Why did Nature not create some materials?

It is hard to tell whether or not Nature made all possible crystal types – perhaps they are present in small traces, too minute to be separated. But it is interesting that we can think of these compounds and predict their properties even before they are synthesized. This talk reminded me of a point I have struggled to understand for decades. There are some organic reactions that produce one compound at in a temperature range and its isomer at a different temperature range. I am wondering if it is possible to use these methods to model chemical reactions as well.