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The methylene-linked bicyclic guanidine based on the 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2-a]pyrimidine (hppH) framework provides a versatile platform able to support trigonal-planar, tetrahedral, and square-planar metal centers. 相似文献
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Beer L Haddon RC Itkis ME Leitch AA Oakley RT Reed RW Richardson JF VanderVeer DG 《Chemical communications (Cambridge, England)》2005,(9):1218-1220
The resonance stabilized bis-thiadiazinyl framework holds potential as a stable and versatile building block for the design of radical-based conductors and magnetic materials. 相似文献
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Beer L Britten JF Brusso JL Cordes AW Haddon RC Itkis ME MacGregor DS Oakley RT Reed RW Robertson CM 《Journal of the American Chemical Society》2003,125(47):14394-14403
New synthetic routes to 1,2,3-dithiazolo-1,2,3-dithiazolylium salts, based on double Herz condensations of N-alkylated 2,6-diaminopyridinium salts with sulfur monochloride, have been developed. The two prototypal 1,2,3-dithiazolo-1,2,3-dithiazolyl radicals HBPMe and HBPEt have been prepared and characterized in solution by cyclic voltammetry and EPR spectroscopy. Measured electrochemical cell potentials and computed (B3LYP/6-31G) gas-phase disproportionation enthalpies favor a low on-site Coulombic repulsion energy U in the solid state. The crystal structures of HBPR (R = Me, Et) have been determined by X-ray crystallography (at 293 K). Both consist of slipped pi-stacks of undimerized radicals, with many close intermolecular S- - -S contacts. Magnetic, conductivity, and optical measurements have been performed and the results interpreted in light of extended Hückel band calculations. The crystalline materials are paramagnetic above 100 K, with room-temperature conductivities sigma(RT) of 10(-5)-10(-6) S cm(-1); the slightly greater conductivity of the R = Et compound can be associated with a more well developed band structure. We suggest a Mott-Hubbard insulator ground state for these materials, with an on-site Coulomb repulsion energy U of about 1.0 eV. 相似文献
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A specific gas-chromatographic and a non-specific colorimetric method for the deterrmination of phenols in cigarette smoke are described. The rapid, non-specific method has been correlated with the specific procedure so that the amount of phenol in smoke can be predicted with ± 15% at the 95% confidence level. The trapping effficiency of phenols by Cambridge filter pads is also presented. 相似文献
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