Expanding the Scope of Molecular Mixed Crystals Enabled by Three Component Solid Solutions

Crystalline solid solutions (mixed crystals) formed from molecular compounds are a long-known class of multicomponent solids whose composition can be varied, at least in principle, in continuum. Should such control occur in mixed crystals over a wide range of compositions, then it follows that some structural and physical properties would also be tuned in continuum. However, the potential utility of mixed crystals as molecular materials has been hindered by their limited accessibility across a broad range of compositions and difficulties associated with their preparation. We address these matters herein through the use of mechanochemistry and solution crystallization to study three-component mixed crystals. In addition to expanding the composition range of previously known mixed crystals, we demonstrate that anthracene (ant) and phenazine (pnz), which tend to crystallize as separate phases, form mixed crystals with a third molecule which is miscible in both, namely, acridine (acr). The three-component mixed crystal is only accessible mechanochemically as solution methods afford phase separation. If this observation is general, then it could have broad implications for this understudied class of molecular crystals.