The structures of two Co(III) complexes containing A-bonded nitrite ions and one of the N4 tetradentate ligands R, R-picchxn (N, N'-bis(2-picolyl)-1R, 2R-diaminocyclohexane) or R-picpn (3P-methyl-l, 6-bis(2- pyridyl)-2, 5-diazahexane) have been determined by X-ray analyses. Λ-β-[Co(R, R-picchxn)(NO2)2] CIO4. H2O is triclinic, space group P1, with a = 8.611(2), b = 9.188(1), c = 8.576(1) Å, α = 117.60(1), β = 96.40(1), γ = 73.69(1)° and Z = 1. The structure was refined by full-matrix least-squares methods to R = 0.035 for 2712 non-zero reflexions. Δ-β-exo-[Co(R-picpn)(NO2)2]CIO4. H2O is orthorhombic, space group P212121, with a = 7.664(1), b = 15.121(3), c = 18.429(4) Å and Z = 4. The structure was refined as above to R = 0.040 for 2063 non-zero reflexions. In the R, R-picchxn complex both amine nitrogen atoms of the tetradentate have the same relative configuration, whereas in the R-picpn diastereoisomer their relative configurations are opposite. In the latter complex this permits the exo methyl group substituent to adopt a nearly ideal equatorial position in the central chelate ring. Hydrogen bonding networks in the two structures, which link the complex cations to the perchlorate ions and lattice water molecules, are apparent.