Preparation of coordination compounds

Complications apart, reactions in which the coordination number of an electron acceptor is increased are called addition reactions, and when it is unchanged they are called substitution reactions. The coordination number decreases for dissociation reactions. Reactions involving valence state changes are called oxidation or reduction reactions, as appropriate. 

An important classification of complexes depends on the speed with which 

Complexes involving low valence states, organometallic complexes for instance, are usually inert. However, inertness relates to kinetics and kinetics depend on mechanism. An organometallic compound which normally reacts slowly may spontaneously catch fire, or, less dramatically, rapidly oxidize, if exposed to air. Not surprisingly, special inert atmosphere techniques have to be used in preparing such compounds. Gaseous oxygen, of course, is a diradical, with two unpaired electrons, and so it is not unexpected that it should react rather differently to many other potential reactants. 

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Synthetic methods for the preparation of coordination compounds of heterocycles are considered in the majority of references given earlier and elsewhere (74MI1 82MI3 95MI8). 

This type of behavior is not limited to amine hydrochlorides, and amine hydrobromides and hydrothiocyanates undergo similar reactions. Some of the reactions of amine hydrochlorides and hydrothiocyanates are useful in the preparation of coordination compounds containing the amines. The important characteristic is that ammonia or a protonated amine is a conjugate acid of a weak base and is able, therefore, to react as an acid. 

To synthesize coordination compounds with weak ligands, methods have been developed whereby water is either absent from the start or is removed through a chemical reaction/ In this contribution the preparation of coordination compounds of some divalent metals with nitromethane, ethanol, acetone, diphenyl sulfoxide, and acetonitrile are described. These descriptions are merely examples of simple general methods for the preparation of coordination compounds of Mg, Mn, Fe, Co, Ni, Cu, Zn, and Cd with weak ligands, such as those mentioned above and acetic acid, nitrobenzene, hydrogen cyanide, tetrahydrofurane, dioxane, diglyme (l,l-oxybis[2-methoxyethane]), 1,4,7,10,13,16-hexa-oxacyclooctadecane (18-trown-6), ethyl acetate, and 2,4-pentanedione (acetylacetone in the neutral ketonic form). ... 

Different valence states are also a fairly widespread type of unit variability. By analogy with macromolecular complexes (Section II), it may be expected that homopolymerization and copolymerization of metal-containing monomers would prevent or retard redox processes involving participation of metal ions. Experimental data confirm the fact that a polymeric matrix stabilizes complexes of metals in low oxidation states (e.g., Pd" ). Moreover, the stability of the Cu+ state during polymerization (including thermal polymerization) of copper acrylate controls the use of this method for the preparation of coordination compounds of Cu". The polymeric framework plays a stabilizing role, whereas the metal ions that are localized on the surface layer are oxidized to Cu +. However, polymerization of monomers that contain metal ions in high oxidation states is often accompanied by their reduction Fe + ->Fe +, and Mo + ->Mo" (scheme 14). For example, polymerization of Cu " and Fe + acrylates may be accompanied by intramolecular chain termination. This may be attributed to the relatively low standard reduction potentials of these metal ions (7io(Cu + Cu+) = 0.15, o(Fe ->Fe ) = 0.77 V). 

Solvento-complexes are effective reagents for the preparation of coordination compounds. For example, the first syntheses of nickel(II) diaminates and triaminates were performed with water as the reaction medium. The reactions were complete within several hours and the resulting compounds contained water of crystallization in various amounts depending on the techniques used for drying the samples.6 7 a similar reaction6/7 has been performed with ethanol as the solvent, Eq. 4.1 ... 

The solution to many important problems in coordination chemistry begins with synthesis but the development of a synthetic method is not necessarily an end in itself. Coordination compoimds are employed in many areas of chemistry and other fields. Often problem solving begins with synthesis and the synthesis may be performed by those relatively unfamiliar with the discipline. The authors hope that this text, that deals with synthetic coordination chemistry, will be usefol to those engaged in the preparation of coordination compounds for which a variety of end uses are likely. 

Trialkyl- and triarylarsine sulfides have been prepared by several different methods. The reaction of sulfur with a tertiary arsine, with or without a solvent, gives the sulfides in almost quantitative yields. Another method involves the reaction of hydrogen sulfide with a tertiary arsine oxide, hydroxyhahde, or dihaloarsorane. X-ray diffraction studies of triphenylarsine sulfide [3937-40-4], C gH AsS, show the arsenic to be tetrahedral the arsenic—sulfur bond is a tme double bond (137). Triphenylarsine sulfide and trimethylarsine sulfide [38859-90-4], C H AsS, form a number of coordination compounds with salts of transition elements (138,139). Both trialkyl- and triarylarsine selenides have been reported. The trialkyl compounds have been prepared by refluxing trialkylarsines with selenium powder (140). The preparation of triphenylarsine selenide [65374-39-2], C gH AsSe, from dichlorotriphenylarsorane and hydrogen selenide has been reported (141), but other workers could not dupHcate this work (140). 

Solvates are perhaps less prevalent in compounds prepared from liquid ammonia solutions than are hydrates precipitated from aqueous systems, but large numbers of ammines are known, and their study formed the basis of Werner s theory of coordination compounds (1891-5). Frequently, however, solvolysis (ammonolysis) occurs (cf. hydrolysis). Examples are ... 

Werner spent the next 20 years obtaining experimental evidence to prove his theory. (At the University of Zurich, there remain several thousand samples of coordination compounds prepared by Werner and his students.) He was able to show, for... 

There is an extensive literature devoted to the preparation and structure determination of coordination compounds. Thermal analysis (Chap. 2, Sect. 4) has been widely and successfully applied in determinations [1113, 1114] of the stoichiometry and thermochemistry of the rate processes which contribute to the decompositions of these compounds. These stages may overlap and may be reversible, making non-isothermal kinetic data of dubious value (Chap. 3, Sect. 6). There is, however, a comparatively small number of detailed isothermal kinetic investigations, together with supporting microscopic and other studies, of the decomposition of coordination compounds which yields valuable mechanistic information. 

Cyclopropyl iodides like 70 and bromides are good substrates for the exchange reaction (equation 44)77,82,83 reaction is stereoselective and sufficiently fast at low temperatures, thus allowing the preparation of functionalized compounds. If a coordinating group like an ester is present in a. gem-dihalocyclopropane like 71, the cA-halogen substituent is exchanged selectively in ether (equation 45). ... 

The study of coordination compounds of the lanthanides dates in any practical sense from around 1950, the period when ion-exchange methods were successfully applied to the problem of the separation of the individual lanthanides,131-133 a problem which had existed since 1794 when J. Gadolin prepared mixed rare earths from gadolinite, a lanthanide iron beryllium silicate. Until 1950, separation of the pure lanthanides had depended on tedious and inefficient multiple crystallizations or precipitations, which effectively prevented research on the chemical properties of the individual elements through lack of availability. However, well before 1950, many principal features of lanthanide chemistry were clearly recognized, such as the predominant trivalent state with some examples of divalency and tetravalency, ready formation of hydrated ions and their oxy salts, formation of complex halides,134 and the line-like nature of lanthanide spectra.135... 

A recipe for the preparation of Prussian Blue was published 20 years after its discovery.10 " Since materials containing iron, potash and nitrogenous matter such as blood or animal hooves may have been heated together in more remote times, ferrocyanides [hexacyanoferrates(II)] probably antedate Diesbach s discovery. They contain Fe—CN bonds and may thus possibly be considered as the first known examples of coordination compounds containing transition metal—carbon bonds (organometallic compounds). 

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