Hydrothermal syntheses, crystal structures and thermal properties of open-structure materials, Pr(III)-succinate complexes with 3D networks

Abstract

Rare-earth dicarboxylate open structure materials {[Pr(H₂O)]₂[O₂C(CH₂)₂CO₂]₃} _n (1) and {[Pr(H₂O)]₂[O₂C(CH₂)₂CO₂]₃ · H₂O} _n (2) have been synthesized by reaction of succinic acid with nitrate salts of Pr(III) under hydrothermal conditions (150°C, 4 days). Complex 1 crystallizes in the triclinic space group with a = 7.8828(8) Å, b = 8.1247(8) Å, c = 14.2271(14) Å, α = 96.907(2)°, β = 96.962(2)°, γ = 103.600(2)°, and Z = 2. Complex 2 is in the monoclinic space group C2/c with a = 20.104(4) Å, b = 7.9343(16) Å, c = 14.013(3) Å, β = 121.08(3), and Z = 4. X-ray diffraction analysis reveals that the complexes are constructed by succinic acid bridging the chains of edge-sharing PrO₈(H₂O) polyhedra to form 3D network structures. 1 and 2 possess different topological structures due to the difference in the conformations of coordinated succinic acid. Thermal decomposition kinetics of 1 and 2 are also discussed in detail. Non-thermal kinetic decomposition shows that, for 1, the possible reaction mechanisms of the three steps are three dimensional pervasion with n = 2, nucleation and growth with n = 1/4, nucleation and growth with n = 1/4, respectively, and the kinetic equations may be expressed as dα/dT = (A/β)exp(−E/RT){3/2(1 − α)^2/3[1 − (1 − α)^1/3]⁻¹}, dα/dT = (A/β)exp(−E/RT){1/4(1 − α)[−ln(1 − α)]⁻³}, and dα/dT = (A/β)exp(−E/RT){1/4(1 − α)[−ln(1 − α)]⁻³}, respectively; for 2, the possible reaction mechanisms of the three steps are nucleation and growth with n = 1/4, chemical reaction, nucleation and growth with n = 1. Kinetic equations may be expressed as dα/dT = (A/β)exp(−E/RT){1/4(1 − α)[−ln(1 − α)]⁻³}, dα/dT = (A/β)exp(−E/RT)[(1 − α)²], and dα/dT = (A/β)exp(−E/RT)(1 − α).

Keywords:

• Praseodymium complexes
• Succinic acid
• Hydrothermal synthesis
• Crystal structure
• Thermal properties

Acknowledgements

We wish to express our sincere thanks to the National Natural Science Foundation of China (No. 20571036), SRF for ROCS, SEM and Education Foundation of Liaoning Province in China (05L212) for financial assistance.