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.