Other Exchange Reactions

Rapid cis-trans isomerization was detected in bridging diiron carbene complexes of type [Cp2Fe2(CO)2(/tA-CO)(/Lt-C(SMe)SR)] while in the bis(tricar-bonyliron) complex (25) the fluxional process concerned Fe(CO)3 moiety rotation, with one of the exo moieties rotating approximately three times faster than the other moiety.  

There have been two reports of fluxional dinuclear cobalt complexes. The first concerns the complexes [Co2(CO)4(/it-R2PCH2PR2)2] (R = Me, Ph). These exist in solution as equilibrium mixtures of CO bridged and nonbridged isomers which can be distinguished by variable-temperature NMR. The AG values for the process were 41.5 (R = Me) and 47.0 (R = Ph) kJ mol in contrast to the very rapid fluxionality of [Co2(CO)g] for which AG is estimated to be ca 27 kJ mol from studies in a hexane matrix. The binuclear cobalt complexes are of type [ (i -Cp)Co 2(/it2- i -QHxSe)] (x = 6, 10, 12). The fluxional process 

Cis-trans isomerization also occurs in the dinuclear chlorine-bridged pal-ladium(II) complex [ Pd(CH2SiMe2C5H4N)Cl 2]. NMR bandshape analysis gave the activation parameters AG = 68.6kJmor AH = 63.6kJmor and AS = 7.0JK mor.  

A number of review articles have described the applications of multinuclear NMR methods for studying structures and internal rearrangements of metal clusters. The more specific cluster types covered were transition metal carbonyl clusters/ chiral clusters/ and mixed metal clusters containing carbyne or ketenylidene bridges.  

---

NOig) -f "NOa Caq) "NO(g) -f N03 (aq) Other exchange reactions that have been used are ... 

There are many other exchange reactions between two minerals, for example. 

Studies on other exchange reactions of the tetraalkyl anions are fairly limited and are summarized in Table V. Williams and Brown have provided the only quantitative data and have proposed mechanisms for both lithium and alkyl exchange (153). They have suggested that the lithium exchange between (LiR)4 and LiMR4 proceeds with the rate-determining step... 

Two other exchange reactions have been reported cyclopentadienyl-thallium and pentafluorophenylsilver react with a copper(I) halide to give cyclopentadienylcopper complexes (86) and pentafluorophenylcopper (203), respectively. 

Other exchange reactions have been reported between organocopper compounds and mercuric halides 40, 73, 209). 

Hydrolysis (the reverse of the preparative reaction) and other exchange reactions of the metal /3-diketonates have been studied in some detail in order to probe the mechanisms of inorganic substitution reactions. As mentioned in Section 4.1, there has been intense study of the intramolecular rearrangements of M(dike)3 complexes. Decomposition of metal /1-diketonate complexes to give high-purity metals or metal oxides is of technological importance. 

Irreversible destruction of the source molecules to initially form the free radicals, is a slow process compared with any other exchange reactions. Conversion from the source is matched at steady state by the downward mixing of the soluable reservoir term for wash out below the troposphere. 

Based on results of the H-autunite/uramphite exchange reaction (see footnote llll) as reported by Vesely et a . (1965). Other exchange reaction measurements by these authors lead to AG/(Na-autunite) = -1137.6 kcal/moI, and AC/(K-autunite) = -1149.4 kcal/mol, in good agre ent with the tabulated values. 

Besides hydrolysis, one can also utilize other exchange reactions in the preparation of disperse systems. It is, however, important to remember that a substantial amount of electrolyte, which is often present in the solution, may result in a loss of colloidal stability. One can sometimes remove excess electrolyte by washing and subsequent peptization of the precipitate. It is advantageous to prepare disperse systems at high supersaturations, which can be reached upon mixing concentrated solutions of reactants. The sols of Prussian Blue, various sulfides, stannic acid and its compound with colloidal gold (Cassian Purple) are all made by this method. 

Other exchange reactions occur for example, CO may be formed through the neutral exchange... 

If we would confine ourself that the total system consists of these two subsystems, then no other exchange reactions would be possible. In equilibrium, we would have the total energy, the total entropy, the total volume, and the total mol number to be constant, i.e.. 

The equations for any other exchange reaction, and indeed for any other mechanism, can be derived similarly. However, in most cases, the rate equations for isotope exchange are derived by the method of King and Altman and various extensions of the same also, the rate equations may be derived efficiently by the net rate constant method (Chapter 4). In most cases, the rate equations for isotope exchange are far too complicated to permit the determination of the usual kinetic constants. Nevertheless, ffiere are a number of simplifying assumptions which will permit the derivation of manageable rate equations in specific cases (Boyer, 1959 Fromm eta/., 1964 Darvey, 1973). 

---