2,830 research outputs found
SBE-type metal-substituted aluminophosphates: detemplation and coordination chemistry
The detemplation process in Me-SBE (Me = Co^2+, Mg^2+, and Mn^2+) aluminophosphates was studied to elucidate materials stability and framework characteristics. In addition, the hydrothermal synthesis conditions were optimized to obtain materials with minimal phase impurities. This was accomplished by means of decreasing reaction temperature and increasing aging periods. Scanning electron microscopy analysis of the Mg- and Mn-SBE as-synthesized samples revealed square plates with truncated corner morphologies grown in aggregated fashion and contrasting with the previously reported hexagonal platelike morphology of Co-SBE. Cautious detemplation in vacuum, using an evacuation rate of 10 mmHg/s and a temperature of 648 K, resulted in surface areas of about 700, 500, and 130 m^2/g for Mg-, Co-, and Mn-SBE, respectively. Thermal gravimetric analysis and in situ high-temperature powder X-ray diffraction analyses indicate the frameworks for all of the SBE variants experienced collapse upon treatment with helium at temperatures above 700 K and subsequently formed an aluminophosphate trydimite dense phase. Detemplation in air at all times resulted in framework destruction during detemplation. In situ differential scanning calorimetry−powder X-ray diffraction data showed that the SBE frameworks experience breathing modes related to specific endothermic and exothermic scenarios during air treatment. Decomposition and elimination of the organic template during vacuum treatment was verified by Fourier transform infrared spectroscopy. X-ray photoelectron spectroscopy revealed that most of the Co atoms in vacuum-treated samples are in tetrahedral coordination, while the Mn atoms exhibit various coordination states. Ultraviolet-visible, electron paramagnetic resonance, and magic-angle spinning nuclear magnetic resonance (MAS NMR) spectroscopy corroborated the latter result in addition to providing evidence for the formation of Mn extra framework species. ^(27)Al MAS NMR spectra for vacuum-detemplated Mg-SBE samples prior to and after dehydration confirmed the reversible formation of aluminum octahedral sites. This, however, did not affect the porous nature of detemplated Mg-SBE samples as these are capable of adsorbing 19 water molecules per super cage at 298 K
{Tris[2-(5-bromo-2-oxidobenzylideneamino)ethyl]amine}manganese(III)
In the title complex, [Mn(C27H24Br3N4O3)], the MnIII ion is six-coordinated in a distorted octahedral environment by three N atoms and three O atoms from the trianion of the hexadentate ligand tris[2-(5-bromo-2-oxidobenzylideneamino)ethyl]amine. All three N (and O) atoms are cis to each other. The three N and the three O atoms are in a fac conformation among each other
Tracing Recent Star Formation of Red Early-type Galaxies out to 1
We study the mid-infrared (IR) excess emission of early-type galaxies (ETGs)
on the red-sequence at 1 using a spectroscopic sample of galaxies in the
fields of Great Observatories Origins Deep Survey (GOODS). In the mass-limited
sample of 1025 galaxies with 10 and
, we identify 696 24 m detected (above the
5) galaxies and find them to have a wide range of NUV- and -[12
m] colors despite their red optical colors. Even in the sample of
very massive ETGs on the red sequence with 10
, more than 18% show excess emission over the photospheric emission
in the mid-IR. The combination with the results of red ETGs in the local
universe suggests that the recent star formation is not rare among quiescent,
red ETGs at least out to if the mid-IR excess emission results from
intermediate-age stars or/and from low-level ongoing star formation. Our
colorcolor diagram including near-UV and mid-IR emissions are efficient not
only for identifying ETGs with recent star formation, but also for
distinguishing quiescent galaxies from dusty star-forming galaxies.Comment: 25 pages, 9 figures, accepted for publication in Ap
Solid State NMR Characterization of Complex Metal Hydrides systems for Hydrogen Storage Applications
Solid state NMR is widely applied in studies of solid state chemistries for hydrogen storage reactions. Use of ^(11)B
MAS NMR in studies of metal borohydrides (BH_4) is mainly focused, revisiting the issue of dodecaborane formation
and observation of ^(11)B{^1H} Nuclear Overhauser Effect
catena-Poly[[[aquamanganese(II)]-di-μ-sulfato-[aquamanganese(II)]-μ-N,N,N′,N′-tetrakis(2-pyridylmethyl)hexane-1,6-diamine] hexahydrate]
In the polymeric title compound, {[Mn2(SO4)2(C30H36N6)(H2O)2]·6H2O}n, the two Mn2+ ions are bridged by two sulfate anions to form dinuclear complexes, and these dinuclear species are linked by the hexadentate ligand N,N,N′,N′-tetrakis(2-pyridylmethyl)hexane-1,6-diamine (tphn), forming a one-dimensional chain structure running in the [101] direction. The repeat unit of the polymer, Mn2(SO4)2(H2O)2(tphn), is disposed about a twofold axis passing through the centre of the dinuclear unit. The coordination geometry around the Mn centre is distorted octahedral. Two methylene groups are each disordered equally over two positions
Optical Spectroscopy of Supernova Remnants in M81 and M82
We present spectroscopy of 28 SNR candidates as well as one H II region in
M81, and two SNR candidates in M82. Twenty six out of the M81 candidates turn
out to be genuine SNRs, and two in M82 may be shocked condensations in the
galactic outflow or SNRs. The distribution of [N II]/H{\alpha} ratios of M81
SNRs is bimodal. M81 SNRs are divided into two groups in the spectral line
ratio diagrams: an [O III]-strong group and an [O III]-weak group. The latter
have larger sizes, and may have faster shock velocity. [N II]/H{\alpha} ratios
of the SNRs show a strong correlation with [S II]/H{\alpha} ratios. They show a
clear radial gradient in [N II]/H{\alpha} and [S II]/H{\alpha} ratios: dLog ([N
II]/H{\alpha})/dLog R = -0.018 {\pm} 0.008 dex/kpc and dLog ([S
II]/H{\alpha})/dLog R = -0.016 {\pm} 0.008 dex/kpc where R is a deprojected
galactocentric distance. We estimate the nitrogen and oxygen abundance of the
SNRs from the comparison with shock-ionization models. We obtain a value for
the nitrogen radial gradient, dLog(N/H)/dLogR = -0.023 {\pm} 0.009 dex/kpc, and
little evidence for the gradient in oxygen. This nitrogen abundance shows a few
times flatter gradient than those of the planetary nebulae and H II regions. We
find that five SNRs are matched with X-ray sources. Their X-ray hardness colors
are consistent with thermal SNRs.Comment: 19 pages, 24 figures, 5 tables, ApJ accepte
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