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41.
Journal of Thermal Analysis and Calorimetry - The paper presents the results of investigation on the development of frits for single fast-firing glazes with variable BaO content based on the... 相似文献
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Błażej Gierczyk Wojciech Ostrowski Marcin Kaźmierczak 《Magnetic resonance in chemistry : MRC》2012,50(4):271-277
2‐Aryl‐1,3,4‐selenadiazoles were studied by 1H, 13C, 15N and 77Se NMR spectroscopy. The results (chemical shifts and coupling constants) were correlated with Hammett substituent parameters as well as calculated chemical shifts and bond lengths. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
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Dr. Maria Książek Dr. Marek Weselski Marcin Kaźmierczak Aleksandra Tołoczko Dr. Miłosz Siczek Dr. Piotr Durlak Dr. Juliusz A. Wolny Prof. Dr. Volker Schünemann Prof. Dr. Joachim Kusz Dr. Robert Bronisz 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(63):14419-14434
Reaction of 1,2-di(tetrazol-2-yl)ethane (ebtz) with Fe(BF4)2⋅6 H2O in different nitriles yields one-dimensional coordination polymers [Fe(ebtz)2(RCN)2](BF4)2⋅nRCN (n=2 for R=CH3 ( 1 ) and n=0 for R=C2H5 ( 2 ) C3H7 ( 3 ), C3H5 ( 4 ), CH2Cl ( 5 )) exhibiting spin crossover (SCO). SCO in 1 and 3 – 5 is complete and occurs above 160 K. In 2 , it is shifted to lower temperatures and is accompanied by wide hysteresis (T1/2↓=78 K, T1/2↑=123 K) and proceeds extremely slowly. Isothermal (80 K) time-resolved single-crystal X-ray diffraction studies revealed a complex nature for the HS→LS transition in 2 . An initial, slow stage is associated with shrinkage of polymeric chains and with reduction of volume at 77 % (in relation to the difference between cell volumes VHS−VLS) whereas only 16 % of iron(II) ions change spin state. In the second stage, an abrupt SCO occurs, associated with breathing of the crystal lattice along the direction of the Fe–nitrile bonds, while the nitriles reorient. HS→LS switching triggered by light (808 nm) reveals the coupling of spin state and nitrile orientation. The importance of this coupling was confirmed by studies of [Fe(ebtz)2(C2H5CN/C3H7CN)2](BF4)2 mixed crystals ( 2 a , 2 b ), showing a shift of T1/2 to higher values and narrowing of the hysteresis loop concomitant with an increase of the fraction of butyronitrile. This increase reduces the capability of nitrile molecules to reorient. Density functional theory (DFT) studies of models of 1 – 5 suggest a particular possibility of 2 to adopt a low (140–145°) value of its Fe-N-C(propionitrile) angle. 相似文献
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We establish a new refinement of the right-hand side of the Hermite–Hadamard inequality for convex functions of several variables defined on simplices. 相似文献
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Bis(N‐Confused Porphyrin) as a Semirigid Receptor with a Chirality Memory: A Two‐Way Host Enantiomerization through Point‐to‐Axial Chirality Transfer 下载免费PDF全文
Prof. Piotr J. Chmielewski Dr. Marta Siczek Prof. Marcin Stępień 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(6):2547-2559
The adduct formation of protonated bis(N‐confused porphyrin) (BNCP, 3,3′‐bis(meso‐tetratolyl‐2‐aza‐21‐carbaporphyrin) with chiral anions, carboxylic acids, and alcohols was studied in solution by means of 1H NMR and circular dichroism (CD) spectroscopic analysis and DFT methods. The addition of enantiopure guests to the acidified BNCP resulted in optical activity that vanished after neutralization. Pairs of the 1H NMR‐distinguishable diastereomers were formed when enantiopure guests were applied, although a single form was observed upon the addition of the racemic mixtures in each case. Unidirectional configuration change that led to diastereomeric excess was observed in several instances. Such an excess was memorized by metalation of the adducts with AgBF4, thus resulting in optically active silver(III) complexes of BNCP with some enantiomeric excess. Absolute configurations of BNCP cations and bis(zinc) and bis(silver(III)) complexes were determined on the basis of time‐dependent (TD)‐DFT calculations of their CD spectra. It was shown that some of the chiral carboxylates induced opposite directions of enantiomerization of di‐ and tetracations or di‐/tetracation and bis(zinc) complexes. The source of the optical activity of the equimolar diastereomeric mixture of adducts is discussed. 相似文献