排序方式: 共有69条查询结果,搜索用时 93 毫秒
1.
Shiraz A. Markarian Liana S. Gabrielyan Karine R. Grigoryan 《Journal of solution chemistry》2004,33(8):1005-1015
FT IR ATR spectra of urea/dimethyl sulfoxide and urea/diethyl sulfoxide mixtures in the S=O and N—H stretching vibration regions at different molar ratios have been measured. On the basis of the band deconvolution data, various types of intermolecular associated forms, including dimers and hydrogen-bonded urea–sulfoxide complexes, have been revealed. The latter has been confirmed also by ab initio calculations. 相似文献
2.
3.
4.
The governing dynamics of fluid flow is stated as a system of partial differential equations referred to as the Navier-Stokes system. In industrial and scientific applications, fluid flow control becomes an optimization problem where the governing partial differential equations of the fluid flow are stated as constraints. When discretized, the optimal control of the Navier-Stokes equations leads to large sparse saddle point systems in two levels. In this paper, we consider distributed optimal control for the Stokes system and test the particular case when the arising linear system can be compressed after eliminating the control function. In that case, a system arises in a form which enables the application of an efficient block matrix preconditioner that previously has been applied to solve complex-valued systems in real arithmetic. Under certain conditions, the condition number of the so preconditioned matrix is bounded by 2. The numerical and computational efficiency of the method in terms of number of iterations and execution time is favorably compared with other published methods. 相似文献
5.
Structure–reactivity studies of chloro and isothiocyanato diorganotin (IV) complexes based on multidentate N‐donor ligands: Synthesis,spectral characterization and crystal structures 下载免费PDF全文
The reaction of [SnMe2Cl2] with the bidentate ligand 4,7‐phenanthroline (4,7‐phen) resulted in the formation of [SnMe2Cl2 (4,7‐phen)]n ( 1a ) which is probably a polymeric chain in solution. On the other hand, the reaction of [SnEt2Cl2] with 4,7‐phen afforded the complex [Sn2Et4Cl4 (κ1‐N‐4,7‐phen)2(μ‐κ2‐N,N‐4,7‐phen)] ( 1b ) which dissociates in dimethylsulfoxide solution. The reaction of [SnR2Cl2] (R = Me, Et) with 2,2′‐biquinoline (biq) yielded the complexes [SnMe2Cl2 (κ2‐N,N‐biq)] ( 2a ) and [SnEt2Cl2 (κ1‐N‐biq)2] ( 2b ) in the solid state. Moreover, the reaction of [SnR2Cl2] (R = Me, Et) with the tridentate ligand 4′‐(2‐furyl)‐2,2′:6′,2″‐terpyridine (ftpy) resulted in the formation of ionic penta‐ and hexa‐coordinated tin complexes [SnMe2Cl (ftpy)][SnMe2Cl3] ( 3a ) and [SnEt2Cl (ftpy)]Cl ( 3b ). The reaction of [SnMe2 (NCS)2] with ftpy afforded the hepta‐coordinated complex [SnMe2 (NCS)2(ftpy)] ( 4a ). The products were fully characterized using elemental analysis, and infrared, UV–visible, multinuclear (1H, 13C, 119Sn) NMR, DEPT‐135°, HH‐COSY and HSQC NMR spectroscopies. The crystal structure of complex 3a reveals that it contains the simultaneous presence of penta‐ and hexa‐coordinated tin (IV) atoms. Notably, the crystal structure of complex 4a shows that tin (IV) is hepta‐coordinated in a pentagonal bipyramidal geometry SnC2N5 by three nitrogen atoms of ftpy, two nitrogen atoms of NCS? and two Me groups with trans‐[SnMe2] configuration. These data indicate the influence of halide or pseudo‐halide group on the coordination number and geometry of tin. Hirshfeld surface analysis and two‐dimensional fingerprint plots were calculated for 3a and 4a which show the π–π interaction between molecules in the solid is relatively weak. 相似文献
6.
Ali Hossein Kianfar Sanam Asl Khademi Roghaye Hashemi Fath Mahmoud Roushani Mojtaba Shamsipur 《Journal of the Iranian Chemical Society》2013,10(2):347-355
The VO(IV) complexes of tridentate ONN Schiff ligands were synthesized and characterized by IR, UV–Vis and elemental analysis. The electrochemical properties of the vanadyl complexes were investigated by cyclic voltammetry. A good correlation was observed between the oxidation potentials and the electron-withdrawing character of the substituents on the Schiff base ligands, showing the following trend: MeO < H < Br < NO2. The thermogravimetry (TG) and differential thermoanalysis (DTA) of the VO(IV) complexes were carried out in the range of 20–700 °C. The VOL1(OH2) and VOL2(OH2) decomposed in three steps, whereas the VOL3(OH2) and VOL4(OH2) complexes decomposed in two steps. The thermal decomposition of these complexes is closely related to the nature of the Schiff base ligands and proceeds via first-order kinetics. The structures of compounds were determined by ab initio calculations. The optimized molecular geometry and atomic charges were calculated using MP2 method with 6-31G(d) basis. The results suggested that, in the complexes, V(IV) ion is in square-pyramid N2O3 coordination geometry. Also the bond lengths and angles were studied and compared. 相似文献
7.
Mohammadi Ziarani Ghodsi Khademi Mahdieh Mohajer Fatemeh Anafcheh Maryam Badiei Alireza Ghasemi Jahan B. 《Research on Chemical Intermediates》2022,48(5):2111-2133
Research on Chemical Intermediates - The synthesis of 4-Aryl-(3,5-dimethyl-1,4,7,8-tetrahydro-dipyrazolo[3,4b:4′,3′e]pyridine derivatives was accomplished using Fe3O4@SiO2@(BuSO3H)3... 相似文献
8.
Isaiah Adelabu Patrick TomHon Mohammad S. H. Kabir Shiraz Nantogma Mustapha Abdulmojeed Iuliia Mandzhieva Dr. Jessica Ettedgui Dr. Rolf E. Swenson Dr. Murali C. Krishna Prof. Thomas Theis Prof. Boyd M. Goodson Prof. Eduard Y. Chekmenev 《Chemphyschem》2022,23(2):e202100839
Signal Amplification By Reversible Exchange in SHield Enabled Alignment Transfer (SABRE-SHEATH) is investigated to achieve rapid hyperpolarization of 13C1 spins of [1-13C]pyruvate, using parahydrogen as the source of nuclear spin order. Pyruvate exchange with an iridium polarization transfer complex can be modulated via a sensitive interplay between temperature and co-ligation of DMSO and H2O. Order-unity 13C (>50 %) polarization of catalyst-bound [1-13C]pyruvate is achieved in less than 30 s by restricting the chemical exchange of [1-13C]pyruvate at lower temperatures. On the catalyst bound pyruvate, 39 % polarization is measured using a 1.4 T NMR spectrometer, and extrapolated to >50 % at the end of build-up in situ. The highest measured polarization of a 30-mM pyruvate sample, including free and bound pyruvate is 13 % when using 20 mM DMSO and 0.5 M water in CD3OD. Efficient 13C polarization is also enabled by favorable relaxation dynamics in sub-microtesla magnetic fields, as indicated by fast polarization buildup rates compared to the T1 spin-relaxation rates (e. g., ∼0.2 s−1 versus ∼0.1 s−1, respectively, for a 6 mM catalyst-[1-13C]pyruvate sample). Finally, the catalyst-bound hyperpolarized [1-13C]pyruvate can be released rapidly by cycling the temperature and/or by optimizing the amount of water, paving the way to future biomedical applications of hyperpolarized [1-13C]pyruvate produced via comparatively fast and simple SABRE-SHEATH-based approaches. 相似文献
9.
10.