Phosphorus crystal structure white

White phosphorus has a white waxy appearance that turns slightly yellow with age and impurities. There are two allotropic forms of white phosphorus. The alpha (a) form has a cubic crystal structure, and the beta (P) form has a hexagonal crystalline structure. White phosphorus is extremely reactive and will spontaneously burst into flame when exposed to air at a temperature of about 35°C. It must be kept under water. But this property of spontaneous combustion has made it useful for military applications. 

At normal temperature, white phosphorus exists in the cubic a-form, which is stable from -77°C to its melting point (44.1°C). The crystal data of a-white phosphorus are a = 1.851 nm, Z = 56 (P4), and D = 1.83 g cm-3, but its crystal structure is still unknown. At -77°C the cubic a-form transforms to a hexagonal P-form with a density of 1.88 g cm-3. 

The element phosphorus when condensed from the vapor forms waxy, colorless crystals, called white phosphorus. These crystals and the vapor contain P4 molecules, with the tetrahedral structure shown in the drawing. Each of the six interatomic distances in the molecule has the value 2.20 A. 

Chlathrates may, in a way, be regarded as supramolecular adducts in the crystalline state. C ) forms a series of these compounds which in most cases are obtained by simple cocrystallization of their constituents. Known examples are the inclusion compounds with hydrocarbons tike pentane or nonane, etc., but chlathrates of Qo or C70 have also been found with hydroquinone in the presence of benzene. In these cases the fullerene molecules occupy interstitial spaces within the crystal structure of hydroquinone and form donor-acceptor complexes. Further inclusion compounds with fuUerenes are known for ferrocene and other inorganic substances such as sulfur (Sg), white phosphorus (P4) or complexes hke (PhCN)2PdCl2 and PhsPAuCl (also refer to Section 2.5.3). For the complex of > with ferrocene the crystal structure of the first is found with the latter inserted into the given gaps. The whole stracture can only exist because ferrocene is too weak a reducing agent to transform > into Qo. 

Red phosphorus. Red to violet powder polymorphism Roth et al, J. Am. Chem. Soe. 69, 2881 (1947) Corbridge, loc. cit. Crystal structure of one form, Htttmfs phosphorus Thum, K-rehs, Acta Cryst 25B, 125 (1969). The proparties of red phosphorus are intermediate between those of the white and black Forms. Sublimes at 416", triple point 589-5" under 43.1 atm. d 2.34. Inso] in organic solvents. So] in phosphorus tribromide. Less active than the white form reacts only at high temp. Yields the white modification when distilled at 290". Catches fire when heated in air to about 260 and burns with formation of the pantoxide. Bums when heated in an atmosphere of chlorine. 

Comparison of the decomposition products with the crystal structures of the corresponding substances shows that the equilibrium composition of products is observed only for white phosphorus, having the cubic structure. For elements with structures other than cubic, evaporation occurs with the formation (partial or complete) of binary molecules. Thus, the distinctive feature of crystals with cubic structure to sublime with the formation of equilibrium primary products manifests itself for all the substances considered above oxides, nitrides and white phosphorus. 

The simplest applications of thermodynamics to chemically significant systems involve the phase transitions that pure substances undergo. The phase of a substance is a form of matter that is uniform throughout in chemical composition and physical state. The word phase comes from the Greek word for appearance. Thus, we speak of the solid, liquid, and gas phases of a substance, and of different solid phases distinguished by their crystal structures (such as white and black phosphorus). Kphtse transition, spontaneous conversion of one phase to another, occurs at a characteristic temperature for a given pressure. Thus, at 1 atm, ice is the stable phase of water below 0°C, but above 0°C the liquid is more stable. The difference indicates that, below 0°C, the chemical potential of ice is lower than that of liquid water, //(solid) < //(liquid) (Fig. 1), and that above 0 C, //(liquid) < //(solid). The transition temperature is the temperature at which the chemical potentials coincide and //(solid) = //(liquid). 

Figure 2 ORTEP 3 view of cyanocobalamin (vitamin B12) as created by POV-Ray 3D graphics tool. Crystal structure data were obtained from Cambridge Structural Database (CSD), code COVDEW01. Colors of atoms carbon - white, hydrogen - yellow, nitrogen - blue, oxygen - red, phosphorus - green, cobalt -pink. (Courtesy of Moncol J and Koman M, Slovak University of Technology, Bratislava, Slovakia, with permission.)...

If white phosphorus and sulphur are mixed together at temperatures below 100°C, only solid solutions were at one time believed to be formed, as indicated in the phase diagram [2,2a,2b] in Figure 4.11. The a phase has the crystal structure of orthorhombic sulphur, built from Sg rings with 4 molecules in solid solution. The p phase, on the other hand, has the structure of white phosphorus, with Sg ring molecules in solid solution. 

Okudera H, Dinnebier RE, Simon A (2005) The crystal structure of y-P4, a low temperature modification of white phosphorus. Z Krist 220 259-264... 

Figure 33 Crystal structures of the inclusion complexes (a) (H443)(H2P207 ) + and (b) (H676)(ox) +. Carbon (Grey), Nitrogen (Blue), Hydrogen (White), Oxygen (Red), and Phosphorus (Orange).

White phosphorus is metastable and is hexagonal below -76.9 C. From this temperature and up to the melting point it is cubic. Red phosphorus is more stable than white but still metastable. It has a very disordered crystal structure. Black phosphorus is stable up to about 400 C and has an orthorhombic structure with [Pg.989]

In 2000 Katayama et al. [35] conducted an in situ X-ray dillraction experiment on liquid phosphorus which strongly suggested a first order liquid-liquid phase transition between a molecular liquid and a polymeric liquid. This was particularly notable because not only did it occur in the stable liquid, as opposed to the more conunon metastable supercooled liquid, it also demonstrated coexistence of the two phases. This was clearly visible from a weighted sum of the diffraction patterns from either side of the transition compared to the diffraction pattern at the transition (Fig. 2.9). The coexistence was also apparent from in situ X-ray radiography [36] and had been suggested by ab initio MD simulations [54], However a further, more extensive, in situ X-ray diffraction investigation by Monaco et al. [53] established that the transition was in fact between a polymeric liquid and a molecular fluid the latter being the fluid form associated with the metastable white phosphorus crystal, which takes a molecular tetrahedral structure. Therefore while undoubtedly a first order liquid-fluid phase transition, phosphorus did not provide the first evidence for a first order liquid-liquid phase transition. 

Data given apply to white phosphorus, t Crystal structures are for the most common allotropes. 

There are only two requirements for the compounds and materials to be used by VIM They should be highly insoluble in the electrolyte solution used and they must possess electroactivity, i.e., the ability to be either oxidized or reduced in the accessible potential window of the experiment. Most importantly, there is no restriction with respect to the electronic conductivity. Even insulators like white phosphorus can be studied, because the electrochemical reaction which can take place at the three-phase boundary compound-electrodesolution can often deliver sufficient charge to give measurable currents. One can easily distinguish three different kinds of compounds, those which are not electroactive, those which are irreversibly destroyed in the electrochemical reactions, and those which can be reversibly reduced and oxidized. The latter compounds are characterized by possessing the ability to exchange electrons with the electrode and ions with the solution. This ability requires solid compounds that can house ions through features of their crystal structure, e.g., channels or interlayers. 

Black phosphorus is formed when white phosphorus is heated under very high pressure (12 000 atmospheres). Black phosphorus has a well-established corrugated sheet structure with each phos phorus atom bonded to three neighbours. The bonding lorces between layers are weak and give rise to flaky crystals which conduct electricity, properties similar to those ol graphite, it is less reactive than either white or red phosphorus. 

We had previously demonstrated that the stable (phosphino)(silyl)carbene 16 [31] reacts with trimethylsilyl trifhioromethanesulfonate to give the phosphino-substituted carbocation 17 [32], one of the very few stable phosphorus analogues of iminium salts [33]. The same synthetic strategy was adopted to prepare the diphosphino carbocation 17 or its valence isomer 2"Pa. A dichloro-methane solution of bis(diisopropylamino)phosphenium triflate was added at 0°C to a pentane solution of the carbene 16. The adduct 2 rPa [34] was isolated in 66% yield as extremely air sensitive white crystals (melting point 89-90°C) by recrystallization from tetrahydrofuran at -5°C (Scheme 13). The symmetrical three-membered ring structure was evident from the spectroscopic data (31P NMR s, S + 7.3 ppm, 13C NMR t, <549.6 ppm, ]PC 7.3 Hz, 29Si NMR t, <5-10.7 ppm Jpsz 10 Hz). 

Two more stable phosphorus allotropes are red and black phosphorus. Small amounts of these are are also produced for special purposes from the white phosphorus product of the electric arc furnace. Red phosphorus is obtained by heating white phosphorus at 400°C for several hours, which yields a complex polymeric material, more dense (2.20 g/cm ) and considerably more stable than the white variety. Red phosphorus is not only stable in air, but far less toxic than white phosphorus. Black phosphorus is more dense again (2.25-2.69g/cm ), and has a different more complex structure. It is obtained by heating the white variety at 220 to 370°C for 8 days plus requires either a pressure exceeding 10 kg/cm or a seed crystal of black phosphorus. This product has a structure resembling graphite, is a good electrical conductor, and can be lit with a match only with difficulty [10] (Table 10.3). 

Initial structure-property relationships have been studied using examples like diamond/graphite and white/red phosphorus (see Sect. 4.3), the modifications have been established from the same C atoms or P atoms respectively. However, the substances are drastically different in their chemical structure and therefore in their characteristic properties. The misconceptions could be corrected with the consideration that the individual C atom or P atom show absolutely no properties like color or density. Such characteristics can be determined only when a little crystal is visible (see Sect. 4.3). 

Atomic weight 30.975. Pure phosphorus is white, translucent, soft and readily cut. It is brittle when cold and shows a crystalline structure at break surfaces. Beautiful crystals are obtained by... 

Orthorhombic black phosphorus was originally produced by the action of high pressure on the white or red form [36], It was later made by the action of heat on white mixed with mercury and in the presence of a seed crystal of black. This form of the element has a continuous double-layer structure in which each P atom forms three bonds of length 2.23 A, pyramidally disposed at mutual angles of lOO (Figure 4.3). It is a semiconductor and exhibits flakiness similar to mica and graphite layer structures. ... 

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