Intermolecular Interactions

A multiproperty approach for the evaluation of the existing three-patameter correspnding states principles (CSP) and calculation of the corresponding states parameters is presented. This technique is based on the assumption that contribu­tion of the third parameter to the thermopbysical properties is much smaller than the contributions of the first two parameters. The: first two parameters are, generally, the molecular energy and length, ϵ/k and  σ (or critical temperature and volume, Tc and Vc). Based on the present multiproperty technique, several existing three-parameter CSPs are evaluated.  It is demostrated that the three- parameter CSP, which is based on the two-and three-body intermolecular potential parameters, effectively satisfies the requirements of this technique, The corresponding states parameters of several compounds, including normal alkane hydrocarbons (CH4 to C20H42), for which proper thermophysical data are available, are calculated through the present technique, and they are reported here.

The influence of presence of counter ions and π-complexation with benzene on the bonding and
magnetic properties of Al4
2, the most studied all-metal cluster, is studied here. It is shown that
complexation by either counter ions or benzene decreases the delocalization index between
Al atoms and the magnitude of bond magnetizability, that is a Quantum Theory of Atoms in
Molecules, QTAIM, -based magnetic index of aromaticity. Benzene forms two types of π-complexes
with the Al4 framework; CH–π (T-shaped) complexes and parallel π–π stacking (PPS) complexes.
It is shown that variation in the p-charge of the Al4 framework affects the relative stability of the
T-shaped/PPS complexes. Free Al4
2 forms a stable T-shaped anion–π complex with benzene but
in the presence of cations, formation of PPS complexes is more favourable, energetically. It is
suggested that this property could be used for designing molecular switches and tuneable anion
sensors.

The ability to form strong intermolecular interactions by linear glucosamine polysaccharides with collagen is strictly related to their nonlinear dynamic behavior and hence bio-lubricating features. Type III collagen plays a crucial role in tissue regeneration, and its presence in the articular cartilage affects its bio-technical features. In this study, the molecular dynamics methodology was applied to evaluate the effect of deacetylation degree on the chitosan affinity to type III collagen. The computational procedure employed docking and geometry optimizations of different chitosan structures characterized by randomly distributed deacetylated groups. The eight different degrees of deacetylation from 12.5% to 100% were taken into account. We found an increasing linear trend (R2 = 0.97) between deacetylation degree and the collagen–chitosan interaction energy. This can be explained by replacing weak hydrophobic contacts with more stable hydrogen bonds involving amino groups in N-deacetylated chitosan moieties. In this study, the properties of chitosan were compared with hyaluronic acid, which is a natural component of synovial fluid and cartilage. As we found, when the degree of deacetylation of chitosan was greater than 0.4, it exhibited a higher affinity for collagen than in the case of hyaluronic acid.

A round trip was made from ideal gas to supercritical and subcritical states of gases and liquids. It has been shown that, with increasing pressure and decreasing temperature, the translational motion of molecules is transformed into the rotational motion of single molecules, molecular pairs, bimolecules and oligomolecules. This results in higher order phase transitions. Each phase consists of two types of particles that are in dynamic equilibrium, with higher pressures and lower temperatures dominated by particles requiring less space for movement. The fluid consists of oligomolecules and bimolecules, at V<Vc/2, and bimolecules and molecular pairs, at Vc/2<V<Vc. Saturated vapor consists of translational and rotating single molecules at V>2Vc and rotating single molecules and rotating pairs at Vc<V<2Vc. At the conditions of the critical point, the molecules are in the form of rotating pairs, and at the conditions of the triple point are in the form of rotating oligomolecules. This is shown in the thermodynamic diagrams of entropy-volume and pressure-volume.

Developing novel energetic materials of high detonation performance and low sensitivity is one of the primary objectives related to explosive research. By employing ab-initio calculations, a series of energetic ionic salts based on 5,5 ′-bitetrazole-1,1 ′-diolate (BTO) were thoroughly investigated to understand the structure-property-performance interrelationship. The physicochemical and detonation characteristics of these energetic ionic salts including structural, electronic, vi-brational and performance parameters (heat of formation, detonation pressures, and detonation velocities) were discussed in detail. The strong intermolecular hydrogen bonding environment between the BTO 2− anion and various cations are mainly responsible for prominent detonation performance and enhanced molecular stability. Such strong intermolecular hydrogen bonds are observed in hydrazine and hydroxylammonium cation compared to other cations. To predict the accurate band gap, electronic band structures of the studied EIS were calculated using HSE06 hybrid functional and are found to be wide band gap insulator with a bandwidth ranging from 4.33-5.05 eV. Careful inspection of various EIS revealed that the hydroxylammonium and hydrazine cations produce the highest density relative to other cations when combined with BTO anion. The detonation characteristics of BTO 2− are computed using EXPLO5 code. In particular, HA-BTO and TKX-50 exhibit high detonation pressure (38.85 and 40.23 GPa) and detonation velocities (9.94 and 9.91 km/s), superior to those of traditional nitrogen-rich energetic materials with moderate sensitivities. These results highlight the importance of hydrogen bonding interactions in designing energetic salts for the next-generation explosives, propellants, and pyrotechnics.

Hydrogen bonding is an important non-covalent interaction that plays a key role in most of the CHNO-based energetic materials, which has a great impact on the structural, stability, and vibrational properties. By analyzing the structural changes, IR spectra, and the Hirshfeld surfaces, we investigated the high-pressure behavior of 3,6-dihydrazino-s-tetrazine (DHT) to provide detailed description of hydrogen bonding interactions using dispersion-corrected density functional theory. The strengthening of hydrogen bonding is observed by the pressure-induced weakening of covalent N−H bonds, which is consistent with the red shift of NH/NH 2 stretching vibrational modes. The intermolecular interactions in DHT crystals lead to more compact and stable structures that can increase the density but diminish the heat of detonation, Q. The calculated detonation properties of DHT (D = 7.62 km/s, P = 25.19 GPa) are slightly smaller than those of a similar explosive 3,6-bis-nitroguanyl-1,2,4,5-tetrazine (D = 7.9 km/s, P = 27.36 GPa). Overall, the crystallographic and spectroscopic results along with Hirshfeld surface analysis as a function of pressure reveal the presence of strong hydrogen bonding networks in the crystal structure of DHT.

Herein, we report a series of fluorinated porphyrins, 5,10,15,20-tetrakis(2′,6′-difluorophenyl)porphyrin, MT(2′,6′-DFP)P where M = 2H, 1; Co(II)·(MeOH)2, 2; Cu(II), 3; Zn(II)·(MeOH)2, 4 and Zn(II)·(THF)3, 5 have been structurally characterized by single crystal X-ray diffraction analysis. All the compounds are crystallized in monoclinic crystal system and the crystal structures of 2, 4 and 5 features octahedral geometry whereas 3 exhibits square planar geometry. The compounds 1, 3 and 2, 4 are isostructural, show similar molecular crystal packing and comparable intermolecular interactions. The supramolecular self assembly of compounds 1–5 is dominated by a variety of intermolecular interactions such as Csingle bondH⋯F, Csingle bondH⋯π, Csingle bondF⋯π and F⋯F. Furthermore, the role of weak intermolecular interactions in the crystal packing has been analysed and quantified using Hirshfeld surface analysis.

We have measured X-ray absorption spectra for acetic acid molecules in an organic solvent in order to study the effect of hydrogen-bonding formation. The spectral shapes distorted by saturation effect were compensated by using a new correction procedure for X-ray absorption based on the changes in the concentration of the samples. A resonance peak shift was observed when the acetic acid molecules formed a cyclic dimer in hexane solution, which is similar to the behavior of cluster molecules in vacuum. This is the first report on the XAS spectral changes due to cyclic dimer formation in a solution.

Five acetylene-furan dimer structures are identified using ab initio calculations at the second-order Møller-Plesset (MP2) level of theory. The structures are stabilized by two basic types of intermolecular interactions: the CHctdotO and the CHctdotπ interaction. The CHctdotπ interaction appears in two variants, depending on which molecule provides the hydrogen atom and which molecule the π system. The MP2 results indicate that the CHctdotπ interaction between one of the hydrogen atoms of acetylene and the π system of furan as found in structure A is the strongest interaction, followed by the in-plane CHctdotO interaction in the second most stable acetylene-furan dimer structure B. A matrix isolation study shows the acetylene-furan dimer to exist in an argon matrix, but likely rather as structure B than as A. High level coupled cluster calculations with up to triple excitations (CCSD(T)) yield the interaction energy of structure A as about -2.4 kcal/mol in the complete basis set limit and find structure B to be nearly isoenergetic with -2.3 kcal/mol. This is confirmed in calculations employing the density functional theory combined with symmetry adapted intermolecular perturbation theory (DFT-SAPT) approach yielding interaction energies of -2.3 and -2.0 kcal/mol for A and B, respectively. DFT-SAPT also helps to understand the importance of the electrostatic, induction and dispersion interaction energies and their respective exchange counterparts for the stability of the various acetylene-furan dimer structures. The CHctdotO and CHctdotπ interactions are furthermore analyzed with the help of the atoms in molecules (AIM) theory.

Some ultrasonic investigations in binary mixtures of molten salts with a common ion and reciprocal salt pair mixtures have been carried out. Prissiajnyi et al had reported data on ultrasonic velocity and adiabatic compressibilities for four molten salt pairs with a common ion. They calculated isothermal compressibility, molar ultrasonic velocity, excess molar volume and excess isothermal compressibility in such systems on the basis of a hole theory. In the present investigation, several acoustical and thermodynamically parameters of CdBr2 + KBr, CdCl2 + KCl, LiBr + LiCl and LiBr +KBr have been studied. While the first two systems are investigated at 973 K and the other two systems are studied at 1023 K. The ultrasonic velocities and adiabatic compressibilities data for these systems have been taken from the literature for these studies. The interactions prevailing in these binary mixtures have been interpreted from the obtained results.