Zhu Li , Jia Jinliang , Yang Xuwu, Gao Shengli
South China of Agricultural University, Science of College, Guangzhou, Guangdong, 510642, China; Shaanxi Key Laboratory of Physico-Inorganic Chemistry, Department of Chemistry, Northwest University, Xi’an Shanxi, 710069, China)
Received March 12, 2008; South China of Agricultural University for financial Support (4900K07283)
AbstractThirteen solid complexes were synthesized with sodium diethyldithiocarbamate (NaEtdtc·3HO), 1,10-phenanthroline (o-phen·O) and hydrated lanthanide chlorides in absolute ethanol, which are identified as a general formula of RE(Etdtc)(phen) (RE=La, Pr, Nd, Sm~Lu). IR results revealed that two sulfur atoms in NaEtdtc 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.
The series of complexes containing lanthanide sulfide have well biological activity, the usage of them as antiseptic and insecticide have been attended widely[1]. they also could be used as the precursors of ceramics and thin film materials[2], grease additive and accelerant of vulcanizing rubber[3]. Preparation, spectroscopic properties and the crystal structure of some complexes had been reported [4-5]
Thermodynamic data could offer better interpretation to the essence of lanthanide-sulfide bonds and stability of this series of complexes, and part investigation has been carried out concerning the thermochemical properties for these complexes[6-7].In this paper, constant Cvolume combustion energy of thirteen complexes have been determined, the standard enthalpies of combustion and standard enthalpies of formation have been calculated on the basis of the constant-volume combustion energies of the complexes, respectively. The gained thermodynamic quantities presented the “triplet effect”of rare earth, suggesting that a certain amount of covalence is present in the chemical bonds of the complexes.
1 EXPERIMENTAL
1.1 Reagents
Lanthanide chloride hydrate, NaEtdtc·3HO, -phen·O, absolute ethanol and CHCl 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 P10 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 areidentified as a general formula of RE(Etdtc)(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·-1 at 25℃, and the experimental result were (17775.09 ± 7.43) J·KC(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·gC(Table 2) ，which is in good agreement with (-33468 ± 4 ) J·gC[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 1Analytical results related to the compositions of the complexes (%)
| Sample | RE | ||||
| La(Etdtc)(phen) | 18.21(18.18) | 42.53(42.45) | 9.09(9.17) | 25.07(25.18) | 4.87(5.01) |
| Pr(Etdtc)(phen) | 18.30(18.40) | 42.23(42.36) | 9.10(9.14) | 25.07(25.12) | 4.79(5.00) |
| Nd(Etdtc)(phen) | 18.59(18.75) | 42.08(42.16) | 9.01(9.10) | 24.87(25.01) | 4.69(4.98) |
| Sm(Etdtc)(phen) | 19.42(19.39) | 41.81(41.82) | 9.00(9.03) | 24.79(24.81) | 4.97(4.94) |
| Eu(Etdtc)(phen) | 19.57(19.56) | 41.72(41.74) | 9.04(9.01) | 24.77(24.76) | 4.89(4.93) |
| Gd(Etdtc)(phen) | 20.12(20.10) | 41.44(41.46) | 8.97(8.95) | 24.56(24.59) | 4.91(4.90) |
| Tb(Etdtc)(phen) | 20.28(20.27) | 41.29(41.37) | 8.99(8.93) | 24.52(24.54) | 4.92(4.89) |
| Dy(Etdtc)(phen) | 20.85(20.63) | 40.77(41.18) | 8.80(8.89) | 24.89(24.43) | 4.68(4.86) |
| Ho(Etdtc)(phen) | 20.99(20.88) | 24.82(24.36) | 40.82(41.05) | 8.81(8.86) | 4.57(4.67) |
| Er(Etdtc)(phen) | 20.30(20.27) | 24.50(24.54) | 41.26(41.37) | 8.99(8.93) | 4.95(4.89) |
| Tm(Etdtc)(phen) | 21.10(21.28) | 24.32(24.23) | 40.67(40.85) | 8.89(8.82) | 4.76(4.82) |
| Yb(Etdtc)(phen) | 21.47(21.68) | 24.18(24.11) | 40.81(40.64) | 8.85(8.78) | 4.68(4.80) |
| Lu(Etdtc)(phen) | 22.01(21.87) | 24.10(24.05) | 40.65(40.54) | 8.64(8.75) | 4.64(4.79) |
The data in brackets are calculated values.
Table 2Experimental results for the combustion energies of benzoic acid and thianthrene
| Samples | Mass of complexes m /g |
Calibrated heat of combustion wire q/J | Calibrated heat of acid /J |
Calibrated /K |
Combustion energies of complexes /(J·g-1 |
| 0.99702,0.78940 | 10.35, 8.10 | 24.78, 20.89 | 1.4834, 1.1746 | 17790.45, 17789.88 | |
| benzoic acid | 0.83060, 0.96869 | 12.60,12.60 | 20.43, 17.43 | 1.2382, 1.4418 | 17758.93, 17780.82 |
| 0.99485, 0.90036 | 12.60, 9.28 | 20.80, 21.67 | 1.4800, 1.3429 | 17798.18, 17745.97 | |
| mean±SD | 17775.09±7.43 | ||||
| 0.48860, 0.48886 | 12.60, 11.70 | 1383.69, 1384.41 | 0.9998, 1.0015 | 33514.62, 33558.98 | |
| thianthrene | 0.49011, 0.48798 | 12.60, 12.60 | 1387.90, 1381.96 | 1.0028, 0.9977 | 33511.58, 33484.26 |
| 0.48835, 0.48823 | 12.60, 12.60 | 1382.99, 1382.65 | 0.9977, 0.9992 | 33456.78, 33520.31 | |
| mean±SD | 33507.76±14.13 |
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 theCbend vibration of benzene ring of -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,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 , thusCN moves to ahigher wave number. Comparing with 986cm-1 of diethyldithiocarbamate, the increment of 9~18 cm-1 in wave number ofcss stretching vibration in the complexes can be attributed to the new formed cycle, because its formation increases the vibration intensity ofCN[12]. The changes inCN andCSS 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.
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, themax were listed in Table 3. Intraligand transition (→, →*) were displayed at about 329.56nm and 380.12nm for the free ligand NaEtdtc·3HO [14], and characteristic transition (→*) of -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 NaEtdtc·3HO 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 toelectrons of nitrogen atoms of o-phenhaveexcursionto the 5 blank orbits of RE3+, and resulting to the increment ofelectron conjugate action for the whole system, when-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
| Ligands and complexes | OH | T | ─ | CN | CSS | (CSS ) | max |
| LnCl·O (<4) | 33493393 | ||||||
| -phen· | 3388 | 1617,1587, 1561, 1504 | 854, 739 | 265.05 | |||
| NaEtdtc·3 H | 3366 | 1477 | 986 |
|
|||
| La(Etdtc)(phen) | 1624, 1588, 1572, 1516 | 848, 729 | 1480, 1516 | 995 | 266.59 | ||
| Pr(Etdtc)(phen) | 1622, 1589, 1570, 1515 | 851, 730 | 1480,1515 | 997 | 11 | 266.93 | |
| Nd(Etdtc)(phen) | 1624, 1589, 1572, 1516 | 851, 730 | 1482, 1516 | 997 | 11 | 267.26 | |
| Sm(Etdtc)(phen) | 1623, 1589, 1571, 1516 | 852, 730 | 1481, 1516 | 995 | 267.77 | ||
| Eu(Etdtc)(phen) | 1624, 1589, 1572, 1516 | 852, 730 | 1482, 1516 | 1002 | 16 | 267.49 | |
| Gd(Etdtc)(phen) | 1624, 1589, 1572, 1516 | 852, 730 | 1481, 1516 | 1003 | 17 | 267.94 | |
| Tb(Etdtc)(phen) | 1624, 1589, 1572, 1516 | 852, 730 | 1482, 1516 | 1003 | 17 | 267.91 | |
| Dy(Etdtc)(phen) | 1624, 1589, 1572, 1517 | 853, 730 | 1482, 1517 | 1001 | 15 | 267.85 | |
| Ho(Etdtc)(phen) | 1625, 1589, 1572, 1517 | 853, 730 | 1482, 1517 | 1006 | 20 | 268.10 | |
| Er(Etdtc)(phen) | 1625, 1590, 1572, 1517 | 853, 730 | 1482, 1517 | 1007 | 21 | 267.30 | |
| Tm(Etdtc)(phen) | 1625, 1590, 1572, 1517 | 853, 730 | 1482, 1517 | 1007 | 21 | 268.39 | |
| Yb(Etdtc)(phen) | 1625, 1590, 1572, 1517 | 854, 730 | 1481, 1517 | 1006 | 20 | 267.95 | |
| Lu(Etdtc)(phen) | 1625, 1590, 1572, 1517 | 854, 730 | 1482, 1517 | 1004 | 18 | 267.89 |
Figure 1 UV absorption curves of ligand -phen(1) and Complexes La(Etdtc)(phen)(2),Sm(Etdtc)(phen)(3) and Lu(Etdtc)(phen)(4)
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(Etdtc)(phen) (s) + (g) = RE (s) + 27CO (g) + 19 HO+ 6 SO (g) + (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)
= (products) – (reactants) (3)
where is the total amount in mole of gases which present in products or in reactants, = 8.314 J·K-1·mol-1, = 298.15K.
The standard enthalpies of formation of the complexes () are calculated by Hess’s law according to the thermochemical equation above (1)
(RE(Etdtc)(phen), s) = (RE3, s) + 27 (CO, g) + 19 (HO,l)
+ 6 (SO, g) + (N , g)] – (RE(Etdtc)(phen), s) (4)
where (RE, 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; (CO, g) = (-393.51 ± 0.13) kJ·mol-1, (HO, l) = (-285.830 ± 0.042) kJ·mol-1, (SO, g) = ( -296.81 ± 0.20) kJ·mol-1 [17,18], The final results are also listed in Table 4.
Table 4Combustion energies, standard combustion enthalpies and standard enthalpies of formation of the complexes at 298.15K
| Complexes | / (kJ·mol-1 | / (kJ·mol-1 | / (kJ·mol-1 |
| La(Etdtc)(phen) | -17455.98 ± 7.98 | -17475.19 ± 7.98 | -1257.78 ± 8.84 |
| Pr(Etdtc)(phen) | -17840.67 ± 10.38 | -17859.88 ± 10.38 | -888.22 ± 11.55 |
| Nd(Etdtc)(phen) | -18674.22 ± 8.33 | -18693.43 ± 8.33 | -47.03 ± 9.17 |
| Sm(Etdtc)(phen) | -17406.90 ± 9.69 | -17426.11 ± 9.69 | -1317.99 ± 10.45 |
| Eu(Etdtc)(phen) | -17410.63 ± 8.95 | -17429.84 ± 8.95 | -1238.06 ± 9.75 |
| Gd(Etdtc)(phen) | -18673.71 ± 8.15 | -18692.92 ± 8.15 | -51.28 ± 9.17 |
| Tb(Etdtc)(phen) | -17646.95 ± 8.64 | -17666.16 ± 8.64 | -1084.04 ± 9.49 |
| Dy(Etdtc)(phen) | -16730.21 ± 9.25 | -16749.42 ± 9.25 | -2019.68 ± 10.19 |
| Ho(Etdtc)(phen) | -18213.19± 8.18 | -18232.40 ± 8.18 | -544.46 ± 9.33 |
| Er(Etdtc)(phen) | -18436.62± 9.11 | -18455.83 ± 9.11 | -329.48 ± 9.91 |
| Tm(Etdtc)(phen) | -18161.61± 8.46 | -18180.82 ± 8.46 | -599.91 ± 9.73 |
| Yb(Etdtc)(phen) | -17954.08± 8.11 | -17973.29 ± 8.11 | -770.36 ± 9.02 |
| Lu(Etdtc)(phen) | -17898.22± 8.59 | -17917.43 ± 8.59 | -859.95 ± 10.12 |
Figure 2plot of Dn( CSS ) against the atomic number (Dn(CSS) is the stretching vibration difference betweendiethyldithiocarbamate and complexes
Figure 3Plots of and against the atomic numbers (ZRE) of rare-earth for the complexes
3 CONCLUSIONS
and of the complexes are plotted against the atomic numbers of the elements in the lanthanide series, as showed in Fig.3. The curves show the “tripartite effect”of rare earth, which is consistent with the observed result in Fig.2, suggesting that a certain amount of covalence is present in the chemical bonds between RE3+ and ligands that is caused by the incomplete shield of 5 orbital to 4f electrons. The experimental results is in good agreement with Nephelauxetic effect of 4f electrons of rare earth.
On the basis of Fig.3, the corresponding thermochemical data (standard combustion enthalpies, standard enthalpies of formation )of Ce(Etdtc)(phen) and Pm(Etdtc)(phen) could be estimated.