Substitution reactions in the absence of solvents

The direct reaction between an anhydrous salt and a liquid ligand can be used to prepare metal complexes. In many cases, the liquid ligand present in very large excess also serves as a solvent for the reaction mixture. One method, which can be used to synthesize metal ammines, involves the addition of a metal salt to liquid ammonia followed by evaporation to dryness. Evaporation occurs readily at room temperature, because ammonia boils at -33°C. The dry residue obtained is essentially the pure metal ammine. For example, [Ni(NH3)6]Cl2 can be prepared in this way by reaction (11). 

this is not the method of choice, because aqueous ammonia is more convenient to use and generally gives the same result. However, in some cases. 

One method used for the preparation of [Pt(en)2]Cl2 or [Pt(en)3]Cl4 is the direct reaction between ethylenediamine and PtCU or PtCLt, respectively. The technique is to add slowly the solid platinum salts to the liquid ethylenediamine. This addition is accompanied by a vigorous evolution of heat, which is to be expected whenever a strong acid is added to a strong base. Recall (Section 2.1) that in terms of the Lewis definition of acids and bases, the formation of coordination compounds involves an acid-base reaction. In this particular case, the platinum ions are the acids and ethylenediamine is the base. Metal dimethylsulfoxide complexes have been prepared and characterized. One method used to prepare some of these complexes is a direct reaction (12) in the absence of any added solvent. 

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