High electron affinity groups

Scheme 1-17. High-electron-affinity PPV derivatives with electron-withdrawing groups on the aromatic ring.

Elements at the right of the p block have characteristically high electron affinities they tend to gain electrons to complete closed shells. Except for the metalloids tellurium and polonium, the members of Groups 16/VI and 17/VII are nonmetals (Fig. 1.62). They typically form molecular compounds with one another. They react with metals to form the anions in ionic compounds, and hence many of the minerals that surround us, such as limestone and granite, contain anions formed from non-metals, such as S2-, CO,2-, and S042-. Much of the metals industry is concerned with the problem of extracting metals from their combinations with nonmetals. 

Transition metal complexes (1) of 1,2-dicyanoethylene-1,2-dithiol (maleonitrile), mnt, have received special study since this ligand can stabilize transition metals in a variety of oxidation states and the high electron affinity of the terminal cyanide groups aids the delocalization of charge within the complex, thus reducing potential coulombic repulsions. 

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