Ion-dipole bonding

Dissolution of ionic and ionizable solutes in water is favored by ion—dipole bonds between ions and water. Figure 6 illustrates a hydrated sodium ion,... 

Fig. 6. Hydrated sodium ion,, in aqueous solution (4).The H2O molecules form ion—dipole bonds to the central metal ion. The waters are in...

If the bonds are ionic or ion-dipole bonds, the magnetic moments are those of the isolated central ions, given in the first column of moments in Table III. If the complex involves electron-pair bonds formed from sp alone, such as four tetrahedral sp3 bonds, the magnetic moments are the same, for the five d eigenfunctions are still available for the remaining electrons. The hydrazine and ammonia complexes mentioned above come in this class. 

It is then shown that (excepting the rare-earth ions) the magnetic moment of a non-linear molecule or complex ion is determined by the number of unpaired electrons, being equal to ms = 2 /S(S + 1), in which 5 is half that number. This makes it possible to determine from magnetic data which eigenfunctions are involved in bond formation, and so to decide between electron-pair bonds and ionic or ion-dipole bonds for various complexes. It is found that the transition-group elements almost without exception form electron-pair bonds with CN, ionic bonds with F, and ion-dipole bonds with H2O with other groups the bond type varies. 

Ionic or Ion-dipole Bonds Octahedral Covalent Bonds ... 

When the multiplicity of a complex is the same for ionic or ion-dipole bonds and for covalent bonds, the decision as to which extreme bond type is the more closely approached in any actual case must be made with the aid of less straightforward arguments. Sometimes theoretical energy diagrams can be constructed with sufficient accuracy to decide the question. A discussion of crystals based on the Born-Haber thermochemical cycle has been given by Rabinowitsch and Thilo3), and more accurate but less extensive studies have been made by Sherman and Mayer4). 

Crown-ethers can incorporate protonated primary amine compounds by formation of ion-dipole bonds with the oxygen atoms of the chiral selector. Crown-ethers have been widely used for the separation of several pharmaceuticals both in aqueous and non-aqueous media." ... 

Crown ethers are large-ring cyclic ethers with several O atoms. A typical example is 18-crown-6 ther, Fig. 14-l(a). The first number in the name is the total number of atoms in the ring, the second number is the number of O atoms. Crown ethers are excellent solvaters of cations of salts through formation of ion-dipole bonds. 18-Crown-6 ether strongly complexes and traps K, [from, e.g., KF, as shown in Fig. 14-1(6)]. 

An ion-dipole bond is another electrostatic attraction between an ion and several polar molecules. When an ionic substance is dissolved in a polar solvent, it is this kind of interaction that takes place. The negative ends of the solvent aligned themselves to the positive charge, and the positive ends aligned with the negative charge. This process is solvation. When the solvent is water the process is the same but called hydration ... 

This linking of one T and one O sheet to form a TO layer is the simplest way to produce a clay mineral. A crystal of kaolinite consists of extremely many of those TO layers. Between the TO layers no ordinary chemical bond exists. Water molucules and hydrated ions can be found there. These water molecules are bound to the TO layer by means of an ion dipole bond and the water molecules themselves are interlinked by means of H bridges. This collection of physical bonds keeps the TO sheets together. The different kinds of kaolinite which are found in nature exhibit different packings of the TO layers with respect to each other directly above each other or shifted in position. 

The complexes [Ni(H20)4]2+, [Ni(NH3)4]2+ etc. are, however, paramagnetic with = 2.6—3.2. Here, therefore, the bonding is obviously different and the moment indicates the presence of ion-dipole bonding with the same electron structure as the Ni2+ ion, or the formation of 4 bonds using the 4s and the three 4p levels and with the 8 non-bonding electrons in the five 3d levels. In both cases a tetrahedral arrangement with two unpaired electrons is to be expected. 

Figure 19. Ca(polyP) solvated by PHB. A. Drawing depicting the solvation of Ca(polyP) by PHB in the bilayer forming a Ca2+-selective channel.13 B. Drawing of the cross section of PHB/polyP channel. C. Putative coordination geometry of Ca2+ in PHB/polyP. Ca2+ forms ionic bonds with four phosphoryl oxygens of polyP and ion-dipole bonds with four ester carbonyl oxygens of PHB to form a neutral complex with distorted cubic geometry.25...

Hydration and Hydrolysis. The various oxidation states of plutonium form strong ion-dipole bonds with water to become strongly hydrated in aqueous solution. To a first approximation, we can expect the hydration numbers of the first coordination sphere to be the same as the most probable coordination numbers suggested in the preceeding section. This means values of 8 or 9 for Pu(lll), 7 or 8 for Pu(Vl), and, perhaps, 4 for PuOj and 6 for PuOj. However, the polarization of the water dipoles of the primary hydration layer leads to attraction of additional waters of hydration. Estimates of the total number of waters of hydration for trivalent lanthanides and actinides have been given as 12 - 15 model of a small number of... 

Ion-dipole forces are a combination of the partial charges of a dipole and the charge of an ion. When table salt (NaCl) dissolves in water, an ion-dipole bond is formed between the sodium and chloride ions and the polar water. Coulomb s Law also explains ion-dipole forces. 

Figure 1.6. Dipole-dipole attraction 1.2.5 Ion-Dipole Bonding (Solvation)...

A preliminary classification of the weak forces which hold together well-separated units such as the individual molecules in ice or napthalene has already been made (p. 82). The strongest of these are often termed electrostatic, signifying that the forces can be attributed to an interaction of the unmodified, static charge distributions of the separate systems. Examples are the ion-dipole bonds which occur in hydrates and ammoniates. These are usually weaker than ordinary covalent bonds and relatively easily break on heating. The binding force arises (Fig. 62) from the attraction between the... 

Lithium iodide forms a solid complex with ammonia, Li(NH3)4l, but the related hydrate, alcoholate and amine complexes are less stable. These complexes presumably involve ion-dipole bonds (p. 115), the nitrogen lone pairs surrounding the Li+ some covalent character (dative bonding) is also permissible if s and p orbitals on the Li are invoked. The chloride, bromide and iodide of lithium are much more soluble in alcohol and ether than those of the other alkali metals, but this is not always a reliable indication of covalent character. The property is employed in separating lithium from sodium. 

Although each of these ion-dipole bonds (Sec. 1.21) is weak, in the aggregate they supply a great deal of energy. (Wc should recall that the ion dipole bonds in hydrated sodium and chloride ions provide the energy for the breaking down of the sodium chloride crystalline lattice, a process which in the absence of water requires a temperature of 801. ) Just as a hydrogen ion is pulled out oj the molecule by a hydroxide ion, so a halide ion is pulled out by solvent molecules. 

Finally, we must realize that even dissociation of the protonated alcohol is made possible only by solvation of the carbonium ion (compare Sec. 5.13). Energy for the breaking of the carbon-oxygen bond is supplied by the formation of many ion-dipole bonds between the carbonium ion and the polar solvent. 

The transition state can be pictured as a structure in which carbon is partially bonded to both —OH and —Br the C—OH bond is not completely formed, the C—Br bond is not yet completely broken. Hydroxide has a diminished negative charge, since it has begun to share its electrons with carbon. Bromine has developed a partial negative charge, since it has partly removed a pair of electrons from carbon. At the same time, of course, ion-dipole bonds between hydroxide ion and solvent are being broken and ion-dipole bonds between bromide ion and solvent are being formed. 

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