排序方式: 共有42条查询结果,搜索用时 15 毫秒
1.
Four aluminophosphates, A3Al2P3O12 (A = Na, K (1), Rb (2), Tl (3)), have been synthesized by solid-state reactions and characterized by X-ray diffraction and NMR and IR spectroscopic techniques. Aluminum has trigonal bipyramidal coordination in the thallium compound and tetrahedral coordination in the others. Potassium, rubidium and thallium analogues have been structurally characterized by single-crystal X-ray diffraction and found to possess three-dimensional (Al2P3O12)3- anionic frameworks with channels occupied by A+ countercations. These frameworks are built from corner connections of PO4 tetrahedra with AlO4 tetrahedra in 1 and 2 and with AlO5 trigonal bipyramids in 3. Pertinent crystal data are as follows: for 1, orthorhombic space group Pna2(1), a = 8.685(2) A, b = 16.947(2) A, c = 8.458(3) A, Z = 4; for 2, orthorhombic space group Cmc2(1), a = 17.164(2) A, b = 8.6270(6) A, c = 8.8140(14) A, Z = 4; for 3, orthorhombic space group Pna2(1), a = 6.1478(15) A, b = 10.396(3) A, c = 17.787(5) A, Z = 4. Compound 3 is a rare example of an oxide possessing aluminum exclusively in trigonal bipyramidal coordination. 相似文献
2.
Efficient syntheses of xanthenes have been described using a catalytic amount of perchloric acid in water. The high temperature and lengthy reaction time normally required for formation of xanthenes derivatives are not necessary when using a catalytic amount of perchloric acid. The method is relatively inexpensive, easily available, nonvolatile, nonexplosive, and thermally robust to catalyze the reaction at 80 °C by simple heating with good to excellent yields. The advantages of the reaction involve simple reaction protocol, simple workup, and improved synthesis in the presence of perchloric acid as catalyst. 相似文献
3.
4.
A constrained minimax problem is converted to minimization of a sequence of unconstrained and continuously differentiable functions in a manner similar to Morrison's method for constrained optimization. One can thus apply any efficient gradient minimization technique to do the unconstrained minimization at each step of the sequence. Based on this approach, two algorithms are proposed, where the first one is simpler to program, and the second one is faster in general. To show the efficiency of the algorithms even for unconstrained problems, examples are taken to compare the two algorithms with recent methods in the literature. It is found that the second algorithm converges faster with respect to the other methods. Several constrained examples are also tried and the results are presented. 相似文献
5.
Aarons RJ Notta JK Meloni MM Feng J Vidyasagar R Narvainen J Allan S Spencer N Kauppinen RA Snaith JS Faulkner S 《Chemical communications (Cambridge, England)》2006,(8):909-911
Orthogonal protection strategies have been used to prepare a series of luminescent and MRI active lanthanide complexes containing a tuftsin targeting vector that are internalised by macrophage cells. 相似文献
6.
Bonthu Krishna Kishore Reddy K. Prabhakara Rao K. Vidyasagar 《Journal of Chemical Sciences》2006,118(1):117-126
Four new low-dimensional phenylarsonates, A(HO3AsC6H5)(H2O3AsC6H5) (A = Tl(1), Na(2), K(3) and Rb(4)), have been synthesized and characterized by X-ray diffraction, spectroscopic and thermal studies. They crystallize in triclinic
unit cells and have approximately planar arrangement of A+ ions, coordinated to oxygen atoms of phenylarsonates, on both sides. Structure of thallium phenylarsonate as determined by
single crystal X-ray diffraction, is one-dimensional, whereas those of alkalimetal analogues are two-dimensional. Successful
intercalation reactions of compounds1 and2 with primaryn-alkyl amines have been demonstrated.
Dedicated to Prof J Gopalakrishnan on his 62nd birthday. 相似文献
7.
Ortiz O Vidyasagar A Wang J Toomey R 《Langmuir : the ACS journal of surfaces and colloids》2010,26(22):17489-17494
Near-the-surface instabilities with a cusplike morphology were observed in ultrathin photo-cross-linked poly(N-isopropylacrylamide) coatings upon swelling in water. The characteristic wavelength of the instability was approximately 25 times the dry thickness and scaled linearly with coating thickness between 30 and 1200 nm. Above 1200 nm, slippage of the coating along the confining substrate led to reticulated patterns with a much larger wavelength. To help interpret the origin of the instability, the coatings were also exposed to a solvent slightly worse than water (acetone) and a solvent slightly better than water (isopropanol). In all cases, the characteristic wavelength scaled linearly with respect to the swelling induced by each solvent. Both water and isopropanol produced well-defined cusps or folds in the gel surface, while acetone produced semiordered blisters that grew into one another. The features produced in acetone may be a consequence of swelling being close to the threshold value for the loss of planar stability. Through the use of a first-order linear perturbation of the Flory-Rehner model, it is shown that the emergence of a characteristic wavelength is consistent with an inhomogeneous distribution of solvent that results from diffusion of solvent into a dry coating. 相似文献
8.
Alan P. Marchand Dayananda Rajapaksa Vuligonda Vidyasagar William H. Watson Ram P. Kashyap 《合成通讯》2013,43(4):819-825
HEXACYCLO[7.4.0.02,8.03,7.06,11]tridecane-10,13-dione (“homosecohexaprismane-10,13-dione”, 8) has been prepared via a six-step sequence that results in homologation of two of the cyclopentane rings in pentacyclo[5.4.0.02,6.03,10.05,9]-undecane-8,11-dione, 1. The structure of 8 has been established unequivocally via single crystal X-ray structural analysis. 相似文献
9.
Sung C Vidyasagar A Hearn K Lutkenhaus JL 《Langmuir : the ACS journal of surfaces and colloids》2012,28(21):8100-8109
Layer-by-layer (LbL) assemblies have attracted much attention for their functional versatility and ease of fabrication. However, characterizing their thermal properties in relation to the film thickness has remained a challenging topic. We have investigated the role of film thickness on the glass transition temperature (T(g)) and coeffecient of thermal expansion for poly(ethylene oxide)/poly(acrylic acid) (PEO/PAA) and PEO/poly(methacrylic acid) (PEO/PMAA) hydrogen-bonded LbL assemblies in both bulk and ultrathin films using modulated differential scanning calorimetry (modulated DSC) and temperature-controlled ellipsometry. In PEO/PAA LbL films, a single, well-defined T(g) was observed regardless of film thickness. The T(g) increased by 9 °C relative to the bulk T(g) as film thickness decreased to 30 nm because of interactions between the film and its substrate. In contrast, PEO/PMAA LbL films show a single glass transition only after a thermal cross-linking step, which results in anhydride bonds between PMAA groups. The T(g), within error, was unaffected by film thickness, but PEO/PMAA LbL films of thicknesses below ~2.7 μm exhibited a small amount of PEO crystallization and phase separation for the thermally cross-linked films. The coefficients of thermal expansion of both types of film increased with decreasing film thickness. 相似文献
10.