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X-ray Diffraction Facility

The X-ray diffraction facility is part of the Department of Chemistry at the University of Arizona.  It is a shared multi-user instrumentation facility capable of carrying out experimental work on single-crystal and powder samples of chemical compounds for the purpose of determining molecular structure in the solid-state.

The molecular structure of an air-sensitive discrete magnesium/6-methyl-2-pyridone complex containing an unusual Mg-O cubane core.  G. S. Nichol and W. Clegg, Inorg. Chim. Acta., 2006 

The Bruker SMART 1000

We currently have two instruments.  For single-crystal work we have a Bruker SMART 1000 CCD detector, and for powder diffraction and thin-film studies we have a Philips X'Pert MPD diffractometer.  Single-crystal work is routinely carried out at low temperature using an Oxford Cryosystems Cryostream low temperature device.  Air, temperature and light-sensitive structures can be routinely handled.

The Philips X'Pert MPD

We offer both full structure and data collection-only services.  In addition, trained users may carry out their own crystal mounting, data collection and subsequent structural analysis; hands-on use of the facility is strongly encouraged.  Although housed within, and primarily serving. the Department of Chemistry we are open to users from throughout the university.

Growing Good Crystals

Garbage in = Garbage out

In other words, merely trying something which 'looks' crystalline may not result in a structure.  For X-ray crystallography we require 'good quality' crystals and hence:

Good crystals = good diffraction = good data = good result.

So what is a good crystal?  For X-ray diffraction, size really does matter; think somewhere between a grain of salt and a grain of sugar.  The bigger the crystals are, the better the diffraction.  Usually during a synthesis "recrystallisation" means a method of obtaining your product in a pure form and crystal size is unimportant.  It may take just a few seconds on the rotavap, or perhaps overnight in the fridge, to obtain your pure product. 

However for crystallography, "recrystallisation" has a different meaning.  We wish to grow large crystals, large enough that your sample looks like a collection of crystals, and not like a powder.  Growing crystals for a crystal structure usually takes time (occasionally several months!) and requires a bit of patience.  You may spend many weeks developing a synthesis towards your target molecule, so why would you want to rush the preparation of your crystals for analysis?

The best way to grow large crystals is usually to leave your sample somewhere cool and out of the way (and then go to Mexico for a fortnight).  At the back of the fridge in an nmr tube is ideal; here the crystals are unlikely to be disturbed and the smooth surface of the inside of the tube contains few nucleation sites so it is more likely that two or three large crystals will grow as opposed to tens or hundreds of tiny ones.  Deuterated solvents also tend to be conducive to the growth of good crystals.  The little coloured cap used to seal the nmr tube actually allows a very slow evaporation of solvent, encouraging crystal growth.

If you're not up to foreign holidays, or you only have one nmr tube in your whole group, then there are some other methods of crystal growth.

Making structure pictures

Having obtained your structure you will probably want to talk about it somewhere to someone, for which a picture comes in very handy. There are several options for creating structural diagrams, depending on the target audience.

For a paper: you should check the journal's rules since they may specify requirements for colour, size and lettering.  Most accept colour and you should ALWAYS give a colour picture if they will accept it.  Colour pictures look much nicer!

For a poster:  you will want something colourful and visually stunning

For a talk: as for a poster, but now you can create animations and rotating models too.

Packing diagrams are very useful, especially if your compound contains a lot of intermolecular interactions, but they are most effective when used in papers (when increased in size for a poster or talk they look too complicated).

Software thoughts and advice

Picture creation thoughts and advice

Sample submission

  1. Download the correct form from below

  2. Fill in the boxes and email it back to

  3. Either bring your crystals to CSML332 or indicate on the form that you will keep them until they are needed

    And it's as easy as that...


University of Arizona users:

Single crystal submission form (MS Word document)

Powder diffraction submission form (MS Word document)

External users:

Single crystal submission form (MS Word document)

Powder diffraction submission form (MS Word document)

Contact us

Dr Gary S Nichol
Department of Chemistry
The University of Arizona
1306 E University Boulevard
PO Box 210041 Tucson, AZ 85721
telephone: 520-621-4168
fax: 520-621-8407

We are located in the Chemical Sciences Building, which is the new glass-fronted building (highlighted in red) found between Old Chemistry and the CS Marvel building.  Come in the entrance on the west side (your right as you look at the glass front), make a sharp left and CSB132 is where you'll find us.