Bond, dative ionic molecules

Exports of structural descriptors, SMILES and InChl, provide chemical structure information in a simple tab-delimited text file containing CID or SID and either the isomeric SMILES or InChl strings. Given the very nature of the formats of SMILES and InChl, not all chemical structure information can be identically represented. For example, SMILES encodes only covalent bonds, while PubChem supports the additional concepts of ionic, complex, and dative bonds. Most small molecules in PubChem can be reproducibly interconverted between InChl, SMILES, and PubChem ASN.l formats without loss of chemical structure information. 

The diatomic halides and oxides of the alkali and alkaline earth groups must, by definition, have a considerable ionic contribution to their bonding. These diatomics, together with those of Al, Ga and In, are in fact found to lie outside the predicted field for covalent bonds, as shown in Figure 5.6(d). Molecules with dative bonds are expected along the borderline between covalent and ionic types, including several fluorides (of Sb, Si, Sn, Pb, Be and Ag) and chlorides (Si, Sn). They are arbitrarily grouped with the more ionic bonds. 

Similarly one might suspect that a singly, doubly, or triply charged metal cation is a much better electron acceptor than the same atom within a neutral molecule. We suspect, therefore, that the difference between covalent and dative bonds may be blurred in many ionic complexes. 

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