Copper( II ) complexes with N-sulphonyl amino acids. Structure-stability relationships in binary species and ternary complexes with 2,2′-bipyridine

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.