Vibrational spectra, normal coordinate analysis, and hydrogen bond investigation of pyridinium perchlorate

Cation-anion interaction effect on the nonlinear optical behavior of pyridinium-based ionic liquids

Influence of the cation-anion interaction (expressed as internal hydrogen bonds) on the nonlinear optical properties (dipole moment, polarizability, anisotropy of polarizability and first-order hyperpolarizability) for the ionic liquids pyridinium hydrogen sulfate (PHS) and pyridinium bis(dihydrogen phosphate) (P2HP) was investigated in this paper. It was achieved analyzing vibrational modes (FT-IR) and electronic transitions (UV-vis) in PHS and P2HP. Molecular geometry of the title compounds was optimized by means of density functional theory calculations at B3LYP/6-311++G(2d,2p) level. Structural analysis exposed stronger internal hydrogen bonds (H⁷···O³ and H¹⁸···O⁴) between cationic and anionic fragments in the pyridinium hydrogen sulfate than these (H²⁶···O⁴ and H²⁵···O¹²) in pyridinium bis(dihydrogen phosphate). These observations are confirmed by FT-IR and UV-vis methods, where: (i) the infrared bands due to H···O and N-C interactions in P2HP appear at lower frequencies than the same ones in the spectrum of PHS and (ii) the n → π* electron transitions in PHS are more pronounced in comparison with these in P2HP. Based on the weaker cation-anion interaction in P2HP with respect to PHS, the former one is characterized with a remarkably higher first-order hyperpolarizability value. Hence, the ionic liquid P2HP was referred as a better nonlinear optical material than PHS.

Tuning the Computational Evaluation of Spectroscopic, ELF, LOL, NCI analysis and Molecular Docking of Novel Anti COVID-19 Molecule 4-Dimethylamino Pyridinium 3, 5-Dichlorosalicylate

In this work novel antiviral compound 4-(Dimethylamino) Pyridinium 3, 5-dichlorosalicylate was synthesized and characterized by UV-vis, FT-IR, FT-Raman, 1H NMR and 13C NMR spectra. Quantum chemical computations were carried out by Density functional theory methods at B3LYP level. Electronic stability of the compound arising from hyper conjugative interactions and charge delocalization is investigated using natural bond orbital analysis. Assignments of vibrational spectra have been carried out with the aid of Normal coordinate analysis following the SQMFF methodology. TD-DFT approach was applied to assign the electronic transition observed in UV visible spectrum measured experimentally. Frontier molecular orbital energy gap affirms the bioactivity of the molecule and NCI analysis gives information about inter and intra non covalent interactions. ESP recognises the nucleophilic and electrophilic regions of molecule and the chemical implication of molecule was explained using ELF, LOL. The reactive sites of the compound were studied from the Fukui function calculations and chemical descriptors define the reactivity of the molecule. Molecular docking done with SARS and MERS proteins endorses the bioactivity of molecule and drug likeness factors were calculated to comprehend the biological assets of DADS.

A combined DFT and FT-IR study on the surface interactions in alumina supported ionic liquid [H-Pyr]+[HSO4]. SPECTROCHIMICA ACTA. PART A, MOLECULAR AND BIOMOLECULAR SPECTROSCOPY 2020;226:117545. [PMID: 31710889 DOI: 10.1016/j.saa.2019.117545]

The surface interactions in [H-Pyr]⁺[HSO₄]^-/γ-Al₂O₃ system (prepared by wetness impregnation method) are investigated theoretically and experimentally. For that purpose, atoms in molecules theory, natural bond orbital and natural charge population analyses in a combination with a vibrational spectroscopy (FT-IR) are used. It is established that a bond formation between the hydrogen sulfate anion and the alumina influences the IL-support interaction in a great extent. However, a support-cation and a cation-anion interaction in the immobilized [H-Pyr]⁺[HSO₄]^- present as well. A comparative analysis between the experimental and the calculated vibrational modes is carried out and a significant number of infrared bands are assigned. The results indicate a good correlation between the experimental and the theoretical IR frequencies. It is found that the aforementioned interactions affected the vibrational frequencies in the supported IL.

Mechanistic investigation of molecular geometry, intermolecular interactions and spectroscopic properties of pyridinium nitrate

The molecular structure, vibrational frequencies of the fundamental modes and electronic transitions of the ionic liquid pyridinium nitrate ([H-Pyr]⁺[NO₃]^-) have been determined by means of density functional theory (DFT) at B3LYP/6-311++G (2d,2p) level. The chemical bonds nature and the intermolecular interactions in the title compound were investigated using the Quantum theory of atoms in molecules and Hirshfeld surface analysis. Natural bond orbital analysis has been performed in order to elucidate the hybridization and delocalization of electron density within the ion pair [H-Pyr]⁺[NO₃]^-. A detailed vibrational spectral analysis was carried out and the assignments of the observed bands have been proposed on the basis of potential energy distribution. A good correlation between experimental and theoretical IR frequencies was observed. To study the charge transfers occurred in the title molecule, UV-vis analysis was conducted.

Structural and IR-spectroscopic characterization of pyridinium acesulfamate, a monoclinic twin

The crystal structure of pyridinium 6-methyl-1,2,3,-oxathiazine-4(3H)-one-2,2-dioxide [(C5NH6)(C4H4NO4S)], for short, pyH(ace), was determined by X-ray diffraction methods. It crystallizes as a twin in the monoclinic space groupP21/cwitha=6.9878(9),b=7.2211(7),c=21.740(2) Å,β=91.67(1)° andZ=4 molecules per unit cell. The structure was determined employing 1599 reflections withI>2σ(I) from one of the twin domains and refined employing 2092 reflections from both crystal domains to an agreement R1 factor of 0.0466. Besides electrostatic attractions, intermolecular pyH···O=C(ace) hydrogen bonds stabilize the acesulfamate anion and the pyridinium cation into planar discrete units parallel to the (100) crystal plane. The units form stacks of alternating ace−and pyH+ions along theaaxis that favors inter-ring π–π interactions. The Fourier transform-infrared (FT-IR) spectrum of the compound was recorded and is briefly discussed. Some comparisons with related pyridinium saccharinate salts are also made.