236 research outputs found
Methyl 2,2-diphenyl-2-(prop-2-yn-1-yloxy)acetate
The molecular structure of the title compound, C18H16O3, exhibits a new R
2–C(COOMe)(OCH2CCH) group. The C—O—C—C torsion angle is 153.3 (1)°. The dihedral angles are 79.89 (5)° between phenyl/phenyl planes, and 73.13 (5) and 79.05 (8)° for the two COOMe/phenyl plane pairs
Structural, thermodynamic, and local probe investigations of a honeycomb material AgLiMnO
The system Ag[LiMn]O belongs to a quaternary
3R-delafossite family and crystallizes in a monoclinic symmetry with space
group and the magnetic Mn() ions form a honeycomb
network in the -plane. An anomaly around 50 K and the presence of
antiferromagnetic (AFM) coupling (Curie-Weiss temperature
K) were inferred from our magnetic susceptibility data. The magnetic specific
heat clearly manifests the onset of magnetic ordering in the vicinity of 48\,K
and the recovered magnetic entropy, above the ordering temperature, falls short
of the expected value, implying the presence of short-range magnetic
correlations. The (ESR) line broadening on approaching the ordering temperature
could be described in terms of a Berezinski-Kosterlitz-Thouless
(BKT) scenario with K. Li NMR line-shift probed as a
function of temperature tracks the static susceptibility (K) of
magnetically coupled Mn ions. The Li spin-lattice relaxation rate
(1/) exhibits a sharp decrease below about 50 K. Combining our bulk
and local probe measurements, we establish the presence of an ordered ground
state for the honeycomb system AgLiMnO.Our ab-initio
electronic structure calculations suggest that in the -plane, the nearest
neighbor (NN) exchange interaction is strong and AFM, while the next NN and the
third NN exchange interactions are FM and AFM respectively. In the absence of
any frustration the system is expected to exhibit long-range, AFM order, in
agreement with experiment.Comment: 11 pages, 13 figures, accepted in Phys Rev
2-(2-Benzylphenyl)propan-2-ol
There are two molecules in the asymmetric unit of the title compound, C16H18O, a tertiary alcohol featuring a 2-benzylphenyl substituent. Co-operative O—H⋯O hydrogen bonds connect the molecules into tetramers
Unconventional magnetism in the 4d based () honeycomb system AgLiRuO
We have investigated the thermodynamic and local magnetic properties of the
Mott insulating system AgLiRuO containing Ru
(4) for novel magnetism. The material crystallizes in a monoclinic
structure with RuO octahedra forming an edge-shared
two-dimensional honeycomb lattice with limited stacking order along the
-direction. The large negative Curie-Weiss temperature ( = -57
K) suggests antiferromagnetic interactions among Ru ions though magnetic
susceptibility and heat capacity show no indication of magnetic long-range
order down to 1.8 K and 0.4 K, respectively. Li nuclear magnetic
resonance (NMR) shift follows the bulk susceptibility between 120-300 K and
levels off below 120 K. Together with a power-law behavior in the temperature
dependent spin-lattice relaxation rate between 0.2 and 2 K, it suggest dynamic
spin correlations with gapless excitations. Electronic structure calculations
suggest an description of the Ru-moments and the possible importance of
further neighbour interactions as also bi-quadratic and ring-exchange terms in
determining the magnetic properties. Analysis of our SR data indicates
spin freezing below 5 K but the spins remain on the borderline between static
and dynamic magnetism even at 20 mK.Comment: 10 pages, 11 figures. accepted in Phys. Rev.
Prospecting for alternate sources of shikimic acid, a precursor of Tamiflu, a bird-flu drug
Shikimic acid, more commonly known by its anionic form, shikimate, is an important intermediate compound of the
‘shikimate pathway’ in plants and microorganisms1. It is the principal precursor for the synthesis of aromatic amino acids,phenylalanine, tryptophan and tyrosine and other compounds such as alkaloids, phenolics and phenyl propanoids2. It is used extensively as a chiral building
block for the synthesis of a number of compounds in both pharmaceutical and cosmetic industries3. In the recent past, the focus on shikimic acid has increased since it is the key precursor for the synthesis of Tamiflu, the only drug against avian flu caused by the H5N1 virus4,5.
Shikimic acid is converted to a diethyl ketal intermediate, which is then reduced in two steps to an epoxide that is finally transformed to Tamiflu6
Properties of the ferrimagnetic double-perovskite A_{2}FeReO_{6} (A=Ba and Ca)
Ceramics of A_{2}FeReO_{6} double-perovskite have been prepared and studied
for A=Ba and Ca. Ba_{2}FeReO_{6} has a cubic structure (Fm3m) with 8.0854(1) \AA whereas Ca_{2}FeReO_{6} has a distorted monoclinic symmetry with
and
. The barium compound is metallic from 5 K to 385
K, i.e. no metal-insulator transition has been seen up to 385 K, and the
calcium compound is semiconducting from 5 K to 385 K. Magnetization
measurements show a ferrimagnetic behavior for both materials, with T_{c}=315 K
for Ba_{2}FeReO_{6} and above 385 K for Ca_{2}FeReO_{6}. A specific heat
measurement on the barium compound gave an electron density of states at the
Fermi level, N(E_{F}) equal to 6.1. At 5 K, we
observed a negative magnetoresistance of 10 % in a magnetic field of 5 T, but
only for Ba_{2}FeReO_{6}. Electrical, thermal and magnetic properties are
discussed and compared to the analogous compounds Sr_{2}Fe(Mo,Re)O_{6}.Comment: 5 pages REVTeX, 7 figures included, submitted to PR
Magnetic and electron transport properties of the rare-earth cobaltates, La0.7-xLnxCa0.3CoO3 (Ln = Pr, Nd, Gd and Dy) : A case of phase separation
Magnetic and electrical properties of four series of rare earth cobaltates of
the formula La0.7-xLnxCa0.3CoO3 with Ln = Pr, Nd, Gd and Dy have been
investigated. Compositions close to x = 0.0 contain large ferromagnetic
clusters or domains, and show Brillouin-like behaviour of the field-cooled DC
magnetization data with fairly high ferromagnetic Tc values, besides low
electrical resistivities with near-zero temperature coefficients. The
zero-field-cooled data generally show a non-monotonic behaviour with a peak at
a temperatures slightly lower than Tc. The near x = 0.0 compositions show a
prominent peak corresponding to the Tc in the AC-susceptibility data. The
ferromagnetic Tc varies linearly with x or the average radius of the A-site
cations, (rA). With increase in x or decrease in (rA), the magnetization value
at any given temperature decreases markedly and the AC-susceptibility
measurements show a prominent transition arising from small magnetic clusters
with some characteristics of a spin-glass. Electrical resistivity increases
with increase in x, showed a significant increase around a critical value of x
or (rA), at which composition the small clusters also begin to dominate. These
properties can be understood in terms of a phase separation scenario wherein
large magnetic clusters give way to smaller ones with increase in x, with both
types of clusters being present in certain compositions. The changes in
magnetic and electrical properties occur parallely since the large
ferromagnetic clusters are hole-rich and the small clusters are hole-poor.
Variable-range hopping seems to occur at low temperatures in these cobaltates.Comment: 23 pages including figure
Etoricoxibium picrate
In the cation of the title salt (systematic name: 5-{5-chloro-3-[4-(methylsulfonyl)phenyl]-2-pyridyl}-2-methylpyridinium 2,4,6-trinitrophenolate), C18H16ClN2O2S+·C6H2N3O7
−, the mean planes of the two pyridine rings in the bipyridine unit are twisted by 33.9 (2)° with respect to each other. The dihedral angles between the mean planes of the sulfonylbenzene ring and the chloropyridine and methylpyridine rings are 51.2 (0) and 49.3 (9)°, respectively. The picrate anion interacts with the protonated N atom through a bifurcated N—H⋯(O,O) hydrogen bond, forming an R
1
2(6) ring motif with the N atom from the methylpyridine group of an adjacent cation. N—H⋯O hydrogen bonds, weak C—H⋯O and π–π stacking interactions [centroid–centroid distances = 3.8192 (9)and 3.6749 (9)] occur in the crystal packing, creating a two-dimensional network structure along [110]
3,3-Dimethyl-2-benzofuran-1(3H)-one
In the title compound, C10H10O2, all the non-H atoms except the methyl C atoms lie on a crystallographic mirror plane. In the crystal, C—H⋯O hydrogen bonds link the molecules into zigzag chains running parallel to [100]. Weak π–π stacking interactions between the benzene rings [centroid–centroid distance = 3.9817 (5) Å] link the chains in the [010] direction
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