Dipole-induced polymorphs of trans-2-hydroxycycloheptanecarboxylic acid with virtually the same unit cell

Alajos Kálman, László Fábián, Gyula Argay, Gábor Bernáth, Zsuzsanna Gyarmati

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The polymorphs of trans-2-hydroxycycloheptanecarboxylic acid have exactly the same lattice parameters and thus mimic isomorphism. They differ only in their space group: Pna21 versus Pn21a. In form II, the screw axes turn the 18-membered rings of hydrogen-bonded tetramers around the b axis. In this way, the stacking of the layers becomes antiparallel, which cancels out the dipoles within the unit cell. In form I, the same turn around the c axis leaves the stacking of the layers parallel. Thus, the dipoles are canceled out by antiparallel domains in the crystals. Between the antiparallel domains of I, each frontier is a double layer of II. This implies that (a) a pure form of I cannot be isolated and (b) the percentage of II in I may alter from crystal to crystal.

Original languageEnglish
Pages (from-to)34-35
Number of pages2
JournalJournal of the American Chemical Society
Issue number1
Publication statusPublished - Jan 8 2003


ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

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