Retention of crystallinity in bis(guaninium) sulfate hydrate upon partial and full dehydration

• Guaninium sulfate hydrate is a hydrogen-bonded solid with water contained within channels.
• The solid may be partially dehydrated with minimal change in structure and preservation of the channel system.
• Complete removal of water is not accompanied by total loss of crystallinity.
• Careful heating yields “(GH)2SO4” which contains open channels not occupied by water.

Crystals of bis(guaninium) sulfate hydrate ((GH)2SO4. 2.5H2O) have been isolated via slow solvent evaporation. This compound adopts the triclinic space group P1¯ with unit cell parameters a = 9.6300(19) Å, b = 9.8613(19) Å, c = 10.5872(19) Å, α = 78.627(15)°, β = 71.518(15)°, γ = 63.260(14)° and unit cell volume 849.8(3) Å3 at 150 K. The crystal structure displays intricate hydrogen bonding interactions between the guaninium cations, the sulfate anions and water. Guaninium cations are held together in approximately planar ribbons by hydrogen bonds. These ribbons are stacked parallel to the [230] direction and held together by hydrogen bonding to sulfate and water. Channels are formed between the hydrogen-bonded cations and the anions that are filled with water molecules. Remarkably, partial and complete removal of water from this structure is possible without wholescale loss of crystallinity. Partial removal of water to yield (GH)2 SO4. 1.5H2O happens with very limited change to the structure. It is possible to remove all of the water to yield the apohost, G(GH)3(SO4H)SO4 which retains many structural features of the hydrate but contains a different hydrogen bonding chain. The three structures and the relationship between them are described.

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