In an unfortunate series of coincidences, my last post appears to have been prophetic, regarding my partner’s cold, which I mentioned in passing. Where the prophecy lied was the nature of the disease — it turned out to be a monster flu that absolutely wiped me out for two weeks. At best, even standing was too much effort for me for the past couple of weeks. But finally, the illness is over and I can return to business as usual. That business, of course, is crystals.
As you may have read in the guest post I wrote for #RealTimeCheminFocus, I recently had a breakthrough in my project — in the sense that I finally found a way to synthesise the material I had been aiming for all year. I have since been experimenting with a number of synthetic variables to see how many different variations of this material I can make, and how its structure and properties can vary. The material is a coordination polymer, which is an “infinitely” repeating assembly of metal ions and organic ligands. My ultimate aim is to take these compounds through postsynthetic modification — simply, chemical reactions of the coordination polymer to give different properties. In order to do this, I have been working on characterising my compounds so that I can tell how they change once I put them through these experiments.
Today, I was preparing samples to send to an analytical laboratory for elemental analysis. Elemental analysis involves breaking down a compound to its elemental components in order to give a percentage composition of the compound, most often in terms of carbon, hydrogen and nitrogen. Other elements can also be analysed for, but often require more sample, and are more expensive than a “basic” CHN analysis. In most cases, especially if other forms of characterisation are possible, analysis for anything other than these three elements is unnecessary. If a compound contains an impurity that does not contain carbon, hydrogen or nitrogen, it can still be seen in the elemental analysis by proxy, since the impurity will affect the overall percentage composition. Elemental analysis is excellent for determining the exact amount of counter-ions and solvent in coordination polymers, where these variables can be unclear.
For elemental analysis results to be usable, it is critical that the samples I send are as pure and clean as possible. Crystalline samples are preferred, since the composition of a crystal is uniform. Coordination polymers are almost always formed through crystallisation from a reaction mixture, so all that remains is to collect the crystals, wash them of possible soluble impurities and then dry them. In my group, there is also a practice of checking the quality of the sample under a microscope prior to packaging it for elemental analysis. Painstakingly sifting through piles and piles of cubic crystals using a small needle, I found a surprising number of fibres of confusing origin, pieces of glass and other assorted debris. Of course, there is no way to tell by eye whether the sample is truly pure or not, which is why we need this analysis in the first place, but removal of this visible debris can only help make the analysis results more helpful for accurate composition determination.
Besides, looking at the piles of shiny, beautiful crystals that I strived so hard for so long to make fills me with great joy. Just being able to pack up enough material for analysis is a great victory in my book. Let’s just hope that victory doesn’t turn into defeat in confusion once I receive the results.
I am available for correspondence through the comments, and via e-mail at email@example.com. You can also find me tweeting away as @Lady_Beaker.