Syntheses, structures and magnetic properties of two CoII/NiII isostructural coordination polymers based on an asymmetric semirigid tricarboxylate ligand

Two new isostructural complexes, namely, poly[aqua[μ3-2-(4-carboxyphenoxy)terephthalato-κ3 O 1:O 4:O 4′](1,10-phenanthroline-κ2 N,N′)cobalt(II)], [Co(C15H8O7)(C12H8N2)(H2O)] n or [Co(μ3-Hcpota)(phen)(H2O)] n , I, and poly[aqua[μ3-2-(4-carboxyphenoxy)terephthalato-κ3 O 1:O 4:O 4′](1,10-phenanthroline-κ2 N,N′)nickel(II)], [Ni(C15H8O7)(C12H8N2)(H2O)] n or [Ni(μ3-Hcpota)(phen)(H2O)] n , II, have been synthesized by solvothermal reactions. Complexes I and II were fully characterized by IR spectroscopy, elemental analyses, thermogravimetric analyses, and powder and single-crystal X-ray diffraction. They both present two-dimensional structures based on [M 2(μ-COO)2]2+ (M = CoII or NiII) dinuclear metal units with a fes topology and a vertex symbol (4·82). Interestingly, the positions of the two dimeric metal motifs and the two partially deprotonated Hcpota2− ligands reproduce regular flying butterfly arrangements flipped upside down and sharing wings in the ab plane. Magnetic studies indicate antiferromagnetic interactions (J = −5.21 cm−1 for I and −11.53 cm−1 for II) in the dimeric units, with Co...Co and Ni...Ni distances of 4.397 (1) and 4.358 (1) Å, respectively, that are related to double syn–anti carboxylate bridges.

Monsoon Variability Reconstructed from Sedimentological and Mineral Magnetic Studies from Vaghad Tank Deposits, Nashik District, Maharashtra

An attempt made to reconstruct the monsoon variability using sedimentological, geochemical and mineral magnetic studies from deposits in Vaghad Tank, Nashik district, Maharashtra (India). The ~140 years multi-proxy data of the 3.3 meter thick sedimentary section of the tank exhibits some minor changes in sediment characteristics up to the depth of ~150 cm. The grain-size analysis and mineral magnetic studies of 67 samples of sediment suggests that, the sediment dominated by clay. Overall, sedimentary profile does not exhibit any systematic trend in the sediment properties. Finally, the present study concludes no significant changes in the past monsoon conditions have been occurred during the last century but some minor changes in the hydrodynamic conditions have been noticed during the last few decades.

Preparation and Characterization of Nanosized Substituted Perovskite Compounds with Orthorhombic Structure

In this work, five substituted perovskite such as (Gd0.9Sr0.1) Mn0.8Co0.2O3, Tb0.8Sr0.2FeO3, Gd0.6Sr0.4RuO3, SrCe0.95Y0.05O3, and Mn0.6Co0.4SnO3 were synthesized by tartrate and hydroxide precursor method. The resulting samples were characterized by inductively coupled plasma spectroscopy, energy dispersive X-ray analysis, infrared spectroscopy, thermal analysis, X-ray powder diffraction, transmission electron microscope (TEM), selected field of electron diffraction (SAED), d.c. electrical conductivity, Hall effect, dielectric measurements, and low-temperature magnetization measurements. The X-ray diffraction pattern for all compounds was indicated the formation of single-phase perovskite with orthorhombic structure except Tb0.8Sr0.2FeO3 and Mn0.6Co0.4SnO3 perovskite. These compounds showed a cubic and rhombohedral structure, respectively. The lattice parameter and the unit cell volume slightly decreased as ionic radii decrease in agreement with the lanthanide contraction. The average size of cation ˂ RA ˃, mismatch factor (σ2), and tolerance factor (t) gives the combined effects of disorder and inhomogeneity in these compounds. The average particle size determined from TEM was in the range of 22 to 77 nm for all compounds. The temperature dependence of electrical conductivity for all compounds showed a definite break in 500 K to 610 K. except the Gd0.6Sr0.4RuO3 compound, which corresponds to semiconducting behavior. While the Gd0.6Sr0.4RuO3 sample shows a metallic-like semiconductor. The thermoelectric power and Hall effect measurements for all compounds were n-type semiconductivity except the SrCe0.95Y0.05O3 compound. It showed p-type semiconductivity. The frequency dependence of the dielectric constant and dielectric loss in these substituted perovskites were discussed using the Maxwell-Wagner model. Magnetic studies showed that the thermo-magnetic irreversibility for all compounds.

Geochronology, Correlation and Magnetic Studies of Quaternary Ignimbrites in the Taupo Volcanic Zone, New Zealand

<p>Voluminous, rhyolitic ignimbrites erupted from calderas in the Taupo Volcanic Zone (TVZ) of North Island, New Zealand during the last ca. 1.6 Ma, are characterised by geochemical, paleomagnetic, magnetic fabric and isotopic age techniques to determine their stratigraphy and source vent areas. Most of the welded ignimbrites record distinctive thermoremanent magnetism (TRM) directions that can be defined with a precision of less than 5 degrees. On this basis, individual ignimbrites may be identified and correlated. These data indicate that the voluminous Whakamaru group ignimbrites, mapped by various names in different parts of the TVZ, were probably erupted over a period of as little as 100 years. The Kaingaroa and Matahina ignimbrites display very similar TRM directions and may have been emplaced contemporaneously. Ahuroa and Mamaku ignimbrites display TRM directions widely different to that expected from a dipole field, and were emplaced during polarity transitions in Earth's magnetic field. Geochemically, glasses and FeTi-oxides from the TVZ ignimbrites are homogeneous and typical of high-SiO v2 (>75 wt percent) rhyolites. They indicate little evidence of derivation from physically or compositionally zoned magma chambers, and allow individual eruptives to be fingerprinted. Variable compositions of whole pumice clasts from welded units, previously interpreted as evidence for chemical zonation can be explained by glass alteration and variable mineral components. Geochemical and chronological data suggest the Rocky Hill Ignimbrite and/or Unit E ignimbrite (ca. 1 Ma) may be correlatives of the Potaka tephra, found in sedimentary basins outside the TVZ. Rock magnetic fabric studies using anisotropy of magnetic susceptibility of ignimbrites allow paleoflow patterns to be determined. These patterns are generally consistent with source areas inferred from other data. The source for Mamaku Ignimbrite is consistent with an area on the western margin of Lake Rotorua. The Whakamaru group ignimbrites appear to have originated north of Lake Taupo, and in particular from an area near the Western Dome Belt. Glass shards from nonwelded bases of ignimbrites are well suited to dating by the isothermal plateau fission track (ITPFT) method. Any partial fading of the spontaneous tracks has been corrected by a single-step heat treatment of 150 degrees C for 30 days. The resulting ages and their uncertainties are comparable is caret 40Ar/caret 39Ar plagioclase determinations. The following new eruption ages were determined: Whakamaru group ignimbrites (0.34 Plus-minus 0.03 Ma), Matahina Ignimbrite (0.34 Plus-minus 0.02 Ma), Kaingaroa ignimbrite (0.33 Plus-minus 0.02 Ma), informally named unit Downer 8 (0.33 Plus-minus 0.02 Ma), and Mamaku Ignimbrite (0.23 Plus-minus 0.01 Ma). These data suggest a major phase of activity, with several different caldera forming events in the interval ca. 0.35-0.32 Ma. The age of Mamaku Ignimbrite constrains the paleomagnetic excursion recorded in the unit to ca. 0.23 Ma, similar to the age of the Pringle Falls geomagnetic episode recorded in the western USA.</p>

Geochronology, Correlation and Magnetic Studies of Quaternary Ignimbrites in the Taupo Volcanic Zone, New Zealand

<p>Voluminous, rhyolitic ignimbrites erupted from calderas in the Taupo Volcanic Zone (TVZ) of North Island, New Zealand during the last ca. 1.6 Ma, are characterised by geochemical, paleomagnetic, magnetic fabric and isotopic age techniques to determine their stratigraphy and source vent areas. Most of the welded ignimbrites record distinctive thermoremanent magnetism (TRM) directions that can be defined with a precision of less than 5 degrees. On this basis, individual ignimbrites may be identified and correlated. These data indicate that the voluminous Whakamaru group ignimbrites, mapped by various names in different parts of the TVZ, were probably erupted over a period of as little as 100 years. The Kaingaroa and Matahina ignimbrites display very similar TRM directions and may have been emplaced contemporaneously. Ahuroa and Mamaku ignimbrites display TRM directions widely different to that expected from a dipole field, and were emplaced during polarity transitions in Earth's magnetic field. Geochemically, glasses and FeTi-oxides from the TVZ ignimbrites are homogeneous and typical of high-SiO v2 (>75 wt percent) rhyolites. They indicate little evidence of derivation from physically or compositionally zoned magma chambers, and allow individual eruptives to be fingerprinted. Variable compositions of whole pumice clasts from welded units, previously interpreted as evidence for chemical zonation can be explained by glass alteration and variable mineral components. Geochemical and chronological data suggest the Rocky Hill Ignimbrite and/or Unit E ignimbrite (ca. 1 Ma) may be correlatives of the Potaka tephra, found in sedimentary basins outside the TVZ. Rock magnetic fabric studies using anisotropy of magnetic susceptibility of ignimbrites allow paleoflow patterns to be determined. These patterns are generally consistent with source areas inferred from other data. The source for Mamaku Ignimbrite is consistent with an area on the western margin of Lake Rotorua. The Whakamaru group ignimbrites appear to have originated north of Lake Taupo, and in particular from an area near the Western Dome Belt. Glass shards from nonwelded bases of ignimbrites are well suited to dating by the isothermal plateau fission track (ITPFT) method. Any partial fading of the spontaneous tracks has been corrected by a single-step heat treatment of 150 degrees C for 30 days. The resulting ages and their uncertainties are comparable is caret 40Ar/caret 39Ar plagioclase determinations. The following new eruption ages were determined: Whakamaru group ignimbrites (0.34 Plus-minus 0.03 Ma), Matahina Ignimbrite (0.34 Plus-minus 0.02 Ma), Kaingaroa ignimbrite (0.33 Plus-minus 0.02 Ma), informally named unit Downer 8 (0.33 Plus-minus 0.02 Ma), and Mamaku Ignimbrite (0.23 Plus-minus 0.01 Ma). These data suggest a major phase of activity, with several different caldera forming events in the interval ca. 0.35-0.32 Ma. The age of Mamaku Ignimbrite constrains the paleomagnetic excursion recorded in the unit to ca. 0.23 Ma, similar to the age of the Pringle Falls geomagnetic episode recorded in the western USA.</p>