High-pressure Nucleation of Low-Density Polymorphs*

Abstract

New polymorphs β and γ of bis-3-nitrophenyl disulphide, crystallized above 0.3 GPa, are less dense than the ambient-pressure polymorph α. This counterintuitive density relation results from the high-entropy nucleation and subsequent kinetic crystallization. The work performed by pressure compensates the high entropy and temperature product, substantiated in varied conformers and increased chemical potential. Pressure-increased viscosity promotes the kinetic polymorphs, in accordance with empirical Ostwald's rule of stages. It contrasts to mechanochemical techniques, favouring high-density polymorphs.

Keywords: crystal growth; high-pressure chemistry; kinetic crystallization; nucleation; polymorphism.

Figure 1

Conformers in (3‐NO₂‐PhS)₂ (a) polymorph α with torsion angles τ, τ₂ and τ₃ indicated; (b) all molecules of polymorphs α, β, and γ superimposed on the C1‐S1‐S1’ fragment; (c) these rotational enantiomers adjusted to torsion angle τ positive in order to visualise the presence of low‐ E_p and high‐E_p conformers. The plot shows the E_p differences and bars indicate their average values.

Figure 2

Structure of (3‐NO₂‐PhS)₂ polymorphs (a) α; (b) β; and (c) γ. Capital letters A, B, C and D label independent conformers in polymorphs γ and β.