Octahedral, Oh

Vibrational spectra and F nmr studies on all three cations XFe+ and the 1 Mdssbauer spectmm of [lF6][AsF6] establish octahedral (Oh) symmetry as expected for species isoelectronic with SFfi, SeFfi and TeFg respectively. 

The hypervalent chalcogen chemistry has been developed to higher coordinated species with various ligands,7 10 where TBP changes to square pyramidal (SP) or octahedral (Oh), etc. Additional atomic orbitals of E, such as an 5-orbital, may operate to stabilize the structures.10b The concept is also extended over linear a-bonds constructed by m ( > 4) atoms with n electrons (extended hypervalent bonds mc-ne (in > 4)).11 14 The approximate molecular orbital model for mc-ne (m > 4) is also exhibited in Scheme la, exemplified by 4c-6e. 

It is noteworthy that the to-bonded structure for ArF6 differs from that predicted by VSEPR theory. ArF6 is predicted to be of octahedral (Oh) symmetry, with three mutually perpendicular F i- Ar -h F triads and an s-type lone pair. In contrast, VSEPR predicts a pentagonal bipyramid (or other seven-vertex polyhedron) with some or all F-Ar-F angles less than 90°. The calculated equilibrium structure is in agreement with the co-bonding model. 

The number and exact composition of the sheets is used to classify the phyllosilicates. The most important classification for our purposes is the distinction between 1 1 and 2 1-type minerals (Figure 2.1). In 1 1 minerals such as kaolinite, the basal oxygens of the tetrahedral sheet are free to interact with octahedral OH groups forming hydrogen bonds. In contrast, 2 1 minerals such as pyrophyllite or talc contain two tetrahedral sheets sandwiched around an octahedral sheet. These minerals have only basal oxygens exposed on the faces of the tetrahedral sheets and are linked by weak van der Waals forces. The weaker interaction of one 2 1 layer with a second 2 1 layer results in interlayer spaces which, depending on the particular mineral, may be available for contaminant intercalation. 

Fig. 5.1. Common d-orbital splitting patterns in high spin iron(III) complexes of tetrahedral (Td), octahedral (Oh) and tetragonal (D4h or C4v) symmetries.

Fig. 5.32. Splitting of the 4F and 4P free ion terms of high spin cobalt(II) in octahedral (Oh), square pyramidal (C ), trigonal bipyramidal (D ), and tetrahedral (Td) geometries [90,191],...

Figure 7.2. Energy-level diagram of the splitting of the five d orhitals in crystal fields of Td and octahedral Oh symmetry.

Fig. 1. Level scheme for s2 sp electron excitation considering various interactions, electron repulsion, octahedral Oh field and spin-orbit coupling (l.-S) plotted in different sequences...

Atomic charges [ e ] of the FA molecule, octahedral -OH groups participating in the formation of hydrogen bond with the FA molecule in the D-FA system obtained using ChelpG scheme [149]... 

The angle between the OH groups and the surface of kaolinite participating in the formation of hydrogen bonds with the DMSO molecule is 40-50° [150], Calculated geometry parameters of the octahedral OH groups of the intercalated K-DMSO system are in agreement with experimental data [134]. 

For a spherical rotor belonging to the octahedral Oh point group, Table A.43 in Appendix A, in conjunction with the vibrational selection rules of Equation (6.56), show that the only allowed transitions are... 

The choice of this example may seem unnecessarily complicated to start with. However, we have the choice between the mathematical complications of calculating interelectronic repulsion parameters and the physical complications that for instance d1- and d9-systems such as Ti(H20) +3 and Cu(H20) ++ are Jahn-Tc/fer-distorted. Whether one has a static Jahn-Teller effect where the stereochemical configuration of the ground-state is distorted, or one has a dynamic Jahn-Teller effect where the potential surfaces of the excited and groundstates are covered by un-symmetric vibrations, is a subtle question we do not need to treat here. However, it is an empirical fact that these Jahn-TeZ/er-unstable molecules do not have the simple spectra expected from higher symmetries such as the octahedral Oh. 

H. ALUMINOL. Phylosilicate octahedral -OH edge functional group (see Chapter 4). 

The chemical effect on the K(5/Ka x-ray intensity ratios has been studied experimentally for various chemical compounds of 3d transition metals [18-23,26,27]. We choose several simple chemical compounds of Cr and Mn and calculate the K /Ka ratios with the DV-Xa method. For simplicity, we assunje that all compounds are expressed as clusters with the tetrahedral (Td) or octahedral (Oh) symmetry, in which the central metal atpm is surrounded by four or six ligand atoms, respectively. The compounds and clusters used... 

U V- Vis. Spectroscopic measurements in the ultraviolet and visible range of the electronic spectrum (UV-Vis) can be used to probe electronic transitions in certain metal atoms and ion complexes. The energy of an electronic transition can depend upon the symmetry of the metal ion being different for transitions in a metal complex displaying tetrahedral (Td) symmetry from the same metal showing an octahedral (Oh) symmetry. Thus, it is possible to use UV-Vis spectroscopy to interrogate the symmetry of certain metal ions bound to oxide surfaces. We show here a few examples of the use of UV-Vis spectroscopy to characterized supported metal oxides. 

In the present work, we have calculated the K/3 /Koc x-ray intensity ratios for 3d transition elements excited by PI and EC, taking into account both effects described above. The calculations were made using the discrete-variational (DV) X(X molecular orbital (MO) method (19). The electronic states and wave functions in molecules were obtained for tetrahedral (Td) and octahedral (Oh) clusters. The x-ray emission rates were estimated by the DV integration method (20) with the MO wave functions in the dipole approximation. The calculated results are compared with the experimental data. 

It is difficult to demonstrate this on the observed spectra of typical organic systems because of their large number of transitions. Therefore, we have chosen to discuss the spectrum of a simple molecular hydride, rubidium hexahydridoplatinate(IV), Rb2[PtHe] [20]. Every hydrogen is equivalent within this octahedral. Oh, ion and the ions are sufficiently separated that they do not interact. The high mass of platinum completely... 

Ligand field splitting of the d orbitals arises from a combination of o and % bonding interactions with ligands. In octahedral (Oh) geometry two orbitals (eg) are at higher energy... 

From the Al NMR spectroscopy it is possible to follow the amounts of lattice and extra-lattice A1 in the fresh and aged samples studying the signals corresponding to tetrahedral Td A1 (at around -55 ppm) and octahedral Oh A1 (at around 0 ppm) (17). 

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