Synthesis and Characterization of α-Titanium Phosphate/Propylamine Intercalation Compounds Containing Transition-Metal Ions

Abstract

Polycrystalline intercalated TiMxH2−nx(PO4)2· yC3H7NH2·wH2O compounds with transition metal (TM) ions (Mn+ = Co2+, Ni2+, Fe3+ or Cr3+) have been prepared by means of an indirect route and characterised using X-ray diffraction, scanning electron microscopy, chemical and thermal analysis, X-ray absorption and magnetic measurements. These novel pillared layered materials, which were obtained from the monoclinic (P21/c space group) α-Ti(HPO4)2·H2O phase, lose its crystallinity after intercalation. However all the TM ions are octahedrally surrounded by 6 oxygen atoms, although the X-ray absorption spectra evidence a clear dependence on the temperature. Surprisingly, all the materials behave as paramagnetic down to 1.5 K, but they exhibit different colours, what means that they are optically active (Co2+: violet; Ni2+: pale green; Fe3+: yellow; Cr3+: dark green).