Hydrides bond enthalpies, 394

Metal-Hydrogen Bond Enthalpy Contributions. Metal Carbonyl Hydrides... 

Hydride formulae and names Normal boiling point (° C) E-H bond enthalpy (kJ mol-1) (kJmoT 1 at 298 K)... 

Worked example 13.3 Bond enthalpies and group 14 hydrides... 

There is a lively controversy concerning the interpretation of these and other properties, and cogent arguments have been advanced both for the presence of hydride ions H" and for the presence of protons H+ in the d-block and f-block hydride phases.These difficulties emphasize again the problems attending any classification based on presumed bond type, and a phenomenological approach which describes the observed properties is a sounder initial basis for discussion. Thus the predominantly ionic nature of a phase cannot safely be inferred either from crystal structure or from calculated lattice energies since many metallic alloys adopt the NaCl-type or CsCl-type structures (e.g. LaBi, )S-brass) and enthalpy calculations are notoriously insensitive to bond type. 

Tributyltin hydride is a well known reducing agent46, in keeping with the low value of Sn—H bond dissociation enthalpy. This weakness of Sn—H bond has been used by Rathke... 

The 72 kJ mol-1 discrepancy observed for Z)//°[(CO)3Cr-C6H6] alerts us to two important issues (1) Stepwise bond dissociation enthalpies are often very different from their mean (2) bond dissociation enthalpy values may not be transferable from one molecule to another. In other words, how can we assess the assumption that 3(Z)//°)(Cr-CO) in Cr(CO)6 is similar to Z)//j°(Cr-CO) + Z)// (Cr-CO) + DH (Cr-CO) in Cr(CO)3(C6H6) This question will be discussed in section 5.3. With regard to the former issue, the data in figure 5.4 provide further illustration for some first-row hydrides. The values shown in the plot are results from ab initio calculations for the species involved, in excellent agreement with the most accurate experimental data [78]. 

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