Tetrahydroborates decomposition temperature

Fig. 6.22 Decomposition temperature for metal tetrahydroalanates and metal tetrahydroborates versus the Pauling electronegativity of the metal atom, which forms the cation. The horizontal line is at 300 K. A...

Another, quite versatile, route to hydropolyborates is based on the thermal decomposition of tetraorganylammonium tetrahydroborates, R4N[BH4]. Here, the products formed depend on temperature and time. For each hydropolyborate reaction conditions have to be optimized. 

The physical and chemical properties of the tetrahydroborates show more contrasts than the salts of nearly any other anion. The alkali metal salts are the most stable. In dry air, NaBH4 is stable at 300°C and in vacuo to 400°C with only partial decomposition. In contrast, several tetrahydroborates, including the titanium, thallium, gallium, copper, and silver salts, are unstable at or slightly above ambient temperatures. The chemical and physical properties of the tetrahydroborates are closely related to molecular structure. Sodium tetrahydroborate, which is typical of the alkali metal tetrahydroborates except for the lithium salt, has a face-centered cubic (fee) crystal lattice which is essentially ionic and contains the tetrahedral [BHJ- anion. The tetrahydroborates of the polyvalent metals are in many cases the most volatile derivatives of these metals known. Aluminum tris(tetrahydroborate)... 

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