Inorganic compounds, examples geometries

Furthermore, inorganic compounds present coordination geometries different from those found for carbon. For example, although 4-coordinate carbon is nearly always tetrahedral, both tetrahedral and square planar shapes occur for 4-coordinate compounds of both metals and nonmetals. When metals are the central atoms, with anions or neutral molecules bonded to them (frequently through N, O, or S), these are called coordination complexes when carbon is the element directly bonded to metal atoms or ions, they are called organometaUic compounds. 

The tetrahedral geometry usually found in 4-coordinate compounds of carbon also occurs in a different form in some inorganic molecules. Methane contains four hydrogens in a regular tetrahedron around carbon. Elemental phosphorus is tetratomic (P4) and also is tetrahedral, but with no central atom. Examples of some of the geometries foimd for inorganic compounds are shown in Figure 1-4. 

Film density can be measured using geometry-property relationships or by displacement-floatation techniques. In the geometry-property techniques, the volume or area of the sample is determined as well as the mass of a specific volume or area. From this, the density can be calculated directly. For example, aluminum, which has a bulk density of 2.7 g/cm, will form a film with an areal density of 27.0micrograms/cm for a 1000 A film. Some bulk densities (g/cm ) of common inorganic compound film materials are Si02 = 2.20 and TIN = 5.29. 

Packing criteria may be taken into consideration in other cases, as, for example, in that of intercalated compounds. Here the geometry of the repeat mesh of the inorganic layers can be considered constant with the aim of developing reasonable models for their structures [20-22],... 

The yellow to orange compounds 804(118207)2, 864(84 013)2, and 8e4(8b2Fii)2 have been prepared. Crystallographic studies on 804(118207)2 have shown that the cation 8c4 + has square-planar D h) geometry. The structure can be described by valence bond theory in terms of four resonance structures equivalent to (la), or by simple molecular orbital theory in which three of the four n molecular orbitals are filled. " The 8e4 + ions are examples of six-jr-electron systems, and they are thus examples of inorganic aromatic compounds (lb). 

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