Synthesis, structure, and physicochemical investigations of the new α Cu0.50TiO(PO4) oxyphosphate

The room-temperature crystal structure of a new Cu(II) oxyphosphate—α Cu_0.50^IITiO(PO₄)—was determined from X-ray single crystals diffraction data, in the monoclinic system, space group P2₁/c. The refinement from 5561 independent reflections lead to the following parameters: a=7.5612(4)Å, b=7.0919(4)Å, c=7.4874(4)Å, β=122.25(1)°, Z=4, with the final R=0.0198, wR=0.0510. The structure of α Cu_0.50^IITiO(PO₄) can be described as a TiOPO₄ framework constituted by chains of tilted corner-sharing [TiO₆] octahedra running parallel to the c-axis and cross linked by phosphate [PO₄] tetrahedra, where one-half of octahedral cavities created are occupied by Cu atoms. Ti atoms are displaced from the center of octahedra units in alternating long (2.308 Å) and short (1.722 Å) Ti-O(1) bonds along chains. Such O(1) atoms not linked to P atoms justify the oxyphosphate formulation α Cu_0.50TiO(PO₄). The divalent cations Cu²⁺ occupy a Jahn-Teller distorted octahedron sharing two faces with two [TiO₆] octahedra. EPR and optical measurements are in good agreement with structural data. The X-ray diffraction results are supported by Raman and infrared spectroscopy studies that confirmed the existence of the infinite chains -Ti-O-Ti-O-Ti-. α Cu_0.50TiO(PO₄) shows a Curie-Weiss paramagnetic behavior in the temperature range 4-80 K.