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Urea nitrate

Dear Reader,

It has come to my attention that a man and his wife have recently been in court accused of the heinous crime of preparing a terrorist bombing. The explosive in this case is urea nitrate which is formed by the protonation of urea by nitric acid. As I have not heard of this substance before I looked its crystal strucutre. Yu.V.Nelyubina, K.A.Lyssenko, D.G.Golovanov and M.Yu.Antipin published a study of this compound which was published in CrystEngComm 2007, volume 9, page 991. The unit cell looks like this, you might think it does not look very interesting.

Unit cell of urea nitrate

Unit cell of urea nitrate

To get a true idea of what the solid looks like you need to grow this fragment and then trim off some atoms, then you will be able to see the hydrogen bonded layers.

Hydrogen bonded layer in urea nitrate

Hydrogen bonded layer in urea nitrate

When you look at the a different urea salt where the anion is hexafluorosilicate, you can see a different type of layer in the solid. Here the number of possible hydrogen bonds are smaller as there is a much lower charge to radius ratio of the anion. The anion is less coordinating. The layers here again like a chess board. Here is a picture of part of a layer.

Ball and stick version of urea hexafluorosilicate

Ball and stick version of urea hexafluorosilicate

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Spacefilling version of urea hexafluorosilicate

The basic unit in this solid is a protonated urea which is hydrogen bonding to the hexafluorosilicate anion. Here it is in all its glory.

Hydrogen bonding between the protonated urea and the hexafluorosilicate

Hydrogen bonding between the protonated urea and the hexafluorosilicate

 

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