Zhu Li, Yang Xuwu, Chen Sanping, Gao
Shengli, Shi Qizhen Received May 00, 2004; Supported by the National Natural Science Foundation of China (No. 20171036), Education Department of Shaanxi Province (No. 01JK229) and Northwest University (No.02NW02) for financial support Abstract Four ternary solid complexes, Eu(Et2dtc)3(phen) (d), Gd(Et2dtc)3(phen) (e), Tb(Et2dtc)3(phen) (f) and Dy(Et2dtc)3(phen) (g), were synthesized with sodium diethyldithiocarbamate (NaEt2dtc), 1,10-phenanthroline (o-phen) and low hydrated lanthanide chlorides in absolute ethanol by improved method of reference. IR spectra of the complexes showed that the RE3+ (RE=Eu, Gd, Tb, Dy) is coordinated with sulfur atoms of NaEt2dtc and nitrogen atoms of o-phen. The constant-volume combustion energies of complexes, , were determined by a precision rotating-bomb calorimeter at 298.15 K. The standard enthalpies of combustion, , and standard enthalpies of formation, , were calculated for these complexes, respectively.Keywords RE(Et2dtc)3(phen), thermochemistry, combustion energies, standard enthalpies of combustion, standard enthalpies of formation The series of complexes lanthanide sulfide
have been largely used for the precursors of ceramics and thin film materials [1-4].
For instance, the complexes synthesized with [(alkyl)2dtc], o-phen·H2O
and lanthanide salts had been acted as the volatile precursors for preparing lanthanide
sulfide. Their friction properties in lubricant was investigated in literature [5],
and the preparation and properties of these complexes were also documented in literature [6].
In addition, the crystal structure and spectroscopic properties of Eu(Et2dtc)3(phen)
had been reported [7]. 1 EXPERIMENTAL Table 1 Analytical Results Related to the composition for d, e, f and g
a The data in brackets are calculated values.1.3 Apparatus and experimental conditions
Fig.1 Bicyclic structure of the crucible support in the oxygen bomb1.support; 2.x-axle; 3.outside ring; 4.y-axle; 5.inside ring The initial temperature was regulated to (25.0000 ¡À 0.0005) ºC, and the initial oxygen pressure was 2.5 Mpa. The digital indicator for temperature measurement was used to promote the precision and accuracy of the experiment. The correct value of the heat exchange was calculated according to Linio-Pyfengdelel-Wsava formula: D(DT) = nV0 + (+-n) (2) where D(DT) denotes the correct value of the heat exchange; n is the number of readings for the main (or reaction) period; V0 and Vn are the rate of temperature change at the initial and final stages, respectively (V is positive when temperature decreased); , is the average temperature of calorimeter at the initial and final stages, respectively (average temperature for first and last reading); T0 is the last reading of the initial stage; Tn is the first reading of the final stage; is the sum of all the readings, except for the last one of the main period; is the constant. The calorimeter was calibrated with benzoic acid of 99.999 % purity (Chengdu Chemical Reagent Company), which has an isothermal heat of combustion of -26434 J·g-1 at 25ºC. The calibrated experimental results with an uncertainty of 4.18¡Á10-4 were summarized in Table 2. The energy equivalent of the rotating-bomb calorimeter was calculated according to the following equation: W= (3) Where W is the energy equivalent of the rotating-bomb calorimeter (in J·K-1), Q is the combustion enthalpy of benzoic acid (in J·g-1), a is the mass of determined benzoic acid (in g), G is the combustion enthalpy of Ni-Cr wire for ignition (0.9 J·cm-1), b is the length of the actual Ni-Cr wire consumed (in cm), 5.97 is the formation enthalpy and solution enthalpy of acid corresponding to 1 mL of 0.1000 mol·L-1 solution of NaOH (in J·mL-1), c is the volume (in mL) of consumed 0.1000 mol·L-1 solution of NaOH and is the correct value of the temperature rise. Table 2 Result for Calibration of Energy Equivalent of the Rotating-bomb Calorimeter
The analytical methods of final products (gas, liquid and solid) were the same as these in Ref[10], the analytical results of the final products showed that the combustion reactions were complete. 2 RESULTS AND DISCUSSION2.1 IR spectra of the complexes IR spectra of the complexes are similar because of their similar structure. Taking Eu(Et2dtc)3(phen) for example, and referring to the literature [11,12], IR spectra of salt, ligands and the complex depicted in Fig. 2.are assigned as follows: Compared with the spectra of salt, NaEt2dtc·3H2O and o-phen·H2O (3390, 3366 and 3388 cm-1), the characteristic absorption of hydroxyl group is not present in the complex, showing that the complex do not consist of water. As those in the ligand of o-phen, the peaks of 1624, 1589, 1572, and 1516cm-1 are assigned to the skeleton vibration of benzene ring and the peaks of 852, and 730 cm-1 are assigned to the bend vibration of C¨CH in the complex, which display certain shifts in contrast with those of (1617, 1587, 1561, 1504 cm-1) and (854, 739 cm-1) in the ligand. It is thus assumed that two nitrogen atoms in the ligand of o-phen coordinate to Eu3+. Contrasting with that of 1477 cm-1 in the ligand of NaEt2dtc·3H2O, nCN of the complex shifts to higher wave number, and presents a double-bond character in the complex, which can be attributed to that NCS2- group has two main forms of vibration[13]: (1) and (2) (1) (2) (3) the vibration intensity of the latter one is enhanced when the two sulfur atoms of ligand coordinated to Eu3+ to form the new cycle (3), thus nCN moves to the higher wave number. On the other hand, increase of wave number of ncss stretching vibration is observed compared with that of ligand. Obviously, this can be due to the new formed cycle and its formation increases the vibration the intensity of nCN[12]. The changes of nCN and nCSS indicate that the two sulfur atoms of ligand coordinate to Eu3+ in a bidentate manner. The final results demonstrate that it is an octa-coordinated complex, and one pentaatomatomic ring and three tetraatomatomic rings are formed. As for the other complexes, showing the similarity with the complex Eu(Et2dtc)3(phen), the detailed data are listed in Table 3. Fig. 2 IR spectra of the ligands and the complex (a)EuCl3·3.94H2O (b) NaEt2dtc·3H2O (c) o-phen·H2O (d) Eu(Et2dtc)3(phen) Table 3 Data of IR Absorption for Main Groups of Ligands and Complexes (cm-1)
2.2 Combustion energies of
the complexes
2.3 Standard combustion enthalpies
of complexes Table 5 Combustion Energies, Standard Combustion Enthalpies and Standard Enthalpies of Formation for d, e, f and g at 298.15 K
The standard enthalpies of formation of the compounds, (complex, s, 298. 15K), are calculated by Hess's law according to the above thermochemical equation (5) (RE(Et2dtc)3(phen), s) = [(RE2O3, s) + 27(CO2, g) + 19(H2O,l)+ + 6 (SO2, g) + (N2 , g)] - (RE(Et2dtc)3(phen), s) (8) where (Eu2O3, s) = (-1663.00 ¡À 1.62) kJ·mol-1; (Gd2O3, s) = (-1815.60 ¡À 3.60) kJ·mol-1; (Tb2O3, s) = (-1827.6 ¡À 2.0) kJ·mol-1; (Dy2O3, s) = (-1865.39 ¡À 3.89) kJ·mol-1, (CO2, g) = (-393.51 ¡À 0.13) kJ·mol-1, (H2O, l) = (-285.830 ¡À 0.042) kJ·mol-1, (SO2, g) = (-296.81 ¡À 0.20) kJ·mol-1[14,15]£¬ The results of calculation are also listed in Table 5. Fig.3 Plot of fH against the atomic numbers (ZRE) of middle rare-earth for the complexes ¡ñ. ; ¡ö. In Fig.3, values of the complexes are plotted against the atomic numbers of middle rare-earth. obviously, they appears as curve relationship not linear, suggesting a certain amount of covalence is present in the chemical bond between the RE3+ and ligands, which is in agreement with Nephelauxetic effect of 4f electrons of rare earth ions. REFERENCES [2] Bessergenev V I, Ivanova E N, Kovaleskaya Ya A et al. Spring Meeting of Electrochem. Soc. Los Angeles. 1996: 105. [3] Kuzmina N P, Ivanov R A, Paramonov S E et al. Proc.-Electochem.Soc. 1997, 97-25: 880. [4]] Ivanov R A, Korsakov I E, Kuzmina N P et al. J. Mendeleev. Commun. 2000, 3: 98. [5] Zhang Z F, Su C Y, Liu W M et al. J. Wear. 1996, 192: 6. [6] Zhou R, Sun Y H. J. Xinjiang Univ. (Natural Sci. Edi.). 1997, 14 (4): 67. [7] Su C Y, Tan M Y, Tang N et al. J. Coord. Chem. 1996, 38: 207. [8] Su M Z, Li G P. J. Chemistry.(Huaxue Tongbao), 1979, 43: 34. [9] Yang X W, Chen S P, Gao S L et al. J. Instrumentation Science & Technology. 2002, 30 (3): 311. [10] Marthada V K. Journal of Research of the National Bureau of Standard. 1980, 85: 467. [11] Dong Q N. IR Spectroscopy. Beijing : Beijing Chemical and Industrial Press, 1979. [12] Nakamoto K. (Huang D R, Wang R Q. translated) Infrared and Raman Spectra of Inorganic and Coordination Compounds. Beijing: Beijing Chemical and Industrial Press (4th Edi), 1991. [13] Nakamoto K, Fujita J, Condrate R A et al. J. Chem. Phys. 1963, 39 (2): 423. [14] Rederick D R. Experimental Thermochemistry, Interscience Publishers Ltd., London, 1956, 88. [15] Robert C W. CRC Handbook of Chemistry and Physics, Chemical Rubber Publishing Company, Cleveland, 1977-1978, 55: D45. ¡¡ ¡¡ |