Crystal structure of a new monophosphate tungsten(V) bronze with hexagonal tunnels Na 4(WO 3) 8(PO 2) 4

Abstract

A new monophosphate tungsten(V) bronze Na 4(WO 3) 8(PO 2) 4 has been isolated in melted Na–W–P–O system by sealed tube reaction. Its structure has been determined by single crystal X-ray diffraction in the centrosymmetric space group P2 1/ m with parameters a=6.6065(2), b=5.2711(2), c=8.8898(2) Å, β=99.5898(2)°, Z=2, R=0.055, R W=0.065. The obtained Na 4(WO 3) 8(PO 2) 4 is related to the series of monophosphate tungsten bronzes with hexagonal tunnels A x (WO 3) 2 m (PO 2) 4 with A=Na, K. The framework {(WO 3) 8(PO 2) 4 4−} 3∞ consists of ReO 3 type staircase-like layers built up of WO 6 octahedra interlinked by PO 4 tetrahedra and contains hexagonal tunnels running along [010] where the sodium atoms are located. The edge-sharing distorted pentagonal pyramids NaO 6 form infinite zigzag chains along the channels. A comparison of the Na 4(WO 3) 8(PO 2) 4 structure with that of sodium and potassium monophosphate tungsten bronzes is carried out.