Valentinite structure

Examining the inclusion of crystalline compounds Uke salts or metal oxides, it is a frequent observation that the two-dimensional confinement of the space of crystallization causes the formation of structures that differ sometimes completely from those found in the bulk phase. Antimony(III) oxide and potassium iodide may serve as examples here. For the Sb203-filaments inside nanotubes a valentinite structure with a lattice distortion inflicted by the outer restriction is observed (Figure 3.79d). NormaUy, this phase is found at high pressures. At standard conditions, the Sb203 adopts as cubic senarmonite structure with discrete Sb40,5-units. 

The trioxides of arsenic, antimony and bismuth are of structural interest, showing a transition from the molecular lattice characteristic of covalent compounds to an ionic lattice. Arsenic oxide contains As Og molecules, similar in structure to P40g and based on the As tetrahedron. The cubic form of Sb Og is similar, but above 570° this is converted to the macro-molecular valentinite form containing infinite chains (Fig. 179). 

The second form of antimony trioxide, valentinite, has a different type of structure. Instead of finite molecules Sb40e there are infinite double chains of the type shown below, with Sb-0, 2-00 A, 0 bond angles of 116° and 132°, and Sb bond angles of 81°, 93°, and 99°. 

Breunig. H.J. Fork. E. Rosier, R. Becker. G. Mundt, O. Schwarz. W. Common features in the crystal structures of the compounds Z775 (dimethylstibanyl)oxane and -sulfane, and the minerals valentinite and stibnite. Z. Anorg. Allg. Chem. 2000. 626. 1595. 

Fig. 37. The layered ribbons of the structure of valentinite Sb203 projected along [100].

The claudetite structure shown in Figure 39 is a corrugated version of Figure 26f. Bond angles are such that together with the lone pairs an sp bond configuration is approximated, closer than in the case of valentinite. The lone electron pairs frame (or connect) the layers (Table 19). 

Several structural modifications exist, notably the minerals valentinite and senarmontite, along with their synthetic analogues qq.v.y, these may therefore be found from the roasting process. However, the minerals themselves do not appear to have been used as pigments. 

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