For SciFinder-n, start at the chemical substance record:
You can also search by research topic, either by compound or group of compounds: crystal structure of carbonitrides
If you haven't used SciFinder or SciFinder-n before at UC San Diego, you'll need to create an account first
For Reaxys, check the Physical Data list in the substance record for your substance for crystal phase, crystal property system, crystal system, and Space Group for information and associated literature references.
You can also use the Query Builder to search on these properties.