The first examples of nontrigonal pnictogen compound were synthesized by Arduengo and co-workers in 1984, through condensation of a diketoamine with a phosphorus trihalide in the presence of base. This group reported also on the first systematic investigations into its chemical behavior. Later, on similar routes, the corresponding and isostructural arsenic and antimony species were also synthesized. Other synthetic methods involve deprotonation of OH or NH groups in the presence of ECl (E=P, As, Sb and Bi), salt metathesis or reduction of pentavalent pnictogen compounds.