K4MoV8P12O52, a tunnel structure characterized by an unusual valence of molybdenum

A new phosphate of molybdenum (V) K₄Mo^v₈P₁₂O₅₂ has been isolated and its structure solved from a single crystal X-ray diffraction study. It crystallizes in a monoclinic cell, space groupC2–c, with the parametersa = 10.7433(16)Å,b = 14.0839(9)Å,c = 8.8519(7)Å, and β = 126.42(1)°. After refinement of the different parameters, the reliability factors were lowered toR = 0.026 and_w = 0.029. The framework “Mo₈P₁₂O₅₂” can be described as corner-sharing PO₄ tetrahedra,P₂O₇groups, and MoO₆ octahedra. Although the “O₆” octahedron surrounding the molybdenum ion is almost regular, the metal ion is strongly off center so that its coordination is better described as a MoO₅ pyramid. This particular coordination, which characterizes Mo(V), is discussed.