Two-step magnetic transition in hybrid organic-inorganic materials of the (m-xylylenediamine)MeSO4 (Me - Mn, Fe, Co, Ni) type

New hybrid organic-inorganic materials of the (MXDA) MeSO4 type, where Me - Mn-II, Fe-II, Co-II or Ni-II and MXDA - m-xylylenediamine, were successfully synthesised using the solvothermal technique. Crystal structure studies proved that all of the obtained compounds crystallised in the orthorhombic crystal system and the P2(1)ma space group (no. 26). All structures contain layers parallel to the (010) plane, built of metal atoms linked by SO42- anions. These layers are joined via m-xylylenediamine molecules acting as linkers which complete the distorted octahedral coordination sphere of the metal centres; MeO4N2 four oxygen and two nitrogen atoms. Magnetic studies for compounds where Me = Mn-II, Co-II, and Ni-II reveal transitions to magnetic long-range ordered phases with temperatures of 14.4, 33.0, and 25.8 K, respectively, due to a domination of ferromagnetic interaction within the planes; m-xylylenediamine ligands efficiently separate adjacent metal ion sheets, rendering the superexchange coupling between the planes negligible. Nevertheless, at sufficiently low temperatures, dipole-dipole interaction leads to antiferromagnetic ordering of the magnetic moments belonging to adjacent MeSO4 layers. In addition to structure determination and magnetic studies, all materials were analysed using thermogravimetric measurements and temperature-dependent X-ray diffraction to test their thermal stability. The morphology of the crystallites was analysed using a scanning electron microscope. Sample (MXDA) FeSO4 was additionally studied using Mossbauer spectroscopy.