Novel azo-dyes have been synthesized by diazotization of 4-amino benzene-4'-(substituted heterocyclo) sulphonamide derivatives and coupling with 1-oxa-4-thia-spiro[4,4]nonan-2-one (I) and/or with 1-oxa-4-thia- spiro[4,5]decan-2-one (I') in acid medium to give the corresponding 3-azo-(4'-substituted benzenesulphonamido)-1-oxa-4-thia-spiro[4,4]nonan-2-one (II-IX) and/or 1-oxa-4-thia-spiro[4,5]decan-2-one (II'-IX'] as spiro-ligands. Treatment of these ligands with metal salts of iron (Fe3+), copper (Cu2+) and mercury (Hg2+) as chlorides in ethanolic solution furnished the corresponding metal chelates (IIa-c-IXa-c) and/or (II'a-c-IX'a-c). The compounds were tested in vitro for antimicrobial activity to study the structure-activity relationship