The attachment of electrons is known to significantly influence some chemical and biological processes. The chemical differences between Schiff and Mannich bases are characterized by strong intramolecular hydrogen bonds, resulting from the presence of, respectively, single or double carbon-nitrogen bonds in the chelate rings. Differences are especially visible in the hydrogen transfer processes from molecular (O-H⋯N) to the proton transfer (O⋯H-N) forms. The reaction in a Schiff base occurs as an ordinary hydrogen transfer from a donor to an acceptor, while in a Mannich base the transfer of hydrogen occurs simultaneously with a C-N bond scission leading to an intermolecular complex. The attachment of electrons preserves the overall structural topology of the reactants; however, due to differences in electron affinities, reactions switch from endothermic to exothermic and reaction rates in the anionic systems are significantly higher. The difference in electron affinities for particular reactants comes from the fundamental differences in electron binding mechanisms, leading to the valence-bound or dipole-bound states. The observed mechanisms are closely related to the nature and size of the LUMOs of the parent molecules. The transition state of the Mannich base corresponds to the σ and π orbital conversion and possesses the characteristics of the valence-bound state and the dipole-bound electronic state.

Using DFT method, calculations of the structure and energy of adduct of electron and phenol-pyridine complex were made. It has been shown that the additional electron has been located mainly on the pyridine ring. The additional electron causes a change in the geometrical structure of the complex and in particular, in the transfer of the proton in the hydrogen bridge from phenol to pyridine.

The molecular complexes of the pyrazine derivatives with anilic acids were analyzed in terms of the structure of molecules, the vibrational spectra, INS,1HNMR and theoretical approach.

IR and Raman spectra and phase transitions have been studied on various salts of azabicyclo[2.2.2]octane (ABCO) and l,4-diazabicyclo[2.2.2]octane (DABCO) which forms with simple strong acids adducts of 2 : 1, 1 : 1 and 1 : 2 composition. Only 2 : 1 DABCO adducts form homoconjugated cations containing [NH · · · H]+ hy. drogen bonds close to symmetrical ones, showing broad absorption in the low frequency region and strong temperature effect. The Evans holes observed in this case can be ascribed to a coupling of protonic vibrations with skeletal <58 (N-C3) and bas (N-C3) modes.

In the present paper we would like to describe the structural and dynamical properties of crystalline dihydrated complex of melamine (2,4,6–triamino-1,3,5–triazin-1-ium) with squaric acid (3,4-dihydroxycyclobut-3-ene-1,2-dione) abbreviated as MH·SQ. The X-ray diffraction studies show the presence of deprotonated units (C4O4)2- and single protonated melamine cations surrounded by tetrameric water assemblies (H2O)4. The formation of the water tetramers deserves a special attention. IR absorption and Raman spectra reflect a richness of structural units and numerous hydrogen bonds. The presence of the continua in the IR spectra, with a characteristic presence of the Hadži's trio enriched by a numerous submaxima, may be ascribed to the structural units and to the various types of hydrogen bonds. The density functional theory calculation with the periodic boundary conditions was use to precise analysis of experimental data.

A review of selected literature data related to intramolecular hydrogen bonding in ortho-hydroxyaryl Schiff bases, ortho-hydroxyaryl ketones, ortho-hydroxyaryl amides, proton sponges and ortho-hydroxyaryl Mannich bases is presented. The paper reports on the application of experimental spectroscopic measurements (IR and NMR) and quantum-mechanical calculations for investigations of the proton transfer processes, the potential energy curves, tautomeric equilibrium, aromaticity etc. Finally, the equilibrium between the intra- and inter-molecular hydrogen bonds in amides is discussed.

Pyrazine belongs to an interesting class of heterocyclic compounds of moderate basicity that are capable of forming various molecular complexes of intriguing architecture, particularly from the crystallo-chemical point of view. The presence of methyl (-CH3) groups in the pyrazine molecule is of interest to researchers because of the effect of the charge transfer phenomenon on the rotational barrier of the -CH3 group. In the present review we analyzed the structures of various molecular complexes containing proton donors such as p-nitrophenol, picric acid, squaric acid, triiodo hydride, nitric acid and, in particular, chloranilic and bromanilic acids. The interactions, mainly via hydrogen bonds, lead to a variety of crystal structures mostly due to proton transfer to the nitrogen atoms in pyrazine. In this review, the structures of complexes and their crystal-lattice packing studied using X-ray diffraction are discussed. The variety of hydrogen bonds in the complexes studied is best reflected in their infrared absorption spectra. In many cases the absorption continua typical of the strong hydrogen bonds are present. Inelastic neutron scattering (INS) spectra were used to analyze dynamics. The results of tunneling splitting ascribed to methyl groups were also found interesting. This aspect is given focus in this work. One of the main observations from these studies was that methyl groups in the solid state of the molecular complexes rotated more freely than those in pure methyl derivatives of pyrazine.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The crystal and molecular structure of p-N,N′-tetraacetylodiaminodurene (TADD) is reported based on the X-ray diffraction studies. The N-acetyl moieties are planar and all N-acetyl groups are perpendicular to the ring plane. Methyl groups both of acetyl moieties and of durene form a number of non-conventional hydrogen bonds with nitrogen and oxygen atoms. The vibrational spectra very well reflect the structure of molecules and their contacts. They are compared with calculated data by using various theoretical approaches. The neutron scattering spectra show two tunnel lines of low energy values (at ±0.9 and ±2.3μeV at 4K), which can be ascribed to methyl groups of N-acetyl moieties, which behave more freely than those attached to the phenyl ring.

The electric response was analyzed in the vicinity of the structural phase transition at 412 K in the single crystals of 2,5-dichloro-3,6-dihydroxy-p-benzoquinone (chloranilic acid, CLA) with 4,4 '-di-t-butyl-2,2 '-bipyridyl (dtBBP). The dielectric permittivity of the complex measured along the b direction between 300 and 440 K and at frequencies ranging from 500 Hz to 2 MHz indicates two phenomena. At low frequencies, dielectric losses are ascribed to the electric conductivity of the crystal, while at high frequencies, to the dielectric relaxation described by means of the Cole-Cole relationship. The parameters of the dielectric response: the relaxation time, tau, the dielectric increment, epsilon(o) - epsilon(1), and the distribution parameter of the relaxation time, a, were estimated and analyzed. The low-temperature structure of the crystals indicates the antiferroelectric arrangement of the supramolecular hydrogen bonds. The dielectric results also presented for the deuterated crystals of dtBBP CLA proved that the dynamics of protons in the hydrogen bonds are responsible for the mechanism of phase transition. (C) 2015 Elsevier B.V. All rights reserved.

1. kwas chloranilowy (CLa) i kwas kwadratowy (H2sQ) jako donory protonu w kompleksach organicznych 2. struktury kompleksów tetrametylopirazyny z wybranymi protono donorami 3. Widma oscylacyjne kompleksów 4. dynamika grup metylowych w TMP; zastosowanie metod rozpraszania neutronów Piśmiennictwo cytowane G. BaTor, L. soBCZyk 870 prof. dr hab. Grażyna Bator jest profesorem na Wydziale Chemii Uniwersytetu Wrocławskiego. Urodziła się 7 stycz nia 1958 roku w Pleszewie. studia na Wydziale elektroniki Politechniki Wrocławskiej odbyła w latach 1976–1981. doktorat pt. „Badanie dynamiki molekularnej alkoholi trzeciorzędowych metodami dielektrycznymi” napisała pod kierunkiem prof. Zbigniewa Malarskiego i obroniła w 1986 r. na Wydziale Chemii UWr. Po przedstawieniu w 2000 r. rozprawy habilitacyjnej „Badania przemian fazowych w halogenoantymonianach(iii) alkiloamoniowych metodą relaksacji dielektrycznej i widm w podczerwieni” uzyskała stopień doktora habilitowanego. Tytuł profesora uzyskała w 2007 roku. odbyła staże naukowe w kULeuven w Belgii i w ZiBJ w dubnej, Fr. Jest współautorem 134 oryginalnych artykułów naukowych z dziedziny chemii materiałów, w szczególności własności elektrycznych ciał stałych i ferroelektryczności oraz mechanizmów przemian fazowych i dynamiki molekularnej w kryształach molekularno-jonowych. Wypromowała 2 doktorów. Jest kierownikiem specjalizacji „Chemia Materiałów dla Nowoczesnych Technologii” na Wydziale Chemii UWr. prof. dr hab. Lucjan Sobczyk jest emerytowanym profesorem chemii fizycznej Uniwersytetu Wrocławskiego. Urodził się 4 sierpnia 1927 r. w Natalinie, studia chemiczne odbywał na Politechnice Wrocławskiej w latach 1946-1951, aspiranturę w instytucie Precyzyjnej Technologii Chemicznej w Moskwie w latach 1951–1954. Habilitował się w 1962 r. odbywał staże naukowe w Paryżu, aberystwyth i Ljubljanie. Jest autorem lub współautorem 24 książek i skryptów, 34 artykułów i 290 oryginalnych prac badawczych w dziedzinie struktury cząsteczek, oddziaływań międzycząsteczkowych (w szczególności wią zania wodorowego), własności dielektrycznych cieczy i kryształów oraz przejść fazowych. Profesor Lucjan sobczyk wypromował 22 doktorów, spośród których 12 habilitowało się a 9 uzyskało tytuł profesora nauk chemicznych. Jest współtwórcą Wrocławskiej szkoły Chemii Fizycznej – od roku 1968 kieruje seminarium pt. „dielektryczne i optyczne aspekty oddziaływań międzycząsteczkowych”. W 1976 r. został wybrany na członka Polskiej akademii Nauk. Wyróżniony wieloma medalami i wysokimi odznaczeniami państwowymi. Pełnił wiele odpowiedzialnych funkcji na Uczelni i w organizacjach naukowych, w tym jako prezes Polskiego Towarzystwa Chemicznego. Został wyróżniony doktoratem honoris causa Uniwersytetu Leningradzkiego i Uniwersytetu Wrocławskiego a także tytułem profesora honorowego instytutu Niskich Temperatur i Badań strukturalnych PaN we Wrocławiu. WiąZaNia WodoroWe W koMPLeksaCH WyBraNyCH kWasóW orGaNiCZNyCH 871

The crystal and molecular structure of the 2,3,5,6-tetramethylpyrazine (TMP) complex with 2,5-dibromo-3,6-dihydroxy-p-quinone (bromanilic acid, BRA) has been studied and the results are compared with TMP CLA (2,5-dichloro-3,6-dihydroxy-p-quinone (chloranilic acid, CLA) complex. The X-ray structure of TMP BRA complex indicates the formation of dimeric units, in which two BRA(-) anions are connected by two O-H···O (2.646(2) Å) hydrogen bonds, whereas the cations and anions are joined together by strong N(+)-H···O(-) (2.657(2) Å) hydrogen bonds. The results are analyzed in terms of both the methyl group surroundings and the C-H···O and N(+)-H···O(-) (or N···H-O) bridge formations. Both effects, the strength of the N(+)-H···O(-) hydrogen bonds and steric hindrance for the rotations, are responsible for the CH3 group dynamics. For the TMP CLA and TMP BRA complexes, the inelastic neutron backscattering spectra were also investigated. In the case of TMP CLA, four tunneling signals have been observed in the energy range ±30 μeV, which indicates four inequivalent methyl groups in the crystal structure at the lowest temperature. No tunneling splitting is observed in the case of the TMP BRA complex, most probably due to the overlapping with the elastic peak. The tunneling results are consistent with the (1)H NMR spin-lattice relaxation time investigations in a wide temperature range, which also point to the CH3 group tunneling effect in the case of TMP CLA.

An extremely strong H/D isotope effect observed in hydrogen bonded A-H…B systems is connected with a reach diversity of the potential shape for the proton/deuteron motion. It is connected with the anharmonicity of the proton/deuteron vibrations and of the tunneling effect, particularly in cases of short bridges with low barrier for protonic and deuteronic jumping. Six extreme shapes of the proton motion are presented starting from the state without possibility of the proton transfer up to the state with a full ionization. The manifestations of the H/D isotope effect are best reflected in the infra-red absorption spectra. A most characteristic is the run of the relationship between the isotopic ratio nH/nD and position of the absorption band shown by using the example of NHN hydrogen bonds. One can distinguish a critical range of correlation when the isotopic ratio reaches the value of ca. 1 and then increases up to unusual values higher than . The critical range of the isotope effect is also visible in NQR and NMR spectra. In the critical region one observes a stepwise change of the NQR frequency reaching 1.1 MHz. In the case of NMR, the maximal isotope effect is reflected on the curve presenting the dependence of Δd (1H,2H) on d (1H). This effect corresponds to the range of maximum on the correlation curve between dH and ΔpKa that is observed in various systems. There is a lack in the literature of quantitative information about the influence of isotopic substitution on the dielectric properties of hydrogen bond except the isotope effect on the ferroelectric phase transition in some hydrogen bonded crystals.

The subject of the study is the crystal structure of 2,3,5,6-tetramethylpyrazine (TMP) nitrate dihydrate in which two types of hydrogen bonds are formed, namely +N–H⋯O between protonated tetramethylpyrazine and water as well as between OH group (in water molecule) and oxygen atom of the nitrate anion. The structure is well reflected both in infrared and Raman spectra. Particularly clear picture of broad bands above 2000cm−1 is visible. The experimental and calculated Raman spectra are in a relatively good agreement. This crystal structure changes dramatically if the hydrogen-bonded complex is dissolved. In acetonitrile it dissociates with formation of the intermolecular (N–H⋯N)+ hydrogen bonds between two TMP molecules, and free water molecules. In methylenchloride, besides the intermolecular (N–H⋯N)+ hydrogen bonds, the formation of (O⋯H⋯O)+ species between two water molecules is established.

The almost planar molecular complex, formed by 3,4,7,8-tetramethyl-phenantroline (Me4phen) and picric acid (2,4,6-trinitrophenol, PA), has been investigated by using X-ray diffraction, vibrational spectroscopy, tunnel splitting and theoretical analysis. In the crystal of Me4phen·PA two short bifurcated hydrogen bonds N+–H···O− [2.6238(14)Å] and N+–H···N [2.6898(15)Å] are created. Infra-red spectra show the hydrogen bonds are short. The neutron backscattering spectrum of Me4phen⋅PA at 3K shows two tunneling peaks at ca. 1 and 3μeV. The number of the peaks is consistent with X-ray diffraction studies, which disclosed the inequivalence of methyl groups in the crystal structure. The comparison of the tunnel splitting for neat Me4phen and for its complex with picric acid indicates that in the latter case the methyl groups are more strongly engaged in the intermolecular interactions, particularly with nitro group oxygen atoms of picric acid, leading to an increase of the CH3 rotational barrier height.

The aim of the present paper is an analysis of the hydrogen bond properties for the acid-base systems depending on the ability to the proton transfer in the formulation of the Brönsted approach. After definition of the proton transfer equilibrium expressed by using the equation log KPT=ξΔpKN, various examples of different physical properties, such as dipole moments, IR spectra, and nuclear magnetic resonances, are presented which correlate with the ΔpKN value. In such a way, a critical state of hydrogen bonding can be defined that corresponds to the potential of the proton motion for either single minimum or double minimum with low barrier. A particular attention in this paper found electronic spectra which have not been analysed so far and the quantitative analysis of the vibrational polarizability which can reach very high values of the order of electronic polarizability.

The packing properties of 4′-butylo-4-isothiocyanatotolane in the solid state and the liquid crystalline phases were studied by X-ray diffraction and infrared spectroscopy. The crystal structure comprises a herringbone-like packing with an efficient π–π overlap. The factors that shape the unusual broad νas(NCS) band are discussed. Selection of modes involved in the Fermi resonance interaction with the νas(NCS) vibration is supported by directions of their transition dipole moments obtained at the DFT calculations. A specific rearrangement in the herringbone packing, accompanying transition from the solid state to the isotropic phase was confirmed by the dichroic ratio values.

The complexation of 2,5-dimethylpyrazine (2,5-DMP) with 2,5-dichloro-3,6-dihydroxy-p-benzoquinone (CLA) leads to the formation of the hydrogen bonded OH⋯N infinite chains without any proton transfer. In the high and medium frequency region of the IR spectra a characteristic Hadži’s trio with maxima at ca. 2400, 1800 and 1150cm−1 is observed. The infrared, Raman and inelastic neutron scattering (INS) spectra are compared with those calculated by using the DFT methods applied to the crystalline state. The optimization of the structure by using this theoretical approach is also performed. Very good conformity of the experimental and theoretical structures is visible. The reproduction of vibrational spectra is also good except for the low frequency bands related to the CH3 torsional modes. One gets relatively good agreement by using PWC(dnp) approach. Applications of other theoretical models leads to much higher values of CH3 torsional frequency.