Stoichiometry cation

LiNi02 Stoichiometry, cationic site assignment in Lii-xNii+x02... 

All the complexes metal wide-rim CMPO calix[4]arene studied by crystallographic analysis have the 2 1 Micalix stoichiometry. Cations are complexed by two bidentate CMPO, which keep them apart from the cavity of the calix[4]arene. Thus, these complexes are not real inclusion complexes (Figure 4.8). 

Structure Stoichiometry Cation coordination Oxygen coordination Examples Common characteristics... 

The stoichiometry between two reactants in a precipitation reaction is governed by a conservation of charge, requiring that the total cation charge and the total anion charge in the precipitate be equal. The reaction units in a precipitation reaction, therefore, are the absolute values of the charges on the cation and anion that make up the precipitate. Applying equation 2.3 to a precipitate of Ca3(P04)2 formed from the reaction of Ca and P04 , we write... 

The second step is a -scission, the breaking of a carbon—carbon bond P to the charged carbon. The sum of the two reactions is the stoichiometry of the overall cracking reaction R H — RH + olefin. R+, a relatively stable carbenium ion such as the /-butyl cation, is a chain carrier. The role of the catalyst is to donate the proton to start the chain. This is a greatiy simplified representation. 

Table 3 is arranged by crystal class (14). The crystal class of a given pigment is determined almost solely by the ratio of the ionic sizes of the cation and the anion and thek respective valences. Hence, for any given stoichiometry and ionic size ratio, only one or two stmctures will be possible. In some classes (spkiel, zkcon), a wide range of colors is possible within the confines of that class. Pigments within a given class usually have excellent chemical and... 

Another source of departure from stoichiometry occurs when cations are reduced, as for example in tire reduction of zinc oxide to yield an oxygen-defective oxide. The zinc atoms which are formed in tlris process dissolve in the lattice, Zn+ ions entering interstitial sites and the coiTesponding number of electrons being released from these dissolved atoms in much the same manner as was found when phosphorus was dissolved in the Group IV semiconductors. The Kroger-Viirk representation of dris reduction is... 

It is not necessary for a compound to depart from stoichiometry in order to contain point defects such as vacant sites on the cation sub-lattice. All compounds contain such iirndirsic defects even at the precisely stoichiometric ratio. The Schottky defects, in which an equal number of vacant sites are present on both cation and anion sub-lattices, may occur at a given tempe-ramre in such a large concentration drat die effects of small departures from stoichiometry are masked. Thus, in MnOi+ it is thought that the intrinsic concentration of defects (Mn + ions) is so large that when there are only small departures from stoichiometry, the additional concentration of Mn + ions which arises from these deparmres is negligibly small. The non-stoichiometry then varies as in this region. When the departure from non-stoichio-... 

The propensity for iodine to catenate is well illustrated by the numerous polyiodides which crystallize from solutions containing iodide ions and iodine. The symmetrical and unsymmetrical 13 ions (Table 17.15) have already been mentioned as have the I5- and anions and the extended networks of stoichiometry (Fig. 17.12). The stoichiometry of the crystals and the detailed geometry of the polyhalide depend sensitively on the relative concentrations of the components and the nature of the cation. For example, the linear ion may have the following dimensions ... 

M2Ti04 (M = Mg, Zn, Mn, Fe, Co) have the spinel stmcture (MgAl204, p. 248) which is the third important stmcture type adopted by many mixed metal oxides in this the cations occupy both octahedral and tetrahedral sites in a cep array of oxide ions. Ba2Ti04, although having the same stoichiometry, is unique amongst titanates in that... 

LCo(H20)6] ion, and bidentate /V-donor ligands such as cn, bipy and phen form octahedral cationic complexes [Co(L-L)3] , which are much more stable to oxidation than is the hexaammine [Co(NH3)6l . Acac yields the orange [Co(acac)2(H20)2] which has the tram octahedral structure and can be dehydrated to [Co(acac)2l which attains octahedral coordination by forming the tetrameric species shown in Fig. 26.3. This is comparable with the trimeric [Ni(acac>2]3 (p. 1157), like which it shows evidence of weak ferromagnetic interactions at very low temperatures. fCo(edta)(H20)] is ostensibly analogous to the 7-coordinate Mn and complexes with the same stoichiometry, but in fact the cobalt is only 6-coordinate, 1 of the oxygen atoms of the cdta being too far away from the cobalt (272 compared to 223 pm for the other edta donor atoms) to be considered as coordinated. 

Various crown ethers (p. 96) with differing cavity diameters provide a range of coordination numbers and stoichiometries, although crystallographic data are sparse. An interesting series, illustrating the dependence of coordination number on cationic radius and ligand cavity diameter, is provided by the complexes formed by the lanthanide nitrates and the 18-crown-6 ether (i.e. 1,4,7,10,13,16-... 

Pyridyl)benzothiazole with [Re(CO)5X] (X = Cl, Br) forms the chelate structures 18 (X = C1, Br) (01ICA(314)91). With silver triflate, dehalogenation occurs followed by formation of 18 (X = OTf). The latter refluxed in acetonitrile gives the cationic complex of stoichiometry [Re(CO)3L(AN)](OT0-... 

As an example of a different type of oxide, we may consider ZnO. This oxide evolves oxygen and forms cations in interstitial positions (Zn O) or (Zn O), and free electrons (eo). If the interstitial zinc ions are only singly charged, the reaction describing the non-stoichiometry may be written... 

Fig. 17. Membrane current, Xq, of a dioleoyllecithin membrane, A. as a function of Valinomycin concentration at 1 M KC1 and B. as a function of KC1 concentration at 10"7 M Valinomycin. The linearity and slope of one indicates a carrier mechanism with a 1 1 carrier to cation stoichiometry. Reproduced with permission from Ref.811...

One of the most important parameters that defines the structure and stability of inorganic crystals is their stoichiometry - the quantitative relationship between the anions and the cations [134]. Oxygen and fluorine ions, O2 and F, have very similar ionic radii of 1.36 and 1.33 A, respectively. The steric similarity enables isomorphic substitution of oxygen and fluorine ions in the anionic sub-lattice as well as the combination of complex fluoride, oxyfluoride and some oxide compounds in the same system. On the other hand, tantalum or niobium, which are the central atoms in the fluoride and oxyfluoride complexes, have identical ionic radii equal to 0.66 A. Several other cations of transition metals are also sterically similar or even identical to tantalum and niobium, which allows for certain isomorphic substitutions in the cation sublattice. 

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