Lanthanide(III) 1,4-Phenylenediacetate Complexes: The Relation Between the Structure and Thermal Properties

The series of isostructural lanthanide coordination polymers with the empirical formula Ln₂(PDA)₃(H₂O)]·2H₂O, where PDA = 1,4-phenylenediacetate anion = C₈H₈(COO)₂]^2?; Ln = La-Lu(III), and Y(III) were produced in the reaction of LnCl₃·nH₂O with ammonium salt of 1,4-phenylenediacetic acid in water solution. The compounds were characterised structurally using powder X-ray diffraction, elemental and thermogravimetric analyses as well as FT-IR spectroscopy. Thermogravimetric analyses show that in the range 60–170 °C the dehydration process occurs. The thermal stability of dehydrated compounds, Ln₂(PDA)₃ increased from about 200–350 °C in the whole series of complexes. Single-crystal X-ray diffraction analysis for the Gd(III) complex revealed that the compound crystallizes in the monoclinic P2₁/c space group with a = 21.863(2) Å, b = 10.035(1) Å, c = 13.854(1) Å, β = 91.53(1)° and V = 3,038.5(4) ų. The complex contains one-dimensional gadolinium-carboxylato chains, which are connected with the –CH₂–C₆H₄–CH₂– spacers of PDA ligand to the three-dimensional metal–organic framework.