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 lowtemperature phase transition. Solid HacacPy exists as the enol tautomer with a short intramolecular hydrogen bond. At 100 K, its donorÁÁÁacceptor distance is 2.450 (8) Å and the compound adopts space group C2/c, with the N and para-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 t 2 subgroup P " 1 1 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 lowtemperature 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.

Proton disorder in a short intramolecular hydrogen bond investigated by single-crystal neutron diffraction at 2.5 and 170 K

“…The region of the intramolecular O1Á Á ÁO2 hydrogen bond, with an acceptor-donor distance of 2.438 (4) Å , is not involved in any significant intermolecular contact. The bridging proton associated with the alternative sites H2O and H1O remains disordered even at the low data collection temperature of 2.5 K (Table 2), but the neutron diffraction experiment allows the refinement of realistic O-H distances (Scheme 2); they may be compared to those encountered in related intramolecular OÁ Á ÁO hydrogen-bonded systems with similar donor-acceptor distances, such as HacacPy (see Scheme 1), with OÁ Á ÁO = 2.432 (8) and O-H = 1.028 (12) Å (Truong et al, 2017c), and 3,4-diacetylhexa-2,4-diene-2,5-diol, with OÁ Á ÁO = 2.434 (1) and O-H = 1.081 (2) Å (Piccoli et al, 2008). A compilation of neutron diffraction experiments covering 75 inter-and 37 intramolecular OÁ Á ÁO hydrogen bonds, with donor-acceptor distances shorter than 2.6 Å , has been communicated in the supporting information of a previous publication (Ş erb et al, 2011).…”

“…In contrast, the O-HÁ Á ÁO geometry in 9-hydroxy-5-methylphenalenon (Kiyanagi et al, 2005) does change with temperature; in one of the two independent molecules, proton ordering and the formation of a superstructure are observed upon cooling. We had observed proton ordering as the consequence of a structural phase transition in HacacPy (Truong et al, 2017c).…”

“…The uncoordinated molecules HacacCN (Silvernail et al, 2001) and HacacPy (Truong et al, 2017c) share a common structural feature: in the solid, their pentane-2,4-dione part exists as the enol tautomer. HacacPy undergoes a phase transition associated with proton ordering at 50 K (Truong et al, 2017c). In this contribution, we report the structure of uncoordinated (1), with an emphasis on the intramolecular hydrogen-bond geometry.…”

Combined X-ray and neutron single-crystal diffraction in diamond anvil cells

“…It provides precise information on crystal and magnetic structures, including the reliable and accurate characterization of anisotropic displacement parameters in materials with highly absorbing elements. Typical investigations at HEiDi focus on (i) ionic conductors relevant for energy applications and data storage (Ceretti et al, 2018), (ii) superconductors (Jin et al, 2016), (iii) multiferroic materials (Regnat et al, 2018), (iv) small-molecule structures, in which hydrogen bridges play a key role as a structure building element (Truong et al, 2017(Truong et al, , 2018, or (v) complex zeolitic crystal structures (Gatta et al, 2018).…”

Argentophilic Interactions in Two AgI Complexes of 3-(2-(Pyridin-4-yl)ethyl)pentane-2,4-dione, a Promising Ditopic Ligand

“…Following that report, first the groups of Domasevitch [12][13][14] and Maverick [15][16][17], later others [18], including our group [19], have used the compound in coordination chemistry. The structure of the uncoordinated ligand was established in 2017 by temperature-dependent neutron diffraction [20]. The nitrile-substituted acetylacetone HacacCN [21,22] is more restricted with respect to its N donor capabilities [23][24][25][26][27][28][29][30][31][32][33].…”