http://www.chemistrymag.org/cji/2001/036027pe.htm |
Jun. 1,
2001 Vol.3 No.6 P.27 Copyright |
Zhong Yun, Zhang Weiguang, Ren Tianhui
#(Dept.of Chem., South China Normal University, Guangzhou 510631; #Dept.of Chem., Shanghai Jiaotong University,Shanghai,201100, China)
Recerived Jan.7, 2001. This work is funded by the National Natural Science Foundation of China and the Natural Science Foundation of Education office in Guangdong Province.
Abstract Eight complexes of light rare earth with dioctyldithiocarbamate have been prepared by using dioctylamine,carbon disulfide and rare earth chloride(RE=La-Tb,except for Pm) as reactants in air. They are characterized by elemental analyses, IR spectra, H NMR spectra and TG-DTA technique. The results show that in the complexes every ligand coordinates to RE ion through two sulphur atoms. The load-carrying capacity and anti-wear property of two complexes(La,Nd) are evaluated by using a four ball test machine. It is shown that these novel compounds have excellent load-carrying capacity and good anti-wear property.Keyword rare earth complex, dioctyldithiocarbamate, preparation, tribological properties 1. INTRODUCTION
Since Brown[1] had prepared the solid rare earth complexes with diethyldithiocarbamate firstly. many complexes of rare earth ions with dithiocarbamates were extensively studied. RNH3[RE(RHDTC)4] (RHDTC=RHNCS2; R=Me, Et; RE=La, Nd, Sm-Gd)[2], RE(Et2DTC)3bipy (RE=La, Pr, Nd, Sm-Lu, Y; Et2DTC=N,N-diethyldithiocarbamate; bipy=2,2'-bipyridyl)[3] and other similar complexes[4] had been prepared before 1996. These similar complexes used as additives of lubricating oils[5-7], rubber accelerators[8] and their biochemical activity[9] have been reported. However, the synthesis of these complexes need to be carried out at the condition without air and water. In this paper, we improved the process of synthesis and prepared eight rare earth ( RE=La-Tb, except for Pm ) complexes with dioctyldithiocabamate (see the Fig.1) in air. The composition and tribological properties of these new complexes were investigated.
Fig.1 Structure of dioctyldithiocarbamate 2. EXPERIMENTAL
2.1 Reagents
Rare earth oxides(Shanghai Yuelong Chemical Company) with purity not less than 99.9%.
Dioctylamine and carbon disufide are analytically pure and made in China.
2.2 Measurements
The metal ion was determined by EDTA titration using xylenol-orange as indicator. Carbon, nitrogen and hydrogen were determined by using a Carlo Erba 1106 elemental analyser. The IR spectra were recorded on a 170 SX FTIR spectrometer in the region of 600 - 200 cm-1 and on 5D-X spectrometer in the region of 4000- 400 cm-1 in KBr pellets. The H NMR spectra were recorded on a EM360 spectrometer by using carbon tetrachloride as solvent. Thermal analyses(TG and DTA)were performed on a Beijing PCT-2 thermobalance. The load-carrying capacities and anti-wear properties were evaluated on a MRS-10A four-ball lubricant test machine(Jinan test machine factory) at 1450 rpm with a test duration of 30 min at room temperature.
2.3 Preparation of anhydrous rare earth chlorides and the ligand
Rare earth chlorides were prepared according to the literature method[10].
Potassium dioctyldithiocarbamate((C8H17)2NCS2K) was obtained by reaction of dioctylamine, carbon disulide and potassium hydroxide(molar ratio 1:1:1) in methanol medium. The product was washed by water,vacuum dried over P4O10-CaCl2 and verified by IR and H NMR spectroscopy.
2.4 Preparation of the complexes
0.066 mol dioctylamine was dissolved in 10 ml methanol. To this solution was slowly added 0.028 mol carbon disulfide at 0掳C and continually stirred at room temperature for 1 hour. Then 10 ml solution of 0.014 mol RECl3 (RE=La-Tb, except for Pm) in methanol was slowly added to this solution. Continually stirred at room temperature for 10 hour. The product was filtered and washed with methanol three times. The product was dissolved in ethyl ether and filtered. Filtrate was volatilized in air and then dried in vacuum over P4O10-CaCl2. 3. RESULTS AND DISCUSSION
3.1 The composition of the complexes Table 1 Elemental analyses data
Complex formula |
Yield (%) | C% | H% | N% | RE% |
| La(S2CNC16H34)2Cl·5H2O | 70 | 45.42 (45.52) |
8.29 (8.77) |
3.04 (3.12) |
15.65 (15.48) |
| Ce(S2CNC16H34)2Cl·3H2O | 50 | 47.37 (47.33) |
8.54 (8.64) |
3.23 (3.25) |
15.91 (16.24) |
| Pr(S2CNC16H34)2Cl·4H2O | 55 | 46.23 (46.32) |
8.26 (8.69) |
2.91 (3.18) |
16.05 (15.98) |
| Nd(S2CNC16H34)2Cl | 60 | 50.81 (50.24) |
8.92 (8.43) |
2.98 (3.45) |
17.74 (17.74) |
| Sm(S2CNC16H34)2Cl | 55 | 49.61 (49.86) |
8.38 (8.37) |
3.41 (3.42) |
18.21 (18.36) |
| Eu(S2CNC16H34)2Cl | 55 | 49.39 (49.77) |
8.79 (8.35) |
3.57 (3.41) |
18.87 (18.52) |
| Gd(S2CNC16H34)2Cl·4H2O | 55 | 45.36 (45.48) |
8.26 (8.53) |
3.05 (3.12) |
17.20 (17.51) |
| Tb(S2CNC16H34)2Cl·H2O | 50 | 48.74 (48.30) |
8.29 (8.34) |
3.16 (3.31) |
18.55 (18.80) |
The most important IR peaks of ligand and complexes are reported in Table2. The ligand and all complexes have strong absorptions in the range of 1480-1488cm-1, which is assigned to the C=N stretching frequency[11]. It shows in some extent a mixing of the bands at 1300cm-1 [n (C-N)] and 1660 cm-1 [n (C=N)], suggesting a considerable double bond character in the C-N bond. In the range 978-989cm-1, the presence of a single strong band due to a n (CSS) mode in the spectra of the complexes is strongly indication of the bidentate behaviour of the dithio ligand in the complexes, otherwise a doublet is expected in the 1000±70 region in the case of monodentate coordination[12,13]. Appearance of n (RE-S) bands in far-IR spectra of the rare earth complexes indicates the formation of RE-S bond[14]. Table2 The most important IR bands (cm-1)
Compounds |
n (C-N) | n (CSS) | n (RE-S) |
| K(S2CNC16H34)·XH2O | 1480Vs | 980s | ------ |
| La(S2CNC16H34)2Cl·5H2O | 1480Vs | 980s | 320w |
| Ce(S2CNC16H34)2Cl·3H2O | 1488Vs | 982s | 330w |
| Pr(S2CNC16H34)2Cl·4H2O | 1486Vs | 989s | 330w |
| Nd(S2CNC16H34)2Cl | 1484Vs | 985s | 330w |
| Sm(S2CNC16H34)2Cl | 1480Vs | 979s | 330w |
| Eu(S2CNC16H34)2Cl | 1484Vs | 979s | 330w |
| Gd(S2CNC16H34)2Cl·4H2O | 1484Vs | 979s | 330w |
| Tb(S2CNC16H34)2Cl·H2O | 1480Vs | 978s | 330w |
3.3 H NMR
spectra
The H NMR data of potassium salt and rare earth complexes were reported in Table3. The d (H3C-CH2-) and d (-H2C-) of the potassium salt and the rare earth
complexes had little difference. The d (-N-H2C-)
of rare earth complexes were somewhat small comparing to the potassium salt because of
different metal ions.
Compounds |
d (-N-H2C-) | d (H3C-CH2-) | d (-H2C-) | |||
| K(S2CNC16H34)·XH2O | 4.25(4H) | 3.85(6H) | 1.24(24H) | |||
| La(S2CNC16H34)2Cl· 5H2O | 2.94(8H) | 3.85(12H) | 1.25(48H) | |||
| Ce(S2CNC16H34)2Cl· 3H2O | 2.80(8H) | 3.85(12H) | 1.25(48H) | |||
| Pr(S2CNC16H34)2Cl· 4H2O | 2.87(8H) | 3.91(12H) | 1.29(48H) | |||
| Nd(S2CNC16H34)2Cl | 2.53(8H) | 3.93(12H) | 1.30(48H) | |||
| Sm(S2CNC16H34)2Cl | 2.87(8H) | 3.92(12H) | 1.27(48H) | |||
| Eu(S2CNC16H34)2Cl | 2.86(8H) | 3.92(12H) | 1.27(48H) | |||
| Gd(S2CNC16H34)2Cl· 4H2O | 2.78(8H) | 3.94(12H) | 1.28(48H) | |||
| Tb(S2CNC16H34)2Cl· H2O | 2.84(8H) | 3.90(12H) | 1.28(48H) |
3.4 Thermal
analyses
The thermal analysis studies were performed by means of TG and DTA techniques. K(S2CNC16H34)·XH2O
loses water molecules at 137oC. It decomposed at 248oC and continuous weight loss was
detected to 491oC, at this temperature the ligand decomposed
completely. Lanthanum complex (La(S2CNC16H34)2 Cl·5H2O)
lost five water molecules when heated to 121oC. The weight loss found in this process is 9.75%
(calc. 10.03%). On raising the temperature further, the complex decomposed exothermically
at 231oC.
Subsequently other exothermic peaks and continuous weight loss was detected up to 490oC. At this temperature La2(S2O7)3
is formed. The total weight loss found(56.25%) was approximately consistent with that
calculated(55.09%).
According to the above experimental results of elemental analysis, IR
spectra, H NMR spectra and TG-DTA technique, we propose that the possible structure of the
complexes is
·X H2ORE=La-Tb, except for Pm; X=0~ 5 3.5 Tribological property
3.5.1 load-carrying capacity
Fig. 2 The PB value of complexes Two novel rare earth complexes (La,Nd) added to liquid paraffin in concentration of 0.25wt% and 1.00wt%, respectively. The load-carry capacity (PB value) of these two complexes and liquid paraffin are shown in Fig. 2. The result indicates that PB value raised 90% than that of liquid paraffin when the concentration was 0.25wt% and raised 134% when the concentration was 1.00wt%. It expresses that these two complexes had excellent load-carrying capacity. We can learn that there is no difference between these two complexes from Fig. 2.
 |
 |
| Fig. 3 Effects of concentration of complexes on wear (four-ball, 300N, 30min) | Fig. 4 Effects of load on wear (four-ball, 0.25wt%, 30min) |
3.5.2 Anti-wear property
The anti-wear properties of complexes as additives in liquid paraffin relative to
concentration and load are shown in Fig. 3 and 4. The result in Fig. 3 indicates that
these complexes possess good anti-wear property in liquid paraffin when the concentration
varied from 0.25wt% to1.00wt%. The smaller the concentration is, the better the anti-wear
capacity. The result in Fig. 4 indicates that these complexes also possess good anti-wear
capacity in liquid paraffin when the load varied from 100N to 300N. The harder the load
is, the better the anti-wear capacity. We can also
learn from figures 3 and 4 that there is no obvious difference between different rare
earth element.
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