Containing Interstitial Boron Atoms

Three further borido clusters have been documented Co6(CO)lgB, HRu6(CO)17B, and [Ru6(CO),7B]. Co6(CO),8B is reported to be a product in the reaction of Co2(CO)g with BBr3 at 60°C or after exposing Co2(CO)g to 8-10 atm of B2H6. No structural data are available, and characterization is by elemental analysis and infrared spectroscopy only (22). The only closo homonuclear metalloboride cluster to be structurally characterized to date is HRu6(CO),7B (27). It is produced thermally at 75°C when 

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Many borates are known that contain non-metal cations. Examples include the ammonium borates [39], such as the commercial products ammonium pentaborate, NH4[B506(0H)4] 2 H2O, and ammonium tetraborate, (NH4)2 [6405(011)4] 2 H2O, both of which contain isolated borate anions shown above (Figs. 5a and 6a, respectively) [40]. Isolated borate anions containing more than six boron atoms are rare. However, the mineral ammonioborite [(NH4)3[Bi502o(OH)g] 4 H20 = (NH4)20 5 B2O3 2 2/3 H2O), which may be prepared synthetically by prolonged reflux of a saturated solution of ammonium pentaborate, contains the unusual isolated anion [Bi502o(OH)g] , shown in Fig. 10 [41]. This anion is not known to occur in any metal borate, its formation is apparently directed exclusively by the ammonium cations which can donate H-bonds to interstitial water and the borate structural unit. 

Boron Nitride, Metal Borides, and Related Spedes.— Alo.o6BeB3 05, Le. BeB3 belongs to the space group P6/mmm, and contains B12 icosahedra and other polyhedral units of Be and B atoms. The linkages between the polyhedra resemble those in /3-rhombohedral boron. Aluminium atoms occupy interstitial... 

Because the radius of an octahedral cavity is 0.414 times the metallic radius of the metal atoms on the surface of the cluster, only the first-row main-group atoms can be incorporated in this site. There are several octahedral carbido- and nitrido-clusters, but examples are also known that incorporate hydrogen and boron. A series of related clusters include [Ru6H(CO)i8] , [Ru6B(CO)i7] , [RueQCO)] ], and [Ru6N(CO)i6] , all of whieh contain a fully encapsulated interstitial heteroatom lodged in the center of the octahedral cavity. 

Interstitial alloys are formed between metals and non-metaUic or semi-metallic elements such as boron, phosphorus, carbon and nitrogen the latter occupy holes in the metal structure, which may however have to expand or re-arrange to accommodate them. Carbides and nitrides of metals of the first Transition Series form spontaneously during catalytic reactions where the reactants contain these atoms, and are themselves catalytically active. They do not exist as stable compounds of the noble metals of Groups 8 to 10. 

Recall that in contrast to substitutional alloys, where one metal atom substitutes for another in the lattice, interstitial alloys contain atoms of one kind that fit into the holes, or interstitial sites, of the crystal structure of the other. In metals with the interstitial elements hydrogen, boron, nitfogen, or carbon, the aUoy that results retains its metallic properties. 

If two types of foreign atoms coexist in a semiconductor, a similar situation may occur. This was demonstrated in a classic experiment by Reiss and Fuller in which a single crystal of silicon containing boron was immersed in molten tin containing lithium. Since boron substitutes for silicon atoms in the lattice, it acts as an acceptor, while lithium dissolves interstitially and therefore becomes a donor according to the following relations ... 

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