Metal-organic framework compounds
Metal-organic framework (MOF) compounds with Fe coordination centers have been shown to exhibit high electronic mobility as well as nanoscale ferromagnetism. 57Fe Mössbauer spectra of such materials provide information about the local coordination geometry, electronic structure, spin states and magnetic properties at the iron centers. Below, Mössbauer spectra of a perthiolated coronene (PTC) based MOF compound where Fe centers are linked to the network via dithiolene bridges are shown. At room temperature the spectrum consists of a single quadrupole doublet with isomer shift IS = 0.21 mm/s and quadrupole splitting QS = 2.89 mm/s which suggests a square planar FeS4 coordination geometry and an intermediate spin state S = 3/2. The line asymmetry reflects a texture effect. Below 10 K, a broad magnetic hyperfine pattern emerges which is in agreement with nanoscale ferromagnetism as suggested by magnetization measurements.