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1Author    Snezhana BakalovaRequires cookie*
 Abstract    o lv e n t E f fe c ts o n th e F lu o re s c e n c e P r o p e r tie s o f M e th y ld ih y d ro q u in o lin o n e s The absorption and fluorescence spectra and the fluorescence quantum yields of two methyl-2,3-dihydro-4(lH)-quinolinones in various solvents are reported. In some solvents deuteration-induced fluorescence enhancement has been observed. The solvent effects in aprotic solvents are consistent with the general type of solvent interaction. For protic solvents, solute-solvent complexation in the excited state is suggested. 
  Reference    Z. Naturforsch. 46a, 823—827 (1991); received May 24 1991 
  Published    1991 
  Keywords    Fluorescence, Dihydroquinolinones, Hydrogen bond 
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 TEI-XML for    default:Reihe_A/46/ZNA-1991-46a-0823.pdf 
 Identifier    ZNA-1991-46a-0823 
 Volume    46 
2Author    Matthias Frey, PeterG. JonesRequires cookie*
 Title    Secondary Bonding Interactions in Some Halopyridinium and Dihalopyridinium Halides  
 Abstract    The packing motifs of 2-and 3-chloropyridinium chloride can be interpreted in terms of classical hydrogen bonds N+-H -C 1~ and non-classical C-H--C1" interactions, with halo-gen-halogen contacts playing a subordinate role. In the corresponding bromine derivatives, Br--Br interactions are much more important. Of the dihalo derivatives, 3,5-dichloropyridinium chloride crystallises with classical linear hydrogen bonds of the form N+-H -C1_ , but its chlorine-chlorine interactions are at best weak; the corresponding bromine derivative displays aggregates of bromine atoms and three-centre hydrogen bonds N+-H (-B r")2 . 
  Reference    Z. Naturforsch. 56b, 889—896 (2001); received May 15 2001 
  Published    2001 
  Keywords    Pyridinium, Halides, Hydrogen Bonds 
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 TEI-XML for    default:Reihe_B/56/ZNB-2001-56b-0889.pdf 
 Identifier    ZNB-2001-56b-0889 
 Volume    56 
3Author    M. Grottel, A. Kozak, Z. PająkRequires cookie*
 Title    *H and 19 F NMR Study of Cation and Anion Motions in Guanidinium Hexafluorozirconate  
 Abstract    Proton and fluorine NMR second moments and spin-lattice relaxation times of polycrystalline guanidinium hexafluorozirconate and its deuterated analogue were studied in laboratory (60 MHz) and rotating (H, = 20 G) frames over a wide range of temperature. An analysis of the experimental results enabled us to reveal a dynamical inequivalence of two crystallographically independent cations and an unexpected high mobility of nonspherical anion dimers. A comparison of the ions dynamics in 2:1 complex studied with the guanidinium 1:1 and 3:1 complexes has shown a significant contribution of the hydrogen bonds to the potential barriers hindering the anion reorien-tations. At low temperatures a proton motion in the hydrogen bond and at 400 K a solid-solid phase transition have been discerned. 
  Reference    Z. Naturforsch. 51a, 991—996 (1996); received May 14 1996 
  Published    1996 
  Keywords    NMR, Ion Motions, Hydrogen Bonds, Phase Transitions 
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 TEI-XML for    default:Reihe_A/51/ZNA-1996-51a-0991.pdf 
 Identifier    ZNA-1996-51a-0991 
 Volume    51 
4Author    Nobuo Nakamura, Hirotsugo Masui, Takahiro UedaRequires cookie*
 Title    Effect of Intermolecular Hydrogen Bonding on the Nuclear Quadrupole Interaction in Imidazole and its Derivatives as Studied by ab initio Molecular Orbital Calculations  
 Abstract    Ab initio Hartree-Fock molecular orbital calculations were applied to the crystalline imidazole and its derivatives in order to examine systematically the effect of possible N-H---N type hydrogen bond-ing on the nuclear quadrupole interaction parameters in these materials. The nitrogen quadrupole coupling constant (QCC) and the asymmetry parameter (r?) of the electric field gradient (EFG) were found to depend strongly on the size of the molecular clusters, from single molecule, to dimer, trimer and to the infinite molecular chain, i.e., crystalline state, implying that the intermolecular N-H -N hydrogen bond affects significantly the electronic structure of imidazole molecule. A certain correla-tion between the QCC of l4 N and the N-H bond distance R was also found and interpreted on the basis of the molecular orbital theory. However, we found that the value of the calculated EFG at the hy-drogen position of the N-H group, or the corresponding QCC value of 2 H, increases drastically as /C* when R is shorter than about 0.1 nm, due probably to the inapplicability of the Gaussian basis sets to the very short chemical bond as revealed in the actual imidazole derivatives. We suggested that the ob-served N-H distances in imidazole derivatives should be re-examined. 
  Reference    Z. Naturforsch. 55a, 315—322 (2000); received August 26 1999 
  Published    2000 
  Keywords    Hydrogen Bond, Nuclear Quadrupole Interaction, Molecular Orbital, Imidazole 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0315.pdf 
 Identifier    ZNA-2000-55a-0315 
 Volume    55 
5Author    Taka-Aki Nihei, Shin'. Ichi, Ishimaru, Ryuichi IkedaRequires cookie*
 Title    C1 NQR Studies of Hydrogen Transfer in Crystalline /7-Chlorobenzoic Acid  
 Abstract    35 C1 NQR frequencies and spin-lattice relaxation times 7, Q were measured inp-ClC 6 H 4 C0 2 H(PCB A) and p-ClQF^CC^DtPCBA-d,) at 77-333 K. T lQ in PCB A gave a shallow minimum of 8.0 ms at ca. 110 K, which could be explained by a double proton transfer mechanism in the carboxylic acid dimer referring to *H NMR data giving a T 1H minimum at almost the same temperature. PCBA-d, showed temperature dependent NQR frequencies quite analogous to those in PCBA, whereas their r 1Q behavi-our was quite different in its minimum value and its temperature as well as temperature gradient. These results were explained by suppressed deuteron tunnelling and the Ubbelohde effect. 
  Reference    Z. Naturforsch. 55a, 355—358 (2000); received August 27 1999 
  Published    2000 
  Keywords    CI NQR, Hydrogen-Bond, Hydrogen-transfer, Tunneling 
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 TEI-XML for    default:Reihe_A/55/ZNA-2000-55a-0355.pdf 
 Identifier    ZNA-2000-55a-0355 
 Volume    55 
6Author    Masao Hashimoto, Akiko Shono, Yoshiyuki Mido, Haruo Niki, Hiroshi Hentona, Koichi ManoRequires cookie*
 Title    Narrowing of the 3 5 CI NQR Lines of Trichloroacetamide Caused by Its Ferroelectric Phase Transition  
 Abstract    Dielectric measurements on single crystals and DSC of the title compound (monoclinic, space group P2 X) revealed a ferroelectric transition at ca. 355 K (AH xs 0.5 kJ mol"Powder x-ray diffraction indicated that the high temperature phase is also monoclinic and the change in volume at the transition is very small. A displacement of hydrogen atoms is considered as responsible for the appearance of ferroelectricity. The 35 C1 NQR signals at ca. 77 K were considerably broad, but a drastic narrowing took place after the compound had once experienced the phase transition. A tentative assignment of the NQR spectrum was made from a calculation of the NQR frequencies based on the CNDO/2 method. Another phase transition was evidenced by a small drift of the DSC curve and a slight anomaly of the dielectric behavior around 358 K. The present *H NMR experi-ments gave no indication of the onset of torsional motion of the NH 2 group reported to occur at ca. 210 K. 
  Reference    Z. Naturforsch. 45a, 327—333 (1990); received August 26 1989 in revised form November 1 1989 
  Published    1990 
  Keywords    NQR, Phase transition, Ferroelectricity, Hydrogen bond, Disordered structure 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0327.pdf 
 Identifier    ZNA-1990-45a-0327 
 Volume    45 
7Author    R. Alf Steudel, Angela Albertsen, M. Onika Kustos, Joachim PickardtRequires cookie*
 Title    X-Ray Structural Analysis and Vibrational Spectra of Sodium Cysteine-S-sulfonate, +H3N C H (C 0 0 )CH 2S 20 3Na -3 /2 H 20 [1]  
 Abstract    The title com pound crystallizes orthorhombically (space group C 222,) with a = 797.0, b = 870.3 and c = 2739.0 pm. The anions are zwitterions which are heavily involved in intra-and intermolecular NH --O and OH -O hydrogen bonding. The two types o f sodium cations are coordinated by six oxygen atoms each o f which belongs to either S 0 3 groups (N a 2) or water molecules and S 0 3 groups (N a l). A second type o f water molecules is not coordinated to the cations. The SS bond length is 208.2 pm. Infrared and Raman spectra o f the title com pound are reported and tentatively assigned. The SS stretching vibration is observed at 409 cm -1. 
  Reference    Z. Naturforsch. 48b, 555—560 (1993); received July 23 1992 
  Published    1993 
  Keywords    Cysteine, S-Sulfonate, Structure, Spectra, Hydrogen Bonds 
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 TEI-XML for    default:Reihe_B/48/ZNB-1993-48b-0555.pdf 
 Identifier    ZNB-1993-48b-0555 
 Volume    48 
8Author    Norbert Kuhn3, Joanna Fahl3, Roland Boeseb, Gerald HenkelcRequires cookie*
 Title    Zur Reaktion von 2,3-Dihydroimidazol-2-ylidenen mit Pentafluorpyridin: Carbene als Reaktionspartner in der nucleophilen aromatischen Substitution [1] On the Reaction of 2,3-Dihydroimidazol-2-ylidenes with Pentafluoropyridine: Carbenes as Reactants in Nucleophilic Aromatic Substitution [1]  
 Abstract    The 2,3-dihydro-l,3,4,5-tetraalkylimidazol-2-ylidenes 3 (R = Me, i'so-Pr) react immediately with pentafluoropyridine to form the 2-tetrafluoropyridylimidazolium salts 4 in good yields. In contrast with the tetramethyl derivative 4a, alkyl fluoride is eliminated from the isopropyl salt 4b to give 1 -isopropyl-4,5-dimethyl-2-tetrafluoropyridylimidazole, which dimerises via hydrogen bridges in the solid state (7). The X-ray structures of l,3-diisopropyl-4,5-dimethyl-2-tetrafluoropyridylimidazolium chloride (5) and 7 are reported. 
  Reference    Z. Naturforsch. 53b, 881—886 (1998); eingegangen am 9. April 1998 
  Published    1998 
  Keywords    Carbenes, Imidazoles, Pyridines, Nucleophilic Aromatic Substitution, Hydrogen Bonds 
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 TEI-XML for    default:Reihe_B/53/ZNB-1998-53b-0881.pdf 
 Identifier    ZNB-1998-53b-0881 
 Volume    53 
9Author    BirteA. Hrens, PeterG. Jones, Sonderdruckanforderungen An, ProfP G Dr, Jo­Requires cookie*
 Title    P olysulfonylam ine, C X X II  
 Abstract    [1] N ich t-kon ven tion elle W asserstoff­ brücken in B is[diphenylphosphino-(diphenylphosphinselenid)m ethan]-gold(I)-di(m ethansulfonyl)am id Polysulfonylamines, CXXII. Non-Conventional Hydrogen Bonds in Bis[diphenylphosphino(diphenylphos-phinselenide)methane]gold(I) Di(methanesulfonyl)amide In the crystal structure of (dppmSe)2Au+ N (S 0 2C H 3)2-(dppm = Ph2PCH2PPh2) chains are formed from non-conventional hydrogen bonds of the type C -H --0 . Within these chains two bi­ furcated hydrogen bond systems are present, each involving one methylene hydrogen (H ---0 2.51, 2.65 A) and one phenyl hydrogen (H — O 2.31, 2.35 A) as donors. 
  Reference    Z. Naturforsch. 54b, 1474—1477 (1999); eingegangen am 16. Juli 1999 
  Published    1999 
  Keywords    Gold(I), Hydrogen Bonds, X-Ray Data 
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 TEI-XML for    default:Reihe_B/54/ZNB-1999-54b-1474_n.pdf 
 Identifier    ZNB-1999-54b-1474_n 
 Volume    54 
10Author    Maciej Kubicki3, Teresa Borowiak3, WieslawZ. AntkowiakbRequires cookie*
 Title    Hydrogen Bonds in "Carboxyoximes": the Case of Bomane Derivatives  
 Abstract    The tendency of forming mixed carboxyl-to-oxime hydrogen bonds was tested on the series of bomane derivatives: one with the acid function only (bomane-2-erajfo-carboxylic acid), one with the oxime function (2,2'-diethylthiobomane-3-oxime), and one with both oxime and carboxylic functions (bomane-2-oxime-3-endo-carboxylic acid). The crystal structures of these compounds were determined by means of X-ray diffraction. In bomane-2-^n^/o-carboxylic acid and 2,2'-diethylthiobom ane-3-oxime 'homogenic' hydrogen bonds were found, and these hydrogen bonds close eight-and six-membered rings, respectively. By contrast, in bomane-2-oxime-3-era/o-carboxylic acid 'heterogenic' hydrogen bonds between carboxylic and oxime bonds were found. This carboxylic-oxime, or 'carboxyoxime' system is almost always present in compounds which have both oxime and carboxylic groups; therefore it can be regarded as an element of supramolecular structures (synthon). The presence of such synthons can break the tendency of carboxylic acids and oximes towards crystallizing in centrosymmetric structures. 
  Reference    Z. Naturforsch. 55b, 677—684 (2000); received March 16 2000 
  Published    2000 
  Keywords    Bom ane Derivatives, Hydrogen Bonds, Supramolecular Synthons 
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 TEI-XML for    default:Reihe_B/55/ZNB-2000-55b-0677.pdf 
 Identifier    ZNB-2000-55b-0677 
 Volume    55 
11Author    M. S. De Giam, M. G. Iam Biagi, D.M S EsquivelRequires cookie*
 Title    Hydrogen Bond Indices and Tertiary Structure of Yeast tRNAPhe  
 Abstract    The rigidity and stability of the tertiary structure of yeast tR N A Phe is related to a bond index obtained in an IEHT (iterative extended Hückel theory) calculation. The index permits a quantitative estimate of the electron density along the hydrogen bond, having thus an appealing physical meaning. The results indicate that Hoogsteen-type bonds have, as expected, greater electronic population than Watson-Crick type ones. Other non-Watson-Crick pairs, the wobble pair and G|5—C48, exhibit high values of the index for the N H ... O bond. In the triples, the electron density of the hydrogen bridges does not weaken (compared with the one of the pairs involved). Contour density maps are shown and dipolar moments of pairs and triples are qualitatively discussed. 
  Reference    Z. Naturforsch. 38c, 621 (1983); received March 29 1983 
  Published    1983 
  Keywords    tRNAPhe, Tertiary Structure, Hydrogen Bond, Bond Index, Non-Watson-Crick Pairs 
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 TEI-XML for    default:Reihe_C/38/ZNC-1983-38c-0621.pdf 
 Identifier    ZNC-1983-38c-0621 
 Volume    38 
12Author    Masao Hashimoto, Takahiro Isono, Haruo Niki, Takuya HigaRequires cookie*
 Title    Fade-Out of 35 C1 NQR in Chloral n-Butylhemiacetal  
 Abstract    Continuous wave and pulsed NQR, dielectric absorption and infrared (IR) measurements were carried out to investigate the origin of the peculiar temperature dependence of the S/N ratio of the 35 C1 NQR in the title compound. The dielectric and IR experiments evidenced a thermally activated jumping motion of the H atom participating in O-H O H-bonds. As T x and T 2 below 120 K were much longer than T 2 * of about 10 us, the line broadening in this temperature region was attributed to static lattice defects. A random freezing of the jumping motion may be the origin of the defects. In the range 120-170 K, S/N was extremely low and T 2 was less than 10 |is, probably having a minimum in between. The short T 2 is considered to be responsible for the low S/N. A minimum of S/N at about 240 K is attributed to a 7\ minimum (less than 10 (is) at that temperature. 
  Reference    Z. Naturforsch. 45a, 472—476 (1990); received August 26 1989 in revised form December 1 1989 
  Published    1990 
  Keywords    NQR, Relaxation times, Hydrogen bond, Dielectric absorption, Disordered structure 
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 TEI-XML for    default:Reihe_A/45/ZNA-1990-45a-0472.pdf 
 Identifier    ZNA-1990-45a-0472 
 Volume    45 
13Author    Takashige Shimizu, Tetsuo Asaji, Daiyu Nakamura, Ryuichi IkedaRequires cookie*
 Title    Uniaxial Reorientation of Octahedral Complex Anions Excited in Triethylammonium Hexachlorostannate (IV) Crystals  
 Abstract    The temperature dependence of the 35 C1 NQR spin-latticew relaxation time T1Q has been deter-mined for the three resonance lines observed in [(C2H5)3NH]2SnCl6. The higher frequency lines fade out around 150 K upon heating, whereas the lowest line shows up to room temperature no anomaly, although these three lines are assigned to chlorines belonging to the same complex anion. The T1Q values of the higher two lines decrease exponentially around the fade-out temperature, where T iq of the lowest line shows no such behavior. These results are explained by the onset of uniaxial reorientations of the octahedral complex ions by 90° about the Cl-Sn-Cl axis containing the lowest frequency chlorines. The activation energy (£J of this reorientation (22-24 kJ moP 1) is the lowest so far reportd for [SnCl6] 2-ions. £a about the other axes is 67 kJ mop 1 , indicating a remarkable anisotropic reorientation. 
  Reference    Z. Naturforsch. 47a, 283—287 (1992); received July 19 1991 
  Published    1992 
  Keywords    Spin-Lattice Relaxation, NQR, NMR, Reorientational Motion, Hydrogen Bond 
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 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0283.pdf 
 Identifier    ZNA-1992-47a-0283 
 Volume    47 
14Author    Yoshio Kume, Maki Tokoro, Tetsuo Asaji, Ryuichi Ikeda, Daiyu NakamuraRequires cookie*
 Title    Reorientational Motion of Hydrogen Bonded Octahedral Complex Anions in Hydrazinium Hexachlorostannate(IV), (N 2 H 5 ) 2 SnCl 6 , as Studied by 35 C1 NQR Spin-Lattice Relaxation Measurements  
 Abstract    The temperature dependences of NQR frequencies and spin-lattice relaxation times, T1Q, of 35 C1 in (N2H5)2SnCl6 were measured. Four NQR signals distributed in a fairly wide frequency range were observed, the lowest-frequency line exhibiting an anomalous positive temperature coefficient. The highest-frequency line showed a steep temperature dependence. These results could be interpreted by considering the intermolecular interaction between CI and -NH2 in N2H^. Below ca. 250 K, T1Q of the upper three signals exhibited a gradual decrease upon heating, explainable by lattice vibra-tions, while a shallow Tig minimum, ascribable to the modulation of electric quadrupole interaction, was observed at ca. 11ÖK for the lowest-frequency signal. The reorientation of [SnCl6] 2 ~ was elucidated to be highly anisotropic, in that it reorients about one of the CI-Sn-Cl axes much more frequently than about the other two axes. The activation energies were determined to be 62 and 94 kj mol -1 for the respective reorientations. 
  Reference    Z. Naturforsch. 47a, 288—292 (1992); received July 17 1991 
  Published    1992 
  Keywords    Key word: Spin-Lattice Relaxation, NQR, NMR, Reorientational Motion, Hydrogen Bond 
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 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0288.pdf 
 Identifier    ZNA-1992-47a-0288 
 Volume    47 
15Author    Takeshi Kyan, Hamagawa, Takahiro Isono, Masao HashimotoRequires cookie*
 Title    Hiroshi  
 Abstract    The crystal structure of cyclohexylhemiacetal (cycHx-CH) was determined at 296 K: monoclinic, space group P2 Jc, a =1028.7 (9), b = 609.5 (1), c = 1811.9 (4) pm, and ß = 99.79 (3)°, Z -4, R = 0.0552. The three 5s Cl NQR lines in cycHx-CH, T., T2, and T2*, were measured by a pulsed method at 80-300 K. Below 200 K Tf 1 obeyed the T law well, indicating that the spin lattice relaxation is governed by lattice vibrations. The reorientation of CC13 seems to be responsible for the sharp T: drop observed above 250 K. Shoulders in the T { vs. 1/T curves indicate the presence of Ti minima at about 240 K. A fluctuation of the EFG due to a dynamic disorder of hydrogen atoms in the OH groups is assumed to explain the T x minima. 
  Reference    Z. Naturforsch. 47a, 299 (1992); received July 25 1991 
  Published    1992 
  Keywords    Chlorine NQR, Spin-lattice relaxation, Hydrogen bond, Crystal structure 
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 TEI-XML for    default:Reihe_A/47/ZNA-1992-47a-0299.pdf 
 Identifier    ZNA-1992-47a-0299 
 Volume    47 
16Author    Ivar Olovsson, Halina Ptasiewicz-Bak, GarryJ. MclntyreRequires cookie*
 Title    Superposition and Polarization Effects on the Electron Density of Lone Pairs  
 Abstract    There appears to be conflicting experimental evidence on the redistribution of the electron density in the lone-pair and other regions of a molecule due to the interaction with its nearest neighbours. In some experimental as well as theoretical deformation density maps a decrease in the lone-pair density has been reported, whereas in other cases an increase has been found. It appears that two major, counteracting factors are responsible for these differences (apart from experimental errors in the diffraction studies and limited accuracy in the theoretical calculations): an increase in the lone-pair density is expected due to the polarizing influence of the neighbours, whereas simple superposition of the isolated monomer deformation densities will lead to an apparent decrease due to the overlap with the negative contours of the neighbouring atom. Depending on which of these factors is the dominant one, an increase or decrease may thus be observed. These points are illustrated by recent results on nickel sulfate hexahydrate and some other hydrogen-bonded compounds. The electron density based on the fitted deformation functions of all atoms in the structure is compared with the individual densities calculated from deformation functions of the separate monomers. In this way the effects of simple superposition of the individual densities have been studied, and a partitioning of the electrostatic and polarization contributions to the hydrogen bonds and other relatively weak bonds to the oxygen lone-pairs attempted. 
  Reference    Z. Naturforsch. 48a, 3—11 (1993); received January 30 1992 
  Published    1993 
  Keywords    Electron density, Superposition effects, Polarization effects, Lone pairs, Hydrogen bonds 
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 TEI-XML for    default:Reihe_A/48/ZNA-1993-48a-0003.pdf 
 Identifier    ZNA-1993-48a-0003 
 Volume    48 
17Author    Masao Hashimoto, Shuji Matsumoto, Masakazu Kunitomo, Haruo Niki, Hirotaka Odahara, Katsuji TamakiRequires cookie*
 Title    35C1 NQR Relaxation and Hydrogen Bond in Some Chloral Hemiacetals  
 Abstract    The crystal structure of chloral ethylhemiacetal has been determined at 291 K: monoclinic, space group C f -P 2 lt Z = 2, a = 854.5(1), b = 594.0(3), c = 853.3(1) pm, ß = 108.30(2)°, R = 0.0962. A sharp decrease of the spin lattice relaxation time 7i found for the 35C1 N Q R o f the CC13 groups in chloral methyl-, ethyl-and n-heptylhemiacetals is attributed to the onset of reorientation of the group over a potential barrier o f ca. 39, 37, and 32 kJ/m ol, respectively. An unusual vs. 1/T curve with a 7i minimum superimposed on the sharp decrease of 7\ due to the reorientation was observed for each of the three Cl N Q R lines of nH p-C H . This phenom enon is tentatively ascribed to a fluctuation of EFG caused by jum ping m otion o f the hydrogen atom s in the OH groups. 
  Reference    Z. Naturforsch. 49a, 279 (1994); received August 16 1993 
  Published    1994 
  Keywords    Crystal structure, Hydrogen bond, Chlorine N Q R, Spin lattice relaxation 
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 TEI-XML for    default:Reihe_A/49/ZNA-1994-49a-0279.pdf 
 Identifier    ZNA-1994-49a-0279 
 Volume    49 
18Author    J.M M CordeiroRequires cookie*
 Title    Effective Pair Potentials and Structure of Water  
 Abstract    Classical Monte Carlo calculations have been performed in order to investigate the ability of the TIP4P, SPC, and SPCE water models to reproduce the structural features of liquid water. The simula-tions were carried out in the NPT ensemble at 4 thermodynamic conditions. The results are compared with recent neutron diffraction data. Essentially, the three models capture equally well the thermody-namic and structural features of water. Although they were parametrized to reproduce the water prop-erties at ambient conditions, the agreement with the experimental pair correlation functions was even better at supercritical conditions. This is because the effective pair potentials have some difficulty to re-produce cooperative interactions, like hydrogen bonds. These interactions are less effective at super-critical conditions, where the liquid behaves roughly like a gas 
  Reference    Z. Naturforsch. 54a, 311—316 (1999); received December 16 1998 
  Published    1999 
  Keywords    Monte Carle Simulation, Non-polarizable Water Models, Radial Distribution Functions, Hydrogen-bonds 
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 TEI-XML for    default:Reihe_A/54/ZNA-1999-54a-0311.pdf 
 Identifier    ZNA-1999-54a-0311 
 Volume    54 
19Author    T.Stanley Cameron, JamesD. Healy, RobertA. Shaw, Michael WoodsRequires cookie*
 Abstract    The structure of the title compound was determined by X-ray crystallography. The compound is a cyclic dimer with short N--O and N---S contacts. 
  Reference    (Z. Naturforsch. 31b, 1421—1422 [1976]; received July 19 1976) 
  Published    1976 
  Keywords    X-ray, Crystal Structure, Phosphorus Acid-Base Cyclic Dimer, Hydrogen-Bond 
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 TEI-XML for    default:Reihe_B/31/ZNB-1976-31b-1421_n.pdf 
 Identifier    ZNB-1976-31b-1421_n 
 Volume    31 
20Author    SvenM. Jessen, H. Orst Küppers, DeanC. LuehrsRequires cookie*
 Title    Hydrogen Bonding in Acid Li-, Ni-, Tetrabutylammonium, and Ammonium Salts of Benzene-1,2,4,5-tetracarboxylic Acid (Pyromellitic Acid)  
 Abstract    Four acid salts o f pyromellitic acid (benzene-1,2,4,5-tetracarboxylic acid) have been syn­ thesized and studied by X-ray diffraction and IR spectroscopy. (1) Dilithium dihydrogen py-romellitate pentahydrate, Li2[C6H 2(COO)4H 2] • 5 H zO; monoclinic, P 2 1/m, a = 6.214(2), b = 19.647(7), c = 6.592(2)Ä , ß = 115.90(2)°, Z = 2, R = 0.068, Rw = 0.067. (2) Hexaaquanickel dihydrogen pyromellitate, [N i(H 20) 6][C6H 2(C 0 0) 4H2]; monoclinic, P2/m, a = 6.528(1), b = 9.927(2), c = 6.472(1)Ä , ß = 115.57(1)°, Z = 1, R = 0.044, /?w = 0.039. (3) Tetrabutylammoni­ um trihydrogen pyromellitate, [(C4H 9)4N][C6H-,(COO)4H 3]; monoclinic, P 2 ,/c, a = 9.719(4), b = 18.823(8), c = 15.795(5) Ä, ß = 107.42(3)°, Z = 4, R = 0.059, Rw = 0.039. (4) Diam m onium dihydrogen pyromellitate, [N H 4],[C6H ,(CO O)4H2]; monoclinic, P 2 l/c\ a = 4.7665(6), b = 11.681(3), c = 10.149(2) Ä, ß = 102'. 19(2)°, Z = 2, R = 0.045, Rw = 0.039. Com pounds 1, 2, and 3 show very short intramolecular hydrogen bonds between adjacent carboxylic groups (O -O distances 2.384(6), 2.386(5), 2 . 3 8 7 (3) respectively). Com pound 4 forms intermolecular hy­ drogen bonds (O -O distance 2.642(2) A). The different hydrogen bonding modes are also evi­ dent in the IR spectra. 
  Reference    Z. Naturforsch. 47b, 1141—1153 (1992); received October 1 1991 /March 27 1992 
  Published    1992 
  Keywords    Pyromellitates, Hydrogen Bonds, Crystal Structure, Acid Pyromellitates, IR Spectra 
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 TEI-XML for    default:Reihe_B/47/ZNB-1992-47b-1141.pdf 
 Identifier    ZNB-1992-47b-1141 
 Volume    47