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Updated: Aug 17, 2026

Line Shape Analysis of Dynamic NMR Spectra for Characterizing Coordination Sphere Rearrangements at a Chiral Rhenium Polyhydride Complex
Published on: July 27, 2022
Concomitant polymorphism and a temperature-dependent phase change in
Janet M S Skakle1, John N Low, James L Wardell
1Department of Chemistry, University of Aberdeen, Meston Walk, Old Aberdeen AB24 3UE, Scotland.
Abstract:
The title compound, C(18)H(17)NO(4), crystallizes from ethanol at ambient temperature as two concomitant polymorphs (I) and (II), both monoclinic P2(1)/c with Z' = 1. The less abundant form (I) undergoes a reversible phase-transition at ca 173 K to a third monoclinic polymorph (III), P2(1)/n, with Z' = 2, while the more abundant polymorph (II) is unchanged down to 120 K. In each polymorph of (I)-(III) the molecules are linked by pairs of O-H...O hydrogen bonds into cyclic dimers which are crystallographically centrosymmetric in (I) and (II), and approximately, but not crystallographically, centrosymmetric in (III). There are no direction-specific interactions between the hydrogen-bonded dimers in polymorph (I); in polymorph (II) the dimers are linked into sheets by C-H...N and C-H...pi(arene) hydrogen bonds; in polymorph (III) the dimers are linked into chains by a C-H...pi(arene) hydrogen bond. The interconversion of polymorphs (I) and (III) is a simple displacive phase transition.
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