Pyramidal crystals

Tetrahydrostrychnine, CgjHggOgNg. HgO. This substance, also formed by the electrolytic reduction of strychnine, crystallises from alcohol in prisms, m.p. 202°, gives colour reactions of the strychnidine type, and yields both neutral and acid salts the hydrochloride, B. HCl, occurs in small needles readily soluble in water and the dihydriodide, B. 2HI. 2HjO, in pyramidal crystals. The base yields an amorphous nitrosoamine, the hydrochloride of which crystallises from warm water in lustrous, yellowish prisms. It also furnishes a crystalline monoacetyl derivative, and on heating with hydrochloric acid or phosphorus oxychloride is dehydrated to strychnidine. 

Basic Tellurium Nitrate, Te203(0H)N03, which has already been mentioned (p. 379), is formed when a solution of tellurium or tellurium dioxide in nitric acid is evaporated without excessive heating.6 It crystallises in rhombic pyramidal crystals (a b c=0-590 1 0-607).7... 

Figure 8.11 Formation of pyramidal crystals of a-glycine attached to the /V palmitoyl-(R,S) -lysine monolayers. (Reproduced with permission from [16]).

Scheme I. Average a/c ratios of developing pyramid crystals with transition into cubes and schematic drawing of growth process in the gel spheres.

It crystallizes from ether in large pyramidal crystals melting point 127°. It is soluble in hot alcohol, and a little in cold alcohol. It has lost all of the basic properties of the ammonia and does not form salts with acids. This shows the negative or acid influence of the phenyl radical as compared with the methyl radical. 

Figure 9. Arrangement of thallium ions in thallous azide. Dotted outline shows the unit cell, and the full line indicates the geometry of the pyramidal crystals which commonly form from solution. The arrow indicates the direction in which decomposition takes place.

Wiede, K. A. Hofmann and H. Hiendlmaier, E. H. Eiesenfeld and co-workers, A. Werner, and A. Wesch prepared chromium triamminotetroxide, Cr04.3NH3, as previously indicated. The salt appears in brown, doubly refracting prisms when rapidly cooled, the hot soln. furnishes rectangular plates. 0. Wiede reported the axial ratios of the rhombic, pyramidal crystals to be a h c=l 0076 1 1 308. 

Give the symmetry designation of the following pyramidal crystal ... 

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