Phosphorus structure model

A transition structure model was proposed which accounts for the high selectiv-ities obtained for some of the substrates [80]. In the structure shown in Scheme 6.37 the two phosphorus atoms of the Tol-BINAP ligand and the two car-... 

VII. Structural Models of Phosphorus-Containing Hydrotreating Catalysts... 

Structural models of phosphorus-containing hydrotreating catalysts have been proposed from catalyst characterization data and results characterizing the reactions of model compounds. Poulet et al. (79) reported a structural model of MoP/Al catalysts (Fig. 35) in which the phosphorus-containing species exist in three different states (i) isolated phosphorus oxo-species interacting with the alumina support, (ii) phosphorus directly incorporated into the M0S2 slab, and (iii) phosphorus oxo-species bound to both M0S2 and the alumina surface. 

Mangnus et al. (70) proposed a structural model for Co—Mo — P/Al catalysts (Fig. 36) whereby phosphorus exists mainly as AIPO4 on the alumina surface. In this model, a fraction of the molybdenum sites at the edges of the M0S2 slabs interact with AIPO4 through complex... 

The review of phosphorus models by Lewis and McCechan (2002) showed that one of the major differences in phosphorus cycling models is the number of inorganic and organic phosphorus pools and the ability to measure them in the laboratory. Models such as CENTURY have included phosphorus pools that are conceptually important for the model structure, but are difficult to measure. For example, the CENTURY model includes separate pools for parent phosphorus, strongly sorbed phosphate and occluded phosphorus, while... 

A detailed study of the aluminum phosphate AlPO-53 in both its as-made and calcined forms was described. A variety of solid-state NMR experiments showed the local environment of the aluminum and phosphorus atoms proposed in a previous structural model from powder X-ray diffraction. ... 

The lnP(001)(2 X 4) Reconstruction The In-rich InP(001)(2 x 4) reconstruction is the most widely investigated and best understood (001) surface of the phosphorus-containing III-V compound semiconductors. A number of publications concerning structural, electronic, optical, and other properties have been reported. As a result Schmidt et al. could propose an atomic structure model for this surface, the so-called mixed-dimer structure [41]. This model also represents the energetically most favorable InP(OOl) structure for In-rich surface conditions [41, 42, 73]. Since then, this model has been substantiated by both experimental [41, 74-76] and theoretical results [41, 77]. 

Radical IV can be considered as a unique phosphorus radical species. Reduction of the parent macrocycle with sodium naphtalenide in THF at room temperature gave a purple solution. The FPR spectrum displayed a signal in a 1 2 1 pattern, with flp(2P)=0.38 mT. DFT calculations on radical IV models indicated a P-P distance of 2.763 A (P - P is3.256 A in the crystal structure of the parent compound and the average value of a single P-P bond is 2.2 A). According to the authors, the small coupling constant arises from the facts that the principal values of the hyperfine tensor are of opposite sign and that the a P P one electron bond results from overlap of two 3p orbitals [88]. 

Ab initio calculations (MP2/6-31G ) of the parent compound of 8 revealed that the most stable arrangement of the dimer adopts Dih symmetry (Fig. 5). Interestingly, the four Li ions and the two phosphorus centers constitute an octahedral skeleton with relatively short Li-Li and Li-P distances of 2.645 and 2.458 A, respectively. Charge analysis (22) undoubtedly supports the electrostatic bonding model for this system because of the high net charges of the natural atomic orbitals (NBO) at Li (+0.768) and P (-1.583), while NBO-Lewis resonance structures support stabilization through delocalization (Fig. 5). 

The reason for this behavior in the case of the double-bonded structures ( A -type phosphorus) is the easy dimerization of the P=C bond. Tricoordinate planar (or nearly planar) phosphorus ( B - and C -type bonding) can be stabilized by repyramidalization when the cyclic electron delocalization is disturbed or lost (e.g., in a chemical reaction). The fine balance between these energetic effects cannot easily be predicted by using analogies or other simple models. Such predictions, however, can be made by using the sophisticated methods of computational chemistry, leaving the field of the chemistry of the aromatic phosphorus compounds an interesting research area with unexpected results in the future. 

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