Rep:Mod:awc106 module2 PROJECT

Mini Project: Ammonia-Borane

Ammonia borane NH₃BH₃ is a Lewis acid-base pair moleucle. NH₃BH₃ is also under scrutiny as a very promising molecule for the sotrage of hydrogen to be used as a new fuel. Ammonia-borane is 19.6% by weight hydrogen.

is ammonia borane staggered or eclipsed? what is the energy difference between these conformers? how does this energy difference compare to that of ethane? what can you say about the bonding in this compound relative to the organic analogue? what is the stability of ammonia-borane relative to the suggested reactants (NH4Cl and NaBH4), which form NH4BH4 and NaCl, then H2 is released. You should calculate E(reactants)-E(products) ammonia-borane is isoelectronic with ethane. But whereas ethane has an extremely low melting point, the former melts around 110°C. Can you find an explanation? (Hint: is there a way of modelling the solid state of this species? Are any of the techniques described in Module 3 relevant?) Reference:Borane leads the way to alternative fuels an article from Chemistry World (02 July 2008) Reference:Ammonia�borane: the hydrogen source par excellence? Dalton Trans., 2007,�2613 - 2626, DOI: 10.1039/b703053c

Ammonia Borane

Table 1: NH3BH3
	Staggered			Eclipsed
Results	Image	HOMO	Results	Image	HOMO
	Ammonia-Borane			Ammonia-Borane

Ammonia-borane is isoelectronic with ethane. It is thus beneficial to compare the two molecules.

Table 2: Ethane
	Staggered			Eclipsed
Results	Image	HOMO	Results	Image	HOMO
	Ammonia-Borane			Ammonia-Borane

What is the stability of NH₃BH₃ relative to the reactants? NH₃BH₃ is synthesised according to the following scheme:

Hydrogen (H₂) is the released resulting in NH₃BH₃. Therefore we must compare the relative energies of the reactants and products and calculate E(reactants)-E(products).

Table 3: Products and Reactants
NH4+	BH4-	NH4BH4
		File:Gerojj9nh7nimo2.jpg
File:Geroh7jd8nimo2999ij.jpg	File:Ger776jjsd7soh7nimo2.jpg	File:Gejc8rojj9nh7nimo2.jpg