text: Pyridine is a Lewis base, donating its pair of electrons to a Lewis acid. Its Lewis base properties are discussed in the ECW model. Its relative donor strength toward a series of acids, versus other Lewis bases, can be illustrated by C-B plots. One example is the sulfur trioxide pyridine complex (melting point 175 °C), which is a sulfation agent used to convert alcohols to sulfate esters. Pyridine-borane (, melting point 10–11 °C) is a mild reducing agent.
  Transition metal pyridine complexes are numerous. 
  Typical octahedral complexes have the stoichiometry  and . Octahedral homoleptic complexes of the type  are rare or tend to dissociate pyridine. Numerous square planar complexes are known, such as Crabtree's catalyst. The pyridine ligand replaced during the reaction is restored after its completion.
  The η coordination mode, as occurs in η benzene complexes, is observed only in sterically encumbered derivatives that block the nitrogen center.