Synthesis, structure determination and magnetic behaviour of the first porous hybrid oxyfluorinated vanado(<scp>iii</scp>)carboxylate: MIL-71 or Vⁱⁱⁱ₂(OH)₂F₂{O₂C-C₆H₄-CO₂}<b>·</b>H₂O

Abstract

A new type of three-dimensional vanadium(III) dicarboxylate, MIL-71 or VIII2(OH)2F2{O2C-C6H4-CO2}·H2O, has been obtained under hydrothermal conditions from aqueous mixtures of vanadium, 1,4-benzenedicarboxylic acid, and HF. MIL-71cal or VIV2O2F2{O2C-C6H4-CO2} is obtained by calcination of the parent compound in air at 250 °C. The three-dimensional structure of MIL-71 (S.G.: Cmmm; a = 21.4477(8) Å, b = 7.1449(2) Å, c = 3.8246(2) Å, and Z = 2) consists of layers built from corner-sharing {VIIIO2(OH)2F2} octahedra connected by the terephthalate linkers. The role of fluorine in this structure is understood by comparison with the already known hybrid vanado(III)carboxylates. The thermal behavior of the two solids has been investigated using TGA and X-ray thermodiffractometry. Finally, magnetic measurements performed on both MIL-71 and MIL-71cal reveal a canted antiferromagnetic behavior with Néel temperatures below 20 K.