Phase transition and proton ordering at 50?K in 3-(pyridin-4-yl)pentane-2,4-dione.

ABSTRACT: Single-crystal neutron diffraction experiments at 100 and 2.5?K have been performed to determine the structure of 3-(pyridin-4-yl)pentane-2,4-dione (HacacPy) with respect to its protonation pattern and to monitor a low-temperature phase transition. Solid HacacPy exists as the enol tautomer with a short intramolecular hydrogen bond. At 100?K, its donor···acceptor distance is 2.450?(8)?Å and the compound adopts space group 2/, with the N and -C atoms of the pyridyl ring and the central C of the acetyl­acetone substituent on the twofold crystallographic axis. As a consequence of the axial symmetry, the bridging hydrogen is disordered over two symmetrically equivalent positions, and the carbon–oxygen bond distances adopt intermediate values between single and double bonds. Upon cooling, a structural phase transition to the subgroup occurs; the resulting twins show an ordered acetyl­acetone moiety. The phase transition is fully reversible but associated with an appreciable hysteresis in the large single crystal under study: transition to the low-temperature phase requires several hours at 2.5?K and heating to 80?K is required to revert the transformation. No significant hysteresis is observed in a powder sample, in agreement with the second-order nature of the phase transition.

SUBMITTER: Truong K 

PROVIDER: S-EPMC5744419 | biostudies-literature | 2017 Dec

REPOSITORIES: biostudies-literature