Synthesis, Characterization And Thermochemistry On The Rare Earth Complexes With Pyromellitic Acid

Synthesis,characterization and thermochemistry on the rare earth complexes with pyromellitic acidFourteen lanthanide complexes of pyromellitic acid were synthesized and their properties were characterized.Their thermochemical characteristics were discussed in this paper.The difference on synthesis and structure of rare earth and transitional metal crystals were compared,and found the coordination rules of rare earth.All complexes were identified as the general formula of RE(Hbtec)·nH₂O(RE= La-Nd,Tb-Lu,n=3;RE=Sm-Gd,n=2;Hbtec=C₁₀H₃O₈^3-)by chemical and elemental analyses.IR spectra of the complexes showed that the partial carboxyl coordinated with rare earth ions.As for FS spectrum of the complexes,Gd(Hbtec)·2H₂O and Tb(Hbtec)·3H₂O have higher efficiency of intramolecular energy transfer and stronger fluorescence characters,which may be used as potential optical materials.The decomposition of the complexes were studied by TG-DTG technique.The results showed that the complexes were more stable than ligand.The decomposition of the complexes were speculated to lose H₂O firstly,then ligands,except that the losen of coordinate H₂O and ligands of Er,Tm,Yb and Lu complexes synchro happened.The final products of rare earth oxide were obtained by completely decomposed.The constant-volume combustion energies,â–³_cU,for the solid complexes were determined by an RBC-â…¡type precision rotating-bomb calorimeter at 298.15K.The standard molar enthalpies of combustion,â–³_cH_m^θ,and standard molar enthalpies of formation,â–³_fH_m^θ,were calculated for these complexes,respectively.The results are as follows:Unit:kJ·mol^-1â–³_cU:-3609.67±0.84(La);-3314.90±1.03(Ce);-3901.00±1.17(Pr); â–³_cU:-3609.67±0.84(La);-3314.90±1.03(Ce);-3901.00±1.17(Pr);-3548.99±0.99(Nd);-3409.43±0.77(Sm);-3930.45±0.66(Eu);-3504.61±0.84(Gd);-3885.69±0.95(Tb);-3942.97±0.96(Dy);-3794.10±1.28(Ho);-4041.62±0.66(Er);-3995.30±0.85(Tm);-3457.64±0.84(Yb);-3441.56±0.99(Lu)â–³_cH_m^θ:-3603.47±0.84(La);-3309.32±1.03(Ce);-3894.05±1.17(Pr);-3542.79±0.99(Nd);-3403.23±0.77(Sm);-3924.25±0.66(Eu);-3498.41±0.84(Gd);-3879.49±0.95(Tb);-3936.77±0.96(Dy);-3787.90±1.28(Ho);-4035.42±0.66(Er);-3989.10±0.85(Tm);-3451.44±0.84(Yb);-3435.36±0.99(Lu)â–³_fH_m^θ:-2513.67±22.24(La);-3002.42±22.25(Ce);-2232.24±22.28(Pr);-2582.00±22.28(Nd);-2445.68±19.27(Sm);-1842.51±19.35(Eu);-2346.95±19.21(Gd);-2274.45±22.43(Tb);-2216.27±22.36(Dy);-2375.09±22.62(Ho);-2135.97±22.45(Er);-2176.89±22.40(Tm);-2677.15±22.42(Yb);-2724.48±22.56(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,showing the "quadripartite effect" of rare earth.On the basis of the curves,the corresponding standard enthalpies of combustion of Pm(Hbtec)·3H₂O could be estimated as being -3150 kJ·mo1^-1and -2910 kJ·mol^-1, respectively.From the crystal structure analysis of[Er(H₂btec)_1/2(btec)_1/2(H₂O)]·(CH₃OH)(1)and[Co(C₁₀H₂O₈)(H₂O)₄]·0.5(btec)·H₂O(2),the crystal structure of the complexes were determined.The crystal system of the complex(1)were determined as Triclinic system,space group P-1,a=6.052(3)(?),b=9.328(4)(?),c=13.136(6)(?),α=100.282(7)°,β=98.652(7)°,γ=95.917(8)°,V=714.9(6)(?)³,Dc=2.134g/m³,Z=2, R₁=0.0596,wR₂=0.1457,the coordination polyhedron can be described as a triangule dodecahedron,coordination number of Er³⁺was eight.The crystal system of the complex(2)were determined as Monoclinic System,space group C_2/c, a=20.082(4)(?),b=11.330(2)(?),c=13.136(6)(?),α=11.330(2)°,β=95.495(4)°,γ=90°,V=3536.3(12)(?)³,Dc=1.578g/m³,Z=4,R₁=0.0541,wR₂=0.1499.The coordination polyhedron can be described as a tiny contorted octahedron, coordination number of Co³⁺was six.And the crystal structure of the two complexes were particularly analyzed and compared.