Zhu Li ^a, Jia Jinliang ^a, Yang Xuwu^b, Gao Shengli^b
(^aSouth China of Agricultural University, Science of College, Guangzhou, Guangdong, 510642, China; ^bShaanxi Key Laboratory of Physico-Inorganic Chemistry, Department of Chemistry, Northwest University, Xi'an Shanxi, 710069, China)

Abstract Thirteen solid complexes were synthesized with sodium diethyldithiocarbamate (NaEt₂dtc·3H₂O), 1,10-phenanthroline (o-phen·H₂O) and hydrated lanthanide chlorides in absolute ethanol, which are identified as a general formula of RE(Et₂dtc)₃(phen) (RE=La, Pr, Nd, Sm~Lu). IR results revealed that two sulfur atoms in NaEt₂dtc and two nitrogen atoms in o-phen coordinate to RE³⁺ in bidentate fashion, respectively. UV spectrum of the complexes suggested energy transfer between o-phen and RE³⁺ is the primary process, and the main absorbtion peaks showed a slight red shift than that of o-phen. The constant-volume combustion energies of complexes were determined by a precise rotating-bomb calorimeter at 298.15K. The standard enthalpies of combustion and standard enthalpies of formation were calculated for these complexes, respectively. The experiment results showed "triplet effect" of rare earth.
Keywords rare earth sulfocompound; constant-volume combustion energy; standard enthalpy of combustion; standard enthalpy of formation; triplet effect

1 EXPERIMENTAL
1.1 Reagents
Lanthanide chloride hydrate, NaEt₂dtc·3H₂O, o-phen·H₂O, absolute ethanol and CHCl₃ are the same as the Ref.^[6-7]. thianthrene (mass fraction: 99 %, Tokyo Kasei Kogyo Co. Ltd.) and benzoic acid (purity: 99.999 % , Chengdu chemical reagent company) have been recrystallized and sublimed three times before using, respectively. The final products were kept in vacuum over P₄O₁₀ to dryness.
1.2 Preparation and composition of the complexes
The methods of preparation for the complexes are the same as those in Ref.^[6-7]. RE³⁺ was determined with EDTA by complexometric titration; C, H, N and S analyses were carried out by Vario EL III CHNOS of German. The final results are showed in Table 1. they are identified as a general formula of RE(Et₂dtc)₃(phen).
1.3 Apparatus and experimental conditions
The constant-volume combustion energies of the complexes were determined by a precise rotating-bomb calorimeter (RBC-type II), The main experimental procedures and structure were described previously^[8]. The correct value of the heat exchange was calculated according to Linio-Pyfengdelel-Wsava formula^[9].The initial temperature was regulated to (25.0000 ± 0.0005) ℃, and the initial oxygen pressure was 2.5MPa. The digital indicator for temperature measurement was used to promote the precision and accuracy of the experiment.
    The calorimeter was calibrated with benzoic acid of 99.999 % purity, which has an isothermal heat of combustion of -26434 J·g^-1 at 25℃, and the experimental result were (17775.09 ± 7.43) J·K^–1 (Table 2), the precision was 4.18×10^-4. To determine the standard combustion energies of sulfur-containing compounds, the constant-volume combustion energy of thianthrene has been determined as being (-33507.76 ± 14.13) J·g^–1 (Table 2) ，which is in good agreement with (-33468 ± 4 ) J·g^{–1 [10]}. The precision and the accuracy were 4.22×10^-4 and 1.19×10^-3, respectively, the calorimetric system is accurate and reliable.
   The analytical methods of final products (gas, liquid and solid) were the same as these in Ref.^[8], the analytical results of the final products indicated that the combustion reactions were complete.

Table 1 Analytical results related to the compositions of the complexes (%)

Table 2 Experimental results for the combustion energies of benzoic acid and thianthrene

SD=

2 RESULTS AND DISCUSS
2.1 IR spectra of the complexes                         
IR spectra of the complexes are similar because of their similar structure^[11,12]: the peaks of about 3340 cm^-1 are assigned to the characteristic absorption of hydroxyl group in hydrated lanthanide chlorides and ligands, which is not present in the complexes , showing that the complexes does not contain water. The skeleton vibration and the n_C–H bend vibration of benzene ring of o-phen in the complexes are shift to higher wave number compared to that of the free ligand, suggesting that two nitrogen atoms of o-phen coordinate to RE³⁺. In contrast to that of 1477 cm^-1 in the ligand diethyldithiocarbamate, n_CN of the complex shiftes to higher wave number(1480~1517 cm^-1), and presentes a double-bond character in the complex, which can be attributed to two main forms of vibration in the NCS group ^[13]: (i) and (ii) the vibration intensity of the later will be enhanced when the two sulfur atoms of the ligand diethyldithiocarbamate coordinate to RE³⁺ to form the new cycle (ⅲ), thus n_CN moves to a higher wave number. Comparing with 986cm^-1 of diethyldithiocarbamate, the increment of 9~18 cm^-1 in wave number of n_css stretching vibration in the complexes can be attributed to the new formed cycle, because its formation increases the vibration intensity of n_CN^[12]. The changes in n_CN and n_CSS indicate that the sulfur atoms of diethyldithiocarbamate coordinate to RE ³⁺ in bidentate manner. The coordinate number is eight. The main IR absorbtion data of the ligands and the complexes were listed in Table 3.

         (i)                 (ii)                       (iii)
2.2 UV spectra of the complexes                  
The UV spectra of the complexes and ligands were determined by a instrument of Perkielmer Lambda 40 of America, the l_max were listed in Table 3. Intraligand transition (p→p*,  n→p*) were displayed at about 329.56nm and 380.12nm for the free ligand NaEt₂dtc·3H₂O ^[14], and characteristic transition (p→p*) of o-phen was present at 265.05 nm^[15]. As for the complexes, the absorption peaks were well similar, whether shape, absorbency or place of peaks (Fig.1), which demonstrate that energy transfer between o-phen and RE³⁺ is the primary process^[15], and strong absorption of o-phen fully or partly shield that of NaEt₂dtc·3H₂O in the complexes^[17]. In addition, the main absorption peaks of the complexes show a slight red shift than that of o-phen, which was due to pelectrons of nitrogen atoms of o-phen have excursion to the 5d blank orbits of RE³⁺, and resulting to the increment of p electron conjugate action for the whole system, when s-coordinate band of the complexes were formed between nitrogen atoms of o-phen and RE ³⁺.

Table 3 The main UV and IR absorbtion data of the ligands and the complexes

2.3 Combustion energies, standard combustion enthalpies and standard enthalpies of formation for the complexes
The methods of determination and calculation of the constant-volume combustion energies () for the complexes are the same as benzoic acid and thianthrene^[6].
    The standard combustion enthalpies of the complexes () refer to the combustion enthalpy change of the following ideal combustion reaction at 298.15 K and 100 kPa.
RE(Et₂dtc)₃(phen) (s) + O₂ (g) = RE₂O₃ (s) + 27CO₂ (g) + 19 H₂O+ 6 SO₂ (g) + N₂ (g) (1)
(RE=La, Pr, Nd, Sm~Lu)
    The standard combustion enthalpies of the complexes are calculated by the following equations:
(complex, s, 298.15K) =(complex, s, 298.15K) +RT (2)
= n_g (products) - n_g(reactants) (3)
where n_g is the total amount in mole of gases which present in products or in reactants, R = 8.314 J·K^-1·mol^-1, T = 298.15K.
    The standard enthalpies of formation of the complexes () are calculated by Hess's law according to the thermochemical equation above (1)

where (RE₂O₃, s) = (-1793.14 ± 0.79) (La), (-1823.39 ± 6.69) (Pr), (-1808.12 ± 1.00) (Nd), (-1808.12 ±1.00) (Sm), (-1663.00 ± 1.62) (Eu), (-1815.60 ± 3.60) (Gd), (-1827.6 ± 2.0) (Tb), (-1865.39 ± 3.89) (Dy), (-1880.92 ± 4.81) (Ho), (-1897.29 ± 4.88) (Er), (-1888.66 ± 5.86) (Tm), (-1814.50 ± 2.22) (Yb), (-1881.96 ± 7.53) (Lu) kJ·mol^-1; (CO₂, g) = (-393.51 ± 0.13) kJ·mol^-1, (H₂O, l) = (-285.830 ± 0.042) kJ·mol^-1, (SO₂, g) = ( -296.81 ± 0.20) kJ·mol^{-1 [17,18]}, The final results are also listed in Table 4.

Table 4 Combustion energies, standard combustion enthalpies and standard enthalpies of formation of the complexes at 298.15K

稀土含硫配合物的恒容燃烧能测定及标准摩尔生成焓计算
朱丽^a 贾金亮^a 杨旭武^b 高胜利^b
(^a华南农业大学 理学院 广东 广州 510642; ^b西北大学化学系  陕西省物理无机化学重点实验室 陕西 西安 710069)
摘要 在无水乙醇中，通过二乙基二硫代氨基甲酸钠（NaEt₂dtc），1，10-邻菲咯啉（o-phen）和水合氯化稀土盐反应制备得到了13种稀土含硫固态配合物，其通式为RE(Et₂dtc)₃(phen) (RE=La, Pr, Nd, Sm~Lu)。配合物的红外光谱表明配体NaEt₂dtc中的硫原子和o-phen中的氮原子均与RE³⁺双齿配位。紫外光谱显示在配合物中邻菲咯啉与稀土离子之间的能量传递为主要过程，且其最大吸收峰的位置相对邻菲咯啉的都有微小红移。在298.15K下，通过RBC- II型精密转动弹热量计测定了配合物的恒容燃烧能，并分别计算了标准摩尔燃烧焓及标准摩尔生成焓。所得实验结果显示出了稀土元素的“三分组效应”。
关键词 稀土含硫配合物； 恒容燃烧能； 标准摩尔燃烧焓；标准摩尔生成焓；三分组效应

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