Inner coordination compounds

Ill an inner compound an additional valence hnnd has been formed between two atoms of an already existing structure, usually by loss of ihe elements of water or other simple substance. Inner compound formation commonly results in the formation of a ring. The inner esters, inner anhydrides, and inner coordination compounds are well-known classes of inner compounds. 

INNER COORDINATION COMPOUNDS A particular type of non-localized bond occurs in the so-called inner coordination compounds. This group of compounds may be illustrated by reference to the copper salt of aminoacetic acid (glycine). This compound dissociates only weakly in solution, it possesses a colour similar to the ammino complexes of copper and does not react with ammonia. These properties all tend to show that copper atom has a saturated valency and may be explained by considering the copper as bound to both the hydroxyl and the amino groups. In accordance with our concept of the nature of the bond between a metal and an amino group in such a compound, the structure of the complex will be represented by resonance amongst the forms I to IX X... 

The formation of inner coordination compounds is connected with the presence in the organic molecule of atoms which may exist in more than one valency state, e,g,... 

The formation of such complexes is conditioned by steric factors in the a- and amino acids, when the ring consists of five or six atoms respectively, a coordination compound is formed, but an increase in the number of atoms separating the amino and carboxylic acid groups (in y, 8, , etc amino acids) generally inhibits the formation of cyclic inner coordination compounds. 

In view of the general objection to the term complex compound, it would be desirable to have an alternate expression for inner complex compound. For the purposes of this paper the expression inner coordination compound will be used. 

Although the term inner coordination compound is usually restricted to the meaning given above, some writers have used it as synonymous with nonionic coordination compound to include nonchelate compounds like [Co(NH3)3(N02)8] and partially chelated compounds ... 

Quadridentate coordinating groups may also lead to neutral bodies to which the term inner coordination compound could well be applied ... 

It has been established, that both DN and Ibp form complex compounds with ions Eu(III), Sm(III), Tb(III) and Dy(III), possessing luminescent properties. The most intensive luminescence is observed for complex compounds with ion Tb(III). It has been shown, that complexation has place in low acidic and neutral water solutions at pH 6,4-7,0. From the data of luminescence intensity for the complex the ratio of component Tb Fig was established equal to 1 2 by the continuous variations method. Presence at a solution of organic bases 2,2 -bipyridil, (Bipy) and 1,10-phenanthroline (Phen) causes the analytical signal amplification up to 250 (75) times as a result of the Bipy (Phen) inclusion in inner coordination sphere and formation of different ligands complexes with component ratio Tb Fig Bipy (Phen) = 1 2 1. 

The inner coordination sphere of the dimer is shown in Figure 5. By the normal rules of electron counting, the rare-gas configuration is obeyed at platinum if a Pt=Pt double bond is invoked. Yet the Pt-Pt distance of 2.765(1)A is a normal or slightly long, single bond. One thus wonders if the compound might be a... 

The more selective kind of ion exchange, the chelating ion exchange [22], suffers often from kinetic limitations, which limit the application range to cationic compounds with fast ligand exchange kinetic for the inner coordination sphere. Ion exchange is well suitable for preconcentration as well as for separation of chemically similar compounds. 

Acido compounds, containing only deprotonated acid anions in the inner coordination sphere, for example, K[Ag(CN)2]. 

A change of salt anions allows us to carry out controlled syntheses of definite types of coordination compounds. Thus, metal halides are widely used to prepare molecular (Sec. 3.1.1.1) and ti-complexes (Sec. 3.1.1.3). Metal acetates are mostly applied in the syntheses of metal chelates and, especially, inner-complex compounds (Sec. 3.1.1.2). Di- and polynuclear structures are formed under use of the anions mentioned above, which, in some cases, determine (see Sec. 3.1.1.4) a type and donor centers of bridge fragments. At the same time, the mentioned approach to choice of salts of metal complex-formers has many exceptions, although it is useful. 

The properties of the elements of the sixth period are influenced by lanthanide contraction a gradual decrease of the atomic radius with increasing atomic number from La to Lu. The elements of groups 5 to 11 for the fifth and sixth periods have comparable stmctural parameters. For instance, Nb and Ta, as well as the pair Mo and W, have very similar ionic radii, when they have the same oxidation number. As a result, it is very difficult to separate Nb and Ta, and it is also not easy to separate Mo and W. Similarly, Ag and Au have nearly the same atomic radius, 144 pm. Recent studies of the coordination compounds of Ag(I) and Au(I) indicate that the covalent radius of Au is even shorter than that of Ag by about 8 pm. In elementary textbooks the phenomenon of lanthanide contraction is attributed to incomplete shielding of the nucleus by the diffuse 4f inner subshell. Recent theoretical calculations conclude that lanthanide contraction is the result of both the shielding effect of the 4f electrons and relativistic effects, with the latter making about 30% contribution. 

The basis of the method is akin to the Pfeiffer effect [8] except that, in this instance, the roles of the ligands are reversed and reorganization of the inner sphere and not the outer sphere of the metal is intimately involved. The racemate originates in the solution environment and the enantiomer is part of the coordination compound (vide infra). Calculation of the enantioexcess is most easily done using spectral differences. Figure 5 shows the CD spectrum for the parent complex (lowest curve) where M is Cu(II) and L is L-tartrate in strong base together with a series of curves in which the L-pseudoephedrine concentration has been systematically increased. An isosbestic point at 538 nm is obvious [51]. 

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