Divalent octahedral coordination

C and the ligand-field splitting, Aq, for some divalent, octahedrally coordinated transition metal ions are tabulated below. 

Layered double hydroxides (LDH) are another emerging class of layered crystals due to their wide range of applications in catalysis, sorbent, ion exchangers, stablizer and fire retardance [81, 82]. The LDHs have a brucite-like structure, where divalent octahedrally coordinated M(II) ions are partially substituted by trivalent M(III) ions. As a result, the positively charged metal oxide/hydroxide layers are neutralized by other charge-balancing anions. The general chemical formula of LDHs is [M ", M " (0H)J i+(A ) -nH,0 where, M = Li+, Mg, Co, Zn, Ni, etc. M + = Al +, Cr , Fe, etc., and A = Cl, NOj, COj, , etc. [83]. The... 

These are of two main types compounds of M", which for platinum have been known since the beginning of this century and commonly involve the stable [PtMes] group and compounds of the divalent metals, which were first studied by J. Chatt and co-workers in the late 1950 s and are commonly of the type [MR2L2] (L = phosphine). In the Pt" compounds the metal is always octahedrally coordinated and this is frequently achieved in interesting ways. Thus the trimethyl halides, conveniently obtained... 

Table 5.53 lists the general classification of micas with their main compositional terms. Stoichiometry obeys the general formula XF2 3Z40io(OH,F)2, where X = interlayer cations, Y = octahedrally coordinated cations of the 2 1 mixed layer, and Z = tetrahedrally coordinated cations of the 2 1 mixed layer. It must be noted that several compositional terms are indeed solid mixtures of more elementary components. In particular, glauconite has a complex chemistry and an Al Si diadochy of 0.33 3.67. (R and R terms in table 5.53 identify generic divalent and trivalent cations, respectively.)... 

The spectra of ordinary hydrated salts of divalent manganese are of type I, and are essentially indistinguishable. In general, these salts contain the Mn++ ion octahedrally coordinated with oxygen. Figure 2 presents spectra of the crystalline manganous salts Fig. 3, the noncrystalline. Spectra of manganous salts show maxima at 16 and 60 ev. and a minimum... 

The other end of the series, K3[Cr(NCS)e], has a spectrum with a pronounced preliminary peak at 16 ev., which peak increases in magnitude throughout the series in Fig. 18. The location of the peak might imply divalent chromium. However, from diffraction type arguments and the interpretation of the K3Co(CN)e spectrum of Fig. 13, this new peak introduced by the NCS group may be attributed to the Cr—C distances, i.e., to the second octahedral coordination sphere. As two and then four NCS ions are introduced into the coordination sphere, this preliminary peak is... 

Contrary to the case with pyridines, octahedral species [M(azole)6]2+ have been found, both in the solid state and in solution, for all the azoles lacking a substituent next to the donor atom. This appears to be a quite general observation for divalent metal ions with mainly electrostatic interactions. With monovalent ions (e.g. Cu+) or metal ions with a strong preference for a non-octahedral geometry (e.g. Pt2+), species [M(azole)p] + (p = 2, 3, 4) are usually found. With large metal ions such as Cd2+, octahedral coordination may be found even with ligands bearing a bulky substituent.19... 

Octahedral coordination of Tiiv is also present in the titanium silicates ETS-4 and ETS-10. The structure of these materials is reported to be similar to that of zorite, and they can be described as microporous crystals with uniform pores similar in dimensions to classical small- and large-pore zeolites. In ETS-4 and ETS-10, there are two monovalent cations or one divalent cation for each Tilv ion (Kuznicki, 1989, 1990 Kuznicki et al., 1991a, 1991b, 1991c, 1993 Deeba et al., 1994). A recent report of the synthesis of ETS-10 with tetramethyl-ammonium chloride indicates a ratio of monovalent cations to Tilv of 1.6 (Valtchev et al., 1994). The acidic properties of these materials have not been reported. A material modified by the addition of Al3+ has been obtained, ETAS-10, which, after exchange with NH4 salts, exhibits acidic properties but these are due to the presence of Al3+ and not to the Tilv (Deeba et al., 1994). 

The systematic study of bimetallic t-butoxides of tin and mono- and divalent metals carried out by Veith (see Table 12.10) established that the complexes of M Sn"(OBu )3 composition are formed by all alkaline metals, while those of M Snlv(OBu )5 are formed only by K, Rb, and Cs. It has been therefore concluded that Sn(OR)2 should be stronger Lewis acids than Sn(OR)4 [1692], In the molecules of its bimetallic complexes, the atoms of Sn11 have a /-tetra-hedral coordination, all the OR-groups being bridging. The compounds of Snlv display octahedral or distorted octahedral coordination (see also Chapter 4). 

The known Fe(OAlk)2 are green polymeric substances. The diffuse reflectance spectrum of Fe(OMe)2 indicates the octahedral coordination of iron atoms [6], According to the X-ray powder data its structure is isomorphous to those of other divalent metals, — i.e., resembles that of Fe(OH)2 (Mg(OH)2 type) [1656], The solubility is characteristic only of the derivatives of rather branched radicals — CH2Ph, CPh3 [114,941] — or of the phenoxides solvated by such bulky ligand as Dipy [941], The octahedral coordination is observed not only for the methoxide but quite unexpectedly for the derivatives 3,5-sus-... 

LDHs, which belong to the clay family, present several and various applications in different fields, such as catalysis or medicine. The general formula for these compounds is [Mi xnMxni(OH)2]+.Ax, nH20 (labelled [M11-Mm-A]) where the Ms are divalent and trivalent cations and A is an anion. LDH is composed of infinite sheets of positively charged brucite-type Mg(OH)2, where trivalent cations have replaced a fraction x of divalent cations in octahedral coordination. The interlamellar space is occupied by anions, keeping the electroneutrality of the structure, and completed by water molecules. 

An octahedral sheet (0) is defined as a two-dimensional array of cations (usually, Al, Mg, Fe) octahedrally coordinated by oxygen and/or OH. The individual octahedra share edges, and the composition of the sheet can vary from M2(0,0H) (all trivalent cations and termed dioctahedral) to M3(0,0H)g (all divalent cations and termed trioctahedral), where M signifies the cation. The octahedral sheet forms the basis of the layer-hydroxide minerals, gibbsite (M = Al) and brucite (M = Mg). 

Figure 11.6 Molecular orbital energy level diagrams computed for iron octahedrally coordinated to oxygen. Left divalent iron in the [Fe06]-1° cluster (based on Sherman, 1991) right trivalent iron in the [Fe06]-9 cluster (from Sherman, 1985a). Orbital energies have been scaled relative to zero for the non-bonding 6rlu level.

If these compounds crystallized in their antistructure, which is a 2H—MoSa structure with all octahedral holes filled, semiconductivity would be feasible by assuming the cation in trigonal-prismatic coordination to be divalent and the one in octahedral coordination to be tetra-valent. 

In rickardite CtuTes additional cation valence electrons are available from the octahedrally-coordinated cations which will be divalent. In Cu3Te2 the cations would just furnish enough valence electrons to saturate the cation-anion bonds, assuming Cu+ on tetrahedral and Cu2+ on octahedral sites. However, the compound would be metallic because of a metallic dy band of Cu2+, since the structure is only weakly deformed (c/a = 1.09 for the f.c. tetragonal anion sublattice). Moreover, the exact 3 2 stoichiometry seems to lie beyond the homogeneity range (217). 

One of the simplest structures is the sodium chloride or rock salt structure shown in Figure 3(a). Here the anions are CCP and all of the octahedral holes are filled leading to perfect octahedral coordination for both the cation and anion. This is a highly 3D structure and is found for oxides formed with a wide variety of medium and large divalent cations. These include the oxides of the alkaline earths except beryllium (which is too small), CdO, and the divalent oxides of Mn, Fe, Co, and Ni. 

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