The plumbide CeZnPb – Structure,magnetism, and chemical bonding

The plumbide CeZnPb was synthesized from the elements in a sealed tantalum ampoule. Its YPtAs-type structure was refined on the basis of single-crystal X-ray diffraction data: P6₃/mmc, a = 463.7(2) and c = 1669.6(6) pm, wR2 = 0.1161, 189 F² values, and 12 variables. CeZnPb crystallizes with a superstructure of AlB₂. The zinc and lead atoms form puckered [Zn₃Pb₃] hexagons, which are stacked in a sequence ABB′A′. The Zn–Pb distances within the layers are 278 pm. The shortest interlayer distance occurs between the zinc atoms of adjacent layers (305 pm). Susceptibility measurements of CeZnPb show Curie–Weiss behavior with an experimental magnetic moment of 2.47(1) μ_B/mol CeZnPb. CeZnPb shows two antiferromagnetic transitions at T_N1 = 3.8 K and T_N2 = 2.6 K. Magnetization measurements at 2 K show two metamagnetic transitions at critical fields of approximately 1.1 and 7.0 kOe, underlining the antiparallel spin alignment at zero field. The electronic and magnetic structure is discussed based on scalar relativistic computations using the augmented spherical wave (ASW) method within density functional theory (DFT). As a result, our calculations employing the generalized gradient approximation (GGA) reveal a delicate competition of ferro and antiferromagnetic interactions. Only after properly taking into account the electronic correlations present in CeZnPb via a GGA + U treatment we are able to correctly describe the antiferromagnetic ground state. In addition, our calculations give a clue to the metamagnetic transitions as being due to the inherent geometric frustration of the cerium spin system.     

The International Conference “Fullerenes-93

Information Congresses, Conferences, Symposia, Meetings, and Seminars in the Field of Chemical Sciences Held with the Participation of the Russian Academy of Sciences

The International Conference Fullerenes-93     

The 3rd International Conference on Ion Exchange, ICIE ''''03

First Circular / Pre-registration (e-mail edition) July 14-18, 2003 Kanazawa Institute of Technology, Nonoichi, Ishikawa Pref., JAPAN Organized by Japan Association of Ion Exchange (JAIE) INVITATION On behalf of the Japan Association of Ion Exchange (J…     

The Chemistry of Fused Cyclotriazaphosphole – Synthesis,Reactions, Mechanism and Conformation

Abstract

Fused tricyclotriazaphosphole was first synthesized in our laboratory. It is a very interesting series in phosphoorus us heterochemistry.     

The ILAC Arrangement – Part I

As of August 2001, 38 laboratory accreditation bodies of the International Laboratory Accreditation Cooperation (ILAC) have signed the multi-lateral, mutual recognition arrangement (the ”ILAC Arrangement”) to promote the acceptance of accredited test and calibration data. This Arrangement provides significant technical underpinning to international trade. Until now, there has been no international mutual recognition agreement in laboratory accreditation, which has been a hindrance for some types of international trade. The key to the Arrangement is the developing global network of accredited testing and calibration laboratories that are assessed and recognised as being competent by ILAC Arrangement signatory accreditation bodies. The signatories have, in turn, been peer-reviewed and shown to meet ILAC’s criteria for competence. Now that the ILAC Arrangement is in place, governments can take advantage of it to further develop or enhance trade agreements. The ultimate aim is increased use and acceptance by industry, as well as government, of the results from accredited laboratories, including results from laboratories in other countries. In this way, the free-trade goal of ”a product tested once and accepted everywhere” can be realised.     

Evaluation of Accuracy for the Measurement of Octanol–Water Partition Coefficient by MEEKC

Microemulsion electrokinetic chromatography (MEEKC) has been widely used as an indirect tool to measure octanol–water partition coefficients (logP _ow) of various kinds of compounds. In this paper, we present for the first time a mathematical model of the precision of logP _ow (ΔlogP _ow) as a function of the deviation of migration time (Δt _m) in MEEKC, and more importantly evaluated the accuracy of the MEEKC. Our model shows that for a given microemulsion system, there is an interval of migration times, where a high precision in the determination of logP _ow can be obtained. However, when the migration time approaches either the migration time of the electroosmotic flow or that of the microemulsion phase, the precision of logP _ow deteriorates rapidly. The model was experimentally verified by the microemulsion system with migration times of 6.50 and 32.00?min for the electroosmotic flow and microemulsion phase, respectively, and we found the useful logP _ow interval to be 0.50–5.50. The paper also demonstrates that the calibration constants between migration times t _m and predicted logP _ow values could be transferred with high accuracy from one MEEKC system to another as long as both systems are set up to use the same operational parameters.     

The XIth International symposium “polymers and light”

Information Congresses, Conferences, Symposia, Meetings, and Seminars in the Field of Chemical Sciences Held with the Participation of the Russian Academy of Sciences

The XIth International symposium polymers and light     

Chemical bonding in equiatomic cerium intermetallics – The case of CeMgSn,CePdSn, and CeMgPb

The electronic and magnetic structures and the properties of chemical bonding in isopointal CeMgSn and CePdSn (both phases belong to the family of TiNiSi related intermetallics, space group Pnma) and CeMgPb belonging to the family of CeScSi intermetallics, space group I4/mmm, have been investigated within the density functional theory (DFT). The charge analyses indicate negatively charged tin and lead leading to assign the compounds as stannides and plumbides, as also illustrated by the mapping of the electron localization function ELF. Calculations within spin-degenerate non-magnetic spin-polarized ferro- (SP-F) and SP-antiferromagnetic configurations led to assign a major role of Ce 4f states in the onset of ordered moments within SP-AF ground states from energy differences. Chemical bonding analyses from crystal orbital overlap populations revealed the strongest interactions for Ce–Sn in CeMgSn, Ce–Pb in CeMgPb, and Ce–Pd in CePdSn.     

The Evaluation of Two-Dimensional Madelung Constant For NaCl Crystal Structure

The following documentation is an evaluation of the two-dimensional Madelung constant for the NaCl structure. The infinite series for the structure is formulted asThe first term in the formula converges to 41n2. The series after K =2 in the second term is put together with the third term and a constant- 4/ 2 is left. The combination of the third term and the series after K=2 in the second term is assumed to be 8 Sn. The converging series Sn can be solved on a computer. The seven significant figures of the two-dimensional Madelung constant for the NaCl structure is then determined as 1. 615558.     

The International System of Units��a case for reconsideration

The International System of Units (SI) follows a concept that goes back to Maxwell. At that time, a logic sound foundation of mathematics was not yet available. This has lead to concepts and terms that are contradictory and in conflict with today??s standard mathematical concepts. The inconsistencies that have evolved in metrology due to the lack of appropriate notions are pointed out. This is most important, as the metrology is a field that is internationally well organized under the umbrella of the Meter Convention, an international treaty for acting on all matters relating to units of measurement. Committees and working groups under the Meter Convention have a leading role in the elaboration of important metrological guides, among others the International Vocabulary of Metrology. Therefore, it is highly desirable that their publications use well-founded concepts and terminology. It is consensus that it is desirable to find a system of units on invariant properties of nature and not on human artifacts, e.g., the prototype of the kilogram. However, the current proposals to improve that are in conflict with standard scientific concepts. It is shown in the paper how these inconsistencies can be avoided. The argumentation is based on the interpretation of numbers developed by mathematicians like Cantor, Dedekind, Peano, and others that have led the logic foundation of mathematics with set and number theory. This foundation excludes dogmas that have been forwarded in the last century under the umbrella of the Meter Convention.     

Quantitative Evaluation of Infrared Absorbance Spectra – Lorentz Profile versus Lorentz Oscillator

We present the theoretical basis for a profound upgrade of the method of absorbance band fitting (“band deconvolution”), which requires only minute changes in the code of corresponding spectrometer software. This upgrade is based on a (re-)connection of the damped harmonic oscillator model (“Lorentz oscillator”) and the Lorentz profile used for band fitting. Based on this reconnection, we provide a proper extension to multiple oscillators. As a result, band fitting allows directly obtaining all oscillator parameters with very good accuracy, at least for the not too strong oscillators present in organic and biological matter. Accordingly, this could be the initial spark to open the way to a long-awaited paradigm shift in infrared spectroscopy: Away from a mere oscillator position-based, towards an also intensity-based quantitative interpretation of spectra. As an extra, absorbance band fitting (“Poor Man's Dispersion Analysis”), allows to obtain the index of refraction function in one go.     

The structure of mimetite,arsenian pyromorphite and hedyphane – A near-infrared spectroscopic study

Electronic and vibrational spectra of mimetite, arsenian pyromorphite and hedyphane minerals have been analysed and the spectra related to the mimetite and arsenian pyromorphite and hedyphane mineral structure. The chief spectral feature in the electronic spectra at ∼10 000 cm⁻¹ (1.00 μm) with variable band position and intensity results from the ferrous ion. The splitting of Fe(II) band is large in mimetites with a separation of 1415 cm⁻¹. An additional band shown by arsenian pyromorphite at 10 735 cm⁻¹ (0.93 μm) is assigned to Cu(II) dd-transition. The substitution of Fe(II) causes a blue shift for Cu(II) band in mimetites and the intensity of this band is enhanced at ∼11 140 cm⁻¹ (0.90 μm). The change in colour from brown to orange-yellow relates to the amount of Cu and/or Fe impurities in the mimetite minerals.     

On The Fluorometric Method for the Measurement of β-Cyanoalanine Synthase Activity

Abstract

A modification of a fluorescence assay method for β-cyanoalanine synthase has been described which involves the direct coupling of the product of cyanide and cysteine to resazurin, to produce the fluorescent resosurfin, The fluorescence produced was found to be directly proportional to the rate of the reaction.     

The Vanadium Redox Reactions – Electrocatalysis versus Non-Electrocatalysis

Catalytic effects of surface groups on porous carbon electrodes are claimed in literature for the redox reactions V(II)/V(III) and V(IV)/V(V). The literature is critically analysed also in relation to work of this group. A method how to overcome the problem of assessing the electrochemically active surface area on porous electrodes is presented. Applying this method, no catalytic effects for above reactions can be substantiated. It is further pointed out that the parameters electrochemical potential and temperature need to be used to assess electrocatalysis.