Electron spin resonance studies of d5 ions (Fe3+ and Mn2+) in lead oxide-lead halide glasses

Electron spin resonance (ESR) of d5 ions (Fe3+ and Mn2+) has been investigated in PbO---PbF2 and PbO---PbCl2 glasses in wide ranges of composition. ESR spectra of d5 ions in these glasses exhibit significant differences which we have attributed to at least three important causes: (i) The ionic potentials of Fe3+ and Mn2+ are different. Hence Fe3+ ions tend to acquire their own environment while Mn2+ ions take up substitutional (Pb2+ ion) positions. (ii) The sizes and nephelauxetic behaviours of O2- and F- ions are similar. Thus even when there is a mixed anionic coordination, the environment of Mn2+ ions is highly symmetrical in oxyfluoride glasses. The Mn2+ spectra in oxychloride glasses are considerably different. (iii) Increase in halide ion concentration increases the ionicity of lead-ligand bonding and favours a more symmetrical environment around dopant ions in halide-rich glasses. The features in ESR spectra have been interpreted in the light of known behaviour of d5 ions in glasses and also in the context of known structural features of PbO---PbX2 glasses. Dopant ions appear to cluster at high concentrations although isolated low-symmetry sites are still observed. Effects of crystallization and annealing upon ESR spectra have also been investigated.

Interaction of Metal Ions with 2'-Deoxyribonucleotides. Crystal and Molecular Structure of a Cobalt(l1) Complex with 2'-Deoxyinosine 5'-Monophosphate

The crystal structure of the cobalt( 11) complex with 2'-deoxyinosine 5'-monophosphate (5'- dlMP), [Co(5'-dlMP) (H,0),]-2H20, has been analysed by X-ray diffraction. The complex crystallizes in the space group P2,2,2, with a = 6.877(3), b = 10.904(2), c = 25.421 (6) A, and Z = 4. The structure was solved by the heavy-atom method and refined to an R value of 0.043 using 1 776 unique reflections. The cobalt ion binds only to the 6-oxopurine base of the nucleotide at the N(7) position, the octahedral co-ordination of the metal being completed by five water oxygens. The phosphate oxygens are involved in hydrogen bonding with the co-ordinated water molecules. The structure is closely similar to that of the corresponding ribonucleotide complex. The nucleotide has the energetically preferred conformation: an anti base, a C(3') -endo sugar pucker, and a gauche-gauche conformation about the C(4')-C( 5') bond. The significance of sugar puckering in the monomeric complexes of general formula [ M (5'-nucleotide) (H20),] is explained in terms of the structural requirements for metal-water-phosphate bridging interactions.

Configuration mixing in the s-hole states of metal ions

Configuration interaction calculation have been carried out on the s-hole states of Mn2+ Fe2+ (both high- and low-spin configurations). Co2+, Ca2+, K+ and Na+ including configurations involving virtual orbitals. The results show good agreement with the multiplet structures found in X-ray photoelectron spectra of these ions.

Crystal and molecular structures of alkali- and alkaline-earth-metal complexes of N,N-dimethylformamide

Structures of lithium, sodium, magnesium, and calcium complexes of NJ-dimethylformamide (DMF) have been investigated by X-ray crystallography. Complexes with the formulas LiCl.DMF.1/2H20, NaC104.2DMF, CaC12.2DMF.2H20, and Mg(C104)2.6DMF crystallized in space groups P2]/c, P2/c, Pi, and Ella, respectively, with the following cell dimensions: Li complex, a = 13.022 (7) A, b = 5.978 (4) A, c = 17.028 (10) A, = 105.48 (4)O, Z = 8; Na complex, a = 9.297 (4)A, b = 10.203 (3) A, c = 13.510 (6) A, /3 = 110.08 (4)O, Z = 4; Ca complex, a = 6.293 (4) A, b = 6.944 (2) A, c = 8.853(5) A, a = 110.15 (3)O, /3 = 105.60 (6)", y = 95.34 (5)", Z = 1; Mg complex, a = 20.686 (11) A, b = 10.962 (18) A,c = 14.885 (9) A, /3 = 91.45 (5)O, Z = 4. Lithium is tetrahedrally coordinated while the other three cations are octahedrally coordinated; the observed metal-oxygen distances are within the ranges generally found in oxygen donor complexes of these metals. The lithium and sodium complexes are polymeric, with the amide and the anion forming bridging groups between neighboring cations. The carbonyl distances become longer in the complexes accompanied by a proportionate decrease in the length of the central C-N bond of the amide; the N-C bond of the dimethylamino group also shows some changes in the complexes. The cations do not deviate significantly from the lone-pair direction of the amide carbonyl and remain in the amide plane. Infrared spectra of the complexes reflect the observed changes in the amide bond distances.

Requirement for calcium ions in mycobacteriophage I3 DNA injection and propagation

Ca2+ ions are absolutely necessary for the propagation of mycobacteriophage I3 in synthetic medium. These ions are required for successful infection of the host and during the entire span of the intracellular development of the phage. A direct assay of the phage DNA injection using 32[P] labelled phage, showns that Ca2+ ions are necessary for the injection process. The injection itself is a slow process and takes 15 min to complete at 37°C. The bacteria infected in presence of Ca2+ tend to abort if the ions are subsequently withdrawn from the growth medium. The effect of calcium withdrawal is maximally felt during the early part of the latent period; however, later supplementation of Ca2+ ions salvage phage production and the mature phage progeny appear after a delayed interval, proportional to the time of addition of Ca2+.

Coordination Behaviour of Imino Hydrazone Ligands towards Nickel (II) and Copper (II) Ions

The complexing ability of a new series of ligands, β-N-arylimine hydrazones, toward Ni (II) and Cu (II) ions has been studied. The isolated complexes are characterised on the basis of elemental analysis, spectroscopic methods and magnetic susceptibility measurements. The ligands are notentially bidentate in character coordinating to divalent metal ions through the N1 and N5 nitrogens. Square planar geometry of the metal ions is suggested on the basis of experimental evidence.

“Let’s see if you can see me”: Making connections with Google Earth™ in a preschool classroom

Bringing a social interaction approach to children’s geographies to investigate how children accomplish place in everyday lives, we draw on ethnomethodological and conversation analytic approaches that recognize children’s competence to manipulate their social and digital worlds. An investigation of preschool-aged children engaged with Google Earth™ shows how they both claimed and displayed technological understandings and practices such as maneuvering the mouse and screen, and referenced place through relationships with local landmarks and familiar settings such as their school. At times, the children’s competing agendas required orientation to each other’s ideas, and shared negotiation to come to resolution. A focus on children’s use of digital technologies as they make meaning of the world around them makes possible new understandings of place within the geographies of childhood and education.

Complexes of rare earth perchlorates with di-2-pyridyl ketone

Abstract is not availabe.

Metal ions in molecular association of porphyrins

Molecular association of porphyrins and their metal derivatives has been recognized as one of the important properties for many of their biological functions. The association is classified into (i) self-aggregation, (ii) intermolecular association and (iii) intramolecular association. The presence of metal ions in the porphyrin cavity is shown to alter the magnitudes of binding constants and thermodynamic parameters of complexation. The interaction between the porphyrin unit and the acceptor is described in terms of π-π interaction. The manifestation of charge transfer states both in the ground and excited states of these complexes is shown to influence the rates of excited state electron transfer reactions. Owing to paucity of crystal structure data, the time-averaged geometries of many of these complexes have been derived from magnetic resonance data.

An alternative approach to selective sea water oxidation for hydrogen production

Sea water electrolysis is one of the promising ways to produce hydrogen since it is available in plentiful supply on the earth. However, in sea water electrolysis toxic chlorine evolution is the preferred reaction over oxygen evolution at the anode. In this work, research has been focused on the development of electrode materials with a high selectivity for oxygen evolution over chlorine evolution. Selective oxidation in sea water electrolysis has been demonstrated by using a cation-selective polymer. We have used a perm-selective membrane (Nafion®), which electrostatically repels chloride ions (Cl−) to the electrode surface and thereby enhances oxygen evolution at the anode. The efficiency and behaviour of the electrode have been characterized by means of anode current efficiency and polarization studies. The surface morphology of the electrode has been characterized by using a scanning electron microscope (SEM). The results suggest that nearly 100% oxygen evolution efficiency could be achieved when using an IrO2/Ti electrode surface-modified by a perm-selective polymer.

Aiming for the management of the small hive beetle, Aethina tumida, using relative humidity and diatomaceous earth

Small hive beetles (SHBs) are a global pest of European honeybee colonies. In the laboratory, the survival of adult SHBs was evaluated in relation to relative humidity (RH = 56, 64, 73, 82 and 96 %) and treatment with diatomaceous earth (DE) across 4 days. Low RH reduced survival. The application of DE reduced survival in addition to RH. Adults treated with corn flour (control) showed no difference in survival from untreated beetles. Scanning electron microscopy images showed no scarification of adult beetle cuticle after exposure to DE; therefore, water loss is likely facilitated through non-abrasive means such as the adsorption of cuticular lipids. The data agree with the hypothesis that DE causes mortality through water loss from treated insects. Egress, ingress, mortality and the egg-laying behaviours of beetles were observed in relation to a popular in-hive trench trap with and without the addition of DE. Traps filled with DE resulted in 100 % mortality of beetles compared with 8.6 % mortality when no DE was present. A simple method for visually determining beetle sex was used and documented.

Effective earth and space science analogies

There are several good reasons why Earth and Space Science should be a part of any science curriculum. Nearly everything we do each day is connected in some way to the Earth: to its land, oceans, atmosphere, plants and animals. By 2025, eight billion people will live on Earth. If we are to continue extracting resources to maintain a high quality of life, then it is important that our children are scientifically literate in a way that allows them to exploit the Earth’s resources in a sustainable way. People who understand how earth systems work can make informed decisions and may be able to help resolve issues surrounding clean water, urban planning and development, global climate change and the use and management of natural resources.

Topochemically controlled hydrogen reduction of scheelite-related rare-earth metal molybdates

Scheelite-related -Ln2Mo3O12(Ln = La, Pr, Nd, Sm, Gd, Tb, or Dy) oxides are reduced by hydrogen at 780–870 K yielding molybdenum (IV) oxides of formula Ln2Mo3O9. The latter crystallize in a tetragonal scheelite (ABO4) type structure where one third of the A sites and a quarter of the anion sites are vacant: Ln2/3(cat)1/3MoO3(an). The reaction Ln2Mo3O12+ 3H2 Ln2Mo3O9(an)3+ 3H2O may be regarded as topochemically controlled, since both the parent and the product phases have scheelite-related structures. Infrared spectra and electrical and magnetic properties of these metastable defect scheelite phases are reported.

Thermal decomposition of rare-earth trioxalatocobaltates

The thermal decomposition of rare-earth trioxalatocobaltates LnCo(C2O4)3 · x H2O, where Ln = La, Pr, Nd, has been studied in flowing atmospheres of air/oxygen, argon/ nitrogen, carbon dioxide and a vacuum. The compounds decompose through three major steps, viz. dehydration, decomposition of the oxalate to an intermediate carbonate, which further decomposes to yield rare-earth cobaltite as the final product. The formation of the final product is influenced by the surrounding gas atmosphere. Studies on the thermal decomposition of photodecomposed lanthanum trioxalatocobaltate and a mechanical mixture of lanthanum oxalate and cobalt oxalate in 1 : 2 molar ratio reveal that the decomposition behaviour of the two samples is different. The drawbacks of the decomposition scheme proposed earlier have been pointed out, and logical schemes based on results obtained by TG, DTA, DTG, supplemented by various physico-chemical techniques such as gas and chemical analyses, IR and mass spectroscopy, surface area and magnetic susceptibility measurements and X-ray powder diffraction methods, have been proposed for the decomposition in air of rare-earth trioxalatocobaltates as well as for the photoreduced lanthanum salt and a mechanical mixture of lanthanum and cobalt oxalates.

Lanthanide coordination in dimethyl sulphoxide and antipyrine complexes of rare earth nitrates

Abstract is not available.