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Difficulties crystallizing tryptamine salts and relationship with ionic liquids

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downwardsfromzero

Boundary condition
As many of you may know, not all salts of tryptamines crystallize easily. In the case of many of them, this is of course due to their hygroscopic properties. Nonetheless, in the course of my meanderings I encountered the wikipedia information about ionic liquids, particularly Ethylammonium nitrate.

This set me thinking. As many of the ionic liquids are based on a nitrogen cation, perhaps some of the 'more difficult' tryptamine salts also have similar low melting point tendencies? What would the melting points of tetrafluoroborates and hexafluorophosphates of simple alkylated tryptamines be?

Just a little thought to put out there, maybe it's total cobblers (and I wouldn't play with the corresponding acids in my kitchen :sick: :?: :!: )
 
I think the low melting points of the salts may have something to do with it, its indicative of relatively 'weak' ionic bonds, as far as ionic bonds go.

So perhaps some of these salts just don't crystallize at room-temperature. My understanding of crystallography is limited, but as far as I know the structure of the salt crystals depends on how the ions pack in the structure, the better the packing, the closer the ions are, and the stronger the bonds. Sodium chloride for instance has beautiful cubic crystals, situates itself in the lattice to have 6 chlorine ions surrounding the sodium ion, giving it the cubic structure. These ionic bonds are extremely strong, it melts at 800C.

So tryptamine salts don't pack as well as NaCl,

So perhaps another reason is that some tryptamine salts pack better than others. Comparing nice solid fumarates with gooey citrates, perhaps the difference is fumarate salts are more 'planar' and perhaps they stack in the lattice. The backbone of fumaric acid is planar sp2 carbon, where the backbone of citric acid is tetrahedral.

Thats my guess anyway, an inorganic chemist could probably tell you more
 
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