Thermochemistry On The Rare Earth Complexes With Salicylic Acid

Thermochemistry on the rare earth complexes with salicylic acidFourteen lanthanide complexes have been synthesized with salicylic acid and hydrated lanthanides chloride, and their properties were characterized. Their thermochemical characteristics were discussed in this paper.All complexes were identified as the general formula of RE(HSal)3·nH2O(RE= La-Sm, n=2;RE=Eu-Lu, n=l;HSal=C7H5O3) by chemical and elemental analyses.IR spectra of the complexes showed that the rare earth ions coordinated with salicylate by carboxyl. As for UV spectrum of the complexes, energy transfer between salicylate and RE~3+ is the primary process. FS spectrum, as a comparison, the complexes Gd(HSal)3H2O, Tb(HSal)3H2O and Dy(HSal)3H2O have higher efficiency of intramolecular energy transfer and stronger fluorescence characters, which may be used as optical materials. Electrochemical behaviours of complexes on the glass-carbon electrode were researched with cyclic voltammetry. It is indicated that the electrochemical process of the complexes was a single electron redox process.The decomposition of the complexes were studies by TG-DTG technique. The results showed that the complexes were more stable than ligand. The decomposition of other complexes were speculated on three stages, except that the decomposition process of Ce Tm Yb Lu complexes was two stages. At the first stage, the decomposition products of all complexes was similar, as— Ln(C6JH4OHCOO)3·1/4- Ln2O2CO3(Ln = La, Pr-Lu;the decomposition products of Ce complex was -1/2Ce(C6H4OHCOO)3·1/4CeOCO3). The final products of rare earth oxide were obtained by completely decomposed.The constant-volume combustion energies, △_cU, for the solid complexes were determined by RBC-II type precision rotating-bomb calorimeter at 298.15K. The standard molar enthalpies of combustion, △_cH_m~0 , and standard molar enthalpies offormation, △_fH_m~0 , were calculated for these complexes, respectively. The results areas follow:Unit: kJ-mol"1&CU: - 9521.64 ±4.56(La);- 9760.57 ± 4.28(Ce);- 9334.09 ± 4.38(Pr);- 9577.31 ±4.32(Nd);- 9576.67 ± 3.86(Sm);- 9029.50 ± 3.96(Eu);- 8978.06 ± 3.92(Gd);- 9087.35 ± 3.84(Tb);- 8953.87 ±4.67(Dy);- 8332.43 ± 4.05(Ho);- 8022.00 ± 3.84(Er);- 8361.32 ± 3.98(Tm);- 8445.62 ± 3.84(Yb);- 8343.00 ± 3.52(Lu)AcHn : - 9521.64 ±4.56(La);- 9761.19 ± 4.28 (Ce);- 9334.09 ± 4.38(Pr);- 9577.31 ±4.32(Nd);- 9576.67 ± 3.86(Sm);- 9029.50 ± 3.96(Eu);- 8978.06 ±3.92(Gd);- 9087.35 ± 3.84(Tb);- 8953.87 ± 4.67(Dy);- 8332.43 ±4.05(Ho);- 8022.00 ± 3.84(Er);- 8361.32 ± 3.98(Tm);- 8445.62 ± 3.84(Yb);- 8343.00 ± 3.52(Lu)Af Hn : - 2353.26 ± 47.02 (La);- 2308.31 ± 47.00 (Ce);- 2544.96 ± 47.02 (Pr);- 2305.24 ± 47.01 (Nd);- 2315.83 ± 47.01 (Sm);- 2488.96 ± 43.82 (Eu);- 2625.06 ± 43.82 (Gd);- 2538.52 ± 43.88 (Tb);- 2671.10 ±43.92 (Dy);- 3302.49 ± 43.98 (Ho);- 3621.26 ± 43.89 (Er);- 3276.60 ± 43.88 (Tm);- 3154.90 ± 43.88 (Yb);- 3288.77 ± 43.91 (Lu)The standard molar enthalpies of combustion and standard molar enthalpies of formation for the complexes were plotted against the atomic numbers of the elements in the lanthanide series, the curves shows the "quadripartite effect" of rare earth, On the basis of the curves, the corresponding standard enthalpies of combustion of Pm(HSal)3-2H2O could be estimated as being -8050 kJmol"1 and -3800 kJmol"1, respectively.From the monocrystal structure of Dy(HSal)3-4H2O, the crystal system of the complex was determined as momoclinic system, space group C2 /c, a=16. 2288 (3) A, 6=14.8706(3)A, c=9.8322(2)A, a=y=900, 0=101.4550(10)°, F=2325.56(8)A3, Dc= 1.833Mg/m3, Z=2, F(000)=l260, u=3.281mm''. The coordination polyhedron can be described as a triangule dodecahedron, coordination number of Dy3+ was eight. And crystal structure of rare earth complexes with salicylic acid was primarilydiscussed according to the known crystal structure of complex.