Crystalline system Tetragonal

Colorless crystalline solid tetragonal crystal system hygroscopic density 2.50 g/cm3 (tetrahydrate 1.71 g/cm ) tetrahydrated salt loses water of crystallization on heating further heating to 550°C causes decomposition soluble in water, tetrahydrate more soluble in water (30.5g/100g at 30°) than the anhydrous salt insoluble in alcohol. 

Primitive three-dimensional lattices have been classified into seven crystalline systems triclinic, monoclinic, orthorombic, tetragonal, cubic, trigonal, and hexagonal. They are different in the relative lengths of the basis vectors as well as in the angles they form. An additional seven nonprimitive lattices, belonging to the same crystalline systems, are added to the seven primitive lattices, which thus completes the set of all conceivable lattices in ordinary space. These 14 different types of lattices are known as Bravais lattices (Figure 3). 

Tellurium dioxide is known in two different crystalline forms. Crystals of the tetragonal system,2 but almost regular (a c — 1 1-1076), of density 5-66, are obtainable from the solution in nitric acid, while the molten dioxide when slowly cooled deposits rhombic needles 3 (a b c=0 4566 1 0-4693) of density 5-93 and identical with the rarely occurring mineral tellurite. 

Isomorphous replacement in isotactic polyaldehydes was shown by A. Tanake, Y. Hozumi, K. Hatada, S. Endo, and R. Fujishige (42). These authors studied the binary polymer systems formed by acetaldehyde, propionaldehyde, n-butyraldehyde, iso-butyraldehyde and w-heptanal. All the copolymers are crystalline over the whole range of compositions. In the case of binary copolymers of acetaldehyde, propionaldehyde and K-butyraldehyde the unit cells have the same tetragonal space group UJa, with the same chain axis (4.8 A), while the dimensions of the a axis change continuously as a function of the copolymer composition. In the case of copolymers of isobutyraldehyde with other aldehydes, the continuous variation of the lattice constants a and c were observed. 

Iron(II) fluoride [7798-28-8], FeF2, can be prepared by the reaction of iron metal and anhydrous HF at elevated temperatures, reaction of anhydrous FeCl2 and HF in a flow system at ca 500°C, reduction of FeF3, or dehydration of the tetrahydrate. The solid can be sublimed and is monomeric in the gas phase above 690°C. Pure FeF2 is a white crystalline compound and has a rutile structure in which the FeF6 octahedra are tetragonally distorted by... 

The ternary iodide Cu2Hgl4, a structural analog of Ag2Hgl4with very similar properties, exists as brown tetragonal crystals at room temperature. Its high-temperature crystalline form (transition temperature is 80°C) belongs to the cubic system and exhibits the red color. 

Porter, M. W. and Spiller, R. C. (1951). Crystals of the tetragonal, hexagonal, trigonal and orthorhombic systems. In The Barker index of crystals. A method for the identification of crystalline substances, Vol. 1, W. Heffer Sons, Cambridge. [14, 95] Porter, M. W. and Spiller, R. C. (1956). Crystals of monoclinic system. In The Barker index of crystals. A method for the identification of crystalline substances, Vol. 2, W. Heffer Sons, Cambridge. [14]... 

A central issue in the field of surfactant self-assembly is the structure of the liquid crystalline mesophases denoted bicontinuous cubic, and "intermediate" phases (i.e. rhombohedral, monoclinic and tetragonal phases). Cubic phases were detected by Luzzati et al. and Fontell in the 1960 s, although they were believed to be rare in comparison with the classical lamellar, hexagonal and micellar mesophases. It is now clear that these phases are ubiquitous in surfactant and Upid systems. Further, a number of cubic phases can occur within the same system, as the temperature or concentration is varied. Luzzati s group also discovered a number of crystalline mesophases in soaps and lipids, of tetragonal and rhombohedral symmetries (the so-called "T" and "R" phases). More recently, Tiddy et al. have detected systematic replacement of cubic mesophases by "intermediate" T and R phases as the surfactant architecture is varied [22-24]. The most detailed mesophase study to date has revealed the presence of monoclinic. 

Gadolinium pyrophosphate Gd4(P207)3, was prepared from gadolinium oxide and sodium pyrophosphate in hydrochloric acid solution. The X-ray pattern showed it to be amorphorous in the vacuum dried state but when heated at 700 and 900°C it became a crystalline solid which indexed in the tetragonal and cubic systems. The presence of the pyrophosphate group in the anhydrous product was confirmed by... 

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