Structural isomerism hydration isomers

Hydration isomers result from the interchange of H2O and another ligand between the first coordination sphere and the ligands outside it. 

The classic example of hydrate isomerism is that of the compound of formula CrCl3 6H20. Green crystals of chromium(III) chloride formed from a hot solution obtained by reducing chromium(VI) oxide with concentrated 

---

Figure 16.18 summarizes the types of isomerism found in coordination complexes. The two major classes of isomers are structural isomers, in which the atoms are connected to different partners, and stereoisomers, in which the atoms have the same partners but are arranged differently in space. Structural isomers of coordination compounds are subdivided into ionization, hydrate, linkage, and coordination isomers. 

We wish to report several metal complexes formed from a phosphorous acid diester of the type OP (H) (OR) 2 which underwent isomerization to form a metal-phosphorus bond as in (a). In the course of our investigations on the complexing properties of polycylic phosphites (9 17) j it was found that 2,8,9-trioxa-l-phosphaadamantane (L) undergoes a rapid, acid hydrolysis in acetone to form two colorless, crystalline hydrolysates, A and B. Only isomer A or L complexed with divalent hydrated metal ions, and it is concluded from infrared evidence that A has isomerized as shown in the following reaction sequence. Supporting infrared and PNMR evidence is presented for the tentatively postulated structures of A and B. 

Geometrical isomer, 382 Heteroatom, 377 Hydration, 391 Isomerization reaction, 394 Kekuld structure, 376 Ketone. 370 Monomer, 395 Nucleic acid, 400 Nucleophile. 386 Nucleophilic addition, 388 Nucleotide, 400 Optical isomers, 383 Pfeptidebond, 399... 

It is not necessary to protonate an enolate to obtain these two isomers. They exist in equUibrium with each other by a proton transfer reaction known as keto-enol tautoffleristn. Tautomerization describes the interconversion of two isomeric structures that differ in the location of a hydrogen atom. Tautomerization requires a change in the kinds of bonds between at least two other sets of atoms in the structures. We encountered this phenomenon in the isomerization reaction of the enol formed in the hydration of an alkyne (Chapter 7). We know that the keto form is more stable than the enol form. As we saw in the last section, this order of stabilities results primarily from the difference between the bond strengths of a carbon—oxygen double bond and a carbon—carbon double bond. 

Geometrical isomer, 406 Heteroatom, 402 Hydration, 416 Isomerization reaction, 419 Kekule structure, 401 Ketone, 390 Monomer, 420 Nucleic acid, 423 Nucleophile, 410 Nucleophilic addition, 412 Nucleotide, 423 Optical isomers, 407... 

---