bluuebunny/crossref_metadata_2025 huggingface dataset:
Crystal structures and crystal chemical relationships of kröhnkite- and collinsite-type compounds Na2
Me
2+(XO4)2 · 2 H2O (X = S, Me = Mn, Cd; and X = Se, Me = Mn, Co, Ni, Zn, Cd) and K2Co(SeO4)2 · 2 H2O
Authors: Wildner M. , Stoilova D.
Published: December 2003

The crystal structures of eight compounds with compositions A
2
Me
2+(XO4)2 · 2H2O (A = Na, X = S, Me
2+ = Mn, Cd; A = Na, X = Se, Me
2+ = Mn, Co, Ni, Zn, Cd; and A = K, X = Se, Me
2+ = Co) were investigated using single crystal X-ray CCD diffraction data. The Mn- and Cd-compounds crystallize in the monoclinic kröhnkite structure type [Na2Cu(SO4)2 · 2 H2O, space group P21/c], the Co-, Ni-, and Zn-selenates in the closely related triclinic structure type of collinsite [Ca2Mg(PO4)2 · 2 H2O, space group P1̅]. Both types are built up from infinite Me(XO4)2(H2O)2 chains, composed of MeO4(H2O)2 octahedra alternating with each two XO4 tetrahedra by sharing corners. A—O bonds and hydrogen bonds link the chains to layers and further on to the three-dimensional structures. The influence of the ionic radii of the various A, Me, and X cations on the distances between these structural units is discussed. Special attention is paid to polyhedral distortions as well as to individual peculiarities of the alkaline coordinations and the hydrogen bonding systems. Thus, the crystal chemical relationships between the two structure types as well as to isotypic copper compounds, which are characterized by the strong octahedral Jahn-Teller distortions, are elucidated.
Solution of the structure and disorder of Ln13Br18B3(Ln = Gd, Tb)
Authors: Oeckler O. , Kienle L. , Mattausch Hj. , Jarchow O. , Simon A.
Published: December 2003

The average structures (Immm) of Gd13Br18B3(A= 3.9923(2) Å,B= 17.0462(12) Å,C= 28.3039(19) Å) and Tb13Br18B3(A= 3.9637(3) Å,B= 16.9063(13) Å,C= 28.1068(18) Å) were solved taking into account Bragg intensities only. The average structure contains an ordered honeycomb arrangement of chains formed from trans edge sharing Tb6B octahedra and disordered and partly occupied chains of double octahedra in the channels. Pronounced diffuse scattering which is elongated in [001]* indicates a 2D order of the structure. High resolution electron microscopy (HRTEM) gives insight into the nature of the ordering and leads to a model of discrete Tb10B2clusters in the channels which are perfectly ordered in layers in a 2 × 2 × 2 supercell. These layers are randomly stacked with well defined translation values to each other along [100].
Structural distortion of theα,β, andγpolymorphs of glycine on cooling
Authors: Boldyreva E. V. , Drebushchak T. N. , Shutova E. S.
Published: December 2003

The effect of cooling down to 150 K on the structures ofα- (s.g.P21/n),β- (s.g.P21), andγ- (s.g.P31) polymorphs of glycine was studied by X-ray single-crystal diffraction. No polymorphic transformations were detected. Relative volume changes and the anisotropy of structural distortion of the three polymorphs of glycine were compared. Maximum contraction of structures was measured in theb-direction for theα- andβ-polymorphs, and in thea-direction for theγ-polymorph. Minimum contraction in theγ-polymorph was measured inc-direction. The structures of theα- and theβ-polymorphs slightly expanded on cooling in the directions close toc. The directions of maximum and minimum lattice strain were related to the directions of weak and strong hydrogen bonds in the structures. Crystal structures for the three polymorphs were refined at 294 K and at 150 K. The effects of cooling on the intramolecular geometry of glycine molecules and on the intermolecular hydrogen bonds in all the three polymorphs were compared. Structural distortion on cooling was compared with that on increasing hydrostatic pressure.
Structural investigation of dichlorobis(benzimidazole)Zn(II) complex
Authors: Sahin E. , İde S. , Kurt M. , Yurdakul S.
Published: December 2003

The molecular structure of the title complex [ZnCl2(C7H6N2)2] was investigated by X-ray diffraction and IR spectroscopy. The Zn(II) complex crystallizes triclinically (P1̅ (no 2); a = 7.440(2) Å, b = 7.734(2) Å, c = 13.3127(4) Å, α = 85.91(2)°, β = 85.97(2)°, γ = 83.05(5)°, Z = 3; V = 757.3(3) Å3). In the molecular structure, the Zn atom is coordinated tetrahedrally by two Cl– anions and two benzimidazole ligands.
Stable Al—Ni—Rh decagonal phase
Authors: Grushko B. , Mi S.
Published: December 2003

Decagonal (D) phase was found to be stable at 1100 °C in a small compositional range around Al70.5Ni15.5Rh14 which overlaps with the overall range of the D-phase in Al—Ni—Co. The Al—Ni—Rh D-phase exhibits the “basic” tenfold diffraction pattern and the basic periodicity of about 0.4 nm with diffuse diffraction layers corresponding to the double periodicity. At 1100°C it coexists with the ternary extensions of binary “Al3Rh” and C—Al5Rh2 and with the liquid, at 1000°C no D-phase was observed.
Electron crystallography of zeolites. 2. Mordenite and the role of secondary scattering on structure determination
Authors: Dorset Douglas L.
Published: December 2003

Electron diffraction intensity data from the zeolite, mordenite, were used in experimental tests of direct phase determinations for crystal structure analysis. Measurement of patterns from platy and acicular microcrystals yields orthorhombic cell dimensions: a = 18.11, b = 20.17, c = 7.50 Å, consistent with the known x-ray structure. The major perturbation to the intensity data is secondary scattering (also known as ´double diffraction′), an incoherent multiple scattering phenomenon, producing strong reflections where weak ones should be found. Although the phase determination itself is not severely compromised, the error in the observed structure factor amplitudes leads to a distortion of the initial potential maps so that only a partial structure can be determined (e.g. one class of T-sites). It is possible to apply an approximate correction to the observed intensity data for secondary scattering, based on the weighted self-convolution of the partial model intensities. With the improved observed structure factor magnitudes all T-sites are found in the Fourier refinement at an overall mean deviation of 0.24 Å from their ideal positions.
Crystal structure determination of systematically intergrown compounds: Li5(OH)2Br3 and Li2(OH)Br
Authors: Friese K. , Hönnerscheid A. , Jansen Martin
Published: December 2003

We carried out a structure refinement of a crystal which was composed of two phases. Phase I was up to now unknown and corresponds to Li5(OH)2Br3 with lattice parameters a = 4.02335(1), c = 21.5638(1) Å, space group I4̅m2. Phase II is Li2(OH)Br with lattice parameters a = 4.04594(3) Å and space group Pm3̅m. The two phases have the a, b-plane in common and consequently part of the reflections overlap systematically. We performed a joint structure refinement of the two phases taking into account all reflections. The structure of Li5(OH)2Br3 is characterized by anti-perovskite like double layers of composition 2 × Li2(OH)Br, which alternate with rock-salt like layers of composition LiBr. Results for Li2(OH)Br are in good agreement with literature and confirm the correctness of the underlying model and the usefulness of the method employed in structure refinement.
Natural and synthetic compounds with kröhnkite-type chains. An update
Authors: Fleck Michel , Kolitsch U.
Published: December 2003

The crystal structures of five new triclinic double salt dihydrates have been determined from single-crystal X-ray diffraction data. The following four compounds all contain kröhnkite-[Na2Cu(SO4)2·2 H2O]-type tetrahedral-octahedral chains: the three isotypic synthetic compounds K2Mg(CrO4)2·2 H2O (a= 5.674(1),b= 6.462(1),c= 7.517(2) Å,α= 110.38(3),β= 95.24(3),γ= 109.86(3)°,V= 236.0(1) Å3,R(F) = 0.036, space groupP1̅, no. 2,Z= 1), K2Mg(MoO4)2·2 H2O (a= 5.884(1),b= 6.491(1),c= 7.700(1) Å,α= 111.67(2),β= 96.59(2),γ= 108.62(2)°,V= 249.8(1) Å3,R(F) = 0.019, space groupP1̅, no. 2,Z= 1) and K2Mn(SeO4)2·2 H2O (a= 5.674(1),b= 6.608(1),c= 7.523(2) Å,α= 110.31(3),β= 95.69(3),γ= 108.35(3)°,V= 244.10(9) Å3,R(F) = 0.024, space groupP1̅, no. 2,Z= 1), and the mineral messelite Ca2(Fe2+,Mn2+,Mg)(PO4)2·2 H2O (a= 5.480(1),b= 5.759(1),c= 6.569(1) Å,α= 90.18(3),β= 102.62(3),γ= 108.45(3)°,V= 191.3(1) Å3,R(F) = 0.022, space groupP1̅, no. 2,Z= 1). The fifth compound, the synthetic dichromate K2Zn(Cr2O7)2·2 H2O (a= 6.794(1),b= 7.735(2),c= 7.834(2) Å,α= 88.97(3),β= 80.90(3),γ= 64.57(3)°,V= 366.5(2) Å3,R(F) = 0.036, space groupP1̅, no. 2,Z= 1) is closely related to the kröhnkite-group; it contains Cr2O7groups assuming the same bridging role thatXO4groups have in kröhnkite-type oxysalts. The atomic arrangements of the title compounds are described and structural relations with other kröhnkite-type and -like compounds are discussed. In addition, related yavapaiite-type sheet structures ofAM′(XO4)2compounds are briefly reviewed, including the rod group symmetry of the underlying kröhnkite-chain building unit. Twelve different space groups have been found for these sheet structures. The previously reported space group symmetries for α-NH4Fe(CrO4)2(P21) and CsTa(PO4)2(P1̅) are obviously incorrect and should be revised toP21/nandC2/m, respectively.
Geometrical isomerism in uranyl chromates I. Crystal structures of (UO2)(CrO4)(H2O)2, [(UO2)(CrO4)(H2O)2](H2O) and [(UO2)(CrO4)(H2O)2]4(H2O)9
Authors: Krivovichev Sergey V. , Burns Peter C.
Published: December 2003

Three uranyl chromate hydrates, (UO2)(CrO4)(H2O)2, [(UO2)(CrO4)(H2O)2](H2O) and [(UO2)(CrO4)(H2O)2]4(H2O)9, have been prepared by evaporation from aqueous solutions. The crystal structure of (UO2)(CrO4)(H2O)2 (monoclinic, C2/m, Z = 16, a = 16.786(2), b = 22.731(2), c = 6.9969(7) Å, β = 90.051(3)°, V = 2669.8(5) Å3) has been solved by direct methods and refined to R1 = 0.065, calculated for 6702 unique observed reflections (|F
o| ≥ 4σF
). The crystal structure of [(UO2)(CrO4)(H2O)2](H2O) (monoclinic, P21, Z = 4, a = 9.7206(14), b = 7.1617(10), c = 11.0909(16) Å, β = 92.388(3)°, V = 771.43(19) Å3) has been solved by direct methods and refined to R1 = 0.052, calculated for 4879 unique observed reflections (|F
o| ≥ 4σF
). The crystal structure of [(UO2)(CrO4)(H2O)2]4(H2O)9 (monoclinic, P21/c, Z = 4, a = 31.397(1), b = 7.1701(3), c = 16.2480(7) Å, β = 97.515(1)°, V = 3626.3(3) Å3) has been solved by direct methods and refined to R1 = 0.051, calculated for 8164 unique observed reflections (|F
o| ≥ 4σF
). Each structure contains chains of composition [(UO2)(CrO4)(H2O)2]. Within the chains, (UO2)O3(H2O)2 pentagonal bipyramids share three equatorial O atoms with CrO4 tetrahedra. The CrO4 tetrahedra in the [(UO2)(CrO4)(H2O)2] chains each share three corners with uranyl polyhedra, and contain one non-shared (terminal) ligand pointing either up or down relative to the plane of the chain. This results in a geometrical isomerism of the uranyl chromate chains that can be described as a sequence of tetrahedra orientations along the chain extension, e.g. ... up-down-up-down ... or ... ududud .... [or (ud)∞]. The structures of (UO2)(CrO4)(H2O)2 and [(UO2)(CrO4)(H2O)2](H2O) are based upon the chains of the (ud)∞ type, whereas [(UO2)(CrO4)(H2O)2]4(H2O)9 contains two types of chains: (ud)∞ and (u)∞. The [(UO2)(CrO4)(H2O)2] chains extend in the same direction in each structure and are linked via hydrogen bonds involving H2O molecules.
Pressure Perturbation Calorimetic Studies of the Solvation Properties and the Thermal Unfolding of Proteins in Solution
Authors: Ravindra R. , Winter Roland
Published: December 2003

In this study, pressure perturbation calorimetry (PPC), a relatively new and efficient technique, was used to study the solvation and volumetric properties of the enzyme ribonuclease A (RNase A) in its native and unfolded state. In PPC, the coefficient of thermal expansion of the partial volume of the protein is deduced from the heat consumed or produced after small isothermal pressure jumps (±5bar), which strongly depends on the interaction of the protein with the solvent or co-solvent at the protein-solvent interface. The effects of various chaotropic and kosmotropic co-solvents (glycerol, sorbitol, urea, guanidinium hydrochloride, K2SO4) on the solvation and unfolding behaviour of RNase A was investigated as well, and the observed volume and expansivity changes are correlated with further thermodynamic properties obtained from differential scanning calorimetry (DSC). Depending on the type of co-solvent and its concentration, specific differences are found for the solvation properties of the protein, and the volume change upon unfolding may even change sign. Taken together, the data obtained lead to a deeper understanding of the solvation process of proteins in different co-solvents in their native and unfolded states.
From Ostwald′s Times to Solid State Ionics: Migration and Localised Hopping of Silver Ions in Crystalline Rubidium Silver Iodide
Authors: Funke K. , Banhatti R.D. , Ross I. , Wilmer D.
Published: December 2003

Since Ostwald′s times, the concepts of ionic motion in condensed matter have been extended to comprise systems with increasingly complex dynamic properties. Today, one of the central problems in the field of SOLID STATE IONICS consists in finding simple, yet relevant rules for the correlated hopping motion of the mobile ions in structurally disordered ionic materials. Rubidium silver iodide, RbAg4I5, belongs to this class of materials. To analyse the hopping dynamics of the mobile silver ions in the three phases of RbAg4I5, we have taken conductivity spectra at frequencies up to the far infrared. Also, a simple set of rules for the development of the ion dynamics with time has been provided by the MIGRATION concept, the acronym standing for MIsmatch Generated Relaxation for the Accommodation and Transport of IONs. In the phasesαandβ, an increasing tendency for correlated forward-backward hopping is observed as the temperature is decreased from 298K to 129K. At the first-orderβ-γphase transition at 121.8K, the number of translationally mobile silver ions is found to be markedly reduced. The conductivity spectra of the different phases of RbAg4I5are well explained by the MIGRATION concept as long as the angular frequency does not exceed the elementary hopping rate of the mobile silver ions. At higher frequencies, an additional dynamic feature is encountered, which is superimposed onto the MIGRATION-type conductivity. This feature, which shows a nearly constant loss (NCL) behaviour, becomes increasingly pronounced as the temperature is lowered. It is caused by a strictly localised motion of interacting silver ions. In our model treatment for the MIGRATION and NCL parts of the dynamic conductivity, the potentially translational and the strictly localised ionic hopping motion are best described with a single elementary hopping rate. Consequently, this rate marks the beginning of the NCL behaviour on the angular frequency scale. This observation is in agreement with earlier results obtained by Leon et al. on solid lithium-ion conductors.
Physical Electrochemistry: Recent Developments
Authors: Kibler L. A. , Kolb D. M.
Published: December 2003

Modern surface-science techniques like scanning tunnelling microscopy and the use of single-crystal electrodes with atomically well-defined surface structures allow a view of electrochemical interfaces and of simple electrochemical reactions at a level of sophistication unheard of at the time of Wilhelm Ostwald.
On the Equilibration of Solid Phases. Some Thoughts on Ostwalds Contributions
Authors: Schmalzried Hermann
Published: December 2003

This paper discusses two of Ostwalds experimental observations which the literature connects with his name. The generalized conclusions Ostwald inferred are presented and discussed. His discoveries deal essentially with the formation of solid phases. Later both played important roles in the field of solid state reactions. The two items are: 1. Ostwalds rule of successive reaction steps (ORS-rule) and 2. the Ostwald-ripening process (ORP-process). Since material scientists and engineers try to obtain special properties of a solid by establishing its microstructure, Ostwalds discoveries and ideas do influence the field of materials science till nowadays.In what follows his farsightedness and his limitations are placed in the context of solid state physical chemistry and its history.
The Struggle for Precise Rate Constants in Gas Phase Reaction Kinetics: The Reaction H + O2⇔ HO + O
Authors: Troe Jürgen
Published: December 2003

A short sketch of the history over the last 100 years of the H2–O2-system in general and of the H + O2⇔ HO + O reaction in particular is given. Only after revision of the enthalpy of formation of OH in the year 2000, experimental and theoretical rate constant determinations approach an agreement within about 10 percent. Further improvements of the modeling depend on more precise thermochemical data for the reaction and on a detailed analysis of the contributions from all electronic states arising from the four open electronic shell species involved. Vibrational zeropoint energy problems of OH in classical trajectory calculations and detailed angular momentum couplings in adiabatic channel treatments have also to be mastered.
The Chemisorption of 2,3-Dimercapto-n-Propane Sulfonate at the Au(111)-Electrode
Authors: Donner C. , Valet O. , Yang Y. , Baumgärtel H.
Published: December 2003

In this paper we report on the adsorption behaviour of 2,3-dimercapto-n-propan-sulfonate (DMPS) on the Au(111) electrode. DMPS is a water-soluble dithiol which is unstable in alkaline solution. The absorption decreases by 50 within two hours.The electrochemical behaviour is in accordance to that of other thiols, including monothiols. The interaction between sulfur and the Au(111) surface leads to a strong chemisorption in the double layer region which is limited by the reductive and oxidative desorption, respectively. The oxidative behavior (OD) of DMPS takes place simultaneously with the oxidation of the gold surface itself.We propose a mechanism for the OD which, in contrast to the well-known mechanism of the sulfur oxidation itself, includes the formation of a goldsulfur complex. This OD mechanism acts like a corrosion and causes an increased roughness of the surface. Therefore, the charge consumed during the OD is exclusively due to the oxidation of Au0to Au3+in form of the complex and in form of the well-known Au2O3oxide.
Ion–Solvent Interactions and Determination of Single-Ion Gibbs Energies of Transfer from the Studies of the Solubility and Dissociation Constants of Oxalic Acid in Aquo + Methanolic Mixtures
Authors: Gumtya S. K. , Lahiri S. C.
Published: December 2003

The solvent effects on the dissociation of the simplest dibasic organic acid were examined from the determination of the first and second dissociation constants of oxalic acid conductometrically and pH-metrically in water + methanol mixtures (0–87 wt% of methanol). The solubility values of oxalic acid and potassium hydrogen oxalate were also determined in water + methanol mixtures. The dissociation constant and the solubility values were used to calculate the Gibbs energies of transfer ΔG
0

t
of oxalic acid (H2OX), bioxalate (HOX−), oxalate (OX2−) and potassium (K+) ions from water to aquo-methanolic mixtures. These represent the quantitative measures of solute or ionsolvent interactions of the respective species in going from water to methanol + water mixtures. pK
1, pK
2 and the solubility values of oxalic acid increase continuously with increase in organic co-solvent. ΔG
0

t
(H2OX) and ΔG
0

t
(H+) are negative i.e. favourable but ΔG
0

t
(H2OX), ΔG
0

t
(OX2−) and ΔG
0

t
(K+) are in general positive and hence unfavourable for the dissociation processes. The increase in basicity fecilitated the dissociation processes but decrease in dielectric constant and H-bonding capability enhance the association processes as the organic co-solvent increases. Attempts have been made to understand the solvation processes in terms of the structure of the aquo + organic mixtures and Walden products. The pK values can be suitably utilised to prepare buffer solutions in methanol + water mixtures. The solvent effect and solvation phenomena can be better understood from the collection of single-ion values of transfer. These may be utilised to calculate the solubilities of electrolytes in methanol + water mixtures.
Formation of Nanoparticles by Photolysis from Metal and Carbon Bearing Molecules
Authors: Emelianov A. , Eremin A. , Jander H. , Wagner H. Gg.
Published: December 2003

The formation of particles following the photolysis of C3O2, Fe(CO)5 and Mo(CO)6, diluted with Ar or He was registered at room temperature. Particle growth was followed by taking light extinction profiles at 633nm and at 220nm for various mixture compositions and pressures. The particles obtained at different conditions were analyzed using transition electron microscope (TEM) technique. It was found that in the pure undiluted gases at the partial pressures shown in the pictures no light absorption and no particle formation could be observed. Light absorption started for partial pressures of the diluent gas > 10mbar. A comparison of particle size measured here at room temperature with data obtained at elevated temperature shows that the data obtained here fit well to the elevated temperature data.
Electrochemical Behavior and Enhanced Stability of a Thin Film of Prussian Blue Deposited under Magnetic Field
Authors: Eftekhari Ali
Published: December 2003

Magnetic field was employed as a useful tool to improve stability of electroactive films deposited on substrate surfaces. To this aim, electrochemical preparation/deposition of Prussian blue (PB) was carried out in the presence of an external magnetic field to form a thin film onto a Pt substrate electrode. The results were compared with a conventional PB modified electrode throughout the research. For the electrode prepared in the presence of the magnetic field, a stronger voltammetric behavior with higher peak current was observed. It was accompanied by higher chemical and electrochemical stabilities of the deposited electroactive film. Spectroscopic measurements were also performed to investigate the influence of the applied magnetic film on the properties of the electroactive film deposited. The results were indicative of the fact that deposition under magnetic filed is accompanied by stronger chemical bonds and different elemental composition of the electroactive material formed on the electrode surface. Based on the experimental results, it was concluded that both Lorentz and magnetic forces are responsible for the behavior observed.
Influence of Iron Content on the Electrical and Dielectric Properties of La0.7Ba0.3Co1−

y
Fe
y
O3
Authors: Khalil M. Sh.
Published: December 2003

Powders of La0.7Ba0.3Co1−

y
Fe
y
O3, LBCF, y=0.0 to 1.0, were prepared by thermal decomposition of metal polymerized complex solutions. Thermal and chemical analyses of cation concentrations were used to confirm the desired composition sintered at 900°C. Powder X-ray diffraction data indicate that all compositions possess the perovskite structure. Cubic unit cell parameters increase with increasing iron content except for y=0.3, which was explained in terms of the average valencies and charge neutrality of Fe and Co ions and oxygen ion deficiency. The electrical properties such as conductivity, dielectric constant and dielectric loss factor of the LBCF samples were studied as a function of frequency (100Hz–1MHz) and temperature (293–625K). Iron substituted samples exhibit semiconductor behavior with decreased electrical conductivity values compared to that of the free Fe sample. The possible conduction mechanisms were discussed. Dielectric studies show apparent high dielectric behavior, which was explained by the double layer capacitor model.
Establishment of Micellar Catalytic Field Using the p-Nitro-o-Carboxylbenzeneazo-8-Amino-quinoline – Cetyltrimethylammonium Bromide – Co(II) Ternary Complexation
Authors: Gao Hong-Wen , Yang Jia-Xiang , Zhao Jian-Fu
Published: December 2003

The micellar catalytic field was proposed in surfactant medium by investigating the complexation between p-nitro-o-carboxylbenzeneazo-8-aminoquinoline (NCBAAQ) and Co(II) at pH 8.8. The cationic surfactant, cetyl trimethylammonium bromide (CTAB) was added and the aggregation of NCBAAQ on CTAB obeys the Langmuir isothermal adsorption. The enrichment of NCBAAQ on CTAB micelle resulted in a sensitive and rapid complexation of NCBAAQ with Co(II). The ternary complexation was characterized by the microsurface adsorption – spectral correction (MSASC) technique. Results showed that the complex Co3NCBAAQ12CTAB78 is formed.
Heteroassociation of Selected Diols with some Tertiary Amines
Authors: Kolbe Alfred , Plass Monika
Published: December 2003

Diols exhibiting the structure (HO)CH2–(CH2)n–CH2(OH) withn=1 up ton=4, (HO)CH2–CH(OH)–CH3and cyclohexan-1,2-diols as well as cyclohexan-1,4-diol, which may establish different intramolecular interactions, are used as model substances to describe the external hydrogen bonding behaviour of multivalent hydrogen bond donors in the presence of hydrogen bond acceptor molecules. In this study, hydrogen bonds formed by the diols with tertiary aromatic amines have been investigated. In solution, different associate formation between the diols and the acceptor molecules as sketched in Fig.1 may occur. Besides 1:1 associates formed by the interaction of one diol molecule with one amine molecule, 1:2 associates may be observed where each OH function interacts with one amine molecule. The equilibrium constants of the associates of those interactions have been studied by FTIR spectroscopy. The results allow a classification of the used diols in three different groups based on the position of the OH groups in the donor molecule. For diols with proton donating OH where no intramolecular hydrogen bond can be formed, the intermolecular hydrogen bonds for a 1:1 system may be described by thermodynamic parameters which are nearly twice the value of the corresponding equilibrium constants of monovalent alcohol systems due to the statistical weight of the OH groups. Secondly, when intramolecular hydrogen bond exists in the diols, the equilibrium constants in the interaction with the amine raise up by a factor ofca.2–3 due to the cooperativity effect. Thirdly, if the OH groups are arranged in 1,2 positions, both OH groups may be described as independent of each other in their intermolecular interaction with the amine.
Bursting Oscillations in the Revised Mechanism of the Hemin – Hydrogen Peroxide – Sulfite Oscillator
Authors: Straube Ronny , Müller Stefan C. , Hauser Marcus J. B.
Published: December 2003

The reaction mechanism for the hemin-mediated oxidation of sulfite by hydrogen peroxide was reinvestigated. This has become necessary due to an erroneous stoichiometric factor used during a previous numerical analysis. A simple correction of the previous model failed to reproduce the experimentally observed bursting oscillations of the pH value. Therefore, we propose an extended mechanism which includes not only the autocatalytic production of H+ and pH-dependent equilibria of hemin species, but also the decomposition of hemin in media of high H2O2 concentration. The dynamic properties of this 7-variable reaction mechanism are in good agreement with previous experimental and numerical observations. A closer analysis reveals that the pH-dependent dimerisation equilibrium of hemin provides only a minor contribution to the onset of oscillations. Therefore, this equilibrium can be neglected yielding a 6-variable version of the revised 7-variable model, while maintaining the local bifurcation structure. The revised mechanisms are considered realistic models that describe the observed dynamical features of the hemin-containing pH oscillator.
Hydrogen Bond Mediated Association of Dinucleotide Analogs
Authors: Basílio Janke Eline M. , Weisz Klaus
Published: December 2003

Several dinucleotide analogs, in which two of the nucleobases adenine, thymine and uracil are connected by a hexadecamethylene linker have been synthesized and studied for their base-base interaction in a chloroform solution. Using 1H NMR spectroscopic techniques intramolecular base pair formation through hydrogen bonding is observed at ambient temperatures but found to strongly depend on the identity of paired bases. Thus, whereas cyclization through intramolecular base-base interactions predominate for adenine–(CH2)16–thymine and adenine–(CH2)16–uracil, no intramolecular adenine-adenine pairing was observed. Upon addition of acetic acid to adenine–(CH2)16–thymine, strong adenine-acetic acid interactions result in the disruption of preformed intramolecular adenine-thymine base pairs.
Revealing CSA Tensors and Hydrogen Bonding in Methoxycarbonyl Urea: A combined 13C, 15N and 13C14N2 Dipolar Chemical Shift NMR and DFT Study
Authors: Macholl Sven , Börner Frank , Buntkowsky Gerd
Published: December 2003

Methoxycarbonyl urea (MCU), a potential long-term nitrogen fertilizer, is studied by 13C and 15N dipolar chemical shift NMR spectroscopy and ab initio calculations. Employing a combination of dipolar chemical shift NMR, selective isotope labeling and ab initio gas phase calculations, possible molecular structures and chemical shielding tensors of all 15N nuclei and of two out of the three 13C nuclei were revealed. Four possible stable configurations of the molecule with different energies were found in the calculations. The CSA tensors were calculated for these configurations. While the calculated 13C(urea) CSA tensor orientation of the configuration with the lowest energy is in good agreement with the experimental tensor orientation, there are pronounced differences between calculated and experimental tensor eigenvalues. These differences are a clear indication of the presence of intermolecular hydrogen bonds in the experimental sample, which are neglected in the gas phase calculations. Four different possible orientations of the experimental 13C(urea) CSA tensor exist, due to symmetry. This ambiguity is solved by comparison with results from GIAO calculations of the 13C CSA tensor, employing the minimum energy configuration (EEZ). It is found that the orientation, where δ11 points approximately in direction of N(imide), δ22 approximately in direction of the C=O bond, and δ33 is oriented perpendicular to the molecular frame, is adopted in the molecule.
The Intramolecular Hydrogen-Bond in Malonaldehyde as Seen by Infrared Spectroscopy. A Four-Dimensional Model Study
Authors: Došlić Nadja , Kühn O.
Published: December 2003

The infrared spectrum of the O–H–O fragment of malonaldehyde is studied using a four-dimensional model. This comprises the OH stretching and the two OH bending vibrations as well an O–O ring deformation mode under the assumption of overall Cs symmetry. The full anharmonic potential energy and dipole moment surfaces are calculated using density functional theory and the respective vibrational eigenvalue problem is solved by an iterative Lanczos method. Fundamental and combination transitions are discussed for the normal species and the symmetrically deuterated isotopomer. Special emphasis is paid to the OH/OD stretching region which reveals the signatures of strong mode mixing what renders a simple assignment in terms of fundamental transitions difficult. In addition results for hot transitions are presented which show a rather different OH/OD band due to the topology of the potential energy surface. The influence of H atom tunneling on the spectrum is briefly addressed employing an alternative three-dimensional model which takes into account the in-plane H atom motion as well as the O–O distance.
Proton Transfer to Organometallic Hydrides via Unconventional Hydrogen Bonding: Problems and Perspectives
Authors: Belkova N. V. , Gutsul E. I. , Shubina E. S. , Epstein L. M.
Published: December 2003

This review summarizes the spectral and theoretical results concerning different ways of proton transfer through hydrogen bonds (HB) to metal atoms (XH···M) and hydride ligands (XH···HM) leading to classical and nonclassical cationic hydrides. The spectral (NMR, IR, UV-Vis in the temperature range 190–290K) and theoretical studies of the structural and energetic characteristics of HB intermediates and proton transfer allow the representation of the experimental energy profiles. The problems concerning the influence of different factors on the processes and potential energy surfaces requiring active investigations in this new area are discussed
Synthesis of Monodisperse Heptanol Stabilized Ruthenium Nanoparticles. Evidence for the Presence of Surface Hydrogens
Authors: Pelzer Katrin , Philippot Karine , Chaudret Bruno
Published: December 2003

The decomposition of Ru(cod)(cot) (1; cod = 1,5-cyclooctadiene, cot = 1,3,5-cyclooctatriene) under an H2 atmosphere (3 bars) in pure heptanol produces crystalline monodisperse nanoparticles of 3nm mean size characterized by TEM and WAXS techniques. Solution NMR studies demonstrate the presence of surface hydrogens due to the synthesis process and suggest a fast exchange between free and coordinated heptanol molecules.
Interpretation of Hydrogen/Deuterium Isotope Effects on NMR Chemical Shifts of [FHF]− Ion Based on Calculations of Nuclear Magnetic Shielding Tensor Surface
Authors: Golubev Nicolai S. , Melikova Sona M. , Shchepkin Dimitri , Shenderovich Ilja G. , Tolstoy Peter M. , Denisov Gleb S.
Published: December 2003

Using ab initio calculations of 1H, 19F magnetic shielding tensors of hydrogen difluoride ion as the functions of three coordinates of symmetry, an attempt is made to estimate the contributions of different vibrational isotope effects to H/D NMR isotope shifts referred in the literature. It is shown that the contributions of the amplitudes of proton stretching and bending vibrations dominate whereas the contribution of the totally symmetric vibration can be neglected. Different signs of the H/D isotope effects on hydron and fluorine chemical shifts are caused by very strong angle dependence of the fluorine magnetic shielding. The agreement of the calculated and measured values is nearly quantitative. An unusually strong paramagnetic deshielding of hydrogen for the equilibrium geometry of the [FHF]− ion is noted.
Computed EOM-CCSD 19F-19F Spin-Spin Coupling Constants in Small Organic Molecules
Authors: Del Bene Janet E. , Alkorta Ibon , Elguero José
Published: December 2003

Two-, three-, and four-bond 19F-19F spin-spin coupling constants (
nJ
FF) for a set of small fluoro-substituted organic molecules have been computed using ab initio equation-of-motion coupled cluster singles and doubles (EOM-CCSD) theory. The computed values reproduce the experimental signs and magnitudes of
nJ
FF. The straight line that relates the experimental and computed coupling constants has a slope of approximately 1 and passes through the point (0,0 Hz) within the uncertainties of the fit. Hence, EOM-CCSD values of
nJ
FF should be excellent predictors of experimental values when these are not available. All of the components of
nJ
FF except for the diamagnetic spin-orbit term may be large and must be evaluated if agreement between theory and experiment is to be obtained.
Quantum Simulations for Isotope Effects of IR + UV Laser Pulses on Symmetry and Selective Hydrogen Bond Breaking
Authors: Elghobashi Nadia , González Leticia , Manz Jörn
Published: December 2003

Intense few-cycle femtosecond (fs) infrared (IR) laser pulses yield dynamical symmetry breaking of oriented strong symmetric hydrogen bonds A···H···A due to nearly coherent vibrational excitation. Consequently, the system evolves with alternate stretches or compressions of the competing bonds A···H and H···A. For a specific stretch of, say, the H···A bond, an ultrashort ultraviolet (UV) laser pulse may induce a nearly instantaneous electronic excitation and/or photo-detachment by means of a Franck–Condon(FC)-type transition to a dissociative potential energy surface of the excited state. The stretched bond, H····A, will then dissociate selectively, yielding preferably the products AH+A. A minor fraction of the other products A+HA may also be formed due to competing wavepacket dispersion. The corresponding isotope effects are investigated by means of the representative laser driven molecular wavepackets which are propagated on ab initio potential energy surfaces and with ab initio dipole coupling for the model systems, FHF− versus FDF−. The resulting quantum dynamics for both systems are nearly equivalent if the driving IR laser fields are scaled with decreasing carrier frequency and amplitudes and increasing durations for the corresponding increasing masses of the isotopomers.
Influence of Cation Exchange on the27Al-NMR Spectra of Zeolites
Authors: Masierak W. , Emmler T. , Buntkowsky Gerd , Gutsze A.
Published: December 2003

The influence of cation exchange on the27Al-NMR spectra of NaA-zeolites has been studied by27Al-MAS- and MQ-MAS-Solid State-NMR. From the27Al-spectra a characterization of the different Al sites in the A zeolites according to their chemical environment and the structural changes on the aluminosilicate network caused by the cation exchange are obtained. It is found that the exchange with cations with smaller ion-radius cause stronger distortions of the27Al-NMR-spectra than exchange with larger cations like Ba2+. Employing MQ-MAS spectroscopy these distortions are revealed as second order quadrupolar effects for the smaller cations and as a combination of chemical shift and second order quadrupolar interaction for the Ba cation. These changes of the quadrupolar coupling are interpreted numerically via calculations of the lowering of the symmetry of the EFG tensor. Finally it is found that the exchange with divalent cations leads to distortions of the zeolitic framework and the formation of an extra-framework aluminum. To the best of our knowledge this is for the first time that evidence for the production of extra frame work aluminum by pure cation exchange without any thermal treatment has been found in type A zeolites.
Solid State NMR Connectivity Studies in Dipolarly Coupled Inorganic Networks: Site Assignments in the Solid Electrolyte Material (CuI)8P12
Authors: Brunklaus Gunther , Chan Jerry C. C. , Eckert Hellmut
Published: December 2003

The local structure of the fast solid ion conductor Cu2P3I2 = (CuI)8P12 is investigated using one- and two-dimensional 31P and 65Cu magic-angle spinning NMR techniques. Peak assignments are proposed on the basis of anisotropic and isotropic spin-spin interactions recovered via radio frequency driven dipolar recoupling (RFDR) and total through bond correlation spectroscopy (TOBSY) methods. Especially the previously proposed R306
14 pulse symmetry (R-TOBSY), which exploits scalar spin-spin interactions for coherence transfer, offers outstanding spectral selectivity with respect to 1
J coupling. Using sufficiently short mixing times it is thus possible to correlate selectively those 31P spins that are directly bonded, thereby providing detailed insights into phosphorus-phosphorus connectivities in the network. The final assignment of the nine resolved 31P resonances to the twelve crystallographically distinct phosphorus sites suggests a significant relationship between 31P chemical shifts and the detailed pyramidal P(P1/3)3 bonding geometry.
2D NMR Nutation Analysis of Non-Thermal Polarization of Coupled Multi-Spin Systems
Authors: Ivanov K. L. , Miesel K. , Vieth Hans-Martin , Yurkovskaya A. V. , Sagdeev R. Z.
Published: December 2003

A new, convenient method of analyzing the spin polarization of a non-equilibrium system of N coupled nuclei is described and applied to photo-reactions exhibiting chemically induced dynamic nuclear polarization (CIDNP). It is based on the Fourier analysis of the variation of NMR line intensities as a function of the radio frequency excitation pulse length. A relationship between the spectral components at various harmonic order and the alignment in the spin multiplet is established. In application to the Norrish type I photolysis of cyclodecanone we demonstrate that at low magnetic field the rate determining step in the reaction kinetics depends on the mutual orientation of at least four pairs of non-equivalent spins.
The Characterization of Metal–Metal Bonds in Unsaturated Binuclear Homoleptic Transition Metal Carbonyls. The Compliance Matrix
Authors: Xie Y. , Schaefer H. F.
Published: December 2003

The compliance matrix (inverse force constant matrix) has been used to estimate metal–metal bond character for the homoleptic transition metal carbonyls Fe2(CO)
n
and Co2(CO)
n
. The results are often in agreement with other methods, but the compliance matrix provides a unique measure while other methods may be ambiguous. The more unsaturated compounds with fewer carbonyls have stronger metal–metal linkages, indicating a general, if not infallible, correlation between the diagonal compliance matrix element and the formal bond order, given by the 18-electron rule. It is found that the apparent metal–metal bond strength, as judged by the compliance matrix, is significantly enhanced by the bridging (as opposed to terminal) carbonyls. Thus one must only make precise comparisons between systems with the same numbers of bridging carbonyls.
Quantum Chemical Investigation of Spin-Forbidden Transitions in Dithiosuccinimide
Authors: Tatchen J. , Kleinschmidt M. , Marian C. M. , Parac M. , Grimme S.
Published: December 2003

The vertical and adiabatic electronic spectra of dithiosuccinimide have been investigated by means of multi-reference Møller–Plesset perturbation theory and combined densitiy functional/multi-reference configuration interaction methods. Geometries of the electronic ground state and several low-lying excited states have been optimised at the level of time-dependent density functional theory. We have determined spin-orbit coupling for correlated wavefunctions utilising a non-empirical spin-orbit mean-field approach. Because of the two thiocarbonyl groups present in the molecule, dithiosuccinimide exhibits a dense spectrum of low-lying valence states. The first two excited singlet states (S
1 and S
2) originate from n → π* excitations. Nearby, three triplet states are located, two n → π* states (T
1 and T
2), and a π → π* triplet excitation (T
3). The experimentally observed strong absorption band with maximum at 3.96 eV arises from the π → π* excited 1
B
2 (S
3) state. Computed radiative lifetimes are presented for the experimentally known phosphorescence from the n → π* excited T
1 state. Further, we find nearly equal probabilities for the spin-forbidden S
0 → T
2 and the spin-allowed S
0 → S
1 transitions in absorption. On these grounds, we assign band number 3 in the spectra measured by Meskers et al. [J. Phys. Chem.
99 (1995) 1134] to this spin-forbidden transition.
Rovibronic States in the X
2
Π State of the CCS− Anion
Authors: Panten D. , Chambaud G. , Rosmus P. , Riaplov E. , Maier J. P.
Published: December 2003

Three-dimensional potential energy functions have been generated ab initio for the X
2Π electronic ground state of CCS− and used in variational Renner–Teller calculations including electron spin. Rovibronic levels (J=P) for J≤5/2 are given for energies up to 4000cm−1. The pattern of the levels is compared with that of CCO−. In the case of CCS− the quartic force fields, equilibrium geometry, electric dipole moment, the electronic affinity and the Franck–Condon factors for the X
2Π(CCS−) → X
3Σ− (CCS) photodetachment spectrum are calculated.
Ab initio MRD-CI Study of the Electronic Spectrum of Tribromomethanol Br3COH and the Photofragmentation along Br–C and C–O Cleavage
Authors: Mühlhäuser M.
Published: December 2003

Multi reference configuration interaction calculations are carried out to compute the electronic spectrum of tribromomethanol Br3COH. The first dipole-allowed transitions are computed at 5.0 eV (11
A″ ← X
1
A′) and 5.4 eV (21
A″ ← X
1
A′) followed by three transitions at 5.5 eV (21
A′ ← X
1
A′) and 6.1 eV (31
A′ ← X
1
A′, 31
A″ ← X
1
A′). The largest oscillator strength (f = 0.08) is obtained for the σ → σ* type excitation 31
A″ ← X
1
A′ computed around 6.1 eV. The corresponding triplet states are also given. Five low-lying excited states in the energy range between 4.5 eV and 5.5 eV are found to be highly repulsive for Br–C elongation, leading to Br2CHOH (X
2
A′) and Br (X
2
P), so that tribromomethanol Br3COH is expected to be important for atmospheric chemistry as reservoir of Br radicals. Photodissociation along C–O cleavage resulting in Br3C (X
2
A′) and OH (X
2
Π) has to overcome a barrier of about 0.7 eV because the low-lying excited states 11
A″, 13
A′ and 13
A″ become repulsive only after elongating the C–O bond by about 0.45 Å.
Theoretical Study of the Dissociation and Isomerization of NCS
Authors: Diehr M. , Chambaud G. , Werner H.-J.
Published: December 2003

Large scale MRCI calculations have been performed to study the electronic ground state and low-lying excited states of the NCS molecule and its isomers. The isomer CNS is found to be stable and linear. It lies 1.29 eV higher in energy than NCS, while CSN has a much higher energy and is unstable. The dissociation energy of the NCS isomer has been calculated to be 4.25 eV. The isomerization paths between the 2Π ground states of both isomers have been mapped by CASSCF and MRCI calculations. The barriers for the NCS → CNS isomerization in 2
A′ and 2
A″ symmetry have cyclic forms and the barrier heights have been calculated to be 2.71 eV and 2.44 eV, respectively (MRCI). For both isomers, the collinear dissociation paths to the (diatomic + atom) fragments have been investigated by CASSCF calculations. Spectroscopic data are given for the X
2Π ground state and for the A
2Σ+ state of CNS. The results are compared with the valence isoelectronic system NCO.
Theoretical Study of the Vertical Electronic Spectra, Electron-Spin g-Factors and Hyperfine Coupling Constants of the (C
2v) Cyclic Radicals C3
+, Si3
+, C3
− and Si3
−
Authors: Bruna P. J. , Grein F.
Published: December 2003

The vertical transition energies and Δg-values of cyclic C3
+, Si3
+ (X
2
B
2), C3
− (12
A
1, metastable) and Si3
− (X
2
A
1) are studied with ROHF MOs, multireference (MRDCI) wavefunctions and 6-311+G(2d) basis sets. Si3
− has at least eight bound states. For each radical, the in-plane components of the g shift, Δgyy
and Δgzz
(with gii
= g
e + Δgii
), have similar negative values (about −1200 ppm for C3
+, C3
− and about −8000 ppm for Si3
+, Si3
−). The Δgxx
’s are larger in magnitude, negative for C3
+, Si3
+ (−11000 and −72000 ppm) but positive for C3
−, Si3
− (8000 and 165000 ppm). The hyperfine coupling constants A
iso, A
dip are evaluated with ab initio CISD, QCISD, CCD, MP4SDQ methods as well as with density functional theory (DFT) methods (SVWN, B3LYP, B3PW91, PW91PW91), using a spin-unrestricted formalism; several basis sets are considered. Both approaches give internally consistent A
iso’s and A
dip’s for each X3
− center, with the (positive) s-spin-density at each basal atom (average A
iso (MHz) = 75 for C3
− and −25 for Si3
−) being smaller than at the apical center (275 and −95 MHz). The results are less satisfactory for X3
+. All treatments agree, more or less, in a larger (positive) s-density at the basal atoms (A
iso(MHz) from 300 to 700 for C3
+, and −80 to −150 for Si3
+), whereas the s-contribution at the apical center depends on the method: for C3
+, it is positive with ab initio but negative with DFT, whereas for Si3
+ the opposite trend is found; as well, A
dip(X3
+) shows unusually large discrepancies for each center. For these radicals, literature values of A
iso and A
dip are not available, either from experimental or multireference ab initio studies, to allow for comparisons with our results.