Tetragonal hydrate

Anhydrous RuO has a tetragonal rutile structure with a slightly distorted octahedral structure, there being two sets of Ru-0 distances at 1.917(8) and 1.999(8) A [645] and has an extensive chemistry as a heterogeneous oxidation catalyst, a topic beyond the scope of this book. It is rarely used as a precursor for Ru oxidations, the hydrated form RuO. nH O (for brevity written below simply as RuO ) being much more effective in this respect. A procedure for converting inactive RuO (presumably the anhydrous form) to the hydrated RuO used in catalytic oxidations has been described [243]. 

The electrostatic modd for the hydrated vanadyl ion consists of V,+ situated in a tetragonal dectric fidd caused by the oxide ion and five water dipoles. The ctystal fidd energy levd diagram for such a situation is given in Fig. 1. 

Figure 2.11 Very high pressure (0.3-2.1 GPa) structural changes of gas hydrates at room temperature. Numerical values (adjacent to square boxes) indicate transition pressures. Hexagonal (sH ) and tetragonal (sT ) hydrate phases are distinct from sH and sT hydrate structures found at normal pressures. (Modified and redrawn from Hirai, H., Tanaka, H., Kawamura, K., Yamamoto, Y., Yagi, T., J. Phys. Chem. Solids, 65, 1555 (2004). With permission from Elsevier.)...

In addition to the three known natural gas hydrates, several other hydrate structures exist. Dyadin et al. (1991) found four hydrate structures and Jeffrey (1984) proposed five additional hydrate structures. These structures have yet to be confirmed in natural gas systems, although new hydrate structures have been identified using x-ray diffraction such as a tetragonal structure for bromine (Udachin et al., 1997b), a trigonal structure for dimethyl ether (Udachin et al., 2001a),... 

X- and Q-band EPR in the temperature range 4.2-300 K were used to obtain data for the Cu(H20)g+ JT complex. The cases of the JT complexes in a site of cubic (or trigonal) symmetry (a), tetragonal elongated symmetry (b), and tetragonal compressed symmetry (c) are analyzed. The crystallo-hydrates are suitable and convenient objects for investigation, as representatives of this class of compounds ... 

A detailed investigation of the surface properties of the tetragonal phase of Zr02 by HRTEM and IR techniques has also been reported (605). The tetragonal phase of zirconia is metastable at low temperatures. Therefore, yttria-stabilized samples were prepared and characterized (606-608). The structural, morphological, and surface hydration features of tetragonal ZrC>2 were investigated by XRD, HRTEM, and IR techniques (606), and the interactions of the surfaces with CO (607) and C02 (608) were reported. 

Two hydrates have been described. The monohydrate, AgF,H20, forms yellowish cubes,4 or large, deliquescent, tetragonal crystals,5 decomposed by heat with formation of a basic salt, AgaF(OH), and evolution of hydrogen fluoride. The dihydrate, AgF,2HaO, crystallizes from concentrated solution in hard, transparent prisms.6... 

There are four different phases of rare earth orthophosphate (RPO4), mostly depending on the cationic radius of rare earth element Monazite (monoclinic, dehydrate, for light lanthanides), xenotime (also typed as zircon, tetragonal, dehydrate or hydrate, for heavy lanthanides and Y +), rhabdophane (hexagonal, mostly hydrate, across the series), and... 

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