Group 17 elements Electron donor-acceptor complexes

Both Lewis-valent and hypervalent compounds of the Group 15 elements may react with electron donors to form electron donor-acceptor complexes. Most of these complexes are... 

The chemical properties of indium are typical of those of Group 13 of the Periodic Table. Most of indium s oxides, salts, and compounds involve the +3 oxidation state (e.g., In203, In[N03]3> and InCl3) many of these compounds are electron-pair acceptors, forming addition compounds with donor molecules (e.g., InBr3 py, py = pyridine). Neutral, cationic, and anionic complexes are also known. Several interesting compounds are derived from the +1 and +2 oxidation states of the element. 

Trihalides of the Group VA elements are pyramidal (C3v) with an unshared pair of electrons on the central atom. Typically, the molecules are Lewis bases, and they form acid-base adducts and metal complexes. In accord with the hard-soft interaction principle, these species are better electron pair donors toward soft electron pair acceptors. Therefore, most of the complexes of these EX3 molecules contain second and third row transition metals or first row metals in low oxidation states. 

A coordination compound, or complex, is formed when a Lewis base (ligand) is attached to a Lewis acid (acceptor) by means of a lone-pair of electrons. Where the ligand is composed of a number of atoms, the one which is directly attached to the acceptor is called the donor atom . This type of bonding has already been discussed (p. 198) and is exemplified by the addition compounds formed by the trihalides of the elements of Group 13 (p. 237) it is also the basis of much of the chemistry of the... 

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