Gems Discovered The

The first paper on piezoelectricity by Jacques and Pierre Curie was presented to the Societe mineralogique de France at the session on the 8th of April 1880 and later to the Academic des Sciences at the session on the 24th of August 1880. Pierre and Jacques Curie at first discovered the direct piezoelectric effect in crystals of tourmaline. They noticed that as result of pressure applied along a particular direction, electrical charges proportional to the pressure and of opposite polarities appear on opposite crystal surfaces. They called this effect polar-electricity . Later, they discovered a similar effect in quartz and other crystals, which have no centre of symmetry. At that time Pierre Curie was only 21 years old. His notes published in Comptes Rendus in 1880 and 1881 are a real gem, as they deal with all essential phenomena (surface charge is proportional to pressure and does not depend on the thickness of the crystal etc.). 

Some new [Cp(q -allyl Mn(CX))2] BF4 complexes have been prepared and their reactions with a range of nucleophiles examined. A new route to carbene complexes by treatment of [Cp (CO)2Mn(ER3), E = Si, Ge, Sn, with gem-di-halides has been discovered.The reactions of [Cp Mn(CX))3] with primary amines give the corresponding sym-dialkylureas. ... 

The impetus for the development of gem-bimetallics was initially to discover alkylidene-transfer reagents akin to Tebbe s reagent [14]. Schwartz prepared bimetallic aluminum—zirconocene derivatives by the hydrometallation of various vinyl metallic compounds [15—17]. Knochel has developed zinc—zirconium gem-bimetallics by hydrozircona-tion of vinylzincs and has used them as alkylidene-transfer reagents [18], More recently, other gem-bimetallics have been developed that exhibit different reactivities of the two carbon—metal bonds. Thus, Normant and Marek have reported the allylmetallation of vinyl metals to afford zinc—magnesium and zinc—lithium gem-bimetallics, which react selectively with various electrophiles such as ClSnBu3, H20, etc. [19, and references cited therein]. However, selective and sequential cleavage of the two carbon—metal bonds... 

Octanitrocubane (ONC) is a white solid, somewhat soluble in hexane and readily soluble in polar organic solvents. The density of one of the ONC polymorphs is very high (1.979gcm"3) but is still lower than the calculated value (the latest and most sophisticated calculation predicts a density above 2.1 gem"3 for the most stable polymorph of ONC) which indicates the existence of a crystal form of ONC much more dense than that synthesized. Kamlet-Jacobs equations predicted that ONC is 15-30% better than HMX [109] (a most powerful currently employed military explosive) and 6% better (perhaps also less shock sensitive) than the recently discovered explosive HNIW [121, 253-258] or CL-20 as shown in Table 2.15. It is interesting to note that both HpNC and ONC have decomposition points well above 200 °C and are not detonated by hammer blows. 

Berthelot notes that the artisan who used these notes while a practical worker in metals, especially the metals used by the jewelers, seemed to be a stranger to the arts of enamels and of artificial gems. It is, therefore, of great interest to discover that the Stockholm papyrus supple-... 

Fortuitously, just as India s supply of diamond was running out, deposits were discovered in Brazil and just as Brazil s were nearly exhausted, huge supplies were found in Africa. Today the African continent is the major supplier of natural diamond to the world. Most gem diamonds come from the coastal deposits in South West Africa whereas Zaire and Angola mines yield industrial quality diamonds. Sizable... 

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