ROTATIONAL SPECTRA OF A SERIES OF POLYCYCLIC AROMATIC HYDROCARBONS

A theoretical study of the rotational spectra of a number of polycyclic aromatic hydrocarbons (PAHs) was carried out on the basis of quantum-chemical calculations by PRIRODA program in the PBE/3ζ approximation. Calculations are given for neutral molecules, their radical anions and radical cations in the rigid top approximation. Twelve neutral PAHs under study have no dipole moment and are not of interest for rotational spectroscopy. Thirteen neutral PAHs have a dipole moment not exceeding 0.09 Debye and, under certain conditions, can be studied in the microwave region. The remaining six compounds are PAHs with methyl and phenyl substituents, their dipole moments are 0.32-0.65 Debye, which makes it possible to study their microwave spectrum. For radical ions, the situation with the dipole moment is as follows: if a neutral molecule does not have a dipole moment, then the corresponding radical ion does not have it either; if the dipole moment of a neutral molecule is nonzero, then for radical ions it increases at least several times. For example, in the benzo [b] chrysene radical anion, the μa-component component of the dipole moment increases by 250 times, the μb-component by 7 times, and the total dipole moment by about 100 times. This effect is more pronounced for radical anions than for radical cations. In this case, it becomes possible to detect the spectrum of if not a neutral molecule, then at least one of its charge states. For a number of compounds, the patterns of various spectroscopic parameters depending on the number of carbon atoms in PAHs were found. In the B3LYP/6-31G(d,p) approximation, quartic centrifugal distortion constants were calculated for five compounds, and their effect on the rotational spectrum was estimated: for many compounds under study, they can have a significant effect on the microwave spectrum. With an increase in PAHs, the centrifugal constants decrease indicating an increase in the rigidity of the molecules. Thus, substituted neutral PAHs, as well as a number of radical ions, may be of interest for experimental studies in laboratory conditions and in space.

The mechanism of Mg2+ conduction in ammine magnesium borohydride promoted by a neutral molecule

Light weight and cheap electrolytes with fast multi-valent ion conductivity can pave the way for future high-energy density solid-state batteries, beyond the lithium-ion battery.

Staircase voltammetry of dissolved redox couple in a thin layer twin electrode cell

A model of reversible and quasi-reversible electrode reaction of dissolved redox couple is developed for the staircase voltammetry and the twin electrode thin layer cell. It is assumed that the neutral molecule is oxidized to a monovalent cation. The calculations were performed for the absence of supporting electrolyte and for its various concentrations. The influence of migration of cations and of IRΩ drop on the peak currents and peak potentials was investigated. Also, the kinetically controlled electrode reactions were simulated. These reactions can be distinguished from the reactions influenced by the resistance in the solution.

Co-crystallization of a neutral molecule and its zwitterionic tautomer: structure and Hirshfeld surface analysis of 5-methyl-4-(5-methyl-1H-pyrazol-3-yl)-2-phenyl-2,3-dihydro-1H-pyrazol-3-one 5-methyl-4-(5-methyl-1H-pyrazol-2-ium-3-yl)-3-oxo-2-phenyl-2,3-dihydro-1H-pyrazol-1-ide monohydrate

The title compound, 2C14H14N4O·H2O, comprises a neutral molecule containing a central pyrazol-3-one ring flanked by an N-bound phenyl group and a C-bound 5-methyl-1H-pyrazol-3-yl group (at positions adjacent to the carbonyl substituent), its zwitterionic tautomer, whereby the N-bound proton of the central ring is now resident on the pendant ring, and a water molecule of crystallization. Besides systematic variations in geometric parameters, the two independent organic molecules have broadly similar conformations, as seen in the dihedral angle between the five-membered rings [9.72 (9)° for the neutral molecule and 3.32 (9)° for the zwitterionic tautomer] and in the dihedral angles between the central and pendant five-membered rings [28.19 (8) and 20.96 (8)° (neutral molecule); 11.33 (9) and 11.81 (9)°]. In the crystal, pyrazolyl-N—H...O(carbonyl) and pyrazolium-N—H...N(pyrazolyl) hydrogen bonds between the independent organic molecules give rise to non-symmetric nine-membered {...HNNH...NC3O} and {...HNN...HNC3O} synthons, which differ in the positions of the N-bound H atoms. These aggregates are connected into a supramolecular layer in the bc plane by water-O—H...N(pyrazolide), water-O—H...O(carbonyl) and pyrazolyl-N—H...O(water) hydrogen bonding. The layers are linked into a three-dimensional architecture by methyl-C—H...π(phenyl) interactions. The different interactions, in particular the weaker contacts, formed by the organic molecules are clearly evident in the calculated Hirshfeld surfaces, and the calculated electrostatic potentials differentiate the tautomers.

Synthesis and Antibacterial Activity of Polyoxometalates with Different Structures

A new inorganic-organic hybrid compound, [{Cu(phen)2}2(H4W12O40)], was synthesized, and its crystal structure was determined. The Keggin anion H4W12O404− was grafted with two coordination units {Cu(phen)2}, forming an electrically neutral molecule. The antibacterial activity of several polyoxometalate compounds with different anionic structures including the new compound was studied. The results show that the compound 1 can inhibit the growth of Enterococcus faecalis FA2 strains and that antibacterial activity of the polyoxometalate compounds is dependent with component elements of POM but is less relative with the anion structures.

Synthesis and Characterization of a Fluorescent Dianthraceno­indacene

A freely soluble dianthracenoindacene derivative has been synthesized using an ‘inside-out’ Friedel–Crafts alkylation method and is the first fluorescent diacenoindacene reported. Linear fusion of the anthracenes is confirmed by X-ray diffraction studies on the neutral molecule as well as its dianion. Based on predictions from our previous studies, this is also the least antiaromatic diacenoindacene derivative yet to be prepared, which is reflected in its highly negative and irreversible reduction. With its paratropicity essentially eliminated, we posit that the molecule is no longer deactivated by a conical intersection, typical of antiaromatic molecules, and therefore fluorescence is restored. This follows the trend shown in the related dianthracenopentalenes, with the reappearance of fluorescence when the outer acene groups are extended to linearly-fused anthracene moieties.