Wemer-type complex

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. 

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. 

The applicability of LFDFT, like LFT itself, is rooted in an effective hamiltonian theory that states that, in principle, it is possible to define precisely a hamiltonian for a sub-system such as the levels of a transition metal in a transition-metal complex or a solid. This condition is possible, because in Wemer-type complexes the metal-ligand bond is mostly ionic and as such allows one to take a spectroscopically justified preponderant electronic d" or f" configuration as well defined ligand-to-metal and metal-to-ligand charge-transfer states are well separated from excitations within this configuration. 

Complexes with the general formula [Co(N02) (NH3)6 J (n = 1-5 omit the charges) are typical Wemer-type complexes and most complexes of the series known up to the age of Werner. However, the series still remain incomplete up to now. 

Very simplified structure of these Wemer-type complexes of Cr(IlI) is shown. 

Two mononuclear Wemer-type complexes based on Pd(III) have been characterized by X-ray crystallography. The X-ray crystal structure of mononuclear Pd (III) complex 1, in which the Pd(III) center is supported by two 1,4,7-trithiacyclo-nonane ligands, was reported in 1987 (Fig. 2) [37-39]. An analogous complex (2), supported by 1,4,7-triazacyclonOTiane ligands, was reported a year later [40]. Both complexes contain distorted octahedral Pd centers, as expected for low-spin (f Pd (III) [6]. Detailed examinatiOTi of the electrochemical and spectroscopic properties of Pd(III) complexes supported by macrocyclic polydentate ligands has indicated that the unpaired electron in 1 and 2 resides predominantly in the orbital [41 6]. 

After the war, which caused tremendous damage all over Japan, the educational systems were reformed, and many new universities were established, which were smaller in size than the earlier universities. With the reconstruction of Japan research in coordination chemistry has become an active field and has been extended to non-Wemer type complexes and organometallic chemistry. Only a few postwar researches will be mentioned here. 

Most studies of the mechanism of substitution in octahedral metal complexes have been concerned with Wemer-type complexes. Organometallic complexes have entered the research field more recently. Among the former, the popular candidates for study have been Cr(lll) (d ) and low-spin Co(III) (d ) species. These complexes are kineti-cally inert and their rates of reaction are relatively slow and readily followed by conventional techniques. Both Rh(lll) and Ir(lII) (both low-spin d ) also undergo very slow substitution reactions. There is no universal mechanism by which octahedral complexes undergo substitution, and so care is needed when tackling the interpretation of kinetic data. 

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). 

Linear Wemer-type coordination polymers are defined as linear polymers, the main chains of which contain coordinate covalent bonds of transition metals. In this article, we restrict the discussion to the linear coordination polymers which can exist as a stable form in solution and thus our purpose is somewhat complementary, for example, to review dimensional inorganic complexes such as those of Miller and Epstein ... 

LFT is an example of effective operator theory and can be employed to construct multiplet states arising from d" (or /") configurations. Hence, it is strictly only apphcable to systems where the ground state and the lower energy excited states are dominated by f-(or / ) orbital contributions. LFT is thus most relevant for relatively ionic Wemer-type transition metal (TM) complexes. 

The monograph is organized essentially in three parts. The first four chapters cover the basic materials. The book starts with a historical perspective and commentary followed by discussions on the principles governing electron, energy transfer, photocatalysis and the chemistry of the charge transfer excited state. Next five chapters deal with the photochemistry of classical/Wemer-type coordination compounds and their applications. Polypyridine complexes by and large received major scrutiny. A survey of their photochemistry is followed by two key recent applications ... 

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. 

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. 

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... 

Such a procedure was used successfully by Wemer to demonstrate that six-coordinate complexes have an octahedral structure. The method starts with the assumption that a six-coordinate system has a structure in which the six ligands are situated at positions symmetrically equidistant from the central atom. If it is further assumed that three of the more probable structures are (1) planar, (2) a trigonal prism, and (3) octahedral (Table 1.5), then it is possible to compare the number of known isomers with the number theoretically predicted for each of these structures. Such a comparison shows that for the second and third compounds in Table 1.5 planar and trigonal prism structures predict there should be three isomers. Instead, complexes of these types were... 

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