How does the inert pair effect affect bismuth chemistry?

The "inert pair effect" significantly influences the chemistry of bismuth by rendering the two electrons in its outermost s orbital chemically unreactive.1

While all elements in the nitrogen group possess a lone pair of electrons, this effect is most pronounced in bismuth. Because these s electrons remain inert, they do not participate in bonding, which has two primary consequences for bismuth chemistry:1

• Instability of the +5 Oxidation State: Although bismuth can theoretically reach a +5 oxidation state, the inertness of the s electrons makes this state rare and unstable. Consequently, bismuth compounds in the +5 state are strongly oxidizing.23
• Loss of Donor Ability: The lone pair of electrons in the nitrogen group typically allows these elements to act as electron pair donors in the formation of complexes. Due to the inert pair effect, this donor ability is nonexistent in bismuth.1

In contrast, bismuth primarily exhibits the +3 oxidation state, as its bonding relies on the three electrons in its p orbitals.21