A series of transition metal complexes of the type [M(ah) 3 ](ClO 4 ) 2 (1-6) [M ¼ Mn II , Fe II , Co II , Ni II , Cu II and Zn II , ah ¼ acetylhydrazine] have been prepared by the reaction of M(ClO 4 ) 2 AE 6H 2 O with acetylhydrazine formed in situ by the reaction of hydrazine hydrate and acetylsalicylic acid methyl ester. The chelating behaviour of acetylhydrazine and overall geometry of these complexes have been spectroscopically investigated by means of FT-IR, 1 H-n.m.r. and electronic spectral techniques, as well as by elemental analysis data, molar conductance values and magnetic susceptibility measurements. Single X-ray structure determination of complex (4) revealed three acetylhydrazine ligands coordinated to nickel ion in a bidentate manner maintaining an octahedral environment. In all other complexes too, an octahedral geometry has been proposed on the basis of results obtained by various physico-chemical studies.