Octahedral atomic arrangement, chemical

Careful purification of solutions of fluorosilane and fluorosilicate anions and a decrease in concentration and temperature result in a fine structure of F NMR spectra due to a non-equivalent arrangement of ligands (Table 16). For example, in the F NMR spectra of octahedral complexes of the type RSiFj" a doublet (equatorial atoms) and a quintuplet are observed whose mutual arrangement depends on the nature of the ligand In fluorine derivatives of penta- or hexa-coordinate silicon with slow exchange, the Hgip values (if they can be determined) are greater for the fluorine atoms with chemical shifts in low field. 

Fig. 1. Interatomic distances (A) for the elongated octahedral F ligand arrangement about the metal atom in AgF, and AuFi (Reprinted with permission from J. Am. Chem. Soc., 113, May 1991, pp. 4192-4198. Copyright 1991 American Chemical Society.)...

In low-temperature X-ray analysis and in neutron diffraction studies the structure of solid HMn(CO)5 was elucidated [9]. The arrangement of the ligands around the Mn atom is octahedral with the four equatorial carbonyl groups somewhat bent toward the axial hydrogen atom. This proves that hydrogen is a small but stereo-chemically active ligand, a fact which had been questioned previously [10]. 

The simple oxide and hydroxide minerals exhibit important characteristics common to all minerals. The relative numbers of various component atoms are given by chemical stoichiometry. These atoms may be arranged in three-dimensional space in different ways. Geothite and lepidocrocite, for example, share the same stoichiometry (FeOOH), but Fe-O and Fe-OH bond lengths and geometric relationships between octahedrally coordinated Fe atoms are different. As a consequence, the coordinative environment and accessibility of Fe atoms to incoming adsorbate molecules are different for the two minerals. In other situations, minerals comprised of different metals, such as hematite (FeiOj) and corundum (AI2O3), have similar three-dimensional structures. In situations where surface structure is more important than the nature of the incorporated metal, hematite and corundum should exhibit similar behavior. 

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