The infrared spectra of metal–ammonia complexes of the type MX2,2NH3(M = Fe, Co, Ni, Cu, Zn, Cd, Hg, Pd, or Pt; X = Cl, Br, or I) together with some related complexes of the type M(SCN)2,2NH3(M = Pd or Pt) have been recorded in the 4000–200 cm.–1 region. Assignments for the NH3 deformation and rocking modes are reported, together with assignments for the metal–nitrogen and metal–halogen stretching frequencies. The latter are discussed in relation to the structures of the complexes, which include examples of tetrahedral, polymeric octahedral, and square planar geometries. The results of an approximate force-constant calculation on the zinc complexes are also reported. The structural data on the complexes are summarised, and additional X-ray data provided. The diffuse-reflectance spectra (10,000–25,000 cm.–1) of cobalt, nickel, and copper complexes are also reported and discussed. The tetrahedral complexes have been studied in the 4000–10,000 cm.–1 region, and the overtone, combination, and electronic bands in this region are assigned.