Main Group Parallels with Binary

4-6 MAIN GROUP PARALLELS WITH BINARY CARBONYL COMPLEXES 

Chemical similarities occur between main group and transition metal species that are electronically equivalent (i.e., species that require the same number of electrons to achieve a filled valence configuration).28 For example, a halogen atom, one electron short of a valence shell octet, may be considered electronically equivalent to Mn(CO)5, a 17-electron species one electron short of an 18-electron configuration. In this section we discuss briefly some parallels between main group atoms and ions and electronically equivalent binary carbonyl complexes. 

Much of the chemistry of main group and metal carbonyl species can be rationalized from the way in which these species can achieve closed-shell (octet or 18-electron) configurations. These methods of achieving more stable configurations are illustrated for the following electronically equivalent species. 

HCo(CO)4are strong acids in aqueous solution. Both types of anions form precipitates with heavy metal ions such as Ag+ in aqueous solution. The parallels between seven-electron halogen atoms and 17-electron binary carbonyl species are sufficiently strong to justify applying the label pseudohalogen to these carbonyls.29 

Similarly, six-electron main group species show chemical similarities with 16-electron organometallic species. As for the halogens and 17-electron organo-metallic complexes, many of these similarities can be accounted for on the basis of ways in which the species can acquire or share electrons to achieve filled-shell configurations. Some similarities between sulfur and the electronically equivalent Fe(CO)4 are listed in Table 4-6. 

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Main Group Parallels with Binary Carbonyl Complexes 557... 

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