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<p>The structural behavior and crystallization of <i>n</i>-butanol under low-temperature and high-pressure conditions have been systematically investigated by single-crystal X-ray diffraction. At ambient pressure and low temperature, <i>n</i>-butanol crystallizes in triclinic space group <i>P</i>1, denoted as phase α, with two crystallographically independent molecules per asymmetric unit (<i>Z</i>’ = 2). The structure of phase α is characterized by alternating polar and hydrophobic layers, stabilized by distinctive zig-zag hydrogen-bonded chains along [100], closely approximating twofold screw axis (2<sub>1</sub>) symmetry. Under high-pressure, a new centrosymmetric phase β (space group <i>P</i>2<sub>1</sub>/<i>n</i>, <i>Z</i>’ = 3) emerges. Phase β have similar aggregation motif stabilized by hydrogen-bonded zig-zag chains as one observed in phase α, but with oppositely oriented intermolecular vectors: (i) one chain relate the molecules by the 2<sub>1</sub> screw axis; and (ii) the other by glide-plane symmetry. Intriguingly, the recurrence of closely related structural motifs in both phases strongly suggests a common crystallization mechanism rooted in the formation of similar pre-associated molecular aggregates. These findings illuminate the sophisticated interplay between thermodynamic parameters and structure, advancing the understanding of linear monoalcohols aggregation.</p>

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A new high-pressure phase of n-butanol and its structural relationship with the low-temperature structure

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  • 发表日期：

    2025年11月14日

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  • Szymon Sobczak

摘要

The structural behavior and crystallization of n-butanol under low-temperature and high-pressure conditions have been systematically investigated by single-crystal X-ray diffraction. At ambient pressure and low temperature, n-butanol crystallizes in triclinic space group P1, denoted as phase α, with two crystallographically independent molecules per asymmetric unit (Z’ = 2). The structure of phase α is characterized by alternating polar and hydrophobic layers, stabilized by distinctive zig-zag hydrogen-bonded chains along [100], closely approximating twofold screw axis (21) symmetry. Under high-pressure, a new centrosymmetric phase β (space group P21/n, Z’ = 3) emerges. Phase β have similar aggregation motif stabilized by hydrogen-bonded zig-zag chains as one observed in phase α, but with oppositely oriented intermolecular vectors: (i) one chain relate the molecules by the 21 screw axis; and (ii) the other by glide-plane symmetry. Intriguingly, the recurrence of closely related structural motifs in both phases strongly suggests a common crystallization mechanism rooted in the formation of similar pre-associated molecular aggregates. These findings illuminate the sophisticated interplay between thermodynamic parameters and structure, advancing the understanding of linear monoalcohols aggregation.