Werner complex

In classical Werner complexes, such as [Co(NH3)6], a relatively high valent metal ion binds to the lone pairs of electronegative donor atoms, typically, O, N, or halide. The M-L bond has a marked polar covalent character, as in L M-NH3, where L represents the other ligands present. The M-NH3 bond consists of the two electrons present in lone pair of free NH3, but now donated to the metal to form the complex. 

The assembly of metal and ligands that we call a complex may have a net ionic charge, in which case it is a complex ion (e.g., [PtCU] ). Together with the counterions, we have a complex salt (e.g., K2[PtCl4]). In some cases, both cation and anion may be complex, as in the picturesquely named Magnus green salt [Pt(NH3)4][PtCl4], where the square brackets enclose the individual ions. 

Ligands with more than one donor atom, such as ethylenediamine (NH2CH2CH2NH2, or en ), can donate both lone pairs to form a chelate ring (1.3). The most favorable ring size is five, but six is often seen. Chelating ligands are much less easily displaced from a complex than are comparable monodentate ligands for the reason illustrated in Eq. 1.1  

When the reactants release six NH3 molecules in Eq. 1.1, the total number of particles increases from four to seven. This creates entropy and so favors the chelate. Each chelate ring usually leads to an additional factor of about 10 in the equilibrium constant for the reaction. Equilibrium constants for complex formation are usually called/orma-tion constants, the higher the value, the more stable the complex. 

Chelate ligands can also be polydentate, as in tridentate 1.4 and hexadentate 1.5. As a tridentate ligand, 1.4 is termed a pincer ligand, a type attracting much recent attention. Ethylenediaminetetracetic acid, (EDTA, 1.5) can take up all six sites of an octahedron and thus completely wrap up many different metal ions. As a common food preservative, EDTA binds free metal ions so that they can no longer catalyze aerial oxidation of the foodstuff. Reactivity in metal complexes usually requires the availability of open sites or at least labile sites at the metal. 

---

Werner complexes can be used to form clathrates with the Cg aromatic isomers (35—42). The aromatic compounds are released upon heating. Since the uptake and release characteristics of the four Cg aromatic isomers are each different, this method has been suggested as a means of separating the isomers. 

Bentone-34 has commonly been used in packed columns (138—139). The retention indices of many benzene homologues on squalane have been determined (140). Gas chromatography of C —aromatic compounds using a Ucon B550X-coated capillary column is discussed in Reference 141. A variety of other separation media have also been used, including phthaUc acids (142), Hquid crystals (143), and Werner complexes (144). Gel permeation chromatography of alkylbenzenes and the separation of the Cg aromatics treated with zeofltes ate described in References 145—148. 

Werner complex See coordination compound. ver-nor, kam,picks ) wet aahing org chem The conversion of an organic compound into ash (decomposition) by treating the compound with nitric or sulfuric acid. wet ash-ii) wettability chem The ability of any solid surface to be wetted when in contact with a liquid that is, the surface tension of the liquid is reduced so that the liquid spreads over the surface.. wed-a bil-od-e ... 

An interesting reaction, the Baudisch reaction, involves the formation of nitrosophenols by the action of hydroxylamine hydrochloride and hydrogen peroxide, in the presence of metallic ions or certain Werner complexes, on aromatic compounds. The products are primarily o-nitrosophenol complexes of the metallic ion. Unfortunately, this reaction requires further development before it can be considered a reliable preparative procedure. 

Lipkowski, J., Pawlowska, M., Sybilska, D., Experimental-study of selectivity and column efficiency in clathrate chromatography using Werner complexes as clathrate host components. 1. Relationship between selectivity of Ni(Ncs)2(4-methylpyridine)4. Guest clathrate sorbents and composition of the mobile phase. J Chromatogr. 1979,176,43-53. 

DPCC are obtained on the basis of metal-containing ligands, which can be classical Werner complexes (Scheme 1.11), salicylaldiminates [140], and other inner-complex compounds, as well as numerous organometallic compounds [112,113,159] ... 

To conclude this section, we note that the reactions of anions, which are not part of a coordination sphere, were known long ago [11], The preparative methods of classic Werner complexes, for instance (3.152) and (3.153), have been developed on their basis ... 

Keywords TDDFT Excitation energies Excited states Transition metal complexes Electronic spectra Metallotetrapyrroles Metallocarbonyls a-diimine complexes Porphyrins Porphyrazines Phthalocyanines Werner complexes Sandwich complexes... 

In Sects. 3-6, various types of TM complexes will be discussed. We start in Sect. 3 with elementary organometallic complexes - the metallocarbonyls and some cyclopentadienyl complexes. In Sect. 4 classical Werner complexes are dealt with. A separate section (Sect. 5) is devoted to the important class of technologically important and widely studied polypyridyl complexes. Section 6 deals with metallotetrapyrroles such as porphyrins and phthalocya-nines. Section 7 contains concluding remarks. 

Several types of Werner complexes have been investigated over the last few years by TDDFT methods. They include metal oxide, metal halide, metal oxyhalide compounds, and transition metal complexes with bidentate ligands such as ethylenediamine and acetylacetonato. 

To end this section, it is worthwhile mentioning the recent TDDFT study by Autschbach et al [107] on the electronic and circular dichroism (CD) spectra of several chiral Werner complexes, since it represents the first application of TDDFT to the computation of the circular dichroism (CD) spectra of transition metal complexes. The absorption and CD spectra of the... 

Transition metal complexes are cationic, neutral or anionic species in which a transition metal is coordinated by ligands. A classical or Werner complex is one formed by 2 metal in a positive oxidation state with donor ligands such as H20, NH3, or halide ions. 

H. Werner, Complexes of Carbon Monoxide and its Relatives An Organometallic Family Celebrates Its Birthday, Angew. Chem. Int. Ed. Engl. 29, 1077-1089 (1990). 

Perhaps the best way to proceed is to simply list the principal properties of a typical Werner complex that needed to be explained (a) salts that contained labile and non-labile anions and solvent (b) coordination numbers and geometries not four and not... 

For practical purposes the field of metal-metal bonds and metal atom clusters can be divided into two broad areas. (1) Those compounds with the metal atoms in formal oxidation states of zero or close to it, including negative ones. For the most part these are polynuclear metal carbonyls, or very similar compounds. In these compounds the M-M bonds are usually long, weak and of order one. (2) Compounds with the metal atoms in low to medium positive oxidation states, and ligands of the same kinds normally found in classical Werner complexes, e.g., halide, sulfate, phosphate, carboxylate or thiocyanate ions, water, amines and phosphines. Compounds of this type include metal-metal bonds of orders ranging from about 1/2 to 4.0. 

Those in which the metal atoms are in somewhat higher oxidation states (+2 to +4) and the ligands are typically halide, sulfide, or oxide ions and some others of the same ilk as those in mononuclear Werner complexes. Clusters of this type are most common among the early transition elements, groups 5-7. 

---