Isomerism hydration

Hydrate isomerism of TiCl3.6H20, yielding [TiCl2(H20)4]" CU as one of the isomers, has already been referred to (p. 965) and analogous complexes are formed by a variety of alcohols. Neutral complexes, [T1L3X3] have been characterized for a variety of ligands such... 

Chromium, tetraaquadichloro-chloride dihydrate hydrate isomerism, 1, 183 Chromium, tetrabromo-solvated, 3, 758 synthesis, 3, 763 Chromium, tetrachloro-antiferromagnetic, 3, 761 ferromagnetic magnetic properties, 3,7559 optical properties, 3,759 structure, 3,759 solvated, 3. 758 synthesis. 3, 759 Chromium, tetrachlorooxy-tetraphenylarsenate stereochemistry, 1,44 Chromium, tetrahalo-, 3,889 Chromium, tetrakis(dioxygen)-stereochemistry, 1,94 Chromium, triamminediperoxy-structure. 1, 78 Chromium, tricyanodiperoxy-structure, 1, 78 Chromium, trifluoro-electronic spectra, 3, 757 magnetic properties, 3, 757 structures, 3, 757 synthesis, 3, 756 Chromium, trihalo-clcctronic spectra, 3, 764 magnetic properties, 3, 764 structure, 3, 764 synthesis, 3, 764 Chromium, tris(acetylacetone)-structure. 1, 65 Chromium, tris(bipyridyl)-... 

Cobalt, dichlorobis(AvY -dimethyl-1,2-ethanediamine)-chloride hydrate isomerization, 1, 468 Cobalt, dich orobis(l,2-ethanediamine)-base hydrolysis, 1, 304 chloride anation, 1, 469 halogen exchange, 1, 468 chloride hydrate isomerization, 1, 468 isomers, 1,191 nitrate... 

A great many metal complexes are prepared by reactions carried out in aqueous solutions. Consequently, solid complexes are frequently obtained as hydrates. Water is also a potential ligand so various possibilities exist for compounds to be prepared with water held in both ways. For example, [Cr(H20)4Cl2]Cl-2ff20 and [Cr(H20)5Cl]Cl2-ff20 have the same formula, but they are obviously different compounds. In the first case, two chloride ions are coordinated and one is present as an anion, whereas in the second case the numbers are reversed. Many other examples of hydrate isomerism are known. 

With secondary alcohols the picture is different. By measuring rates of hydration, isomerization, dehydration, and exchange, in the system of butenes and 2-butanol, Manassen and Klein (7S) proved that the hydration-dehydration intermediate in dilute acid solution is equally bonded to two water molecules ... 

Isomerism in the Metal-ammines.—Werner claimed for the coordination theory that in certain cases isomerism should occur, that isomerism being brought about by different causes. lie divided isomerism in the ammines into five groups, namely, structure isomerism, ionisation isomerism, hydrate isomerism, polymerism, and stereoisomerism. 

Hydrate Isomerism.—As its name implies, this depends on the position of water in the molecule, just as in the case of the acido compounds. If two or more molecules of water are present in a molecule of ammine, the water may be present within the co-ordination complex or outside of it. For instance, the compound Cr en2.(H20)2.Br3 exists in isomeric forms. It may have all the water within the complex, in which case the formula will be [Cr en2(H20)2]Br3. In solution the whole of the bromine is precipitated by silver nitrate. On the other hand, the compound may have one molecule of water in the complex and the other outside, in which case the formula is [Cr en2(IT20)Br]Br2.H20, and only two-thirds of the bromine are precipitated by silver nitrate. Another example of this kind occurs in the cobalt series chloro-aquo-tetrammino-cobaltic chloride, [Co(NTI3)4Cl.H20]Cl2, is violet in colour, and is isomeric with dichloro-tetrammino-cobaltie chloride monohydrate, [Co(N1I3)4CI2]C1.H20, which is green. 

Isomerism in Metal-Ammines—Structure Isomerism—Ionisation Isomerism— Hydrate Isomerism—Polymerism—Stereo-isomerism. 

Often more complex situations arise in which additional tautomers or other forms arise via pH-independent reactions. These can all be related back to the reference ionic species by additional ratios R, which may describe equilibria for tautomerization, hydration, isomerization, etc. (Eq. 6-82).76 In the case illustrated, only one of the ratios, namely R2 or R3, is likely to be a tautomerization constant because, as a rule, H2P and P will not have tautomers. Equations analogous to Eqs. 6-76 to 6-82 can be written easily to derive Kc, K0 and any other microscopic constants desired from the stoichiometric constants plus the ratios R, to R4. While it is easy to describe tautomerism by equations such as Eqs. 6-76 and 6-82 it is often difficult... 

Ionization, hydrate and coordination isomerism are classifications of constitutional isomerism that originated with Werner.27,28 Ionization and hydrate isomerism (equation 1) apply to cases in which there is a ligand exchange between primary and outer coordination spheres, whereas coordination isomerism (equation 2) arises in systems containing at least two metal ions, so that alternative primary coordination spheres are available. 

The term "cutionic water" may be used to describe the situation in which water appears in coordination compounds apparently joined to cations by covalent bonds. However, the fact that a number of such compounds exhibit "hydrate isomerism" is evidence for cationic bonding, as well as it is lor the existence of other harms of these compounds in which Ihe presence of Water is due to electrostatic attractions or ctystal stability requirements. 

Hydrate isomerism is quite analogous to ionization isomerism. The compound Cr(H20)5Ci2+ (C1 )2 H20 contains one Cr—Cl bond and five Cr—O bonds per complex whereas its isomer, Cr(H20)4Clt C1 2H20, has two Cr—Cl bonds and only four Cr—O bonds per complex. The first of these yields three ions per gram-atom of chromium when dissolved in water (as may be checked by freezing-point measurements), whereas the second yields but two ions per complex. Those water molecules not directly coordinated to chromium are probably present as lattice water. ... 

The hydration/isomerization of alpha-pinene catalyzed by zeolite H-BEA is fast and leads mainly to monocyclic terpenes and alcohols with alpha-terpineol 32 as the principal product (up to 48%) (35). The selectivity to bicyclic products is about 26% which, while still too low, is significantly better than the 5% observed for H2SO4. 

Catalytic transformations of terpenes are well documented [213-215], comprising a wide variety of reactions hydrogenation, dehydrogenation, oxidation, hy-droformylation, carbonylation, hydration, isomerization and rearrangement, and cyclization. 

This form of isomerism, sometimes known as hydrate isomerism in the special case where water is involved, is similar in some ways to ionization isomerism. Solvate isomers differ by whether or not a solvent molecule is directly bonded to the metal ion or merely present as free solvent in the crystal lattice or solution. An example is provided by the aqua complex [Cr(H20)JCl3 and its solvate isomer [Cr(H20)5Cl]Cl2.H20. 

Hydrate Isomerism, Coordination Isomerism, and Polymerization Isomerism... 

Ionization isomerism is another case defined by recognizing that an empirical formula allows some options for the coordination sphere of the metal. It is essentially the same situation as hydrate isomerism, but involves ligands other than water. For example, consider the inert cobalt(III) compound CoBr(S04>5(NH3), which forms two different compounds, one violet, the other red. We know these now as [CoBr(NH3)5](S04) and [Co(NH3)5(S04)]Br, which differ in the choice of which anion occupies the coordination sphere, the other remaining as the counter-ion (Figure 4.25). 

---