Diamond-Graphite Hybrids And The Nature Of Amorphous-Carbon And Diamond-Like Carbon

The nature of amorphous carbon has been explored by molecular mechanics by examining the structures of species such as C84Hx and C150Hx, wherein the percentage of sp(3) carbons is progressively increased in a graphitic network. The nature of diamond-like carbon has been similarly investigated by examining the structures of C84Hx and C102Hx where the percentage of sp(2) carbons is varied in an sp(3) network. The dependence of the average coordination number as well as the sp(3)/sp(2) atom ratio on the atom fraction of hydrogen has been investigated in light of the random covalent network model.

Lanthanide chelate complexes of salicyloyl hydrazide-salicylaldehyde schiff base (SHSASB) and anthranilic acid-salicylaldehyde schiff base (AASASB)

New lanthanide complexes of salicylaldehyde-Schiff bases with salicyloyl hydrazide and anthranilic acid, were synthesized by a novel method consisting of refluxing the mixtures of Schiff base ligands and lanthanide trichloroacetate in acetone. Solid complexes of formulae Ln(SHSASB)s*2Hz0 and Ln2(AASASB)s*2Hz0 where Ln = La-Yb and Y, were isolated. Proton NMR and IR spectra for the complexes reveal the bidentate binding of both the Schiff base ligands to the lanthanide ion. Electronic spectra along with the conductance data for the complexes indicate a coordination number of six for the lanthanide ion in the complexes of both the Schiff bases.

Synthesis and Spectroscopic Investigations of Complexes of Lanthanide Nitrates with N-(4-Hethyl-2-Pyridyl)-Acetamide

New complexes of Lanthanide nitrates with N-(4-methyl-2-pyridyl)-acetamide (4-me-aapH) of the general formulae. [Ln(4-me-aapH)2] [NO3] (where Ln=La=La-Yb and Y)have been synthesized and haracterised by chemical analysis, molar conductivity and physical methods such as infrared, 13C NMR an electronic spectra in the visible region. Molar conductance and infrared data point to the presence to the coordinated nitrates groups. Infrared and 13C NMR data have been interpreted in terms of the coordination of the legand to the metal ion through the oxygen of the secondary amide and nitrogen of the hetrocyclic ring, in a bidentate fashion. Coordination number of ten seems probable for the complexes.

Complexes of lanthanide perchlorates with the open-chain pentadentate ligand n,n,$n^{'},n^{'}$-tetramethyl-3,6,9-trioxaundecane diamide

Complexes of lanthanide perchlorates with the ligand N,N,N,N-tetra-methyl-3,6,9-trioxaundecane diamide (TUD) of the composition Ln(TUD)2-(ClO4)3 (Ln triple bond; length as m-dash La, Nd, Ho, Er, Y) were isolated. Electrical conductivity values indicate that all the perchlorate groups are ionic. IR and nuclear magnetic resonance (1H and 13C) data prove that the ligand coordinates to the metal via the three ether oxygens and the two carbonyl oxygens. A probable coordination number of ten can be assigned for all the complexes.

Adsorption isitherms for neutral organic compounds-A hierarchy in modelling: Part IV. Charge of maximum adsorption-Statistical mechanical basis

The charge at which adsorption of orgamc compounds attains a maximum ( \sigma MAX M) at an electrochenucal interface is analysed using several multi-state models in a hierarchical manner The analysis is based on statistical mechamcal results for the following models (A) two-state site parity, (B) two-state muhl-slte, and (C) three-state site parity The coulombic interactions due to permanent and reduced dipole effects (using mean field approximation), electrostatic field effects and specific substrate interactions have been taken into account. The simplest model in the hierarchy (two-state site parity) yields the exphcit dependence of ( \sigma MAX M) on the permanent dipole moment, polarizability of the solvent and the adsorbate, lattice spacing, effective coordination number, etc Other models in the baerarchy bring to hght the influence of the solvent structure and the role of substrate interactions, etc As a result of this approach, the "composition" of oM.x m terms of the fundamental molecular constants becomes clear. With a view to use these molecular results to maxamum advantage, the derived results for ( \sigma MAX M) have been converted into those involving experimentally observable parameters lake Co, C 1, E N, etc Wherever possible, some of the earlier phenomenologlcal relations reported for ( \sigma MAX M), notably by Parsons, Damaskm and Frumkln, and Trasattl, are shown to have a certain molecular basis, vlz a simple two-state sate panty model.As a corollary to the hxerarcbacal modelling, \sigma MAX M and the potential corresponding to at (Emax) are shown to be constants independent of 0max or Corg for all models The lmphcatlon of our analysis f o r OmMa x with respect to that predicted by the generalized surface layer equation (which postulates Om~ and Ema x varlaUon with 0) is discussed in detail Finally we discuss an passing o M. and the electrosorptlon valency an this context.

Glass-Transition In Isopentane - A Monte-Carlo Study

Monte Carlo simulations with realistic interaction potentials have been carried out on isopentane to investigate the glass transition. Intermolecular pair-correlation functions of the glass show distinct differences from those of the liquid, the CH-CH pair-correlation function being uniquely different from the other pair-correlation functions. The coordination number of the glass is higher than that of the liquid, and the packing in the glass seems to be mainly governed by the geometrical constraints of the molecule. Annealing affects the properties of the glass significantly.

2,6-Lutidine-N-oxide complexes of rare-earth bromides

2,6-Lutidine-N-oxide (LNO) complexes of rare-earth bromides of the composition $$MBr_3 .(LNO)_{4_{ - n} } .nH_2 O$$ wheren = l for M = La, Pr, Nd, Sm, Gd, Ho, Er; andn = 0 for M = Y have been prepared and characterised by analyses, conductance and infrared data. Infrared spectra of the complexes indicate that the coordination of ligand to the metal ion takes place through the oxygen of the ligand, and the water molecule in the complexes present is coordinated to the metal. A coordination number of seven has been suggested to all the rare-earth metal ions.

Structure and Bonding in N-Methylacetamide Complexes of Alkali and Alkaline Earth Metals

A detailed crystallographic investigation of N-methylacetamide complexes of Li, Na, K, Mg and Ca has been made in view of its importance in the coordination chemistry and biochemistry of alkali and alkaline earth metals. The metal ions bind to the amide oxygen causing an increase in the carbonyl distance and a proportionate decrease in the central C-N bond distance. The decrease in the central C-N distance is accompanied by an increase in the distance of the adjacent C-C bond and a decrease in the adjacent C-N bond distance. The metal ion generally deviates from the direction of the lone pair of the carbonyl oxygen and also from the plane of the peptide, the out-of-plane deviation varying with the ionic potential of the cation. The metal-oxygen distance in alkali and alkaline earth metal complexes of a given coordination number also varies with the ionic potential of the cation, as does the strength of binding of the cations to the amide. The amide molecules are essentially planar in these complexes, as expected from the increased bond order of the central C-N bond. The NH bonds of the amide are generally hydrogen bonded to anions. The structures of the amide complexes are compared with those of other oxygen donor complexes of alkali and alkaline earth metals. The structural study described here also provides a basis for the interpretation of results from spectroscopic and theoretical investigations of the interaction of alkali and alkaline earth metal cations with amides.

Rapid quenching and glass formation in chalcogenide glasses: Preparation and properties of Ge-As-Te glasses over an extended composition ranges

In Ge-As-Te system, the glass forming region determined by normal melt quenching method has two regions (GFR I and GFR II) separated by few compositions gap. With a simple laboratory built twin roller apparatus, we have succeeded in preparing Ge7.5AsxTe92.5-x glasses over extended composition ranges. A distinct change in T-g is observed at x = 40, exactly at which the separation of the glass forming regions occur indicating the changes in the connectivity and the rigidity of the structural network. The maximum observed in glass transition (T-g) at x = 55 corresponding to the average coordination number (Z(av)) = 2.70 is an evidence for the shift of the rigidity percolation threshold (RPT) from Z(av) = 2.40 as predicted by the recent theories. The glass forming tendency (K-gl) and Delta T (=T-c-T-g) is low for the glasses in the GFR I and high for the glasses in the GFR II.

Post-liquefaction undrained monotonic behaviour of sands: experiments and DEM simulations

This paper presents the results of a series of servo-controlled cyclic triaxial tests and numerical simulations using the three- dimensional discrete element method (DEM) on post-liquefaction undrained monotonic strength of granular materials. In a first test series,undrained monotonic tests were carried out after dissipating the excess pore water pressure developed during liquefaction. The influence of different parameters such as amplitude of axial strain,relative density and confining pressure prior to liquefaction on the post-liquefaction undrained response have been investigated.The results obtained highlight an insignificant influence of amplitude of axial strain, confining pressure and a significant influence of relative density on the post-liquefaction undrained monotonic stress-strain response.In the second series, undrained monotonic tests were carried out on similar triaxial samples without dissipating the excess pore water pressure developed during liquefaction. The results highlight that the amplitude of axial strain prior to liquefaction has a significant influence on the post-liquefaction undrained monotonic response.In addition,DEM simulations have been carried out on an assembly of spheres to simulate post-liquefaction behaviour.The simulations were very similar to the experiments with an objective to understand the behaviour of monotonic strength of liquefied samples from the grain scale. The numerical simulations using DEM have captured qualitatively all the features of the post-liquefaction undrained monotonic response in a manner similar to that of the experiments.In addition,a detailed study on the evolution of micromechanical parameters such as the average coordination number and induced anisotropic coefficients has been reported during the post-liquefaction undrained monotonic loading.

Evidence for a thermally reversing window in bulk Ge-Te-Si glasses revealed by alternating differential scanning calorimetry

Experiments on Ge15Tc85-xSix glasses (2 <= x <= 12) using alternating differential scanning calorimetry (ADSC) indicate that these glasses exhibit one glass transition and two crystallization reactions upon heating. The glass transition temperature has been found to increase almost linearly with silicon content, in the entire composition tie-line. The first crystallization temperature (T-cl) exhibits an increase with silicon content for x<5; T-cl remains almost a constant in the composition range 5 < x <= 10 and it increases comparatively more sharply with silicon content thereafter. The specific heat change (Delta C-p) is found to decrease with an increase in silicon content, exhibiting a minimum at x=5 (average coordination number, (r) = 2.4); a continuous increase is seen in Delta C-p with silicon concentration above x = 5. The effects seen in the variation with composition of T-cl and Delta C-p at x=5, are the specific signatures of the mean-field stiffness threshold at (r) = 2.4. Furthermore, a broad trough is seen in the enthalpy change (Delta H-NR), which is indicative of a thermally reversing window in Ge15Te85-xSix glasses in the composition range 2 <= x <= 6 (2.34 <= (r) <= 2.42).

Lanthanum, praseodymium and neodymium chloroacetates

The monochloroacetates of lanthanum, praseodymium and neodymium of the composition M(ClCH2COO)3·2H2O have been prepared and characterised. The compounds behave as non-electrolytes in dimethylformamide. The infrared spectra are consistent with bidentate coordination of the carboxylate group and show the presence of two types of water molecules, coordinated, and free. With six oxygen atoms from the three acetato groups and one from the water bonded to the metal, a coordination number of seven has been assigned to the rare earths in these compounds. On pyrolysis, the chloroacetates lose water at ~130 °C and yield the oxychlorides at ~500 °C. The X-ray powder patterns of the chloroacetates have been indexed for the monoclinic system, with four molecules per unit cell.

Diphenyl sulphox1de complexes of thorium(IV)

Thorium(IV) is known to form high coordination-number complexes. An attempt has therefore been made to determine the effect of anions on the coordination complexes of diphenyl sulphoxide (DPSO) with thorium(IV). The complexes formed have the formulae [Th(DPSO)6](ClO4)4, [Th(DPSO)4Cl4], [Th(DPSO)4Br4], [Th(DPSO)6I2]I2, [Th(DPSO)4(NCS)4]and [Th(DPSO)3(NO3)4]. In all the complexes, DPSO is coordinated to the metal ion through its oxygen. The electrical conductances in nitrobenzene and in nitromethane, and ebullioscopic molecular weights in acetonitrile, show that the perchlorate and iodide complexes behave as 1:4 and 1:2 electrolytes, respectively; while the other complexes are monomeric and non-electrolytes. The infrared spectra of the solid complexes indicate the ionic nature of the perchlorate, the bidentate nature of the nitrate and the coordination of the thiocyanate through its nitrogen. [Th(DPSO)4Cl4], [Th(DPSO)4Br4]and [Th-(DPSO)3 (NO3)4]decompose endothermically while [Th(DPSO)6](ClO4)4 and [Th(DPSO)4(NCS)4]decompose exothermically, both in air and in nitrogen. The perchlorate complex has octahedral symmetry around the thorium, the halo- and the thiocyanato complexes are 8-coordinate, probably with square antiprismatic structures, while the nitrate complex is 11-coordinate

Enhanced Pair Hydrophobicity in the Water-Dimethylsulfoxide (DMSO) Binary Mixture at Low DMSO Concentrations

We observe a surprisingly sharp increase in the pair hydrophobicity in the water climethylsulfoxide (DMSO) binary mixture at small DMSO concentrations, with the mole fraction of DMSO (x(D)) in the range 0.12-0.16. The increase in pair hydrophobicity is measured by an increase in the depth of the first minimum in the potential of mean force (PMF) between two methane molecules. However, this enhanced hydrophobicity again weakens at higher DMSO concentrations. We find markedly unusual behavior of the pure binary mixture (in the same composition range) in the diffusion coefficient of DMSO and in the local composition fluctuation of water, We find that, in the said composition range, the average coordination number of the methyl groups (of distinct DMSO) varies between 2.4 and 2.6, indicating the onset of the formation of a chain-like extended connectivity in an otherwise stable tetrahedral network comprising of water and DMSO molecules. We propose that the enhanced pair hydrophobicity of the binary mixture at low DMSO concentrations is due to the participation of the two methane molecules in the local structural order and the emerging molecular associations in the water-DMSO mixture.

A MAS NMR investigation of aluminosilicate, silicophosphate, and aluminosilicophosphate gels and the evolution of crystalline structures on heating the gels

Gels of various composition containing SiO2, Al2O3, and P2O5 have been investigated by employing high resolution magic-angle-spinning (MAS) 27Al, 29Si, and 31P NMR spectroscopy. Changes occurring in the NMR spectra as the gels are progressively heated have been examined to understand the nature of structural changes occurring during the crystallization of the gels. 27Al resonance is sensitive to changes in the coordination number even when the Al concentration is as low as 1 mol%. As the percentage of Al increases, the hydroxyl groups tend to be located on the Al sites while Si remains as SiO4/2 (Q4). Mullite is the major phase formed at higher temperature in the aluminosilicate gels. In the case of the silicophosphate gels, Si is present in the form of Q4 and Q3 species. There is a change in the coordination of Si from four to six as the gel is heated. The formation of six-coordinated Si is facilitated even at lower temperatures (~673 K) when the P2O5 content is high. The phosphorus atoms present as orthophosphoric acid units in the xerogels change over to metaphosphate-like units as the gel is heated to higher temperatures. In aluminosilicophosphates, Si is present as Q4 and Q3 species while P is present as metaphosphate units; Al in these gels seems to be inducted into the tetrahedral network positions.