Vibrational Properties of Bulk Boric Acid 2A and 3T Polymorphs and Their Two-Dimensional Layers: Measurements and Density Functional Theory Calculations

Abstract

Boric acid (HBO) is being used effectively nowadays in traps/baits for the management of Aedes aegypti L. and Aedes albopictus Skuse species of mosquitoes, which are the main spreading vectors worldwide for diseases such as malaria, dengue, and zika. Previously, we published results on the structural, electronic, and optical properties of its molecular triclinic HBO-2A and trigonal HBO-3T polymorphs within the framework of density functional theory (DFT). Because of the renewed importance of these materials, the focus of this work is on the vibrational properties of the bulk boric acid 2A and 3T polymorphs. We measured the infrared and Raman spectra of the former, which was accompanied and interpreted through state-of-the-art DFT calculations, supplemented by computations regarding the HBO molecule and two-dimensional layers based on the bulk structures. We identify/assign their normal modes and find vibrational signatures for each polymorph as well as in- and out-of-plane motions and molecular vibrations, unveiling a nice agreement between the DFT level of theory employed and our improved spectroscopic measurements in the wavenumber ranges of 400-2000 cm (infrared) and 0-1500 cm (Raman). We show that a dispersion-corrected DFT functional within the generalized gradient approximation (GGA) can be very accurate in describing the vibrational properties of the boric acid polymorphs. Besides, several issues left open/not clearly resolved in previously published works on the vibrational mode assignments of the bulk and 2D sheets of boric acid are explained satisfactorily. Finally, phonon dispersions and associated densities of states were also evaluated for each polymorph along with their temperature-dependent DFT-calculated entropy, enthalpy, free energy, heat capacity, and Debye temperature. In particular, our DFT calculations suggest a possible way to differentiate the 2A and 3T boric acid polymorphs through Raman spectroscopy and heat capacity measurements.

Synthesis and Characterization of Silica-Supported Boron Oxide Catalysts for the Oxidative Dehydrogenation of Propane

“…At ambient conditions, the Raman spectrum for fresh 1.2 B/SiO 2 contains peaks at 209, 500, and 882 cm –1 that match closely with vibrations observed in the Raman spectrum for boric acid (shown above the spectra for 1.2 B/SiO 2 in Figure ). The vibration at 209 cm –1 has been previously attributed to a lattice-translatory oscillation in boric acid, whereas the peaks at 500 and 882 cm –1 correspond to O–B–O bending and B–O stretching modes, respectively. , Upon dehydration of 1.2 B/SiO 2 at temperatures >100 °C, these features disappear, and instead a small feature at 807 cm –1 can be observed. This is very close to the feature at 808 cm –1 observed in B 2 O 3 (top spectrum in Figure ).…”

Periodic DFT Calculations—Review of Applications in the Pharmaceutical Sciences

“…Calculated through density functional perturbation theory (DFPT), the phonon density of states enables a precise description of a thermodynamic state [161] enabling calculations of Gibbs free energy, enthalpy, entropy and zero-point energy. For example, a quite commonly performed comparison between experimental sublimation enthalpy and the calculated lattice energies requires the vibrational contribution, which is determined via phonon calculations [162,163].…”

“…Calculated through DFPT, the phonon density of states not only enables to obtain a precise description of a thermodynamic state [161] by calculating the Gibbs free energy, enthalpy, entropy, or zero-point energy but also the generation of vibrational spectra such as IR, Raman, and INS. All these calculations are usually characterized by a very good agreement with the experimental results [170,171] and in many cases they reveal the reason (e.g., molecular structure in itself, crystal packing) for spectral differences between two polymorphs [172].…”

Vibrational Modes and Phonon and Thermodynamic Properties of the Metaboric Acid Polymorphs α-, β-, and γ-(BOH)3O3 within a Density Functional Theory Framework

“…Phonon dispersion and densities of states were also evaluated for each polymorph, as well as the temperaturedependent curves for their entropy, enthalpy, free energy, heat capacity, and Debye temperature. In particular, the calculations of Bezerra Da Silva et al 14 suggested a possible way to differentiate the 2A-and -3T crystals by Raman spectroscopy and heat capacity measurements. Following the steps of Bezerra Da Silva et al, 14 results of DFT calculations using a pure GGA functional incorporating an energy term describing dispersive noncovalent interactions will be presented here.…”