Trigonally distorted octahedral site

Oxide mineralogy may influence rates of reductive dissolution in several ways. Hematite (ct-Fe203) and maghemite (y-Fe203), for example, have the same stoichiometry but contain Fe(III) in quite different coordinative environments. Fe(III) in hematite occupies trigonally-distorted octahedral sites, while Fe(III) in maghemite is found in both octahedral and tetrahedral sites (42). Differences... 

Figure 4.10 Polarized absorption spectra of ruby (from Bums, 1984). The ruby formula is (AIq 99gCr0 002)203, and the spectra originate from crystal field transitions within Cr3+ replacing Al3+ ions in trigonally distorted octahedral sites in the trigonal corundum structure. Consequently, the spectra differ slightly for light polarized (a) parallel (Ellc) and (b) perpendicular (E c) to the c crystallographic axis. The group theoretical assignments of the absorption bands are also indicated. [Reproduced from Chemistry in Britain, 1984, p. 1004]...

CsPuF6 was prepared and verified to be isostructural with corresponding compounds of uranium and neptunium. Its decomposition was studied in an inert gas atmosphere and in vacuum. Its spectrum has been measured in the region 400-2000 nm. The energy level structure of Pu5+ in the trigonally distorted octahedral CsPuF6 site was computed from a predictive model and compared with the observed spectrum. 

Ti + is able to create a timable laser in a sapphire lattice (Fabeni et al. 1991). It substitutes the ion of the host crystal in a trigonally distorted octahedral lattice site and is characterized by a strongly polarized band peaking at approximately 750 nm with a decay time of 3.1 ps (Fig. 5.40). 

Tetrahedral site 9 Trigonal site O Distorted octahedral site... 

The structures of the bronzes are built up of (Cr02) sheets with K+ ions inserted in distorted octahedral sites for 0.70 0.77 and trigonal prismatic... 

This compound is isostructural with brucite (Mg(OH)2) and Cdl2. The unit cell is hexagonal with a = 0.3258 nm and c = 0.4605 nm. The structure consists of sheets of corner-sharing, trigonally distorted Fe(OH)6 octahedra stacked along the [001] direction. The Fe" ions occupy only half the available octahedral interstices and this results in a structure in which each filled layer of sites alternates with an empty layer of sites. The OH radical behaves as a single entity. Amakinite is a rare mineral of the composition (Fe,Mg,Mn)(OH)2, also with brucite structure. Fe(OH)2 is readily oxidized by air and even by water, upon which the colour changes from white to brownish. The structure can be maintained up to a replacement of one tenth Fe" by Fe " (Bernal et al., 1959). 

The crystal structure of this protein has been shown to depend on the salt solution from which it is crystallized.45 When crystallized from (NH4)2S04, the insulin hexamer is held together in part by two Zn2+ ions. These can be visualized as being at either end of a cylinder, and each Zn2 has as a ligand one histidine imidazole nitrogen atom from one of three chains. Thus a histidine (his B.10) of each of the six chains is coordinated to Zn2+, three at each Zn2+. The Zn2+ ions occupy octahedral (trigonally distorted) sites overall. 

On a theoretical basis, Pd(III) and Pd(I) ions are probably located in a distorted octahedral or trigonal crystal field (Si or Si/, Sir sites) rather than in a square planar environment. The ESR spectra of adsorbed CO CO /... 

The synthesis of the X2M(Et2Dtc) complexes (X = Cl, Br, I M = As, Sb, Bi) is accomplished by the reaction of the M(Et2Dtc)3 complexes with MX3 in a 1 2 molar ratio in CHC13 (170). The structure of the Br2 As(Et2 Dtc) complex, which is monomeric and a nonelectrolyte in solution, in the solid state shows a loosely held centrosymmetric dimer with bridging bromide ions. The coordination geometry of the five-coordinate As(III) is intermediate between a square pyramid and a trigonal bipyramid, with a stereochemically active lone pair occupying a site of a distorted octahedral coordination sphere (Fig. 9). 

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