Oriented Crystallisation on Supports and Anisotropic Mass Transport of the Metal-Organic Framework Manganese Formate

The oriented in situ crystallisation of microporous manganese(II) formate [Mn(HCO2)2] on different porous supports (e.g. porous alumina and graphite) has been investigated. The anisotropic growth of Mn(HCO2)2 was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The intracrystalline diffusion of methanol in Mn(HCO2)2 was studied by observation of the sorption kinetics by interference microscopy (IFM). It was found that untreated discs of porous alumina and graphite supports exhibit poor densities of Mn(HCO2)2 crystals per supported area. Even lower crystal densities are found for activated supports such as for alumina after basic treatment and for oxidized graphite supports. Improved results have been achieved by replacing formic acid by sodium formate in the synthesis route. Crystal growth on graphite gives results superior to those on alumina with respect to the crystal density as well as the relative orientation of the 1D channel network to the support surface. Methanol uptake from the vapour phase is similar at 25 and 40 °C and gives an adsorption capacity of about 95 mL g–1. The BET surface area was found to be 280 m2 g–1. IFM indicates that diffusion occurs only along one crystallographic axis, thus proving the presence of a 1D channel system. Diffusion coefficients of about 10–12 m2 s–1 for methanol in microporous Mn(HCO2)2 were found. These results can be used to prepare supported metal–organic framework (MOF) membranes for molecular sieving. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)