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A combined structural, vibrational spectroscopy, and solid-state DFT study of the hydrogen-bonded complex of bromanilic acid with 2,6-dimethylpyrazine is reported. The crystallographic structure was determined by means of low-temperature single-crystal X-ray diffraction, which reveals the molecular units in their native protonation states, forming one-dimensional infinite nets of moderate-strength O···H-N hydrogen bonds. The nature of the crystallographic forces, stabilizing the studied structure, has been drawn by employing the noncovalent interactions analysis. It was found that, in addition to the hydrogen bonding, the intermolecular forces are dominated by stacking interactions and C-H···O contacts. The thermal and calorimetric analysis was employed to probe stability of the crystal phase. The structural analysis was further supported by a computationally assisted (13)C CP/MAS NMR study, providing a complete assignment of the recorded resonances. The vibrational dynamics was explored by combining the optical (IR, Raman, TDs-THz) and inelastic neutron scattering (INS) spectroscopy techniques with the state-of-the-art solid-state density functional theory (DFT) computations. Despite the quasi-harmonic approximation assumed throughout the study, an excellent agreement between the theoretical and experimental data was achieved over the entire spectral range, allowing for a deep and possibly thorough understanding of the vibrational characteristics of the system. Particularly, the significant influence of the long-range dipole coupling on the IR spectrum has been revealed. On the basis of a wealth of information gathered, the recent implementation of a dispersion-corrected linear-response scheme has been extensively examined.

We report a joint structural and spectroscopic study of a series of hydrogen-bonded chloranilate and bromanilate complexes with αand βpicolines. Single-crystal structures at 100 K are provided for all the systems analyzed, which were found to form B:XA:XA:B, :(B:XA:B):XA, and B:XA:B type synthons, where XA and B stand for the acid and base molecules, respectively. By extending single-crystal X-ray crystallography onto computationally supported high-resolution solid-state spectroscopy, we provide a comprehensive analysis of spectral signatures that can possibly facilitate the design and recognition of the supramolecular architectures formed by these kinds of synthons. To this end, we employed nuclear magnetic resonance spectroscopy along with complementary optical (infrared, Raman, terahertz time-domain spectroscopy) and neutron (inelastic neutron scattering) vibrational techniques. Despite a large chemical similarity, the studied systems exhibited strikingly different spectral responses. All the spectral signatures and peculiarities arising from structural factors, intermolecular forces, and specific effects are interpreted and discussed in detail. Based on state-of-the-art first-principles calculations for solid-state, in both static and time-evolved manners, the spectral influences of long-range dipole coupling, proton transfer, symmetry-distortion, as well as anharmonicity are covered extensively. In this way, we take the necessary first step needed to gather combined structure−spectroscopy data on low-weight supramolecular synthons, which are important in crystal engineering and materials science.

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We present a joint experimental and computational terahertz (THz) spectroscopy study of the most stable polymorph (form I) of an antihypertensive pharmaceutical solid, felodipine (FLD). The vibrational response has been analyzed at room temperature by combining optical (THz-TDS, FT-IR, THz-Raman) and neutron (INS) terahertz spectroscopy. With the challenging example of a large and flexible molecular solid, we illustrate the complementarity of the experimental techniques. We show how the results can be understood by employing ab initio modeling and discuss current progress in the field. To this end, we employ plane wave formulation of density functional theory (plane wave DFT) along with harmonic lattice dynamics calculations (HLD) and ab initio molecular dynamics (AIMD) simulations. Based on a comprehensive theoretical analysis, we discover an inconsistency in the commonly accepted structural model, which can be linked to a distinct librational dynamics of the side ester chains. As a result, only a moderate agreement with the experimental spectra can be achieved. We, therefore, propose an alternative structural model, effectively accounting for the influence of the large-amplitude librations and allowing for a comprehensive analysis of the vibrational resonances up to 4.5 THz. In that way, we illustrate the applicability of the computationally supported THz spectroscopy to detect subtle structural issues in molecular solids. While the provided structural model can be treated as a guess, the problem calls for further revision by means of high-resolution crystallography. The problem also draws a need of extending the THz experiments toward low-temperature conditions and single-crystal samples. On the other hand, the studied system emerges as a challenge for the DFT modeling, being extremely sensitive to the level of the theory used and the resulting description of the intermolecular forces. FLD form I can be, hence, considered as a testbed for the