K2FeIII0.5TiIII0.5TiIV1.0(PO4)3: Preparation and characterization of a langbeinite-related phosphate containing iron(III) and mixed-valent titanium

Abstract

A potassium mixed iron(III)-titanium(III)-titanium(IV) phosphate K 2FeIII0.5TiIII0.5Ti IV1.0(PO4)3 has been obtained using a two-step flux interaction in evacuated sealed silica tubes. It forms tetrahedrally-shaped dark violet crystals which belong to the cubic system (space group P213) with the cell parameter a = 9.8592(5) Å. The structure was refined from single-crystal X-ray diffraction data. [MO 6] octahedra and [PO4] tetrahedra share their vertices forming a rigid 3D framework. The potassium cations are located in large closed cavities of the framework. A distribution of the 3d metals' valence states in K2FeIII0.5TiIII0.5Ti IV1.0(PO4)3 has been proposed on the basis of magnetic measurements, structure investigations and bond-valence calculations as well as UV/vis and EPR spectroscopy. © 2008 Verlag der Zeitschrift für Naturforschung.