Amide nitrogen co-ordination of CoII and NiII in ternary 2,2′-bipyridine-containing systems. A solution and solid-state study

Abstract

The ternary systems 2,2′-bipyridine (bipy)–M–amino acid [M = Co^II or Ni^II; amino acid (H₂L)=N-p-tolyl-sulfonylglycine (tsgly), -β-alanine (ts-β-ala) or N-benzoylglycine (H₂hip)] were investigated in aqueous solution by means of polarography, electronic spectroscopy and potentiometry, in order to identify the type, number and stability of complex species, as a function of pH and bipy : M : amino acid ratio. With tsgly the prevailing species are [M^II(bipy)_n(HL)]⁺ and [M^II(bipy)_nL](n= 1 or 2), with pK_NH for the deprotonation of sulfonamide nitrogen 7.8(2) and 7.4(2), for Co^II and Ni^II, respectively and the crystal and molecular structure of [Co(bipy)₂(tsglyNO)]·2H₂O (NO indicates binding as a N,O-chelating dianion) was determined. The Co^II is six-co-ordinated by four nitrogen atoms of the bipy moieties, the deprotonated sulfonamide nitrogen and one carboxylic oxygen of the tsgly dianion. On standing in air, an alkaline solution of bipy–Co^II–tsgly turned from orange to wine-red in a few days, indicating the oxidation of Co^II to Co^III. With ts-β-ala and H₂hip metal hydrolysis prevents the formation of deprotonated complexes.