Chapter 4. Energy and thermodynamic properties of boron and aluminium hydrides. 4.1. Energy and thermodynamic properties of boron and aluminium hydrides of groups IA and IIA

The physicochemical properties of borohydrides and aluminium hydrides of alkali and alkaline-earth metals prove the ionic nature of the bonding in these compounds. The energy balance of the formation of borohydrides and aluminium hydrides of Group IA and IIA elements can be expressed by the Born-Haber cycle. The lattice energy of complex hydride compounds is determined indirectly by the Born-Haber thermochemical cycle on the basis of experimental thermodynamic data. Using the known values of the enthalpy of formation of the gaseous borohydride ion ∆_f H°(_298,BH4-)= -96.2±20 kJ/mol^-1 and its crystal radius, as well as new values of the enthalpy of formation of borohydrides, the lattice energy of borohydrides of elements of groups IA and IIA has been determined. The calculations were carried out using the thermochemical cycle and the Kapustinsky equation.