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

Fatemeh Safari,Andrzej Katrusiak

doi:10.1021/acs.jpcc.1c07297

Fatemeh Safari, Andrzej Katrusiak

Open Access

https://doi.org/10.1021/acs.jpcc.1c07297

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Abstract

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.

Highlights

The wide variety of properties displayed by the same chemical compound in its different forms, such as polymorphs, glasses, size-scaledparticles, and epitaxial layers, has stimulated research aimed at obtaining new materials desired for innovative and challenging applications
The method of doping for obtaining new polymorphs is well-known;[21,22] it was not connected to and optimized for specific regions of phase diagrams. The mechanism behind this phenomenon has been explained and verified for several compounds, but this study was inspired by intriguing inconsistencies in the phase diagram of resorcinol[23] and by the recent discovery of polymorph ε obtained by mixing resorcinol with tartaric acid.[24]
Rational doping by molecules larger than the host compound molecules can generate an internal strain in the melt, which mimics external compression and leads to high-pressure polymorphs

Summary

■ INTRODUCTION

The wide variety of properties displayed by the same chemical compound in its different forms, such as polymorphs, glasses, size-scaled (nano)particles, and epitaxial layers, has stimulated research aimed at obtaining new materials desired for innovative and challenging applications. The crystallization process and transformations of the sample crystals and their compression and decompression were observed through a microscope In this way, we could repetitively obtain and identify any of the four polymorphs α, β, ε, and ζ of pure resorcinol in the pressure region up to 1.20 GPa (Table 1). The absence of the higher-pressure polymorph ζ in any of the doped samples shows that sufficiently high internal strain cannot be generated by increasing the dopant concentration alone It appears that when the dopant concentration exceeds some value (which may be different for different host and dopant compounds) the pressure does not increase linearly as a function of cd, as suggested by eq 2. More experimental information is required to better understand the doping and high-pressure polymorphism

■ CONCLUSIONS

■ ACKNOWLEDGMENTS

■ REFERENCES