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Gary S. Nichol William Clegg 《Acta Crystallographica. Section C, Structural Chemistry》2007,63(10):o609-o612
The title compound [systematic name: ammonium pyrimidine‐2,4‐5,6(1H,3H)‐tetrone 5‐oximate], NH4+·C4H2N3O4−, crystallizes from water in the triclinic space group P and is ismorphous with a known rubidium complex [Gillier (1965). Bull. Soc. Chim. Fr. pp. 2373–2384]. The principal feature of the structure is hydrogen bonding; each ammonium H atom acts as a bifurcated donor and three of the four violurate O atoms are bifurcated acceptors, with the fourth acting as a trifurcated acceptor. The pattern of hydrogen bonding around the cation is very similar to the rubidium coordination environment in the related structure. The violurate anions pack as hydrogen‐bonded crinkled tapes, which are linked and separated by the ammonium cations to give a compact three‐dimensional structure. 相似文献
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A. A. Collyer D. W. Clegg M. Morris D. G. Parker G. W. Wheatley G. C. Corfield 《Journal of polymer science. Part A, Polymer chemistry》1991,29(2):193-200
High molecular weight alternating block copolymers of polyethesulphone (PES) and polydimethylsiloxane (PDMS) were prepared by the condensation of dimethylamino-terminated PDMS oligomers and hydroxy-terminated PES oligomers in 1,2-dichlorobenzene. Microphase separation of the block copolymers at exceptionally short block lengths was observed by differential scanning calorimetry (DSC) and transmission electron microscopy (TEM). The Si? O? C intersegment linkage in these materials appeared to display poor hydrolytic stability which is contrary to results obtained for other block copolymers. 相似文献
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It is demonstrated that diffractive photoproduction ofJ P =1? isoscalar states completely violates conventional ideas of vector meson dominance. It is shown that this can be due to processes involving a gluonic system, which can be either a continuum or, possibly, a 3-gluon glueball. In the latter case it is necessarily mixed with several \(q\bar q\) states. 相似文献
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R. L. S. Devine C. T. Foxon B. A. Joyce J. B. Clegg J. P. Gowers 《Applied Physics A: Materials Science & Processing》1987,44(2):195-200
Beryllium diffusion during MBE growth of (Al, Ga)As layers, (Al, Ga)As/GaAs heterojunctions and GaAs/AlAs superlattices has been studied by electrochemical C-V and secondary ion mass spectrometry (SIMS) concentration profiling, in conjunction with transmission electron microscopy. Diffusion times were comparatively short since they were limited to part of the growth sequence, so non-equilibrium effects had a significant influence. The results are consistent with an interstitial-substitutional mechanism in which lattice site incorporation becomes more difficult with increasing band gap enthalpy. Incorporation involves a kick-out reaction which leads to the observed disordering of the superlattices. 相似文献