A solid-state study of tervalent hexachloro-complexes R3MCl6(M= Rh or Ir) and quadrivalent hexachlorocomplexes R2MCl6(M= Mn, Tc, Ru, and Rh) has been carried out by use of X-ray, n.q.r., and i.r. techniques. The 35Cl n.q.r. spectra of the complexes K3RhCl6,H2O, K3lrCl6,H2O, K3lrCl6, and (NH4)3lrCl6,H2O are complex and suggest a low site-symmetry for the anion. This is verified from the low-frequency i.r. spectra of the compounds and a full single-crystal X-ray analysis of K3RhCl6,H2O. The latter complex is orthorhombic and has space-group Pbcn with 8 molecules Z= 8 in a unit cell of dimensions a= 1·2368(9), b= 1·5655(6), and c= 1·2041 (10) nm. The structure was solved from diffractometer data and refined R 0·07 for 920 independent reflexions. The octahedral RhCl63– anions contain six crystallographically independent Rh–Cl bonds ranging in length from 230·2(4) to 236·6(4) pm. The lack of symmetry in the anion appears to be influenced by the neighbouring molecule of water of crystallisation. The n.q.r. spectra of the cubic octahedral quadrivalent complexes R2MCl6(M= Mn, Tc, Ru, or Rh) have been measured and display the same trends as observed previously for the metal hexachloro-complexes of the third transition-series.