High-Pressure Polymorphs Nucleated and Stabilized by Rational Doping under Ambient Conditions.

High-pressure polymorphs can be obtained and stabilized at ambient pressure by utilizing dopants with more voluminous molecules, inducing internal strain in the structures. This effect has been confirmed for doped resorcinol and imidazole derivatives by nucleating and stabilizing their high-pressure phases under ambient conditions. The dopant molecular volume and concentration, as well as the bulk modulus of the polymorph in the binary system, are related to the stability region in the single-component phase diagram. High-pressure isothermal and isochoric recrystallizations yielded pure single crystals of resorcinol ε above 0.20 GPa and a new polymorph ζ above 0.70 GPa. These recrystallizations of pure resorcinol revealed within 1 GPa of the p-T phase diagram the boundaries and the stability regions of four resorcinol polymorphs α, β, ε, and ζ, contrary to the compression experiments on ambient-pressure polymorphs α and β, when the high-pressure phases were hidden behind the wide hysteresis extending to nearly 5 GPa. The hysteresis, originating from the H-bonding networks, hinders the formation of polymorphs ε and ζ when polymorphs α and β are compressed without melting or dissolving the crystals. Polymorph ζ is the only known resorcinol structure built of hydrogen-bonded layers.