New Polymorphs of ROY and New Record for Coexisting Polymorphs of Solved Structures

With six polymorphs coexisting at room temperature, 5-methyl-2-[(2-nitrophenyl)amino]-3-thiophenecarbonitrile (ROY) is the top system in the current Cambridge Structural Database (Feb. 2005)
for the number of polymorphs of solved crystal structures. Here we report two new ROY polymorphs, Y04
and YT04, and the crystal structure of YT04. Y04 is a metastable polymorph that tends to crystallize first
from a melt at room temperature, and YT04 is a product of solid-state transformation of Y04. Despite its
late discovery, YT04 is the densest among the polymorphs at 25 °C and likely the second most stable at
0 K. The conformation of ROY in YT04 is similar to those in the other two yellow polymorphs (Y and YN)
but significantly different from those in the orange and red colored polymorphs (ON, OP, ORP, and R).
Having escaped years of solution crystallization in several laboratories, Y04 and YT04 exemplify polymorphs
that are likely missed by solvent-based screening and discovered through alternative routes.