Potassium, cation, and

If we were to conduct a second solubility experiment in which solutions of KI and NaN03 were mixed, we would find that no precipitate forms. This demonstrates that K and NO3 ions do not form a solid precipitate, so the bright yellow precipitate must be lead(II) iodide, Pbl2. As the two salt solutions mix, cations and r anions combine to produce lead(II) iodide, which precipitates from the solution. On standing, the yellow precipitate settles, leaving a colorless solution that contains potassium cations and nitrate anions. The molecular blowups in Figure depict these solutions at the molecular level. 

The solid-state structure of 72 (Figure 38) consists of a polymer of alternating THF-solvated potassium cations and diamidomethylzincate anions. The alternating zincate ions, which are rotated by about 180° with respect to each other, sandwich the potassium ions. Each potassium ion is -coordinated to one methyldiamidozincate and -coordinated to the other. The zinc-methyl and zinc-nitrogen bonds of the zincate ion are 1.954(5) and 1.989(8) A, respectively. 

Only Cram (36) has published a rationale for the very high (99%) enantiomeric excess achieved in the reaction of methyl vinyl ketone and the hydrindanone in the presence of the chiral crown ether. This mechanism envisions a bimolecular complex comprising the potassium cation and chiral host as one entity and the enolate anion of the hydrindanone as the counterion. Methyl vinyl ketone lies outside this complex. The quinine-catalyzed reaction appears to have a termo-lecular character, since the hydroxyl of the alkaloid probably hydrogen bonds with the methyl vinyl ketone—enhancing its acceptor properties—while the quin-uclidine nitrogen functions as the base forming the hydrindanone—alkaloid ion pair. 

The zincates K [ZnR(tBuNCH=CHN Bu)] contain the diazabutadiene fragment. They have been made, via a series of radical-anion complexes, from the alkylation of B uN = CHCH = N Bu by potassium in the presence of organozinc compounds, and characterized as THF and Et20 adducts, 70 and 71, respectively. Each forms linear coordination polymers comprising alternate potassium cations and zincate anions held together... 

Potassium hydride (KH) is a reactive base possessing a potassium cation and a hydrogen anion (hydride ion). The hydride ion reacts as any other base mentioned thus far and extracts acidic protons generating hydrogen gas and leaving behind anions with associated potassium cations. In this case, the dimethyl cyanomethyl-phosphonate anion, F, is formed. 

A rather complicated solid-state structure is observed for the donor-free deprotonation product 4. Two independent molecular units (Fig. 3, left) are connected via polyagostic contacts between the potassium cations and trimethylsilyl carbon atoms. Two firee coordination sides (indicated by dotted arrows in Fig. 3, right) are used for a further linkage, thus resulting in a polynaeric layer structure. In contrast to the structure of 3a, the two independent molecular units in 4 show an average Ln-C-K angle of 90°. 

As in the previous example, the chirality of the ligand is in close proximity to the palladium binding site, while the pendant group is achiral. Introduction of the crown ether was designed to enhance coordination to the counterion. A ternary complex including the crown ether, potassium cation, and the enolate anion was proposed in which the bulky crown ether blocks approach of the enolate to Cl and provides a chiral pocket around carbon C3 [40]. Enantioselectivities up to 75% were reported [40], which were later revised to 65% [38]. 

Potassium bromide. The potassium cation and the bromine anion Br combine to form the ionic compound potassium bromide. The sum of the charges is +1 + ( 1) = 0, so no subscripts are necessary. The formula is KBr. 

The potassium atom has one more electron than argon, which is the closest inert gas (see Group VIII in the periodic table in Figure 1). Potassium will therefore lose one electron to chlorine, which has one less electron than argon. This means that the compound KCl contains potassium cations and chlorine anions. 

Figure 2.23 The microporous potassium sodium europium silicate AV-9 has a structure similar to the natural sodium calcium silicate monteregianite. Layers containing both edge-sharing NaOg (dark grey) and EuOg (medium grey) octahedra are separated by microporous sheets of silicate tetrahedra. The pore space is filled by extra framework potassium cations and zeolitic water.

The white insoluble solid that s formed is silver chloride. You can drop out the potassium cation and nitrate anion spectator ions, because they don t change during the reaction and are found on both sides of the equation in an identical form. (If you re totally confused about all those plus and minus symbols in the equations, or don t know what a cation or an anion is, just flip to Chapter 6. It tells all you need to know about this stuff.)... 

V Potassiiim bromide. The potassium cation and the bromine anion Br ... 

Cyclophano-crown ether host (Scheme 8), possessing cyclic polyether and cyclophane moieties in a single molecule and ability to simultaneously bind a potassium cation and 6-methoxy-2-naphthonitrile in a water-methanol mixture, is of particular interest, since the contrasting solvent effects can be examined in the same host. Indeed, neutral 6-methoxy-2-naphthonitrile guest forms a 160-fold more stable complex with the cyclophane moiety in more hydrophilic 60 40 water-methanol solvent than in pnre methanol. In contrast, the affinity toward potassium ion is enhanced by a factor of 120 in pure methanol rather than in 60 40 water-methanol. Scheme 8... 

Zeolite ZSM-10 was first synthesized by Ciric more than 25 years ago from aluminosilicate gels containing potassium cations and a diquaternary compound, viz. the l,4-dimethyl-diazonia(2.2.2)bicyclooctane cation (cf. Fig. 13 [77]). Since its first description, only two further reports on the synthesis appeared, one Japanese patent [78] and a very recent publication by Higgins and Schmitt [79], the latter also describing the framework topology of zeolite... 

Cellular metal ion transport is biologically important because our muscular and nervous systems are regulated by charged species. Cells use membrane channels to extract potassium ions selectively from environments containing both K+ and Na+. Because the K+ ion is /argerthan the Na+ ion, this process cannot be accomplished by simply restricting the channel diameter. Dr. Roderick MacKinnon showed that potassium selectivity arises from a preferential interaction between the potassium cation and the atoms of the protein amino acids composing the channel walls. 

Fig. 3 Polyassociation of bis-guanine monomers (G-G) into a two-dimensional supramolecular polymeric array based on the formation of G-quartets, stabilized by potassium cations, and interconversion of the resulting hydrogel with the corresponding sol state through reversible cation binding and release by the [2.2.2] cryptand, modulated by acid-base alternation. The 2D array on the right is represented in an idealized fashion ignoring any defect...

More recently, Normant and coworkers have reported catalysis of the reaction between potassium acetate and benzyl chloride in acetonitrile by polyamines in a two phase system [28]. It seems likely that the catalytic activity reported by Normant et al. is related to the earlier alkylations discussed above. The authors state in their communication, however, their finding that ... quaternary ammonium salts corresponding to the diamines do not activate anions under the experimental conditions used. . In the reaction referred to here, it seems likely that the diamines are playing a dual role. The diamines are probably assisting in the solubilization of the solid (and relatively insoluble) potassium acetate by chelation of the potassium cation and the homogeneous reaction is then probably catalyzed by the quaternary ion formed in situ. That the catalytic activity of the amine depends on the hardness of the cation (the harder the cation, the less catalytic activity) [28] seems to accord with this interpretation although lattice energy differences cannot be discounted. 

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