Nitrogen cluster structure

H3BNH3, which is isoelectronic and isostructural with ethane. However, there is also a rapidly developing interest in boron-nitrogen clusters that are structural and electronic counterparts of boranes rather than classical organic molecules.29 Figure... 

Fig. 12.21 The structures of some representative aluminium-nitrogen cluster compounds. Localized bonding schemes are appropriate for each cage (see problem 12.17 at the end of the chapter).

The presence of one or several nitrides is effective at modifying the metal cluster structure. Face bridging naked nitrides are not known but a nitrogen atom with a T-shaped coordination has been found in [Mo3(N )(0)(C0)4(C5H5)3]. Semi-exposed nitrides have been found in the species with four or five metal atoms they are invariably encapsulated into clusters of higher nuclearity. All the tetranuclear... 

FIGURE 1.223 (a) Model of porous silica nanoparticle (diameter 3.8 nm, pore 1.3 nm in diameter) with different adsorbates (b) nitrogen water at the (c, d) initial surface and (e, f) with trimethylsilyl groups and (g) in a mixture with methane (d, f) cluster structure of adsorbed water (h) individual nanodomain of water of 4.5 nm in diameter (density 1.01 g/cm ) calculations were carried out by the PM6 method (MOPAC2009). 

Almost all natural diamonds are impure and contain substitutional nitrogen. Clusters of N atoms are present in Type la diamonds (the most common defect structure), while Type lb diamonds contain well-separated N atoms, (a) What is meant by substitutional nitrogen (b) In what type of environment will an N atom reside in natural diamond (c) Sketch a diagram to illustrate the band strucmre of diamond, assuming no defects. Explain why diamond is an insulator, (d) The donor-level associated with the nitrogen lies about 1.7 eV below the conduction band. How does this donor level arise Why do natural diamonds not behave as semiconductors ... 

Pyrazole and [Os3(CO)io(AN)2] form two isomeric cluster complexes 90 and 91 (82IC634 84POL1175), corresponding to metallation of both basic nitrogen atoms (the major product having the symmetrical structure 90) and C,N-metallation... 

The elucidation of the crystal structures of two high-spin EPR proteins has shown that the proposals for novel Fe-S clusters are not without substance. Two, rather than one novel Fe-S cluster, were shown to be present in nitrogenase, the key enzyme in the biotic fixation of molecular nitrogen 4, 5). Thus the FeMoco-cofactor comprises two metal clusters of composition [4Fe-3S] and [lMo-3Fe-3S] bridged by three inorganic sulfur atoms, and this is some 14 A distant from the P-cluster, which is essentially two [4Fe-4S] cubane moieties sharing a corner. The elucidation of the crystal structure of the Fepr protein (6) provides the second example of a high-spin EPR protein that contains yet another unprecedented Fe-S cluster. 

There are hundreds of iron-containing enzymes. In general, the iron can exist as (a) a mononuclear site, in which it is coordinated by a tetrapyrrole structure (hemes) or strictly by amino acid residues that donate oxo, nitrogen, or sulfur ligands (b) a dinuclear site in which the irons are bridged by oxo, nitrogen, or sulfur coordination (c) a trinuclear site as in the 3Fe-4S clusters or (d) a tetranuclear site as in the [4Fe-4S] clusters. 

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