Geometry octahedral

Likewise, the corresponding member of and 2e will fall in energy since they are antibonding orbitals. For convenience wo have rotated our coordinate system for the octahedron by 45 to that in 15.35. The components of the important t2g set will now be A z, and yz. Let us concentrate on yz. At the octa- 

FIGURE 15.4. A Walsh diagram for bending one trans L-M-L angle in a ML complex. 

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Uranium hexafluoride [7783-81-5], UF, is an extremely corrosive, colorless, crystalline soHd, which sublimes with ease at room temperature and atmospheric pressure. The complex can be obtained by multiple routes, ie, fluorination of UF [10049-14-6] with F2, oxidation of UF with O2, or fluorination of UO [1344-58-7] by F2. The hexafluoride is monomeric in nature having an octahedral geometry. UF is soluble in H2O, CCl and other chlorinated hydrocarbons, is insoluble in CS2, and decomposes in alcohols and ethers. The importance of UF in isotopic enrichment and the subsequent apphcations of uranium metal cannot be overstated. The U.S. government has approximately 500,000 t of UF stockpiled for enrichment or quick conversion into nuclear weapons had the need arisen (57). With the change in pohtical tides and the downsizing of the nation s nuclear arsenal, debates over releasing the stockpiles for use in the production of fuel for civiUan nuclear reactors continue. 

These hahdes generally display a coordination number of six, have a distorted octahedral geometry, are moisture sensitive, and are easily oxidized when exposed to humid air. 

Chromium (II) also forms sulfides and oxides. Chromium (II) oxide [12018-00-7], CrO, has two forms a black pyrophoric powder produced from the action of nitric acid on chromium amalgam, and a hexagonal brown-red crystal made from reduction of Cr202 by hydrogen ia molten sodium fluoride (32). Chromium (II) sulfide [12018-06-3], CrS, can be prepared upon heating equimolar quantities of pure Cr metal and pure S ia a small, evacuated, sealed quartz tube at 1000°C for at least 24 hours. The reaction is not quantitative (33). The sulfide has a coordination number of six and displays a distorted octahedral geometry (34). 

The anhydrous halides, chromium (ITT) fluoride [7788-97-8], CrF, chromium (ITT) chloride [10025-73-7], CrCl, chromium (ITT) bromide [10031-25-1], CrBr, and chromium (ITT) iodide [13569-75-0], Crl, can be made by the reaction of Cr metal and the corresponding halogen at elevated temperatures (12,36). Other methods of synthesis for the haUdes are also possible (36—38). All of the haUdes have a layer stmcture and contain Cr(III) in an octahedral geometry. They are only slightly soluble in water but dissolve slowly when Cr(II) or a reducing agent such as Zn or Mg is added. 

In both structures the ion is coordinated to six ligands with octahedral geometry. Four water molecules as well as the side chain oxygen atom of a serine residue from the P-loop and one oxygen atom from the (3-phosphate bind to Mg + in the GDP structure. Two of the water molecules are replaced in the GTP structure by a threonine residue from switch I and an oxygen atom from the y phosphate (similar to the arrangement shown in... 

We saw in Chapter 7 that octahedral geometry is characteristic of many molecules (e.g., SF6) in which a central atom is surrounded by six other atoms. (Remember, an octahedron has eight sides, which is irrelevant here it has six comers, which is important) All complex ions... 

The crystal structure of the K(18-crown-6) salt shows a fac-octahedral structure (Ru—H 1.59-1.71 A, Ru—P 2.312-2.331 A) with a large distortion from regular octahedral geometry (H-Ru-H 70-88° P-Ru-P 102-111°) owing to the disparate steric demands of the hydride and tertiary phosphine ligands [95]. 

The second complex has been characterized by X-ray crystallography223. The ruthenium(II) atom is coordinated to three Me2SO molecules via the oxygen atom and to three via the sulphur atom to give the irregular octahedral geometry as shown in Scheme 18. 

Notice the loose use of the term octahedral to describe six-coordinate complexes which are based upon an octahedral geometry, but which, by virtue of the presence of different ligand types, are of lower symmetry than Oh. This is a common usage which should give rise to no difficulties. Note also how introduction of chelating... 

A minor success is also seen in complexes of d and d" ions, in which the distorted octahedral geometries observed may be rationalized (and indeed predicted) in terms of the Jahn-Teller effect, and ultimately in terms of the steric activity of the open d shell. This is a common feature in copper(n) chemistry, and you will... 

In a similar manner, treatment of anhydrous rare-earth chlorides with 3 equivalents of lithium 1,3-di-ferf-butylacetamidinate (prepared in situ from di-ferf-butylcarbodiimide and methyllithium) in THF at room temperature afforded LnlMeCfNBuOils (Ln = Y, La, Ce, Nd, Eu, Er, Lu) in 57-72% isolated yields. X-ray crystal structures of these complexes demonstrated monomeric formulations with distorted octahedral geometry about the lanthanide(III) ions (Figure 20, Ln = La). The new complexes are thermally stable at >300°C, and sublime... 

The same, distorted, octahedral geometry is also found in a number of monomeric diorganotin complexes having two bidentate ligands, such as MejSn(0-NMe-C0-Me)2 (379) and Me Sn(S-CS-NMei)2 (380), or one tetradentate group, such as Me2Sn(salen) (381). 

The success and the failure in locating the regular octahedral geometries as energy minima at the UB3LYP/6-31 + G(d) levels are denoted by the plus (+) and minus (-) signs, respectively... 

Chirality is an important part of today s chemistry and, in this respect, the pseudo-octahedral geometry of hexacoordinated phosphorus derivatives is interesting as it suffices to coordinate to the central atom three identical sym-... 

In a symmetrical octahedral system such as SFg, each polar S—F bond has a counterpart pointing in the opposite direction. The bond polarities cancel in pairs, leaving this molecule without a dipole moment. Example examines molecular variations on octahedral geometry. 

A molecule with a steric number of 6 requires six hybrid orbitals arranged in octahedral geometry. In Chapter 9, sulfur hexafluoride appears as the primary example of a molecule with a steric number of 6 (Figure ). Six equivalent orbitals for sulfur can be constmcted for the inner sulfur atom by combining the 3. S, the three 3 p,... 

The molecular geometry of a complex depends on the coordination number, which is the number of ligand atoms bonded to the metal. The most common coordination number is 6, and almost all metal complexes with coordination number 6 adopt octahedral geometry. This preferred geometry can be traced to the valence shell electron pair repulsion (VSEPR) model Introduced In Chapter 9. The ligands space themselves around the metal as far apart as possible, to minimize electron-electron repulsion. 

In a free metal ion without any ligands, all five d orbitals have identical energies, but what happens to the d orbitals when six ligands are placed around a metal in octahedral geometry The complex is stabilized by attractions between the positive charge of the metal ion and negative electrons of the ligands. At the same time,... 

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