Three-body interactions,rotational invariance and the elastic consistency of lattice dynamical models for face-centred tetragonal indium

The origin of the elastic inconsistency ofdaf, mas andgtf models for non-cubic solids and the failure of their force constants to comply with all the rotational invariance conditions are analysed by resolving the atomic displacements of face-centred tetragonal indium along three mutually perpendicular directions. It is shown that a lattice dynamical model suffers from these deficiencies as a consequence of its neglect of three-body interactions as well as the mixed neighbour interactions associated with the angular forces, while thecgw model which incorporates both these interactions is elastically consistent and its potential energy rotationally invariant. The degree of equivalence that exists among the force constants ofdaf, mas, gtf andcgw models, the distortions introduced by the elastic inconsistency into the phonon dispersion curves of fct indium as well as the consequences of imposing the rotational invariance conditions on the force constants of a lattice dynamical model are discussed.     

Molecular structure of (diethyldithiocarbomoyl)diphenylthiophosphinate

X-Ray study of (diethyldithiocarbomoyl)diphenylthiophosphinate was carried out. AZ-conformation of the diethyldithiocarbomoyl ligand, which results in a short nonvalent intramolecular P...S contact (3.315 Å), is realized in the molecule. Steric hindrances in the molecule increase the P-S-C bond angle to 106.39°.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 1978–1980, October, 1995.The work was financially supported by the International Science Foundation (Gram RH1 000).     

Asymmetric Arrangement of Monolayer in the Multilayer Films of 2-Hydroxy-4,4''''-dihexyloxy-azobenzene

IntroductionConstructionoffunctionalmolecularunitsintostruc turallywell definedsupramolecularassemblieshasattract edgreatattentionduetotheirpotentialapplicationsincomplexelectronicstructuresandmoleculardevices .1 5Amongthevariousfunctionalorganicmolecules ,azoben zenederivativeshavebeenwidelystudiedbecauseoftheirinterestingphotoresponsivebehavior .6 11Extensivestudieshaveshownthatsuitablydesignedazobenzenederivativescanformlongrangeorderedarrangementoftwo orthree dimensionalmolecularlatticeat…     

New stationary phases of conjugated π-electron systems for HPLC—characterization of structure and dynamics by solid state NMR spectroscopy

Four new stationary phases for HPLC were prepared by modifying silica gel with a trifrnctional aminoalkyl silane. A conjugated π-electron system was linked to the amino group either directly or with a carboxylic anhydride as a spacer in between. Characterization and dynamic measurements of the new stationary phases were performed by solid state NMR spectroscopy. The results of the ²⁹si and ¹³C CP/MAS techniques were compared with the recently developed ¹H MAS-only technique. Despite strong homonuclear dipole-dipole interactions it was possible to obtain well resolved ¹H MAS spectra of those stationaru phases with a high degree of crosslinking. Limited mobility of the aromatic ligand fragments is common for all examined stationaryu phases. The chromatographic properties of the new phases were tested by their ability tio sepatate a mixture of eight PAHS. It could be shown that the π-π interaction mechanism is responsible for the separation of the eight PAHs, because the elution order of the PAHs did not changem despite the use of both a nonpolar mobile phase (n-heptane) and a polar mobile phase (methanol/ water mixture).     

The hydrophobic effect in aqueous solutions of nonelectrolytes. I. Self-interactions of alkylureas

In order to clarify some aspects of the hydrophobic interactions, the enthalpies of dilution of monoethylurea, 1,3-dimethylurea, and 1,3-diethylurea have been determined calorimetrically at 25°C. The calorimetric data, expressed in terms of excess enthalpy, permit the evaluation of the pair and triplet interaction coefficients. The analyses of these and of the analogous coefficientsg _xx andg _xxx, derived from osmotic data, indicate a driving force favorable to the interactions among the hydrated solute molecules. Nevertheless, the positive values of theh _xx andh _xxx coefficients seem to suggest that the source of the effect is a rearrangement of the water molecules rather than a direct association of the solute molecules. There are evidences of a strict correlation between the enthalpic and the entropic effects. Preliminary data were presented at the International Conferences on Chemical Thermodynamics at Baden (1973) and Montpellier (1975). The experimental part was carried out at the Istituto Chimico of the University of Trieste. To whom correspondence should be addressed.     

Multiple Bonds between Transition Metals and “Bare” Main Group Elements: Links between Inorganic Solid State Chemistry and Organometallic Chemistry

The last two decades have seen a dramatic development in the study of metal-metal multiple bonds, particular successes being recorded in the field of organometallic chemistry. Syntheses designed to produce novel transition metal complexes with single, double, triple and quadruple metal-metal bonds occupy a most important place in such research, as also do reactivity studies. A striving to establish general principles has provided much of the motivation for such work, but one less obvious goal—the commercial application of the catalytic properties of metal-metal multiple bonding systems, in the medium and long term—should not be overlooked. All aspects of the investigations of metal-metal multiple bonds also apply to a particular class of compound that has, however, enjoyed little lime-light and thus deserves the present review: complexes with multiple bonds between transition metals and substituent-free (“bare”) main group elements. Although based mostly on accidental discoveries, the few noteworthy examples are now beginning to unfold general concepts of synthesis that are capable of being extended and thus are deserving of exploitation in preparative chemistry. The availability of further structural patterns exhibiting multiple bonds between transition metals and ligand-free main group elements might enable preparative organometallic chemistry to expand in a completely new direction (for instance by the stabilizing or activation of small molecules at the metal complex). This essay discusses the chemistry of complexes of bare carbon, nitrogen, and oxygen ligands (carbido-, nitrido-, and oxo-complexes) and their relationships to higher homologues from both a synthetic and a structural point of view.