Oxides M2 Os

The pentoxides of As, Sb, and Bi are included in Chapter 20 nothing is known of the structures of these oxides. We have to deal here with the Group VA pentoxides for Pa20s and UO2.6 see Chapter 28. 

The structures of crystalline oxides (a) / -Nb20s, (b)/f-Ta20s, (c) a-UaOg. The chains of vertex-sharing octahedra or pentagonal bipyramids are normal to the plane of the 

This small group consists of Mn207, which at ordinary temperatures is a deeply coloured oil, TC2O7, and Re207. The last two are yellow, volatile, water-soluble solids. Mn207 is presumably molecular in all states of aggregation, and TC2O7 consists of molecules in the crystalline state. In the centrosymmetrical molecule  

Re207 vaporizes as molecules of the same type, but the crystal has an interesting layer structure (Fig. 12.9(a)) in which equal numbers of metal atoms are in tetrahedral and octahedral coordination. (Contrast the chain ion in 

(a) One layer of the crystal structure of Rc207 the small circles represent O atoms shared between octahedral and tetrahedral groups, that is, the O atoms of the ring in (b). (b) Details of one ring of two tetrahedra and two octahedra. (c) The Re207(H20)2 molecule, 

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