Molecular Crystal Structure of Acetylacetone at 210 and 110 K:  Is the Crystal Disorder Static or Dynamic?

Abstract

The molecular and crystal structure of acetylacetone (AA) was studied at 210 and 110 K in order to reveal the nature of the hydrogen bond and possible crystal disorder. The single crystal was grown by an in situ crystallization from the melt using an IR laser beam producing a molten zone in a Lindeman capillary. At both temperatures the crystals are orthorhombic (space group Pnma, Z = 4) with molecules having a crystallographic mirror plane perpendicular to the mean molecular plane. The intramolecular hydrogen bond is characterized by the O···O distances 2.541(2) and 2.547(1) Å at 210 and 110 K, with the central hydrogen atom equally distributed over the two positions near the oxygens. So, the hydrogen bond in AA has two distinct potential minima that are in agreement with previous NMR data and recent quantum-chemical calculations. The bond lengths C−O and C−C in the cis-enol fragment have averaged values (1.291(1) and 1.402(1) Å at 110 K) corresponding to the superposition of two enol isomers due to the crystallographic symmetry. The nature of the crystal disorder (static or dynamic) is discussed using analysis of the atomic anisotropic displacement parameters. Charge density analysis in AA has been performed using the high-order X-ray diffraction data at 110 K and a multipole model.

Solid‐State NMR Study of the Tautomerism of Acetylacetone Included in a Host Matrix

“…The O ¥¥¥ O distance in 1a,c and in 1b are 2.546 and 4.185 ä, respectively. The first value agrees with both experimental results and elaborate calculations: 2.381 [36] and 2.512 ä [37] by electron diffraction; 2.547 ä by X-ray diffraction at 110 K [31], and 2.535 ä by X-ray diffraction of DPHEAD [32]; and 2.549 or 2.548 ä by MP2/D95 ** [38] or MP2(FC)/6-311 G(2d,2p) [39] calculations, respectively. For 1b, Karle et al [36] experimentally determined the O ¥¥¥ O distance as 2.767 ä, the calculated values [38] being 4.046 and 3.559 ä for the more-and the less stable forms, respectively.…”

“…Besides, Boese et al investigated the structure of 1 at low temperatures (110 and 210 K; CSD entries LIWPIQ and LIWPIQ01, resp.). At these temperatures, 1 exists as a dynamic mixture of 1a and 1c (double-well potential) [31]. We selected the DPHEAD structure (Fig.…”

“…However, a closer examination of the structure 3 ) revealed that 1a (or 1c) is not floating in a void determined by the hydantoin 2 ( 5,5-diphenylimidazolidine-2,4-dione) and 9-ethyladenine (3), but has its Me groups interacting with the p system of the Ph rings of 2 and the OÀH ¥¥¥ O H-atom of 1a (or 1c) close to the N-atom of the 6-NH 2 group of 3. The fact that the O ¥¥¥ N distances are 3.19 ä (OH) and 3.41 ä (CO) probably explains why the H-atom lies 0.36 ä above the molecular plane [31] [32], rendering the sixmembered H-bonded pseudo-cycle nonplanar (Fig. 3).…”

Group-theoretical investigation of the tunneling splitting patterns of enolic acetylacetone

“…Tunneling effects from the three large-amplitude motions splits each vibrational level into several sublevels, and complicates the tunneling splitting patterns of the molecule. Extensive experimental [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] and theoretical [16][17][18][19][20][21][22][23][24] studies for enolic acetylacetone have been presented in the literature, but the studies of the tunneling splitting patterns are still lacking. Since the tunneling splitting patterns depend on the molecular symmetry and intramolecular motions of a molecule, the equilibrium structure and intramolecular motions must be determined before starting this work.…”

Nature of weak inter-and intramolecular interactions in crystals 6. Intramolecular O—H...O bond in enol forms of (phosphoryl)acylacetonitriles

“…4 These interactions are characterized by a lower barrier to proton transfer and a high energy of the hydrogen bond, which is stabilized through π electron density delocalization in the hydro gen bonded six membered ring. It was suggested that the O-H...O bond strength, for which the interatomic O...O distance serves as an estimate, depends on the nature of the substituents at the carbon atoms of the keto enol ring because these distances in structurally similar acetyl acetone, 4 benzoylacetone, 5 and tetraacetylethane 3 differ in value (2.547(1), 2.502(4), and 2.450(1) Å, respectively). However, no such differences were observed in the iso lated molecules of these compounds.…”