The dynamics of the intramolecular short hydrogen bond in the molecular crystal of benzoylacetone and its deuterated analogue are investigated using ab initio molecular dynamics simulations. A study on intramolecular hydrogen bonding in 1-phenyl-1,3-butadione (I) and 1-deuteroxy-2-deutero-1-phenylbut-1-en-3-one (II) crystals has been carried out at 160 K and 300 K on the CPMD method level and at 300 K on the PIMD method level. The analysis of the two-dimensional free-energy landscape of reaction coordinate δ-parameter and ROO distances shows that the hydrogen (deuter) between the two oxygen atoms adopts a slightly asymmetrical position in the single potential well. When the nuclear quantum effects are taken into account, very large delocalization of the bridging proton is observed. These studies indicate that hydrogen bonds in the crystal of benzoylacetone have characteristic properties for the type of bonding model resonance-assisted hydrogen bonds (RAHB) without existing the equilibrium of the two tautomers. The infrared spectrum has been calculated, and a comparative vibrational analysis has been performed. The CPMD vibrational results appear to qualitatively agree with the experimental ones.
Ferroelectric properties of haloantimonates(III)
and halobismuthates(III)
have been detected for as much as 40 structures belonging to 7 different
types of anionic networks, with RMX4, R2MX5, R3M2X9, and R5M2X11 stoichiometries being the most frequently
reported to host these properties. We report on the first ferroelectric
of the halobismuthate(III) family with a R3MX6 stoichiometry, that is, tris(acetamidinium)hexabromobismuthate(III),
(CH3C(NH2)2)3[BiBr6] (ABB), characterized by a one-component organic
network. While the stoichiometry and crystal packing of ABB might seem uncomplicated, the temperature-resolved structural and
spectroscopic studies paint a different picture in which rich polymorphism
in the solid state occurs between tetragonal (paraelastic) and triclinic
(ferroelastic) crystal phases: I (P42/n) → II (P1̅) at 272/277 K (cooling/heating), II (P1̅) → III (P1̅) at 207 K, and III (P1̅)
→ IV (P1) at 98/127 K. The ferroelectric
properties of phase IV have been confirmed by the pyroelectric
current and hysteresis loop measurements; additionally, the acentric
symmetry has been further supported by second harmonic generation
measurements. Crystallographic analysis of phase III reveals
the antiparallel alignment of acetamidinium dipoles, pointing to the
antiferrroelectric nature of this phase. In turn, the character of
the ferroelectric transition (III → IV) should be considered as “displacive” for both cationic
and anionic substructures.) In this report, we also explore the two-photon
absorption property of ABB at 800 nm, a property that
is unexplored for any halobismuthate(III) thus far. We also present
periodic ab initio calculations for ABB crystals. The
Berry-phase approach at the Hartree–Fock and density functional
theory (DFT-D3) method levels is employed for spontaneous polarization
calculations. The origin of ferroelectric polarization is studied
using DFT-D3 and RHF electronic structure calculations, emphasizing
the relationship between P
s and the relative
orientation of organic/inorganic components.
In this paper are presented the results of theoretical studies of the structure in proton motion in a very short O···O and two weak N-H···O intramolecular hydrogen bonds in the nitromalonamide crystal. The dynamics of proton motion in hydrogen bonds were investigated in the NVT ensemble at 298 K using the Car-Parrinello and the path integral molecular dynamics. A very large delocalization of proton in the slightly asymmetrical single well of free energy potential of O-H···O intramolecular hydrogen bond was noted especially in the path integral simulation where quantum effects are taken into account. This hydrogen bond is very strong with the estimated energy of hydrogen bond ca. -27 kcal/mol. The nature of intra- and intermolecular interactions was studied by means of quantum theory of atoms in molecules. The infrared spectra were calculated and compared with available experimental data. CPMD vibrational results appear to be in good agreement with the experimental ones.
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