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Uhl W 《Die Naturwissenschaften》2004,91(7):305-319
This review is focused on the synthesis and the reactivity of tetrahedral organoelement clusters of the heavier elements of third main-group aluminium, gallium, and indium, which have been known for about a decade. They possess the elements in an unusually low oxidation state of +1 and have direct element–element interactions between their four constituents. Each cluster atom is further attached to one terminal and in most cases a bulky organic substituent, which prevents disproportionation by steric shielding. The synthesis of these compounds succeeds by different methods such as the reduction of suitable organoelement(III) halides with alkali metals and magnesium or the treatment of element(I) halides with lithium organyls. They are deeply coloured, and their bonding situation may best be described by delocalized molecular orbitals. They show a singular chemical reactivity, which results in the formation of many secondary products possessing unprecedented structures and properties. The synthesis of organoelement subhalides still containing the elements in low oxidation states is discussed in more detail in the second part of this review. These compounds are easily accessible by the careful oxidation of the clusters with halogen donors such as hexachloroethane or with AlX3/X2 mixtures. They produce dimers via halogen bridges, but in certain cases monomers were observed even for the solid state. They are very effective starting compounds for secondary reactions and the generation of new products containing the elements in unusual oxidation states by salt-elimination reactions, for instance. 相似文献
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Werner Rathmayer 《Die Naturwissenschaften》1965,52(5):114-114
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Werner Loher 《Behavioral ecology and sociobiology》1979,5(4):383-390
Summary The calling song of the -cricket, Teleogryllus commodus, attracts for mating. Both calling and -locomotor activity are under circadian control and the behaviors occur approximately at the same time. Daily playback of calling songs for 3–12 h in constant light failed to entrain -running. Instead, calling acts as an external stimulus which can release -locomotion at any time of the 24-h period, while the clock-induced activity continues to run freely. The stimulatory effect of the calling song causes flexible extension of -locomotor activity, but a subsequent restorative period is necessary. The ecological consequences of acoustical stimulation are discussed. 相似文献
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For the pilotproject ?Effect Monitoring — Biomonitoring of Immission Effects in the Testing Area of Munich”, standardized grass cultures were exposed at 19 locations during 10 series for two weeks each. The grass was analyzed for the accumulation of lead, antimony arsenic, cadmium, and copper. Highest accumulation was observed with antimony near traffic situations. The comparison of the results from the different sampling points identifies motor vehicle traffic as the source of antimony. First examinations of brake linings support this conclusion. Lead is only slightly increased near traffic. Immission-caused copper contents in the grass were found near the overhead tramway cables. The accumulation detection limits for arsenic and cadmium were not exceeded at any of the measuring points. 相似文献