The stability of a series of binary and ternary 2,2′-bipyridine(bipy) complexes of Cu²⁺ with amino acids N-substituted by an arene sulphonic group has been analysed in 0.1 mol dm^–3 NaClO₄ or NaNO₃ at 25 °C. The stability constants determined by d.c. polarography are sensitive to the nature of the amino acid and of the aromatic moiety of the protecting group. The known lowering effect of bipy on the pK for metal-promoted sulphonamide nitrogen deprotonation in the ternary complexes is found to be quantitatively independent of the above structural features. The X-ray structure of the ternary species [Cu(bipy)(Bs-GlyNO)(H₂O)][Bs-GlyNO =N-benzenesulphonylglycinate(2–)] is also presented. The crystals are monoclinic, space group P2₁/c, with a= 8.494(5), = 19.950(4), c= 11.295(7)Å, β= 110.79(4)°, Z= 4, and R= 0.036. The structure consists of [Cu(bipy)(Bs-GlyNO)(H₂O)] units in which the Cu atom exhibits a tetrahedrally distorted square-pyramidal N₃O₂ co-ordination.