Hydrogen bonding between various donors and acceptors has been investigated by employing infra-red, n.m.r. and electronic spectroscopy. The effects of acidity of the acceptor and the basicity of the donor on the thermodynamics of hydrogen bonding have been investigated. The relations between ΔH°, ΔνOH, ΔF° and other parameters have been discussed.
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.
Die Entdeckung von Graphen war eine Sensation für die Chemie, aber auch für die Physik, die Materialwissenschaften und verwandte Gebiete. Die ungewöhnlichen Eigenschaften des Graphens weckten auch ein Interesse an anderen Schichtmaterialien wie Molybdänsulfid und Bornitrid. So sind in den letzten Jahren verschiedene ein‐ und mehrlagige Chalkogenide und andere anorganische Materialien mit interessanten Eigenschaften und Anwendungsmöglichkeiten hergestellt und charakterisiert worden. Dieser Aufsatz gibt eine Übersicht über neue zweidimensionale Nanomaterialien. Dabei behandeln wir nicht nur Synthese und Charakterisierung, sondern auch spektroskopische und optische, magnetische und elektrische Eigenschaften und mögliche Anwendungen. Außerdem werden Kompositmaterialien aus anorganischen Schichtstrukturen mit Graphen und Polymeren und schließlich Borcarbonitride behandelt.
Experimentally a large number of linear relations have been found between the change in OH stretching frequency, Δ, on hydrogen bonding and the hydrogen bond energy, ΔH. A least square treatment of these Δ against ΔH relations is carried out for constant acceptor, variable donor as well as constant donor, variable acceptor systems. Generally, the constant-acceptor plots have much higher values of intercepts than the constant-donor plots. The slopes of the constant-donor plots seem to vary with the basicity of the donor . However, since Δ should go to zero when there is no interaction, it is suggested that the complete Δ against ΔH, relation could be nonlinear. Molecular orbital calculations have been employed to throw light on the Δ against ΔH relation. It is also shown that charge transfer theory when applied to the hydrogen bond predicts a relation between shown that charge transfer theory when applied to the hydrogen bond predicts a relation between ΔH and the quantity (20–2)½ where 0 and , are the free and perturbed OH stretching frequencies.
By roller quenching and water quenching melts of Bi2(Ca, Sr)3Cu2O8+δ, glasses have been obtained. These glasses exhibit two glass transitions as well as two crystallization transitions. Microwave absorption studies show the glass to be weakly superconducting at 77 K, probably due to the presence of ultramicrocrystallites. The glass on crystallization at 870 K gives the crystalline n=1 member of the homologous series Bi2(Ca, Sr)n+1CunO2n+4 and the n=2 member on annealing at 1100 K. The glass route provides a unique means of obtaining the n=2 member of the series. On prolonged annealing of the glass at 1120 K, the n=3 member seems to be formed.
A systematic study has been carried out on the three isomeric cyclohexanedicarboxylates (CHDCs) formed by cadmium and manganese with the three isomeric dicarboxylic acids, in the presence or absence of amines. The CHDCs have been prepared under hydrothermal conditions and their structures established by X-ray crystallography. We have been able to isolate two-dimensional layered structures of 1,2-, 1,3- and 1,4-cyclohexanedicarboxylates and chain structures of 1,3- and 1,4-cyclohexanedicarboxylates. The infinite metal-oxygen-metal linkages are observed only in the case of the 1,2-dicarboxylate. In all the three isomeric cyclohexanedicarboxylates, the e,e conformation is most favored, although the 1,4-CHDCs often contain rings in both the e,e and the a,e conformations.
The transition from the tetragonal (I4/mcm) to the orthorhombic (Imma) structure associated with a change in A- to CE-type antiferromagnetism in the Pr0.5−x Nd x Sr0.5MnO3 has been investigated by X-ray diffraction as well as magnetization and resistivity measurements. The transition is found to occur between x=0.1 and 0.2.
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High-pressure magnetic susceptibility measurements have been carried out on Fe(dipy)2(NCS)2 and Fe(phen)2(NCS)2 in the pressure range 1–10 kbar and tempeature range 80–300 K in order to investigate the factors responsible for the spin-state transitions. The transitions change from first order to second or higher order upon application of pressure. The temperature variation of the susceptibility at different pressures has been analysed quantitatively within the framework of available models. It is shown that the relative magnitudes of the ΔG 0 of high-spin and low-spin conversion and the ferromagnetic interaction between high-spin complexes determines the nature of the transition.
No abstract is provided for this article.
No abstract is provided for this article.
Substitution of Ca by Y in TlCaBa 2 Cu 2 O y does not favour superconductivity, but substitution of Tl by Pb or of Ca by Ln (Ln = Y or rare earth) in TlCaSr 2 Cu 2 O y results in high T c superconductivity (T c π 60-90 K). TlCa 1-x Ln x Sr 2 Cu 2 O y is a new series of high T c superconductors, but the x = 0.0 composition does not exhibit bulk superconductivity.
Ferroelectric bismuth oxides of the general formula (Bi 2 O 2 ) 2+ (A n-1 B n O 3n+1 ) 2- (A = Ba, etc., B = Ti or other transition metal) have been examined by high-resolution lattice imaging electron microscopy. The lattice images show dark bands at the positions of the Bi 2 0 2 layers, with n -1 lines between them due to the layers of the perovskite A cations or, in favourable circumstances, the fully resolved 0.4 nm square perovskite grid. Dislocations and domain boundaries have been imaged for the first time in ferroelectric crystals. The structure of the dislocations and domain walls is discussed in the light of the microstructural evidence.
Solvent effects on the CTTS transitions of halide ions have been examined with particular reference to the role of hydrogen bonding. Hydrogen bonding of halide ions with methanol and water has been studied quantitatively. Thermodynamics for the interaction of halide ions with CCl4 have been reported in CH2Cl2 and CH3CN solvents; CCl4 undoubtedly acts as an acceptor in these systems. Charge-transfer interactions of halide ions with mono-,di- and tri-nitrobenzenes have been investigated in some detail. The donor ability of halide ions varies in the order, I− > Br− > Cl−, as expected on the basis of the ionization potentials. The acceptor ability of nitrobenzenes varies in the expected order, trinitrobenzene > dinitrobenzene > nitrobenzene. Charge-transfer energies for the interaction of halide ions with CCl4 as well as trinitrobenzene do not fall in line with energies found with these acceptors and aromatic donors. Photolysis of a solution of iodide ion in t-butanol in the presence of trinitrobenzene increases the concentration of the radical anion of trinitrobenzene.
Recent spectroscopic data, especially based on electron spectroscopic measurements, have identified that the carriers in the normal state of the high-temperature superconducting cuprates are holes in the oxygen p-band rather than holes on copper in the form of Cu3+. We show that these oxygen holes can form a special kind of single pair (which we designate peroxitons) composed of O-Cu+O-) type species and essentially involving a resonating bond between the three sites. Bose condensation of these peroxitons as well as their effect on magnetic properties are discussed and it is shown that such oxygen holes are fundamental to the mechanism of superconductivity of the high T c cuprates.
The reaction between AgNO3 and iodine has been studied in detail and the products of the reaction are found to be AgIO3, AgI, NO2 and O2. A reaction mechanism involving INO3 as the intermediate has been discussed. The dependence of the reaction on the phase, time, temperature and other factors has been investigated. Thermal decompositions of AgNO3, AgIO3 have also been examined.
