Crystal Growth

Growing and identifying suitable material for X-ray crystallographic analysis: A quick guide.

Good Crystals

The quality of the final result will depend upon the quality of the sample provided. Ideal samples are 0.5 × 0.5 × 0.5 mm cubes with smooth shiny faces, no cracks and no debris stuck on the surface – i.e. if it looks nice, it probably is nice.

Dimensions

Crystals should ideally be no larger than 0.7mm in any dimension. This is not usually a problem as a batch of crystals will contain many different sizes to choose from. Data can be collected from larger crystals, or we can attempt to cut the crystal to size if it is not too fragile. Within that upper bound, the larger the volume of the crystal, the better the data quality that can be obtained. For brick-shaped or needle shaped crystals, the minimum dimension should be greater than 0.1mm. Crystals may also grow as flat "plates" - in these cases suitable crystals will have a plate thickness of greater than 0.05mm. 

(a)Needles. (b)Dried out, split crytsals

The image above shows some fine, needle-like crystals which may be unsuitable for basic analysis if the shortest dimension is < 0.1mm.

Crystal growing tips

1. Do not let the mother liquor dry out completely. This can cause the crystals to become irretrievably stuck to the vessel walls, cause impurities to deposit on the crystals, or cause the crystals to become de-solvated (see 'dried-out' image above) and crumble to dust.
2. Grow the crystals in straight-sided sample tubes. It is very difficult to get crystals out of the following containerswithout a significant risk of the sample being crushed:
   1. round bottom flasks
   2. screw-top sample tubes
   3. nmr tubes
   4. Schlenks
3. Do not vacuum your product down to an amorphous powder; crystals grow slowly.
4. Do not crash the sample out as a microcrystalline powder.

(a) white powder; (b) blue powder