Deprotonated amide nitrogen co-ordination to the cadmium(II) ion in ternary 2,2′-bipyridine complexes with N-sulfonyl amino acids

Abstract

A solid-state investigation of cadmium(II) and zinc(II) ternary 2,2′-bipyridine (bipy), complexes of N-(benzenesulfonyl)glycine (bsgly) and N-(toluene-p-sulfonyl)glycine (tsgly) is presented. The crystal structure of [{Cd(bipy)(tsglyO)₂}₂]1, separated from preparations at pH 7, and of [{Cd(bipy)(bsglyNO)}₄]·8H₂O 2 separated at pH 11 are described. Complex 1 crystallizes in the triclinic space group P, Z= 2, a= 10.474(10), b= 15.902(3), c= 18.202(9)Å, α= 98.49(2), β= 91.17(5) and γ= 98.31(3)°. The structure consists of dimeric units in which the cadmium atoms are bridged by two carboxylic oxygens. Metal co-ordination is via the two nitrogens of a bipy molecule and four carboxylate oxygens from the amino acid monoanion. A long Cd ⋯ O contact completes seven co-ordination. The final R index was 0.0509. Complex 2 crystallizes in the monoclinic space group P2₁/c, Z= 4, a= 12.525(5), b= 15.251(4), c= 21.717(3)Å and β= 92.36(3)°. The structure is built up of tetrameric units in which the cadmium atoms are joined by monoatomic bridging carboxylic oxygens. Each cadmium is six-co-ordinated through bipy nitrogens and sulfonamide nitrogen and carboxylate oxygen of the amino acid molecules. The final R index was 0.0398. Infrared data for the homologous zinc(II) complexes, very similar to those of the above derivatives, indicate that zinc is also able to promote sulfonamide nitrogen deprotonation in these amino acid ligands in the solid state.