Crystallization of sensitive compounds for X-ray diffraction

Sensitive compounds like Boranes, Phosphines, copper, ..are very instable when they come into contact with atmosphere because of water as for borane which immediately able to coordinates one molecule of water, phosphine form oxide, transition metal oxidize.

So, these compounds are manipulate under an inert atmosphere:

1) Under Argon, nitrogen, …..

2) In Shlenk lines to make cycle of vacuum and put argon in the flask

3) Glovebox which is always placed under argon

But, with non-sensitive compounds, the way to obtain good crystal suitable to obtain the X-ray structure is sometimes difficult , so for sensitive compounds , it’s more difficult and there are no many ways.

Some methods to obtain crystal for X-ray are known but not available for all compounds.

One of them is the diffusion :

it consists to put the solid compound into the minimal volume of solvent which permits its solubility, then add a solvent where the compound is no soluble.

For example one diffusion tube can be represented by:

Untitled ACS Document 1996-3

  Scheme 1: Diffusion tube

This tube can be placed into a frizer for several weeks , placed up.

This is one method but …..not easy to obtain good crystals.

An other way of diffusion is the vapor diffusion.

It consists to placed the compound dissolved in a good solvent in a flask then put this flask in a bigger flask which contains an other solvent where the product is no soluble or bad soluble.

vapor_diffusion

            scheme 2: Vapor diffusion tube

This is based on the same principle that the fist one, but as I haven’t still try I can’t estimate the quality of it.

So, if you have read this article, and if you know good ways to obtain crystal suitable for X-Ray with very sensitive compounds let me know…

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