Helical superstructure and charged polarons contributions to optical nonlinearity of 2-methyl-4-nitroaniline crystals studied by resonance Raman, electron paramagnetic resonance, circular dichroism spectroscopies, and quantum chemical calculations

The Raman excitation profiles of solid 2-methyl-4-nitroaniline (MNA) reveal several band enhancements by intermolecular and intramolecular charge transfer states. Calculated excited- and ground-state molecular geometries and excited state distortions qualitatively determined from Raman spectra indicate multiple vibrations leading to MNA dissociation. Also, overtones and combination tones can generate charged polarons, as detected by electron paramagnetic resonance after the exposure to 980 and 1550 nm laser diodes. The MNA space group Ia (C(s)(4)) is nonchiral; however, the electronic circular dichroism (CD) spectra of solution, KBr pellet, and single crystal were recorded. The crystal chirality is elucidated by room-temperature dynamic disorder, possible helical superstructure along the [102] polar axis, and charged polarons presence. The CD spectra ab initio calculations for MNA neutral and negatively charged monomers, dimers, and trimers, lying along the helix, confirmed the chirality. The role of these findings toward efficient optical nonlinearity and electric conductivity failure is discussed.     

Whiskers growing from aqueous solution of natrium molybdate

A special apparatus was built for continuous measurements of concentration changes caused by whiskers growing in polymolybdate solutions.     

Proton transfer and solitonic excitations in model one-dimensional hydrogen-bonded systems

The solitonic models of proton transfer in a molecular hydrogen-bonded chain have been examined with respect to the shape of protonic interaction potential. The kink-like excitations with quadratic, quartic, Morse, and Toda interactions are reported and analyzed.     

Dynamic potential barrier and tunneling

The tunneling transfer probability has been considered within the framework of the time dependent perturbation theory. It has been found that the probability of proton transfer may be enhanced by several orders when a dynamic potential barrier is assumed.     

Intermolecular charge transfer in model hydrogen-bonded systems—biological implications

The electronic structure of the model hydrogen-bonded systems has been studied at the all-valence level in relation to the charge transfer mechanism. It is concluded that together with the intermolecular proton transfer an electronic charge transport occurs for hydrogen bonds of 2.70–3.00 Å in length, i.e., when the proton motion within the bond is anticipated. For elucidation of transport properties of one-dimensional hydrogen-bonded systems the tunneling–hopping model is preferred instead of the band theory. The importance of the proposed mechanism of the charge transfer for biological processes has been emphasized.     

Disordered modifications of cobalt molybdate

The structures of recently discovered new high-temperature modifications of cobalt molybdate, a′-and a″-CoMoO₄, were determined. a′-and a″-CoMoO₄ appear after the phase a-CoMoO₄ is heated above the temperature range 700–1000°C. They seem to be the disordered modifications of a-CoMoO₄ with metal atoms distributed at random in an a-CoMoO₄ oxygen network.The F(hkl) values, calculated for variously disordered a-CoMoO₄ structure, were compared with the observed intensities of diffraction lines changing in the course of a → a′ and a → a″ transitions. It was concluded that a″-CoMoO₄₄ has a completely disordered structure with random distribution of both Co and Mo atoms in oxygen interatomic voids. The a′-CoMoO₄ is a partly disordered modification, with random distribution of some cations only.The temperature and the kind of order-disorder transition depend on the method of preparation of a-CoMoO₄ samples.The disordered modifications of cobalt molybdate may be supercooled—even to room temperature—before it transforms rapidly into low-temperature b-CoMoO₄ form.     

A new synthetic entry to phosphinophosphinidene complexes. Synthesis and structural characterisation of the first side-on bonded and the first terminally bonded phosphinophosphinidene zirconium complexes [mu-(1,2:2-eta-tBu2P=P)[Zr(Cl)Cp2]2] and [[Zr(PPhMe2)Cp2](eta1)-P-PtBu2)

The reactions of lithiated diphosphanes with transition metal chlorides constitute a new general entry to phosphinophosphinidene complexes: the reaction of Cp2ZrCl2(Cp = C5H5) with tBu2P-P(SiMe3)Li (molar ratio approximately 1:1) yields [mu-(1,2:2-eta-tBu2P=P)[Zr(Cl)Cp2]2]; the reaction of Cp2ZrCl2 with tBu2P-P(SiMe3)Li (molar ratio approximately 1:2) and an excess of PPhMe2 in DME yields the first terminally bonded phosphinophosphinidene complex, [[Zr(PPhMe2)Cp2](eta1-P-PtBu2)].     

Highly resolved structure of the electronic spectra of azulene in frozen hydrocarbon matrices

Vibronic structures of electronic spectra of azulene embedded into various hydrocarbon matrices are examined at 77°K. High-resolution spectra are obtained using crystalline matrices of isooctane and methylcyclohexane. The O-O bands of third and fourth electronic transitions (33836 and 35550 cm^?1, respectively, in the low-temperature modification of the isooctane matrix) are identified in the absorption spectrum of azulene. Using the P-P-P approximation with the unified parametrization the lowest excited states energies as well as bond lengths for the S_o and their respective changes in the S₁ and S₂ electronic states are calculated. Differences in the vibrational frequencies found for the respective electronic states of the azulene molecule are discussed in connection with the lack of the mirror symmetry between the S₂←S_o absorption and S₂→S_o fluorescence.     

Impact of the anion and chalcogen on the crystal structure and properties of 4,6‐dimethyl‐2‐pyrimido(thio)nium halides

By the reaction of urea or thiourea, acetylacetone and hydrogen halide (HF, HBr or HI), we have obtained seven new 4,6‐dimethyl‐2‐pyrimido(thio)nium salts, which were characterized by single‐crystal X‐ray diffraction, namely, 4,6‐dimethyl‐2‐oxo‐2,3‐dihydropyrimidin‐1‐ium bifluoride, C₆H₉N₂O⁺·HF₂^? or (dmpH)F₂H, 4,6‐dimethyl‐2‐oxo‐2,3‐dihydropyrimidin‐1‐ium bromide, C₆H₉N₂O⁺·Br^? or (dmpH)Br, 4,6‐dimethyl‐2‐oxo‐2,3‐dihydropyrimidin‐1‐ium iodide, C₆H₉N₂O⁺·I^? or (dmpH)I, 4,6‐dimethyl‐2‐oxo‐2,3‐dihydropyrimidin‐1‐ium iodide–urea (1/1), C₆H₉N₂O⁺·I^?·CH₄N₂O or (dmpH)I·ur, 4,6‐dimethyl‐2‐sulfanylidene‐2,3‐dihydropyrimidin‐1‐ium bifluoride–thiourea (1/1), C₆H₉N₂S⁺·HF₂^?·CH₄N₂S or (dmptH)F₂H·tu, 4,6‐dimethyl‐2‐sulfanylidene‐2,3‐dihydropyrimidin‐1‐ium bromide, C₆H₉N₂S⁺·Br^? or (dmptH)Br, and 4,6‐dimethyl‐2‐sulfanylidene‐2,3‐dihydropyrimidin‐1‐ium iodide, C₆H₉N₂S⁺·I^? or (dmptH)I. Three HCl derivatives were described previously in the literature, namely, 4,6‐dimethyl‐2‐oxo‐2,3‐dihydropyrimidin‐1‐ium chloride, (dmpH)Cl, 4,6‐dimethyl‐2‐sulfanylidene‐2,3‐dihydropyrimidin‐1‐ium chloride monohydrate, (dmptH)Cl·H₂O, and 4,6‐dimethyl‐2‐sulfanylidene‐2,3‐dihydropyrimidin‐1‐ium chloride–thiourea (1/1), (dmptH)Cl·tu. Structural analysis shows that in 9 out of 10 of these compounds, the ions form one‐dimensional chains or ribbons stabilized by hydrogen bonds. Only in one compound are parallel planes present. In all the structures, there are charge‐assisted N⁺—H…X^? hydrogen bonds, as well as weaker C_Ar⁺—H…X^? and π⁺…X^? interactions. The structures can be divided into five types according to their hydrogen‐bond patterns. All the compounds undergo thermal decomposition at relatively high temperatures (150–300 °C) without melting. Four oxopyrimidinium salts containing a π⁺…X^?…π⁺ sandwich‐like structural motif exhibit luminescent properties.