Temperature Form

Dichlorobis(methyldiphenylphosphine)nitrosylcobalt is a dark-brown crystalline solid which is moderately stable in air, but in solution it reacts rapidly with oxygen. The complex is soluble in dichloromethane, chloroform, and tetrahydrofuran and is insoluble in hexane, ethanol, methanol, and ether. The compound has the infrared spectrum, v(NO) = 1750 (s), 1650 (s) cm in CH2CI2, and 1735(s) and 1640(m) cm-i in KBr. The nmr spectrum is T 7.5 CH3 Jph(4 Hz) and t 2.6 (CeHs) in CDCI3. 

A Schlenk-tube apparatus (Fig. 5) with a frit of coarse porosity is flushed 

The low-temperature form is a light-brown crystalline solid which is moderately stable in air but is unstable in solution if exposed to air. Its infrared spectrum shows u(NO) = 1737 cm i (Nujol). 

Shriver, The Manipulation of Air-Sensitive Compounds, McGraw-Hill Book Company, New York, 1969. 

The title compounds are part of a series of four-coordinate complexes of the (MNO) group (M = Co, Rh, and Ir). Until recently, these complexes 

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In addition to H2, D2, and molecular tritium [100028-17-8] the following isotopic mixtures exist HD [13983-20-5] HT [14885-60-0] and DT [14885-61-1]. Table 5 Hsts the vapor pressures of normal H2, D2, and T2 at the respective boiling points and triple points. As the molecular weight of the isotope increases, the triple point and boiling point temperatures also increase. Other physical constants also differ for the heavy isotopes. A 98% ortho—25/q deuterium mixture (the low temperature form) has the following critical properties = 1.650 MPa(16.28 atm), = 38.26 K, 17 = 60.3 cm/mol3... 

Tripolyphosphates. The most commercially important tripolyphosphate salt is sodium tripolyphosphate (STP), Na P O Q. Three distinct crystalline forms are known two are anhydrous (STP-I and STP-II) the other is the hexahydrate [15091 -98-2] Na P O Q 6H20. Sodium tripolyphosphate anhydrous Form I is the high temperature, thermodynamically stable phase sodium tripolyphosphate anhydrous Form II is the lower temperature form which can be readily converted to STP-I by heating to above 417 8° C, the transition temperature. However, the reverse reaction is extremely slow below 417°C. Both anhydrous forms of sodium tripolyphosphate are therefore stable enough to coexist at room temperature. 

Besides the amorphous red P which is a commercial product, there are perhaps five other crystalline or poorly crystalline red modifications that are not produced commercially. These include a triclinic, an orthorhombic, a high temperature form, and two poorly crystalline forms. Red phosphoms varieties are rather stable in air and are of lower reactivity than white phosphoms. 

The stmcture of tridymite is more open than that of quart2 and is similar to that of cristobaUte. The high temperature form, probably S-IV, has a hexagonal unit cell containing four Si02 units, where ttg = 503 pm and Cg = 822 pm > 200° C, space group Pb./mmc. The Si—O distance is 152 pm. 

As-polymerized PVDC is not in its most stable state annealing and recrystaUization can raise the temperature at which it dissolves (78). Low crystallinity polymers dissolve at a lower temperature, forming metastable solutions. However, on standing at the dissolving temperature, they gel or become turbid, indicating recrystaUization into a more stable form. 

Pure silica contains no metal ions and every oxygen becomes a bridge between two silicon atoms giving a three-dimensional network. The high-temperature form, shown in Fig. 16.3(c), is cubic the tetrahedra are stacked in the same way as the carbon atoms in the diamond-cubic structure. At room temperature the stable crystalline form of silica is more complicated but, as before, it is a three-dimensional network in which all the oxygens bridge silicons. 

Ferrite (or a) is the low-temperature form of iron. On heating, it changes to austenite (or y) at 914°C when it is pure, and this form remains stable until it reaches 1391°C when it changes to d-iron (if you have forgotten this, check back to p. 319). The phase... 

As shown in Fig. 7.6, the Mossbauer data show a reduction in Morin transition temperature with increasing shock severity. At temperatures below the transition, increasing shock severity causes greater retention of the higher temperature, weak ferromagnetic contribution. The measure of weak ferromagnetic (WF) fraction (the high temperature form) is a sensitive indication of shock modification. 

Fig. 7.6. The weak ferromagnetic (WF) fraction (high temperature form) of hematite provides a sensitive measure of shock modification. Sample 31G836 is an 8 GPa experiment. Sample 29G836 is a 17 GPa experiment, while 17G846 is a 27 GPa sample (after Williamson et al. [86W03]).

Similar principles apply to ortho- and para-deuterium except that, as the nuclear spin quantum number of the deuteron is 1 rather than as for the proton, the system is described by Bose-Einstein statistics rather than the more familiar Eermi-Dirac statistics. Eor this reason, the stable low-temperature form is orriio-deuterium and at high temperatures the statistical weights are 6 ortho 3 para leading to an upper equilibrium concentration of 33.3% para-deuterium above about 190K as shown in Eig. 3.1. Tritium (spin 5) resembles H2 rather than D2. 

Figure 9.6 Schematic representation and exampies of various chain metasilicates (SiO with repeat distances (in pm) after i, 2,. 7. 9 or 12 tetrahedra (T), ((ht) high-temperature form (hp) high-pressure form].

The reverse transition from a—involves a structural distortion along the c-axis and is remarkable for the fact that the density increases by 26% in the high-temperature form. This arises because, although the Sn-Sn distances increase in the a—transition, the CN increases from 4 to 6 and the distortion also permits a closer approach of the 12 next-nearest neighbours ... 

The low-temperature form (1) converts to the high-temperature form (11) above 417 C and both forms react with water to give the crystalline hexahydrate. All three materials contain the... 

Many of the high-pressure forms of ice are also based on silica structures (Table 14.9) and in ice II, VIII and IX the protons are ordered, the last 2 being low-temperature forms of ice VII and III respectively in which the protons are disordered. Note also that the high-pressure polymorphs VI and VII can exist at temperatures as high as 80°C and that, as expected, the high-pressure forms have substantially greater densities than that for ice I. A vitreous form of ice can be obtained by condensing water vapour at temperatures of — 160°C or below. 

The other HX are not associated in the gaseous or liquid phases but the low-temperature forms of crystalline HCI and HBr both feature weakly... 

Vanadium and sodium neutralize catalyst acid sites and can cause collapse of the zeolite structure. Figure 10-5 shows the deactivation of the catalyst activity as a function of vanadium concentration. Destruction of the zeolite by vanadium takes place in the regenerator where the combination of oxygen, steam, and high temperature forms vanadic acid according to the following equations ... 

The precipitated precursor can be dissolved and re-crystallized from fluorine-free solutions. This provides excellent conditions for deep purification of the material and reduction of problematic impurities such as titanium, fluorine, etc. Peroxometalates decompose at relatively low temperatures forming tantalum or niobium oxides containing small amount of absorbed water. The absorbed water separation is achieved by further thermal treatment - drying and calcination - of the product ... 

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