Covalently bonded extended solids

For obvious reasons CDs (and other dextrins) are potentially good chiral selectors for chromatography on the one hand they can be used as mobile phase additives (CMPA) in TLC45, HPLC46 and CE47 49 and on the other they can be covalently bonded onto solid supports50,51 and silica gei 52- 54 xhis approach can be extended to the preparative resolution of enantiomers41,55,56. 

Covalent or Polymeric Solids In such solids covalent bonds extend throughout the solid and so they may be considered as very large molecules, e.g. diamond, graphite, etc. They are also known as atomic solids. 

In a few substances, known as network covalent solids, covalent bonds extend throughout a crystalline solid. In these cases, the entire crystal is held together by strong forces. Consider, for example, two of the allotropic forms in which pure carbon occurs—diamond and graphite. 

A network-covalent solid is a substance in which covalent bonds extend throughout the crystal, making the covalent bond both an mframolecular and an mtermolecular force. 

Because coordination compounds are usually considered to be covalently bonded, io a first approximation (see Chapter 11). extended complex structures in the solid can readily be related io them. Consider, for example, rhodium penlafluonde Obviously, it could be considered as an ionic structure, Rh5+5F , and indeed the crystal structure7 consists, in part, of hep-arranged fhjonde ions with rhodium in octahedral holes. However, closer inspection of the structure reveals that it consists of tetrnmeric units, Rh4F2ll, that are distinct from one another (Fig. 7.7). The environment about each rhodium atom, an octahedron of six fluonne atoms, is what we... 

Two electrons with opposite spins in the same orbital are described as paired. When extended to molecules, the exclusion principle allows us to understand the pairing of electrons in covalent bonds. The net spin angular momentum of a pair of electrons is zero. If not all electrons are paired in a molecule or solid, magnetic properties arise, as happens with many compounds of transition metals. 

In some solids, atoms are bonded to each other with strong covalent bonds but molecules are not formed. Instead, the covalent bonds form a network of atoms extending throughout a solid crystal. 

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