Orthorhombic dihydrate structure

Dihydrate large transparent crystals orthorhombic bisphenoidal structure density 1.915 g/cm decomposes at 60°C very soluble in water insoluble in alcohol. 

The dehydration and interconversion reactions of the various forms of calcium sulphate [dihydrate, hemihydrate (a and 3 pseudo morphs) and anhydrous salt (hexagonal and orthorhombic structures)] have been studied by Ball et al. [281,590,591] who compared their observations with the available rate and microscopic data. The important features of the complicated behaviour found are summarized in the scheme [281]... 

LiB02 2H20 or L O B203 -4H20, becomes the stable solid phase. Dihydrate crystals are orthorhombic having a density of 1.825 g/mL and a structural formula Li[B(OH)4]. In solution above 150°C a hemihydrate, LiB02 1/2 0, forms and the anhydrous salt crystallizes above 225°C. 

Fig. 12.13. Plan of the unit cell of the orthorhombic structure of cupric chloride dihydrate, CuC12.2H20, projected on a plane perpendicular to the z axis. The heights of the atoms are indicated in fractions of the c translation and hydrogen bonds are represented by broken lines. The corners of the unit cell coincide with the copper atoms at height o.

In further studies on the crystal structures of cyclodextrin complexes, the a-cyclodextrin 4-nitrophenol (1 2) complex was found to have an orthorhombic unit cell. The a-cyclodextrin methylsulphoxide methanol (1 1 2) dihydrate complex had a monoclinic unit cell. In this structure, the methylsulphoxide molecule is on the side of the secondary hydroxy-groups in the a-cyclodextrin cavity such that it forms two hydrogen bonds with adjacent a-cyclodextrin molecules. One methanol molecule is found on the side of the primary hydroxy-group in the cavity while the other is located outside the cavity. The two water molecules are distributed in the space between the a-cyclodextrin molecules. 

---