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Keywords:

  • Manganese;
  • Metal-organic frameworks;
  • Solvothermal synthesis;
  • Crystal engineering;
  • Magnetic properties

Abstract

The reaction of an unsymmetrical ligand, namely 1,2,4-benzenetricarboxylic acid (H3btc), under pH-controlled hydrothermal conditions with a manganese salt leads to the three-dimensional coordination polymer {Mn(H2O)[C6H3(CO2)2(CO2H)]·(H2O)}n (FJU-2). Potassium hydroxide is used as a control agent to modulate the degree of deprotonation of the unsymmetrical H3btc ligand during the hydrothermal reaction, which is essential for the synthesis of the resulting product. The product was characterised by elemental, single-crystal and powder X-ray analyses. The structure of FJU-2 consists of carboxylate- and water-bridged manganese cluster chains which are further cross-connected by the phenyl spacer into a three-dimensional neutral framework. Guest water molecules reside in an elliptically shaped, one-dimensional channel. There are strong hydrogen-bonding interactions between the guest water molecules and host framework that prevent the release of the guest water molecules at lower temperatures, as indicated by the thermogravimetric analysis. The magnetic study shows an antiferromagnetic coupling for FJU-2. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)