Wemer complexes

Wemer complex coordination compound formed between a transition metal ion and ligands... 

While Wemer complexes are based on discrete coordination complexes, another type of coordination compound with a distinctive extension into 2D layers through utilization of ditopic bidentate ligands was developed and first reported by K. A. Hofmann in 1897, Ni(NH3)2Ni(CN)4 2(C6H6). Hofmann-type compounds also exhibit inclusion properties of suitably sized guest molecules. Iwamoto and coworkers prepared a number of derivatives of Hofmann clathrates (Figure 2). 

Figure 1 (a) An example of the Wemer complex, Ni(NCS)2(4-methylpyridine)4 and (b) crystal packing showing inclusion of benzene... 

Fig. 3.6 Some Wemer complexes with the labels written in Werner s own hand. University of Zurich Collection. Photograph courtesy of Roger Rea...

In this section we will take a short walk through the domain of the Wemer complexes and look for electronic structure-correlation relationships. We will do this by considering two plots, shown in Figure 3. This figure is based on a series of CASSCF calculations on octahedral ML transition metal complexes with different ligands, such as NHj, H2O, and the halides F , CL, Br , L. Figure 3a includes results obtained for the ground state of some formal... 

Organometallic Complexes. Wemer-type complexes of chromium and long-chain carboxyflc acids, eg, stearic acid, are water repeUents for fabrics of natural and synthetic fibers. The complexes have a smaU market in the textile industry. 

Silicone products dominate the pressure-sensitive adhesive release paper market, but other materials such as Quilon (E.I. du Pont de Nemours Co., Inc.), a Wemer-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. Silicone 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 rolls, good solvent holdout with respect to adhesives applied from solvent, and good thermal and dimensional stability (see Silicon compounds, silicones). 

The d electrons of classical Wemer-type coordination complexes have a significant impact on structure and reactivity. For example, the experimental hydration enthalpies of the divalent aqua ions (black diamonds, Fig. 2) deviate substantially from any monotonic variation on crossing the series from left to right (19). 

There are two simple types of geometric isomerism possible for octahedral complexes. The first exists for complexes of the type MA2B4 in which the A ligands may be either next to each other (Fig. 12.18s) or on opposite apexes of the octahedron (Fig. 12.18b). Complexes of this type were studied by Wemer, who showed that the proiro and video complexes of tetraamminedichlorocobalt([Il) were of this type (see Chapter 11). A very large number of these complexes is known, and classically they provided a fertile area for the study of structural effects. More recently there has been renewed interest in them as indicators of the effects of lowered symmetry on electronic transition spectra. 

When viewed from the point of view of the Wemer co-ordination theory, it is observed that in these complexes the common co-ordination number is 7, thus [TaF7]K2 and [TaF7]Cu.4ordination number 8 also occurs, thus [TaF8]Na3 and Ta NH,) and less... 

Bauer S, Wolfe I, Wemer N, et al. 1992. Toxicological investigations in the semiconductor industry 1. Studies on the acute oral toxicity of a complex mixture of waste products from the aluminum plasma etching process. Toxicol Ind Health 8 141-156. 

Weixlbaumer, A., Wemer, A., Flamm, C., Westhof, E., and Schroeder, R. (2004). Determination of thermodynamic parameters for HIV DIS type loop-loop kissing complexes. Nucleic Adds Res. 32, 5126—5133. 

In analogy with Eqs. 1.50 and 2.5, the overall surface ligand-exchange reactions in Eqs. 3.46, 3.53, 3.56, 3.65, 3.66, and 4.15b can be dissected into steps by applying the concept of the Eigen-Wilkins-Wemer mechanism, discussed in Section 2.1. Following this perspective, one would decompose the overall surface complexation reaction in Eq. 4.15b into a set of coupled reactions (cf. Eq. 1.50) ... 

Ammonia and amine complexes are among the longest known and most intensively studied. As well as classical Wemer-type complexes such as [Co(NH3)6]3+, metal halides commonly form adducts with NH3 and amines. The complexes are discussed in the appropriate chapters for the elements. 

In order to account for this difference in reactivity, Jorgensen proposed, as Wemer did after him, that the imre-active or masked chlorine is bonded directly to the metal atom. The stmctmes that they proposed, (5) and (6), are both compatible with the experimental facts but again differ in the mode of attachment of the reactive chlorine atoms. JOTgensen considered these atoms as linked to the metal atom through ammonia molecules, whereas Wemer considered them as not linked to any particular atom but attracted by electrostatic forces to the complex cation as a whole. According to Werner s stmcture, a solution of purpureo cobaltic chloride should furnish three ions, a fact confirmed... 

Wemer andMiolati s first publication on this subject showed that the molecular conductances (/r) of coordination compounds decrease as molecules of ammonia are successively replaced by acid residues (negative groups or anions). For cobalt(III) salts, /r for luteo salts (hexaammines) > /r for pur-pureo salts (acidopentaammines) > /r for praseo salts (diaci-dotetraammines). The conductance decreases almost to zero for the triacidotriammine Co(N02)3(NH3)3 and then increases for tetraacidodiammines, in which the complex behaves as an anion. Wemer and Miolati used these measurements to determine the number of ions in cobalt(III) and platinum(II) and -(fV) complexes, which supported the coordination theory and also elucidated the process of dissociation of salts in aqueous solution and the progress of aquation reactions. 

Wemer and Miolati s second article on conductances of complexes showed a complete agreement in magnitude,... 

The technique of isomer counting used by Wemer to prove the configuration of cobalt-ammines and other complexes did not originate with him, but had been used earlier by Wilhelm Kdmer for benzene derivatives in 1874, and was also suggested by Jacobus Henricus van t Hoff in 1875. However, the technique of comparing the number and type of isomers actually prepared with the number and type theoretically predicted for different configurations probably attained its zenith with Wemer. Not only did he use this method to discredit completely the chain theory bnt also to... 

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