Large cations

Addition of halide ions to aqueous copper(II) solutions can give a variety of halo-complexes for example [CuCl4] (yellow square-planar, but in crystals with large cations becomes a flattened tetrahedron) [CuClj] (red, units linked together in crystals to give tetrahedral or distorted octahedral coordination around each copper). 

Iodine is only slightly soluble in water and no hydrates form upon dissolution. The solubiHty increases with temperature, as shown in Table 2 (36). Iodine is soluble in aqueous iodide solutions owing to the formation of polyiodide ions. For example, an equiHbrium solution of soHd iodine and KI H2O at 25°C is highly concentrated and contains 67.8% iodine, 25.6% potassium iodide, and 6.6% water. However, if large cations such as cesium, substituted ammonium, and iodonium are present, the increased solubiHty may be limited, owing to precipitation of sparingly soluble polyiodides. Iodine is also more... 

Iron hahdes react with haHde salts to afford anionic haHde complexes. Because kon(III) is a hard acid, the complexes that it forms are most stable with F and decrease ki both coordination number and stabiHty with heavier haHdes. No stable F complexes are known. [FeF (H20)] is the predominant kon fluoride species ki aqueous solution. The [FeF ] ion can be prepared ki fused salts. Whereas six-coordinate [FeCy is known, four-coordinate complexes are favored for chloride. Salts of tetrahedral [FeCfy] can be isolated if large cations such as tetraphenfyarsonium or tetra alkylammonium are used. [FeBrJ is known but is thermally unstable and disproportionates to kon(II) and bromine. Complex anions of kon(II) hahdes are less common. [FeCfy] has been obtained from FeCfy by reaction with alkaH metal chlorides ki the melt or with tetraethyl ammonium chloride ki deoxygenated ethanol. 

Only with large cations such as Rb, Cs and NRafR = Et, Bu", n-pentyl) has it proved possible to isolate the. solid sulfites The sulfite ion SOs is pyramidal with Cj,. symmetry angle O-S-O 106°, S-O 151 pm. The hydrogen sulfite ion also appears to have C3, symmetry both in the solid state and in solution, i.e. protonation occurs at S rather than... 

In 1826 J. J. Berzelius found that acidification of solutions containing both molybdate and phosphate produced a yellow crystalline precipitate. This was the first example of a heteropolyanion and it actually contains the phos-phomolybdate ion, [PMoi204o] , which can be used in the quantitative estimation of phosphate. Since its discovery a host of other heteropolyanions have been prepared, mostly with molybdenum and tungsten but with more than 50 different heteroatoms, which include many non-metals and most transition metals — often in more than one oxidation state. Unless the heteroatom contributes to the colour, the heteropoly-molybdates and -tungstates are generally of varying shades of yellow. The free acids and the salts of small cations are extremely soluble in water but the salts of large cations such as Cs, Ba" and Pb" are usually insoluble. The solid salts are noticeably more stable thermally than are the salts of isopolyanions. Heteropoly compounds have been applied extensively as catalysts in the petrochemicals industry, as precipitants for numerous dyes with which they form lakes and, in the case of the Mo compounds, as flame retardants. 

The coordination chemistry of Zn" and Cd", although much less extensive than for preceding transition metals, is still appreciable. Neither element forms stable fluoro complexes but, with the other halides, they form the complex anions [MX3] and [MX4] , those of Cd" being moderately stable in aqueous solution. "" By using the large cation [Co(NH3)6] + it is also possible to isolate the trigonal bipyramidal [CdCls] "... 

Since hydrofluoride synthesis is based on thermal treatment at relatively high temperatures, the possibility of obtaining certain fluorotantalates can be predicted according to thermal stability of the compounds. In the case of compounds whose crystal structure is made up of an octahedral complex of ions, the most important parameter is the anion-cation ratio. Therefore, it is very important to take in to account the ionic radius of the second cation in relation to the ionic radius of tantalum. Large cations, are not included in the... 

KMn8016). The Ba2+ and K+ cations partially occupy crystallographic sites at the center of the (2 x 2) tunnels. The presence of these large cations led, for many... 

PDMT = Me2N(CH2)2NMe(CH2)2NMe2) while salts with other large cations like Bu4NAuR4 (R = Me, Et) are benzene soluble [171]. 

An important characteristic feature, common to all these reactions, is the formation of a single product (barrier) phase. In addition, the lattice structures of both reactants and products are relatively simple and information on appropriate physical and chemical properties of these substances is available. Complex iodide formation is of particular interest because of the exceptionally large cation mobilities in these phases. Experimental methods have been described in Sect. 1 and Chap. 2. 

The chemical properties of the alkylarylsulfonates are used in its analytical determination. As anions, LAS and other anionic surfactants react with large cations to salts, which are soluble in organic solvents (e.g., CHC13). By analysis it can be seen that cations such as Hyamine 1622 (25) and methylene blue, which rearrange with LAS to complex (26), are widely spread. These reactions are the basis for the so-called two-phase titration, an extensively used method... 

The two-phase titration is based on the reaction of anionic surfactants with cations—normally large cationic surfactants—to form an ion pair. The preferred cationic is benzethonium chloride (Hyamine 1622, 1) because of the purity of the commercially available product. On neutralization of the ionic charges, the ion pair has nonpolar character and can be extracted continuously into the organic phase, e.g., chloroform, as it is formed. The reaction is monitored by addition of a water-soluble cationic dye, dimidium bromide (2), and a water-soluble anionic dye, disulfine blue (3). The cationic dye forms an extractable... 

Toxin from the jellyfish, Chrysaora quinquecirrhay creates large cation-selective channels with 760 pS conductance and no rectification. The channels are equally... 

The toxic mechanism of action of these various jellyfish venoms is complex. The cardiotoxic reaction seems to focus on calcium transport and is blocked by the prior or post administration of therapeutic doses of verapamil (7J). In neuronal tissue, Chrysaora venom induces large cationic selective channels which open and close spontaneously. These channels are permeable to Na , Li, K, and Cs but not and the channels are present in spite of the treatment with sodium and potassium inhibitors such as tetrodotoxin and tetraethylammonium (14). 

AMnAliiOi9.a (A = La, Pr, Nd, Sm, and Gd) samples were used to investigate the dependence of the catalytic property on A cation, which occupies the large cationic... 

This result suggests that the sintering resistance of samples are enhanced as the ionic radius of A becomes large. It is, therefore, apparent that La is superior as the large cation in the mirror plane of the hexaaluminate in achieving both high thermal resistance and high activity to other tri-valent A cations with small ionic radii. 

The values of hj for different ions are between 0 and 15 (see Table 7.2). As a rule it is found that the solvation number will be larger the smaller the true (crystal) radius of the ion. Hence, the overall (effective) sizes of different hydrated ions tend to become similar. This is why different ions in solution have similar values of mobilities or diffusion coefficients. The solvation numbers of cations (which are relatively small) are usually higher than those of anions. Yet for large cations, of the type of N(C4H9)4, the hydration number is zero. 

---