научная статья по теме PREPARATION, CRYSTAL STRUCTURE AND THERMAL DECOMPOSITION MECHANISM OF COMPLEX [DY(P-MOBA)3PHEN]2 Химия

КООРДИНАЦИОННАЯ ХИМИЯ, 2007, том 33, № 8, с. 622-626

УДК 541.49

Preparation, Crystal Structure and Thermal Decomposition Mechanism

of Complex [Dy(p-MOBA)3Phen]2

© 2007 J. J. Zhang*, S. L. Xu* **, N. Ren***, and H. Y. Zhang*, **

*Experimental Center, Hebei Normal University, Shijiazhuang, 050016 P. R. China **College of Chemistry & Material Science, Hebei Normal University, Shijiazhuang, 050016 P. R. China ***Department of Chemistry, Handan College, Handan, 056005 P. R. China

Received June 20, 2006

1,10-Phenanthroline-tris(4-methoxybenzoate)dysprosium, Dy(p-MOBA)3Phen (where p-MOBA = p-methox-ybenzoate and Phen = 1,10-phenanthroline), (I) has been synthesized. The complex was characterized by various techniques including elemental analysis, UV, IR, XRD, molar conductance, and TG-DTG. The crystals consist of binuclear molecules and monoclinic, space group P21/n: a = 14.143(6), b = 17.550(7), c = 14.493(6) A, в = 117.357(4)°, Z = 2, pc = 1.655 g cm-3, Д000) = 1588; R1 = 0.0176, wR2 = 0.0455. In the complex, each Dy3+ ion is nine-coordinate to one 1,10-phenanthroline molecule, one bidentate chelating carboxylate group, and four bridging carboxylate groups in which the carboxylate groups are bonded to the Dy3+ ions in three modes: bridging bidentate, bridging tridentate, and chelating bidentate. The thermal decomposition mechanism of I has been determined on the basis of thermal analysis. In addition, the lifetime equation at a weight-loss of 10% was deduced as lnx = -28.8361 + 19478.37/T by isothermal thermogravimetric analysis.

The complexes of rare-earth ions coordinated to hy-droxyl, carboxyl, or sulfonic groups make rare-earth metals popular in printing and dyeing. Many of ternary rare-earth complexes with aromatic acid and nitrogen- containing ligands were obtained [1-6]. These show interesting polymeric networks or chain structures [7]. In lanthanide monocarboxylate complexes, the carboxylate groups are coordinated to lanthanide ions in different modes, such as chelating, bridging, and bridging-chelating modes [8]. Dysprosium presents as an important part in many technology kingdoms now. To our knowledge, some Dy(II) complexes have been studied [9-10].

In the previous work, we reported the preparation, crystal structure, and thermal properties of some rare-earth car-boxylic acid complexes [11-18]. In this paper, we have prepared and studied the crystal structure, characteristics, and thermal decomposition processes of the 1,10-phenan-throline-tris(4-methoxybenzoate)dysprosium, Dy(p-OBA)3Phen (where p-MOBA = p-methoxybenzoate and Phen = 1,10-phenanthroline)dysprosium) (I).This research is a part of crystallographic studies of the ternary lan-thanide(III) carboxylate complexes with 1,10-phenanthro-line.

EXPERIMENTAL

Material and apparatus. All regents were obtained from commercial supplies with analytical grade and used without further purification, and all manipulation was carried out in the laboratory atmosphere.

Analysis of C, H, and N were performed on a Carlo-Erba model 1106 element analyzer, and the metal content was assayed using EDTA titration. IR spectra were recorded using KBr pellets in a range of 4000-400 cm-1 on a Bio-Rad FTS-135 spectrometer, UV spectra - on a SHI-MADZU 2501 spectrometer. Molar conductivity was determined by a DDS-307 conductometer (Shanghai exactitude apparatus factory). XRD identification was carried out for the crystalline analyses on a Bruker D8-AD-VANCE X-ray diffractometer in a scanning of 5-55° (20) with CuKa radiation (X = 2500 À). TG and DTG experiments for the title complex were performed using a Per-kin-Elmer TGA7 thermogravimetric analyzer, air was used as a static atmosphere. X-ray diffraction data were obtained by a Bruker Apex II CCD diffractometer with graphite-monochromated MoA^ radiation (X = 0.71073 À) at 293 K. A semiempirical absorption correction based on SADABS was applied. Unique data (Rint = 0.016) were used to solve the structure by direct methods using the SHELXS-97 program and refined on F2 by full-matrix least squares methods using SHELXL-97.

Synthesis complex I. An ethanol solution containing p-methoxybenzoic acid (1.5 mmol) and 1,10-phenanthroline (0.5 mmol) was adjusted to pH 6-7 by using a 1.0 M NaOH solution and then added slowly to a DyCl3 (0.5 mmol) solution under stirring for 1 h, and white precipitates appeared at once. After stirring and deposition, the resulting white precipitate was isolated by filtration and then dried and stored. The mother liquor was

evaporated at room temperature, and colorless crystals were obtained.

For C72H58Dy2N4Oi8

anal. calcd, %: C, 54.31; H, 3.67; N, 3.52; Dy, 20.41. Found, %: C, 54.32; H, 3.52; N, 3.61; Dy, 20.23.

RESULTS AND DISCUSSION

Molar conductivity. The title complex is equable in air. We also obtained the molar conductivity of the title complex in a DMSO solution with DMSO as a reference. We can conclude that complex I is not electrolyte based on the data of 5.59 Ohm1 cm2 mol-1.

Crystallographic study. The summary of the crystal data, experimental details, and structure refinement for the title complex are listed in Table 1. The molecular structure of the complex with atomic numbering scheme is shown in Fig. 1. The selected bond lengths are given in Table 2.

The cluster is centrosymmetric and composed of two Phen ligands, six p-MOBA ligands, and two Dy3+ ions. The Dy-Dy distance is 3.9873(13) A. Each Dy3+ ion is coordinated with two oxygen atom from tridentate bridging carboxylate group, three oxygen atoms from bidentate bridging carboxylate groups, two oxygen atoms from bidentate chelating carboxylate group, and two nitrogen atoms from 1,10-phenanthroline molecule in a distorted mono-capped square-antiprism geometry as shown in Fig. 2. The O(1A) atom is at the capped position. It is similar to that of [Eu(p-MOBA)3Bipy] 2 ■ 1/2C2H5OH [19] but different from that of [Eu(p-MOBA)3Phen]2 [1].

The average Dy-O (Dy-O(L4), Dy-O(24), Dy-O(7), Dy-O(8)) length formed by chelating carboxylate group is 2.506 A and the average Dy-O length (Dy-O(1), Dy-O(5), Dy-O(4A)) that found in bidentate bridging carboxylate groups is 2.324 A. These indicate that the interaction between the dysprosium atom and chelating oxygen atom is weaker than that between the dysprosium atom and bridging oxygen atom of the carboxyl group. The Dy-N bond length is from 2.568 to 2.641 A, whose average distance is 2.604 A. They are little shorter than the corresponding values of 2.543, 2.378, and 2.629 A of [Eu(p-MOBA)3Bipy]2 ■ 1/2C2H5OH. This can be because r(Dy3+) is shorter than r(Tb3+) and r(Eu3+).

Spectral characteristics. The IR spectra of the title complex show strong bands at 1555-1610 and 14001360 cm-1, which strongly indicates that in the complex the carboxyl oxygen atoms participate in coordination to the Dy atoms. The band at 418 cm-1 is assigned to the metal-oxygen ionic bond. All these indicate that the carboxyl group is coordinated to Dy atom [20]. The band of v(C=C) and v(C=N) vibrations at 1617 and 1646 cm-1 in the 1,10-phenanthroline ligand spectrum shifts to 1605 and 1572 cm-1 in the spectra of the complex. Accordingly, the fact demonstrates the coordination of the nitrogen atoms

Table 1. Crystal data and structure refinement for I

Parameter Value

M 1592.22

T, K 273(2)

X, A 0.71073

Crystal system Monoclinic

Space group P21/n

a, A 14.143(6)

b, A 17.550(7)

c, A 14.493(6)

P, deg 117.357 (4)

V, A3 3195(2)

Z 2

Pcalcd g/cm3 1.655

Absorption coefficient, mm-1 2.399

F(000) 1588

Crystal size, mm 0.32 x 0.26 x 0.22

Theta range for data collection, deg 1.96 to 25.03

Limiting indices -16 < h < 16, -20 < k < 15, -15 < l < 17

Reflections collected/unique 17066/5635 (Rint = 0.0221)

Completeness to 9 = 25.03, % 99.9

Absorption correction Semiempirical from equivalents

Max. and min. transmission 1.000000 and 0.766586

Refinement method Full-matrix least-squares on F2

Data/restraints/parameters 5635/0/436

Goodness-of-fit on F2 1.041

Final R indices (I > 2a(I)) R1 = 0.0176, WR2 = 0.0455

R indices (all data) R1 = 0.0218, wR2 = 0.0466

Largest diff. peak and hole, e A3 0.267 and -0.599

624

ZHANG h Hp.

Fig. 1. Structure of the complex I.

of the 1,10-phenanthroline to the Dy3+ ion. This result is consistent with the crystal structure of the complex. The UV spectrum for the complex recorded at room temperature shows the absorption bands at Àmax = 257 nm. Compared with that of the ligands, the absorption bands shift to lower band. This can be caused by the expansion of the n-conjugated system after coordinating with the Dy3+ ion [21]. All these are attributed to the coordination of the free ligands and Dy3+ ion.

XRD. The XRD patterns of the complex are different from the phenomena characteristic of the ligands. The intensity of the peak of the complex gradually decreases. This suggests that the new phase is obtained.

Fig. 2. Coordination geometry about the Dy3+ ion.

Mass loss, % %/min

Fig. 3. TG-DTG curves of the complex I.

Thermogravimetric analysis. TG-DTG technique was applied to determine the stability of the compound, and three mass-loss processes in the range from 25 to 900°C can be seen from Fig. 3. In the first stage of weight loss, 22.95% of the weight were lost in a range of245.62-324.82°C, which can be ascribed to the release of 2 molecules of Phen from the complex (theoretical loss is 22.63%). The IR spectra of the residue at 324.82°C shows that the absorption band of C=N disappears at 1572 cm-1, this ascribes to the length of C=N longer than that of C-O. The second mass loss took place in a temperature range of 324.82-467.67°C, and the mass-loss percentage was 28.97%, which was in agreement with the percent content 28.45 % of 3 molecules ofp-MOBA in the complex. With an increase in the temperature, it was steady at 640.21°C, 23.30% of the complex was left (theoretical value is 23.42%), and the IR spectra of the residue at the temperature was consistent with that of the Dy2O3 sampl

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