Silicon, thermochemical effect

Within this approximation, the DSSE is seen to play a prominent role in the thermochemical stability of the doubly bonded isomers toward dissociation. Fortunately, we know a bit about the effects of substitution on DSSEs for silicon, and we can assume that they will be similar for germanium. 

In this sub-section it is not intended to cover the thermochemical aspects of all substituted silicenium ions described in the literature. Rather, we focus on some selected systems which deem to serve as good representatives and the discussion of which may provide an understanding of the substituent effects operative. Some aspects will also be described later in conjunction with ion/molecule reactions of silicon compounds. 

The application of classical and non-classical (photoacoustic) reaction-solution calorimetry to probe the energetics of metal-ligand bonds in organometallic systems is briefly analysed and illustrated by thermochemical results involving two families of compounds. The classical reaction-solution studies enabled the discussion of the systematics of metal-carbon bond enthalpies in several complexes M(t) -C H ) L. The photoacoustic studies addressed the effect of phenyl goups on the energetics of silicon-hydrogen bonds in phenyl-substituted silanes. 

The thermochemical correlations, the bond terms, and the unshielded core potential method all support a negligible effect of methyl groups on silicon-hydrogen bond dissociation enthalpies. This constancy is also in keeping with the hydridic nature of Si-H bonds in silanes (23). The effect of other substituents is, by comparison, poorly defined (19), although some results have recently become available. For example, it has been shown that silylation destabilizes Si-H bonds D(H SiSiH -H) = 361 8 kJ/mol (19),... 

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