Octahedral molecular structure

Both have octahedral molecular structures (U-F = 1.994 A in UFe) and are volatile under reduced pressure at temperatures below 100 °C. 

Figure 3-17. Examples with symmetry. The sculpture, in Seoul, shows a chemist holding an octahedral molecular structure and is by Eui Soon Choi photograph by the authors.

Figure 5.4 The molecular structure of basic beryllium acetate showing (a) the regular tetrahedral arrangement of 4 Be about the central oxygen and the octahedral arrangement of the 6 bridging acetate groups, and (b) the detailed dimensions of one of the six non-planar 6-membeted heterocycles. (The Be atoms are 24 pm above and below the plane of the acetate group.) The 2 oxygen atoms in each acetate group are equivalent. The central Be-O distances (166.6 pm) are very close to that in BeO itself (165 pm).

The crystal and molecular structure of (PPh3)2(CO)(H)Ir(/u3-B3H7) have been reported.5 The structure is interpreted as a capped octahedral, 7-orbital, 18-electron d4, Irv complex in which the metal-borane bonding occurs predominantly via three two-electron, two-center Ir—B bonds. 

The molecular structures from electron diffraction of zinc dichloride, zinc dibromide, and zinc diiodide have been reinvestigated.612 The important effects halides have on geometry have also been investigated, in particular the changes from octahedral to tetrahedral geometry in the presence of chloride ions have been studied.613... 

Figure If shows the molecular structure of the [Tc6Br6(/t3-Br)5]2- anion. In general, the structure of this anion is similar to the structure of the well-known octahedral halogenide clusters of molybdenum and tungsten [M6X8]4 + (X = Cl,Br, I) [5,8]. The principal difference is that the eight equivalent positions of bridging bromine atoms in the technetium clusters are not fully occupied.

Fig. 2.3-12. Molecular structures of 59, 60, 60a, and topological relationships of 59 and 60 to the corresponding sections from the solid-state structure of elemental aluminum, and structural similarities of the clusters Ali2R6 and In Rs- In the latter cluster the octahedral sections are highlighted.

Figure 10 shows the molecular structures of both the copper(II) and copper(I) congeners. As seen, the copper(II) complex possesses an octahedral S402 coordination, whereas the copper(I) complex assumes a tetrahedral S4 coordination releasing the bonding with the two oxygen atoms. 

Finally, as far as the [Fen(terpy)2]2+ complex is concerned, its molecular structure is known. Its octahedral geometry is tetragonally distorted, in that the bond distance between the iron(II) ion and the central nitrogen atom of terpyridine is considerably shorter (Fe-N= 1.89 A) than the distance between theiron(II) ion and the two more external nitrogen atoms (Fe-N = 1.99 A).110... 

Dithiolenes also form tris complexes of octahedral geometry. Limiting to M(dmit)3 complexes we can cite as a typical example the dianion [W(dmit)3]2-, the molecular structure of which is illustrated in Figure 44.81... 

The molecular structure of the corresponding dianion [Os6(CO)i8] is shown in Figure 34 it has an essentially regular octahedral geometry. 

Figure 36 illustrates the molecular structure of [ReCl(N2) (PMe2Ph)4].51 Also in this case the central metal atom has octahedral geometry with a linearly coordinated nitrogen molecule. 

On the basis of the foregoing discussion it thus would seem that the dihydrogen complexes decompose upon oxidation. Some complexes have been reported to show reversible oxidation.81 Amongst those for which the molecular structure is available we can, for example, mention the octahedral [ReCl(H2)(PMePh2)4], Figure 58.89... 

In addition, G and F matrix elements have been tabulated (see Appendix VII in Nakamoto 1997) for many simple molecular structure types (including bent triatomic, pyramidal and planar tetratomic, tetrahedral and square-planar 5-atom, and octahedral 7-atom molecules) in block-diagonalized form. MUBFF G and F matrices for tetrahedral XY4 and octahedral XY molecules are reproduced in Table 1. Tabulated matrices greatly facilitate calculations, and can easily be applied to vibrational modeling of isotopically substituted molecules. Matrix elements change, however, if the symmetry of the substituted molecule is lowered by isotopic substitution, and the tabulated matrices will not work in these circumstances. For instance, C Cl4, and all share full XY4 tetrahedral symmetry (point group Tj), but... 

These are associated with tetrahedral and octahedral spatial distributions of atoms, and with bonds. The stereodescriptors cis and tram indicate the spatial distribution with reference to a plane defined by the molecular structure, often in relation to a double bond. 

X-ray crystallography, 40 20-21 synthetic models, 40 23-48 xanthane oxidase, 40 21-23 chalcogenide halides, 23 370-377, 413 Chevrel phases, 23 376-377 metal-metal bonding, 23 330, 373 structural data, 23 373-376 as superconductors, 23 376 synthesis, 23 371-372 chloride, 46 4-24, 35-44 heterocations of, 9 290, 291 cluster compounds, 44 45-46 octahedral, 44 47-49, 53-63 electronic structure, 44 55-63 molecular structure, 44 53-54 synthesis, 44 47-49 rhomboidal, 44 75-82 solid-state clusters and, 44 66-72, 74-75, 80-82, 85-87 tetrahedral, 44 72-75 triangular, 44 82-87 cofactor, 40 2, 4-12 anaerobic isolation, 40 5 molybdopterin and, 40 4-8 reduced form, 40 12 synthesis, 40 8-12 xanthine oxidase, 45 60-63 complexes... 

A quantitative treatment of the Jahn-Teller effect is more challenging (46). A major issue is that many theoretical models explicitly or implicitly assume the Bom—Oppenheimer approximation which, for octahedral Cu(II) systems in the vibronic coupling regime, cannot be correct (46,51). Hitchman and co-workers solved the vibronic Hamiltonian in order to model the temperature dependence of the molecular structure and the attendant spectroscopic properties, notably EPR spectra (52). Others, including us, take a more simphstic approach (53,54) but, in either case, a similar Mexican hat potential energy description of the principal features of the Jahn-Teller effect in homoleptic Cu(II) complexes emerges (Fig. 13). 

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