. The bonds (1609 cm1 and 1505 cm1) correspond to stretching vibrations of benzene ring’s C@C. This fact indicates that the non-broken ligands exist in the gaseous product. The reason for the peak splitting may be the conjugation between the benzene ring and carbonyl. Simultaneously, the peaks at 1609 cm1 may be also attributable to the stretching vibration of C@N, which lies in the same range of benzene ring’s C@C. Based on the above analysis, the absorption peaks of evolved gases cannot be distinguished due to the overlapping. So it is possible that in the first thermal decomposition step, complex 1 loses all crystal water molecules. In the second, the ligands are decomposed into aromatic hydrocarbons such as halogenated benzene and a small amount of halogen benzoic acid and aliphatic hydrocarbons as well as small molecules (CO2, H2O). As shown in figure 9(a) to (c), complexes 2 to 4 have similar infrared signals. Hence, here we take the IR spectra of complex 2 as an example to analyze the gaseous species of the thermal decomposition processes. The main gaseous species at T = 675.76 K can be identified by their characteristic absorbance: H2O (3730 cm1 to 3750 cm1); CO2 (2359 cm1 to 2311 cm1, 669 cm1); phen (mC@C, mC@N 1609 cm1, 1504 cm1, mC–N 1282 cm1, 1215 cm1, cC–H 861 cm1, 779 cm1); C7H3ClF2 (m@CH 3076 cm1, mC@C 1609 cm1, 1504 cm1, d@CH 1215 cm1, 1118 cm1, 1079 cm1, mC–Cl 778 cm1, mC–F 908 cm1); C7H3O2ClF2

FIGURE 7. Stacked plot of the FTIR spectra of the evolved gases for complexes 1 to 4 as observed in the online TG-FTIR system at the heating rate of 10 K  min1 (a = complex 1, b = complex 2, c = complex 3, d = complex 4).

46

K. Tang et al. / J. Chem. Thermodynamics 56 (2013) 38–48

FIGURE 8. FTIR spectra of the evolved gases for complex 1 (a, T = 359.96 K; b, T = 691.04 K).

(mC@H 3076 cm1, mC@O 1688 cm1, mC@C 1609 cm1, 1504 cm1, c@CH 904 cm1, 861 cm1, 779 cm1, mC–O 1409 cm1, bOH 1282 cm1, 1211 cm1, mC–Cl 778 cm1, mC–F 908 cm1). This fact is in line with the first stage of the thermal decomposition process corresponding to the loss of phen, H2O, and 2-cl-4,5-dfba ligands. And the organic ligands may be decomposed into chain-like molecules, small molecules or maintain aromatic [16]. 3.6. Heat capacity of complexes 2 to 4 On the basis of the molecular structures and thermal decomposition data, complexes 2 to 4 have no crystal water molecules and there are no losses up to T = 500 K. So the molar heat capacities of complexes 2 to 4 are measured by DSC in the temperature range from 258.15 K to 493.15 K with six parallel experiments. The values of average molar heat capacity of each complex are listed in table 6. The curves of molar heat capacities values against temperature for complexes 2 to 4 are shown in figure 10, from

which we can see that the three curves have some subtle differences in the trend possibly due to the different structures. Over the measured range, there is no obvious endothermic or exothermic peak shown in the curves. The values of experimental heat capacity can be fitted to the polynomial equations with the least squares method using the reduced temperature (x) (x = [T  (Tmax + Tmin)/2]/[(Tmax  Tmin)/2]) [17] with the Tmax = 493.15 K, Tmin = 258.15 K and the T being the experimental temperature. The correlation coefficients of the fitting R2 and the standard deviations results are given in the following. Complex 2 [Nd(2-cl-4,5-dfba)3phenH2O]2 1

C p;m =ðJ  K1  mol Þ ¼ 1574:61414 þ 342:85053x þ 39:98686x2 þ 104:8584x3  398:03763x4  29:81984x5 þ 320:51338x6 R2 = 0.9996, SD = 4.70706.

FIGURE 9. FTIR spectra of the evolved gases for complexes 2 to 4 (a = complex 2, T = 675.76 K; b = complex 3, T = 690.45 K, c = complex 4, T = 697.61 K).

47

K. Tang et al. / J. Chem. Thermodynamics 56 (2013) 38–48

Complex 3 [Eu(2-cl-4,5-dfba)3phen]2 1

C p;m =ðJ  K1  mol Þ ¼ 1928:71213 þ 234:49147x þ 50:91862x2 þ 243:56629x3  292:92833x4  127:38719x5 þ 200:8801x6 R2=0.9998, SD=2.50834. Complex 4 [Ho(2-cl-4,5-dfba)3phen]2 1

C p;m =ðJ  K1  mol Þ ¼ 1749:79525 þ 395:72297x þ 142:46864x2 þ 437:07546x3  353:06112x4  254:24294x5 þ 228:22429x6 R2=0.9998, SD=4.10851. 3.7. Thermodynamic functions of complexes 2 to 4 The smoothed values of molar heat capacity and thermodynamic functions of complexes 2 to 4 are calculated based on the fitted polynomial of the heat capacities as a function of the reduced temperature (x) according to the following thermodynamic equations:

HT  H298:15K ¼

Z

FIGURE 10. Molar heat capacities of complexes 2 to 4 with the temperature (K) by DSC (a = [Nd(2-cl-4,5-dfba)3phenH2O]2; b = [Eu(2-cl-4,5-dfba)3phen]2; c = [Ho(2-cl4,5-dfba)3phen]2).

ST  S298:15K ¼

Z

T

C p;m T 1 dT;

ð2Þ

298:15K T

C p;m dT;

ð1Þ

298:15K

GT  G298:15K ¼

Z

T

C p;m dT  T

298:15K

Z

T

C p;m T 1 dT:

ð3Þ

298:15K

TABLE 6 Experimental molar heat capacities of complexes 2 to 4. T/K

258.15 261.41 264.67 267.93 271.19 274.45 277.71 280.97 284.23 287.49 290.75 294.01 297.27 300.53 303.79 307.05 310.31 313.57 316.83 320.09 323.35 326.61 329.87 333.13 336.39 339.65 342.91 346.17 349.43 352.69 355.95 359.21 362.47 365.73 368.99 372.25 375.51

Cp,m/(J  K1  mol1)

T/K

2

3

4

1103.107 1117.752 1132.527 1146.512 1161.396 1174.841 1188.398 1203.799 1219.01 1234.848 1250.072 1265.94 1281.283 1297.332 1312.849 1328.045 1343.021 1358.186 1374.202 1390.654 1406.199 1422.877 1439.987 1455.788 1468.377 1477.752 1485.388 1493.743 1502.718 1510.944 1517.994 1526.082 1534.049 1543.773 1552.054 1560.192 1569.2

1532.131 1542.68 1553.247 1565.601 1578.483 1591.837 1605.257 1620.268 1635.556 1651.225 1667.145 1683.226 1698.587 1713.905 1728.465 1741.81 1754.983 1768.158 1780.772 1792.611 1804.155 1815.021 1825.274 1836.693 1848.046 1857.304 1865.347 1873.236 1880.343 1886.185 1891.124 1895.135 1899.733 1905.37 1905.887 1914.933 1924.388

1174.729 1191.987 1209.525 1226.711 1243.406 1260.361 1277.879 1296.597 1315.197 1334.328 1355.212 1376.505 1397.683 1419.752 1440.731 1462.071 1482.816 1502.178 1521.609 1541.381 1560.165 1576.768 1593.005 1606.696 1620.196 1631.769 1642.514 1655.548 1666.034 1675.152 1684.2 1692.714 1701.639 1711.948 1721.156 1731.163 1742.831

378.77 382.03 385.29 388.55 391.81 395.07 398.33 401.59 404.85 408.11 411.37 414.63 417.89 421.15 424.41 427.67 430.93 434.19 437.45 440.71 443.97 447.23 450.49 453.75 457.01 460.27 463.53 466.79 470.05 473.31 476.57 479.83 483.09 486.35 489.61 492.87 493.15

Cp,m/(J  K1  mol1) 2

3

4

1579.481 1588.737 1598.846 1609.093 1618.478 1628.334 1641.891 1652.022 1662.822 1672.598 1683.484 1693.281 1703.849 1713.341 1724.11 1733.266 1743.283 1752.418 1759.708 1768.063 1774.788 1781.076 1786.402 1793.246 1801.983 1809.903 1818.215 1828.23 1839.063 1850.533 1865.185 1879.238 1892.639 1910.904 1930.117 1950.434 1952.219

1933.849 1940.592 1948.14 1955.757 1962.887 1971.172 1977.066 1988.885 1993.839 2001.61 2010.291 2020.06 2029.488 2036.434 2042.826 2052.169 2060.098 2069.395 2077.623 2085.941 2093.742 2103.103 2110.89 2121.496 2130.204 2137.697 2147.627 2155.896 2166.775 2176.426 2186.809 2194.61 2204.186 2213.997 2224.183 2233.191 2233.962

1755.032 1767.349 1780.751 1794.692 1807.823 1821.817 1837.05 1852.087 1866.115 1881.882 1896.687 1912.67 1928.637 1944.938 1959.974 1976.059 1993.188 2007.812 2025.332 2042.968 2061.347 2080.002 2098.792 2118.6 2139.135 2158.647 2177.173 2197.668 2218.144 2237.443 2255.675 2273.705 2291.746 2307.723 2323.569 2338.293 2339.463

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K. Tang et al. / J. Chem. Thermodynamics 56 (2013) 38–48

The smoothed values of Cp,m and thermodynamic functions of the complexes relative to the standard reference temperature 298.15 K are tabulated in tables 1 to 3 (see supplementary data) respectively, with an interval of 10 K. 4. Conclusions We successfully synthesized the target products, which have different crystal structures, thermal decomposition processes and heat capacity curves. Complex 1 is an infinite 1D chain polymeric structure formed by the asymmetric units with the mirror image growth pattern. Each center of the asymmetric unit, La3+ ion, is coordinated by bridging, tridentate chelating–bridging modes with carboxylic groups and one phen molecule, giving the coordination number of nine. The structures of complexes 2 to 4 are all the classical dual-core structures. Using the TG/DSC+FTIR technology, we obtain the three-dimensional IR accumulation spectra of the gas products. The smoothed values of Cp,m and thermodynamic functions of complexes 2 to 4 relative to the standard reference temperature 298.15 K are tabulated over the temperature range from 258.15 K to 493.15 K. In addition, complex 3 exhibits the intense fluorescence property. All these properties could be of interest for potential application. Acknowledgments 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). Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.jct.2012.06.032.

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JCT 12-229