Square pyramidal

Figure 8.16 shows the B l spectmm of the B5FI9 molecule. The boron atoms are situated at the comers of a square pyramid. There are four B-FI-B bridging hydrogen atoms and... 

XeOF square pyramid XeOF+3 disphenoid (C ) 67 XeOF-3 pentagonal 69,70... 

Xe02F2 disphenoid (C2 ) Xe02F+ trigonal pyramid 71-73 Xe02F 2 square pyramid 27,55... 

Simple nickel salts form ammine and other coordination complexes (see Coordination compounds). The octahedral configuration, in which nickel has a coordination number (CN) of 6, is the most common stmctural form. The square-planar and tetrahedral configurations (11), iu which nickel has a coordination number of 4, are less common. Generally, the latter group tends to be reddish brown. The 5-coordinate square pyramid configuration is also quite common. These materials tend to be darker in color and mostiy green (12). 

Pentaphenylantimony [2170-05-0], C3QH23Sb, has attracted considerable attention because it possesses square-pyramidal rather than the expected trigonal-bipyramidal geometry, both ia the sohd state and ia solution. The cyclohexane solvate (C3H ) Sb 1/2 and penta-4-tolylantimony... 

The deep violet color of pentaphenylbismuth and certain other pentaarylbismuth compounds has been the subject of considerable speculation. It has been shown by x-ray diffraction (173) that the bismuth atom in pentaphenylbismuth is square—pyramidal. WeU-formed crystals are dichromic, appearing violet when viewed in one plane but colorless in another plane. The nature of the chromophore has been suggested to be a charge-transfer transition by excitation of the four long equatorial bonds ... 

Syntheses, crystallization, structural identification, and chemical characterization of high nuclearity clusters can be exceedingly difficult. Usually, several different clusters are formed in any given synthetic procedure, and each compound must be extracted and identified. The problem may be compounded by the instabiUty of a particular molecule. In 1962 the stmcture of the first high nuclearity carbide complex formulated as Fe (CO) C [11087-47-1] was characterized (40,41) see stmcture (12). This complex was originally prepared in an extremely low yield of 0.5%. This molecule was the first carbide complex isolated and became the foremnner of a whole family of carbide complexes of square pyramidal stmcture and a total of 74-valence electrons (see also Carbides, survey). 

X = F, Cl, and Br, contains the oxochromium(V) cation [23411-25-8], CrO ", exhibits a square pyramidal geometry. Compounds containing this cation are among the most stable Cr(V) compounds. 

At present, all commercial SFM tips are square pyramids, formed by CVD deposition of Si3N4 on an etch pit in (100) Si. The etch pit is bounded by (111) faces, which means that the resulting tip has an included angle of about 55°. Therefore the edge profiles of all features with sides steeper than 55° will be dominated by the profile of the tip. 

Electron diffraction studies in the gas phase reveal an unusual structure in which the 5-coordinate Al atom has square-pyramidal... 

Figure 7.8 The structure of InCls " showing square-pyramidal (C4 ) geometry. The In-Clapex distance is significantly shorter than the In-Clbase distances and In is 59 pm above the basal plane this leads to a Clapex-In-Clbase angle of 103.9° which is very close to the theoretical value required to minimize Cl Cl repulsions whilst still retaining C4, symmetry (103.6°) calculated on the basis of a simple inverse square law for repulsion between ligands. [NEt4]2[TlCl5] is isomoiphous with [NEt4]2[InCl5] and presumably has a similar structure for the ardon.

J. A. Le Bel, whose name is often also associated with this concept, did indeed independently suggest a 3-diitiensional modet for the 4-coordinate C atom, but vigorously opposed the tetrahedral stereochemistry of van t Hoff for many years and favoured an alternative square pyramidal arrangement of the bonds. 

Carbon is known with all coordination numbers from 0 to 8 though compounds in which it is 3- or 4-coordinate are the most numerous. Some typical examples are summarized in the Panel (p. 291). Particular mention should also be made of hypercoordinate non-classical carbo-nium ions such as 5-coordinate CHj", square pyramidal CsHs (cf. the isoelectronic cluster B3H9, p. 154), pentagonal pyramidal C6Me6 " (cf. iso-electronic Bf,Hio, p. 154) and the bicyclic cation 2-norbomyl, C7H] 1... 

---