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101.
102.
X-ray scattering techniques have been used to study the structures of two crystals of Rb1–x
(NH4)
x
H2PO4 withx0.2, near to the boundary between ferroelectric and structural-glass behavior at low temperature. Below about 83K, both crystals develop shortrange incommensurate correlations with a wavevectorq0.13 a
* which are presumably related to the glass properties. On cooling below 70 K, the crystal with the slightly larger NH
4
+
concentrationx, develops the ferroelectric structure in a small fraction of the crystal, while the bulk of the crystal retains the tetragonal structure. The other crystal transforms almost wholly to the ferroelectric phase. The transition to the ferroelectric structure shows considerable hysteresis on heating and cooling, and is spread over about 20 K. The transition is certainly of first order, and the spread in temperature may arise from concentration fluctuations. These results and the structure of the incommensurate modulations are compared with the predictions of a theoretical model for this system. 相似文献
103.
Donohoe TJ Raoof A Freestone GC Linney ID Cowley A Helliwell M 《Organic letters》2002,4(18):3059-3062
[reaction: see text] The stereoselective Birch reduction of 3-methyl-2-furoic acids using a readily available chiral auxilairy is described; by coupling this process to an oxidative cleavage/aldol ring closure sequence we were able to produce highly functionalized and enantiopure dihydropyranones in high yield. This sequence has ample flexibility built into it, either by the use of different electrophiles during reductive alkylation or by subsequent derivatization of the dihydropyranone after ring expansion. 相似文献
104.
105.
The interweaving of two identical acyclic positively charged anion recognizing units around a chloride anion template leads to the formation of an orthogonal supramolecular ensemble which upon subsequent double ring cyclization gives a chloride selective [2]catenane in very high yield. 相似文献
106.
Two new thiosemicarbazone-pyridylhydrazine (THYNIC) hybrid ligands have been synthesized. Copper(II) and copper(I) complexes of the ligands have been prepared and characterized by X-ray crystallography. Cyclic voltammetry measurements show that the copper(II) complexes undergo quasi-reversible reductions at biologically accessible potentials. One of the ligands, bearing a pendant carboxylate arm, has been conjugated to N-alpha-(tert-butoxycarbonyl)-L-lysine. 相似文献
107.
Reaction of HCCUr (Ur = uracil) with [RhCl(PiPr3)2] results in the formation of the vinylidene complex [RhCl(PiPr3)2(CC{H}Ur)]. In the solid state this complex forms a hydrogen bonded network which consists of complementary interactions between uracil groups on neighbouring rhodium complexes and with the methanol of crystallisation. The η2-alkyne complexes [RhCl(PiPr3)2(η2-PhCCUr)] and [Rh(η5-C5H5)(PiPr3)(η2-PhCCUr)] have also been prepared. In contrast to the behaviour of [Rh(η5-C5H5)(PiPr3)(η2-PhCCUr)], [RhCl(PiPr3)2(η2-PhCCUr)] shows little evidence for the formation of hydrogen bonded aggregates in solution. The difference in behaviour between the two species is rationalised on the basis of steric effects. 相似文献
108.
Cobalt N-heterocyclic carbene alkyl and acyl compounds: synthesis, molecular structure and reactivity 总被引:1,自引:0,他引:1
Llewellyn SA Green ML Cowley AR 《Dalton transactions (Cambridge, England : 2003)》2006,(34):4164-4168
The N-heterocyclic-carbene containing cobalt carbonyl compound [Co(IMes)(CO)3(Me)] (IMes = 1,3-bis(2,4,6-trimethylphenyl)-imidazol-2-ylidene), 1, has been synthesised by tertiary phosphine displacement from [Co(PPh3)(CO)3(Me)]. Subsequent carbonylation afforded the acyl derivative [Co(IMes)(CO)3(COMe)], 2. Similarly, the compound [Co(IMes)(CO)3(COEt)], 3, has been synthesised. The compounds 2 and 3 have been shown to react with dihydrogen to form the cobalt hydride compound [Co(IMes)(CO)3(H)], 4. The molecular structures of compounds 1 and 2 have been determined. 相似文献
109.
110.