Orthorhombic crystal system, crystallographic

In the thermodynamic sense, a phase is defined as part of a chemical system in which all the material has the same composition and state. Appropriately, the word comes from the Greek phasis, meaning appearance . Ice, water and steam are the three simple phases of H20. Indeed, for almost all matter, the three simple phases are solid, liquid and gas, although we must note that there may be many different solid phases possible since H20(S) can adopt several different crystallographic forms. As a related example, the two stable phases of solid sulphur are its monoclinic and orthorhombic crystal forms. 

Careful measurement of mineral specimens allowed crystals to be classified in terms of six crystal families, called anorthic, monoclinic, orthorhombic, tetragonal, hexagonal and isometric. This classification has been expanded slightly by crystallographers into seven crystal systems. The crystal systems are sets of reference axes, which have a direction as well as a magnitude, and hence are vectors1. The crystal families and classes are given in Table 1.1. 

Similar conclusion was also valid for similar system, tetrapeptide Tyr-Ala-Phe-Gly [95]. Single-crystal XRD data proved that YAFG peptide very easily forms at least three crystallographic modifications, monocHnic P2j, orthorhombic P2i2i2 and tetragonal P4i2i2. Each crystal contains different amounts of water, monoclinic is mono-hydrate, orthorhombic contains 5.5 water molecules while tetragonal 4 water molecules in the asymmetric unit. SS NMR spectroscopy proved that the orthorhombic crystals are unstable... 

Crystal system tricl = triclinic monocl = monoclinic orth = orthorhombic tetr = tetragonal hex = hexagonal rhomb = rhombohedral cubic = cubic. Structure type Prototype for the structural arrangement of the crystallographic cell. 

Potassium hexacyanochromate(III) is a yellow solid, highly soluble in water, that crystallizes as large square platelets. It crystallizes in the orthorhombic system, with the space group Pcan. The unit parameters are a = 8.53, b = 10.60, c = 13.68 A. Because of its disorder behavior, it presents a complex crystallographic problem. The compound shows a j/cn band at 2131 cm. The molar extinction coefficients in aqueous solution of the two observable d d bands at 376 nm ( A2g —> 72) and 309 nm (4 2 T l ) are 93 and 62 L mol ... 

X-ray crystallographic studies have been carried out on four compounds belonging to three different pseudoazulene systems.9-61129 All studied compounds crystallized in monoclinic or orthorhombic space groups, a situation requiring Cs symmetry of each molecule. The size of the unit cells of the crystal lattice strongly depends upon the pseudoazulene system. The atoms of the pseudoazulene skeleton are all coplanar to within <5 ... 

Single-crystal precession data indicate orthorhombic symmetry with the crystallographic space group Fddd. This system is not isostructural with any other known metal oxyfluoride or metal dioxide. The cell dimensions, determined from Guinier data, are a = 8.370 1 A. b = 10.182 1 A. and c = 7.030 1 A. The indexed powder data are given in reference 6. 

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