Structural changes upon dehydration of Pr(III)(H2O){C6H3(CO2)3} or MIL-81: A new three-dimensional praseodymium 1,2,4-benzenetricarboxylate with a one dimensional inorganic sub-network

A new three-dimensional lanthanide(III) tricarboxylate, MIL-811 or Pr(III)(H2O)(C6H3(CO2)3) has been obtained under hydrothermal conditions. Its three-dimensional structure, which has been determined using X-ray powder diffraction data, is built-up from edge-sharing chains of nine coordinated praseodymium(III) capped square antiprisms linked through 1,2,4-Benzenetricarboxylate (1,2,4-BTC) moieties. Its thermal behaviour has been investigated using TGA and X-ray thermodiffractometry and reveals that dehydration is followed by an irreversible structural change giving the solid MIL-81ht or Pr(III)(C6H3(CO2)3) with both a change in the environment of the rare earth and in the connection mode of the carboxylate.Crystal data for MIL-81: monoclinic space group P21P21 with a=10.272(1) Åa=10.272(1) Å, b=7.057(1) Åb=7.057(1) Å, c=6.232(1) Åc=6.232(1) Å, β=93.668(4)°β=93.668(4)° and Z=2Z=2. Crystal data for MIL-81ht: triclinic space group P-1   with a=9.864(1) Åa=9.864(1) Å, b=7.054(1) Åb=7.054(1) Å, c=5.784(1) Åc=5.784(1) Å, α=90.862(9)°α=90.862(9)°, β=92.439(6)°β=92.439(6)°, γ=91.594(8)°γ=91.594(8)° and Z=2Z=2.

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