Werner-type

Hofmann- and Werner-Type Inclusion Compounds. There is a wide range of clathrates having as the host component inorganic coordination compounds represented by the general formulae M(NH2)2 (CN) and X2Y4. The first formula is typical of Hofmaim-type clathrates... 

Sihcone products dominate the pressure-sensitive adhesive release paper market, but other materials such as Quilon (E.I. du Pont de Nemours Co., Inc.), a Werner-type chromium complex, stearato chromic chloride [12768-56-8] are also used. Various base papers are used, including polyethylene-coated kraft as well as polymer substrates such as polyethylene or polyester film. Sihcone coatings that cross-link to form a film and also bond to the cellulose are used in various forms, such as solvent and solventless dispersions and emulsions. Technical requirements for the coated papers include good release, no contamination of the adhesive being protected, no blocking in roUs, good solvent holdout with respect to adhesives appHed from solvent, and good thermal and dimensional stabiUty (see Silicon COMPOUNDS, silicones). 

The species discussed so far belong to the class we might label Werner-type complexes. We use this description to differentiate from carbonyl-type or other low oxidation state complexes. We stay with Werner-type complexes exclusively until Chapter 6. The radial waveforms for 3d, A-s and Ap orbitals of the metals in such... 

Figure 2-2. Schematic representation of the radial waveforms for 3d, 45 and 4p orbitals in first row transition-metal ions of intermediate oxidation state (Werner-type complexes).

Two other, closely related, consequences flow from our central proposition. If the d orbitals are little mixed into the bonding orbitals, then, by the same token, the bond orbitals are little mixed into the d. The d electrons are to be seen as being housed in an essentially discrete - we say uncoupled - subset of d orbitals. We shall see in Chapter 4 how this correlates directly with the weakness of the spectral d-d bands. It also follows that, regardless of coordination number or geometry, the separation of the d electrons implies that the configuration is a significant property of Werner-type complexes. Contrast this emphasis on the d" configuration in transition-metal chemistry to the usual position adopted in, say, carbon chemistry where sp, sp and sp hybrids form more useful bases. Put another way, while the 2s... 

Experimentally, spin-allowed d-d bands (we use the quotation marks again) are observed with intensities perhaps 100 times larger than spin-forbidden ones but still a few orders of magnitude (say, two) less intense than fully allowed transitions. This weakness of the d-d bands, alluded to in Chapter 2, is a most important pointer to the character of the d orbitals in transition-metal complexes. It directly implies that the admixture between d and p metal functions is small. Now a ligand function can be expressed as a sum of metal-centred orbitals also (see Box 4-1). The weakness of the d-d bands also implies that that portion of any ligand function which looks like a p orbital when expanded onto the metal is small also. Overall, therefore, the great extent to which d-d bands do satisfy Laporte s rule entirely supports our proposition in Chapter 2 that the d orbitals in Werner-type complexes are relatively well isolated (or decoupled or unmixed) from the valence shell of s and/or p functions. 

We can understand this powerful generalization directly from our view of the valence shell in Werner-type complexes as laid out in Chapter 2. Recall that as an extreme limit for Werner-type species, we consider the metal contribution to the valence shell for the first-row elements as 45 and 4p, with 3d orbitals excluded. So,... 

Amongst the consequences to be expected from the change from Werner-type behaviour to carbonyl, low oxidation state chemistry is a breakdown in the efficacy... 

Furthermore, as discussed in Section 6.7, the ability of the elastic d orbitals to function as electron sinks contributes greatly to the rich variety of redox chemistry that is so characteristic of the cf-block elements. Here too, therefore, we recognize the bonding role of the d orbitals in Werner-type complexes as well as in carbonyl-type chemistry. 

A central theme in our approach, which we believe to be different from those of others, is to focus on the changing chemistry associated with higher, middle and lower oxidation state compounds. The chemical stability of radical species and open-shell Werner-type complexes, on the one hand, and the governance of the 18-electron rule, on the other, are presented as consequences of the changing nature of the valence shell in transition-metal species of different oxidation state. 

Bray, M. R., Deeth, R. J., Paget, V. J., Sheen, P. D., 1996, The Relative Performance of the Local Density Approximation and Gradient Corrected Density Functional Theory for Computing Metal-Ligand Distances in Werner-Type and Organometallic Complexes , Int. J. Quant. Chem., 61, 85. 

Although there is a tendency to associate coordinated water with Werner-type complexes, where it is extensively established, organometallic aqua ions are known.945 The simple [(Cp )Co(OH2)3]2+ has been established, and is prepared via Equation (8). The lower pATa is 5.9, similar to values in aminecobalt(III) compounds, and reversible deprotonation and dimerization has been identified as part of the reactions of the aqua ion.946... 

Classifying particles, in filtration, 11 326 Class I hybrids, 13 536, 543, 544 Class II hybrids, 13 536, 543 Clastogenesis, 25 206 Clathrate hydrates, 14 170—171 Clathrate receptor chemistry, 16 797 Clathrates, 12 374 14 159, 170-182 formation of, 10 633-635 26 869 Hofmann- and Werner-type, 14 171-172 phenol-type, 14 180 tri-o-thymotide, 14 179 Claus catalysts... 

Wentworth process, for ethanol separation from water, 8 834-835 Wenzel s equation, 22 111-112 Wenzel contact angle, 22 111 Werner nomenclature scheme, 17 391-392 Werner-Pfleiderer (WP) Compounder, 22 44 Werner-type inclusion compounds, 14 171-172... 

Since we shall not obtain the comparable amount of detailed information on the mechanisms of substitution in octahedral complexes from the studies of more complicated substitutions involving chelation and macrocycle complex formation (Secs. 4.4 and 4.5) it is worthwhile summarizing the salient features of substitution in Werner-type complexes. 

When a metal atom donates electron density to a bound ligand, usually by means of Ji-back bonding, electrophilic substitution reactions may be promoted. This is observed then usually with metals in low oxidation states and is therefore prevalent with organometallic complexes - and less with those of the Werner-type, where the metals are usually in higher oxidation states. Nevertheless there have been detailed studies of electrophilic substitution in metal complexes of P-diketones, 8-hydroxyquinolines and porphyrins. Usually the detailed course of the reaction is unaffected. It is often slower in the metal complexes than in the free ligand but more rapid than in the protonated form. 

The preparation, and even more the resolution, of an asymmetric tetrahedral center in Werner-type complexes has been thwarted by the configurational instability of tetrahedral complexes. However the use of ligands of the strongly a, 7t bonding type imposes stability and the forma-... 

Werner-type complexes with these coordination numbers have been characterized. However a large majority of the complexes showing these coordination numbers are organometallic in nature and generally outside the scope of this book. Examples are shown in Structures 9-11, and discussion of the associated rearrangements will be necessarily brief. 

Kinetic information on the lower oxidation states (Prob. 24) is sparse for Werner-type complexes. Co and Co(II)-bpy complexes are reduced by e to give Co(I) complexes except that the mono species yields Co"(bpy ) (H20)J. The rate constants are in the range... 

Seventeen years is a long time between editions of a book. In order to add some of the vast amount of new material which has been published in that time, I have needed to abridge the older edition and in so doing apologise to oldtimers (myself included ) whose work may have been removed or modified. Nevertheless, the approach used is unchanged. In the first three chapters I have dealt with the acquisition of experimental data and discussed use for building up the rate law and in the deduction of mechanism. In the second part of the book, the mechanistic behavior of transition metal complexes of the Werner type is detailed, using extensively the principles and concepts developed in the first part. 

Although the properties which can be computed are limited, LFT has provided for over half a century a reasonably useful, semi-quantitative picture of metal-ligand bonding in Werner-type coordination complexes (3,25-27). In the present context, the advantage of LFT is its computational efficiency. Therefore, we added LFT to MM to give the ligand field molecular mechanics (LFMM) method (28). 

It is well known that transition-metal salts and metal complexes, unlike non-Werner-type ferrocene compounds, act as inhibitors in the polymerization of vinyl monomers. For example, the radical polymerization of vinylpyridine is strongly inhibited in the presence of Cu(II) or Fe(III)32 However, vinylpyridine with Cu(I)... 

Oxidative reactions of organic compounds with molecular oxygen take place with high efficiency and selectivity in the presence of Werner-type metal complexes used as catalysts. The catalytic effects of metal complexes have received attention also as models for metalloenzymes, which are catalysts that possess special high efficiency and high selectivity for oxidative reactions in vivo. 

The instances of reductive reactions catalyzed by polymer-metal complexes of the Werner type are few compared with the oxidative reactions. 

In these polymer-metal complexes of the Werner type, however, organometallic compounds are formed as reaction intermediates and/or activated complexes. As a result, the properties of polymer-metal catalysts in reductive reactions are different from those of polymer-metal catalysts in oxidative reactions. In the former, the catalytic reactions are very sensitive to moisture and air, and the complex catalysts often decompose in the presence of water and oxygen. Thus, reductive catalytic reactions are carried out under artificial conditions such as organic solvent, high pressure, and high temperature. Oxidative catalytic reactions, on the other hand, proceed under mild conditions aqueous solution, oxygen atmosphere, and room temperature. Therefore, it is to be expected that the catalytic effects of a polymer ligand will differ from the latter to the former. 

Photocalorimetry offers a convenient alternative to other methods of AH determination and, in some instances, may be the only practical method. The ligand substitution reactions of robust Werner-type complexes are a case in point. Conventional thermochemical measurements are complicated by the slowness of the substitution process and/or by competing reactions. Some of these same complexes, however, undergo clean photosubstitutions with high quantum yields and thus are excellent candidates for photocalorimetry. Examples include [Cr(NH3)6]3+, [Cr(CN)6]3-and [Co(CN)6]3-.192 Photocalorimetric measurements of AH have also been obtained for isomerization and redox reactions of coordination compounds.193194... 

When naphtha or naphthenic gasoline fractions are catalytically reformed, they usually yield a Cx aromatics stream that is comprised of mixed xylenes and ethylbenzene. It is possible to separate the ethylbenzene and o-xylene by fractionation. It is uneconomic to separate the m- and p-xylenes in this manner because of the closeness of their boiling points. To accomplish the separation, a Werner-type complex for selective absoiption of p-xylene from the feed mixture may be used. Or, because of the widely different freezing points of the two xylene isomers, a process of fractional crystallization may be used. To boost the p-xylene yield, die filtrate from the crystallization step can be catalytically isomerized. 

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