Cation paired

If the coordination entity is negatively charged, the cations paired with the complex anion (with -ate ending) are listed first. If the entity is positively charged, the anions paired with the complex cation are listed immediately afterward. 

Questions of the analytic control of maintenance of the bivalent metals cations to their joint presence in materials of diverse fixing always were actual. A simultaneous presence in their composition of two cations with like descriptions makes analysis by sufficiently complicated process. Determination of composition still more complicates, if analyzed object is a solid solution, in which side by side with pair of cations (for example, Mg " -Co ", Mn -Co, Zn -Co ) attends diphosphate anion. Their analysis demands for individual approach to working of methods using to each concrete cations pair. 

There is another mechanism for equilibration of the cation pairs A, Aj and B, Bj, namely, inversion at oxygen. However, the observed barrier represents at least the minimum for the C=0 rotational barrier and therefore demonstrates that the C-O bond has double-bond character. 

Dale improved this procedure by conducting the cyclooligomerization in the presence of certain templating cations paired with non-nucleophilic counterions (e.g.,... 

The crystal structure of the complex [PhCH2PPh3][Au(C6F5)Cl] has been determined by X-ray diffraction it consists of an anion-cation pair where the anion shows a two coordinate Au(I) atom bonded to a Cl atom and a C Fs ring and the coordination is almost linear (molecules with two different angles were found but the differences between the two molecules in the asymmetric unit are not significant 177.8(5) and 179.8(4) A) [78]. 

This association has its counterpart that was also variously described as an encounter complex, a nonbonded electron donor-acceptor (EDA) complex, a precursor complex, and a contact charge-transfer complex.10 For electrically charged species such as anion/cation pairs (which are relevant to ion-pair annihilation), the pre-equilibrium association results in contact ion pairs (CIP)7 (equation 3)... 

These short Au-Au contacts may be compared with distances of 2.88 A in metallic gold and 2.60 A in gaseous Au2. The term aurophilicity has been coined by H. Schmidbaur to describe the phenomenon [189,194], The interactions can occur as pairs, squares, linear chains or two-dimensional arrays of gold centres. Examples include the association between dimer units in the dithiocarbamates Au(dtc)2 (Figure 4.16) and the ionic tetrahydrothiophen complexes Au(tht)2 AuXJ (X = halogen), where cations and anions stack with Au—Au 2.97-2.98 A (X = I). The interaction is such that Au(S203)2 pair up, despite their charge, with Au-Au 3.24 A in the sodium salt. Likewise in Aupy AuCl, cations pair up at 3.42 A apart [10, 195]. 

The crystal structure of [Fe(Cp)2]2[Ni(mnt)2]2[Fe(Cp)2] is composed by segregated stacks of pairs of cations, [Fe(Cp)2]+, and zig-zag dimerized anions stacks, with a neutral [Fe(Cp)2] molecule laying beside each anionic dimer [65]. In the case of [Co(Cp)2][Ni(dmit)2], the crystal structure consists of layers composed by two types of chains formed by the [Ni(dmit)2] anions, through short S—S contacts. Cation pairs are located between the anionic stacks [68], In the crystal structure of [Co(Cp)2][Ni(dmit)2]3 2MeCN, the partially oxidized anions form... 

Table 8.5. hmw model parameters for cation-cation pairs and triplets... 

NA i [ l is easily derived when the cations are assumed to be randomly distributed on the cation sub-lattice. The probability of finding an AB (or BA) pair is 2Xa+Xb+ in analogy with the derivation of the regular solution in Section 9.1. iVA+B+ is then the product of the total number of cation-cation pairs multiplied by this probability... 

We now introduce a Fourier transform procedure analogous to that employed in the solution theory, s 62 For the purposes of the present section a more detailed specification of defect positions than that so far employed must be introduced. Thus, defects i and j are in unit cells l and m respectively, the origins of the unit cells being specified by vectors R and Rm relative to the origin of the space lattice. The vectors from the origin of the unit cell to the defects i and j, which occupy positions number x and y within the cell, will be denoted X 0 and X for example, the sodium chloride lattice is built from a unit cell containing one cation site (0, 0, 0) and one anion site (a/2, 0, 0), and the translation group is that of the face-centred-cubic lattice. However, if we wish to specify the interstitial sites of the lattice, e.g. for a discussion of Frenkel disorder, then we must add two interstitial sites to the basis at (a/4, a/4, a]4) and (3a/4, a/4, a/4). (Note that there are twice as many interstitial sites as anion-cation pairs but that all interstitial sites have an identical environment.) In our present notation the distance between defects i and j is... 

Fig. 2. Plot of 4AHj for the alkali nitrates versus the quantity (dt — rf,) /(< ,). The cation pair to which each point corresponds is listed next to each point.

The mechanism for the photoreaction between 133 and cyclohexene can be summarized as in Scheme 8. The initiating electron transfer fluorescence quenching of 133 by cyclohexene resulted in the formation of an w-amino radical-radical cation pair 136. Proton transfer from the 2-position of the cyclohexene radical cation to the nitrogen atom of the a-amino radical leads to another radical cation-radical pair 137. Recombination of 137 at the radical site affords the adduct 134, while nucleophilic attack at the cation radical of 136 leads to another radical pair 138 which is the precursor for the adduct 135. 

Fig. 4.3 Schematic representation of interstitial cationic pair formation (a) and migration from one non bridging oxygen to another in a cation conducting glass (b).

In the second approach, M-POMs containing protons as counter ions were used to fulfill electrostatic binding of M-POM to the support in one stage via the formation of anion-cation pairs (Eqs. 3 and 4) ... 

Normally, the reaction partners in PET reactions are neutral molecules. That is why a donor radical cation—acceptor radical anion pair is obtained by the PET step. These highly reactive intermediates can be used for triggering interesting reactions. Since the PET is not restricted to neutral molecules PET reactions of donor anions and neutral acceptors or neutral donors and acceptor cations resulting in radical—radical anion (cation) pairs are known as well. These reactions are also called charge shift reactions due to the fact that the overall number of charged species is kept constant throughout the PET step. Finally, a PET process of a donor anion and a acceptor cation is possible as well (Scheme 2). 

Fig. 2.4 Structure of goethite. a) Hexagonal close packed anion arrangement and distribution of cations in the octahedral interstices projection on (010) with the cation pairs indicated and the unit cell outlined, b) Projection on (001) with the unit cell and the octahedral arrangementindi-cated. c) Projection down [001]. Dashed circles represent Fe in the next lower layer, d) Arrangement of octahedral double chains. H atoms also shown, e) Ball-and-stick model with unit cell out-...

In initial work, a total of 17 different ILs were evaluated by the solvation parameter model [8]. Ten of these ILs were comprised of imidazolium or pyrolidinium cations paired with different anions. Many of these compounds represent the traditional class of IL solvents that have been used extensively in organic synthesis reactions or in other analytical uses. The remaining seven ILs consisted of substituted ammonium cations that have proven to be successful analyte matrices in matrix-assisted laser desorption ionization (MALDI) mass spectrometry [11]. 

Binding interactions available to these ions are essentially electrostatic in nature, namely, cation-anion attractions responsible for cation-pairing to counter-anions, and ion-dipole interactions that provide the basis for the well-known complexation with crown ethers. 

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