A Manganese(II) 3D Metal–Organic Framework with Siloxane-Spaced Dicarboxylic Ligand: Synthesis, Structure, and Properties

Abstract

A new metal–organic framework {[Mn4(Cx)3(etdipy)5]·2ClO4}n (1) was prepared via the complexation of manganese ion from a Mn(ClO4)2 source with 1,3-bis(carboxypropyl)tetramethyldisiloxane (Cx) and 1,2-di(4-pyridyl)ethylene (etdipy) in the presence of 2,4-lutidine as a deprotonating agent. The single-crystal X-ray diffraction analysis revealed a dense 3D framework structure. The presence in the structure of flexible tetramethyldisiloxane moieties, which tend to orient themselves at the interface with the air, gives the compound a highly hydrophobic character, as indicated by the result of the water vapor sorption analysis in the dynamic regime, as well as the shape and stability of the water droplet on the crystalline mass of the compound. The compound is an electrical insulator, and due to its hydrophobicity, this characteristic is unaffected by environmental dampness. The thermal analysis indicated thermal stability up to about 300 °C and an unusual thermal transition for an MOF structure, more precisely a glass transition at 24 °C, the latter also being attributed to the flexible segments in the structure. The magnetic studies showed dominant antiferromagnetic interactions along the metal ion chain in compound 1.