Octahedral configuration

Other examples are iron pentacarbonyl, Fe(CO)s, and chromium hexacarbonyl, Cr(CO)(j, which have trigonal bipyramidal and octahedral configurations respectively. 

Simple nickel salts form ammine and other coordination complexes (see Coordination compounds). The octahedral configuration, in which nickel has a coordination number (CN) of 6, is the most common stmctural form. The square-planar and tetrahedral configurations (11), iu which nickel has a coordination number of 4, are less common. Generally, the latter group tends to be reddish brown. The 5-coordinate square pyramid configuration is also quite common. These materials tend to be darker in color and mostiy green (12). 

The neutral complexes of chromium, molybdenum, tungsten, and vanadium are six-coordinate and the CO molecules are arranged about the metal in an octahedral configuration as shown in stmcture (3). Vanadium carbonyl possesses an unpaired electron and would be expected to form a metal—metal bond. Steric hindrance may prevent dimerization. The other hexacarbonyls are diamagnetic. 

The lowest coordination number of tantalum or niobium permitted by crystal chemistry formalism is 6, which corresponds to an octahedral configuration. X Me ratios that equal 3, 2 or 1 can, therefore, be obtained by corresponding substitutions in the cationic sub-lattice. A condition for such substitution is no doubt steric similarity between the second cation and the tantalum or niobium ion so as to enable its replacement in the octahedral polyhedron. In such cases, the structure of the compound consists of oxyfluoride octahedrons that are linked by their vertexes, sides or faces, according to the compound type, MeX3, MeX2 or MeX respectively. Table 37 lists compounds that have a coordination-type structure [259-261]. 

The validity of this approach can be demonstrated by the example of several complex fluoride compounds that exhibit ferroelectric properties, such as compounds that belong to the SrAlF5 family [402, 403]. The crystal structure of the compounds is made up of chains of fluoroaluminate octahedrons that are separated by another type of chains - ramified chains. Other examples are the compounds Sr3Fe2Fi2 and PbsWjOgFio. In this case, the chains of iron- or tungsten-containing octahedrons are separated from one another by isolated complexes with an octahedral configuration [423,424]. 

Diverse series of diphenyl sulphoxide (DPSO) complexes of Mn(II), Fe(II), Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Ca(II), Al(II) and Mg(II) with various large anions have been reported187-191. The complexes have the general formula M(DPSO)6(Anion) where M is the metal cation. The reflection spectra in the visible and near-IR region indicate an octahedral configuration around the metal ion surrounded by the DPSO molecules. Comparison with the spectra of DMSO complexes shows that they have almost identical structures. IR spectra indicate that the oxygen atom in the sulphinyl group is the donor atom in all these complexes. 

There is, of course, a close relation between atomic arrangement and bond type. Thus the four single bonds of a carbon atom are directed toward the comers of a tetrahedron But tetrahedral and octahedral configurations are also assumed in ionic compounds, so that it is by no means always possible to deduce the bond type from a knowledge of the atomic arrangement. 

These complexes may be either six-coordinate with an octahedral configuration or five-coordinate with a square-pyramidal configuration, in which the organo ligand occupies the apical position a few form dimers through the interaction of each cobalt with a coordinated atom of the equatorial ligand of the other half (see Section In virtually all groups... 

Distorted trigonal bipyramidal, with R = n-Bu. 229, 230 NH- -Cl hydrogen bonds are formed, as attested by IR spectra and some of the foreshortened N—Hal distances. Other similar structures are known, such as R = Ph, which also yields an aW-trans complex with two molecules of l-methyl-2(3H)-imidazolinethione, that has octahedral configuration. 

It is proposed that polymerisation occurs at active sites involving transition metal atom having an octahedral configuration with one ligand valency. The monomer is having a p bond with titanium and undergoes insertion between the titanium and alkyl group. 

Unlike Si(IV), Cd(II) often takes an octahedral configuration as well as a tetrahedral one it is rather difficult for Si(IV) to take an octahedral configuration under ambient conditions. The isopolycyanocadmate(II) systems built of the CN-linkages among tetrahedral and octahedral Cd atoms can mimic the structures of silicate minerals composed of the tetrahedral Si and other octahedral cations. 

Nickel most commonly forms complexes with a coordination number of six. These have an octahedral configuration and are generally green in color. In aqueous solutions, nickel occurs as the octahedral, hexahydrate ion [Ni(H20)g] (Windholz 1983) which is poorly absorbed by most living organisms (Sunderman and Oskarsson 1991). 

Non-metallocene catalysts have attracted much attention recently.These catalysts generally contain oxygen and/ or nitrogen (and sometimes sulfur and phosphorous) as ligating atoms, and those heteroatoms are often incorporated into a chelate ligand structure. These catalyst precursors often take an octahedral configuration, providing... 

This model was suggested by spectroscopic studies of dipositive 3d ions in molten aluminum chloride (7). The absorption spectra of dipositive Ti, V, Cr, Mn, Fe, Co, Ni and Cu in molten AICI3 can be interpreted on the basis of octahedral configurations of chlorides about the central transition metal ions. An explanation of this fact is made plausible by the following considerations. 

Platinum(IV) has six valency electrons, and a regular octahedral configuration is to be expected in its compounds, as is indeed found to be the case 257). The need for six ligands while the oxidation state is only four leads to some very unusual structures. 

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