The syntheses of the complexes of tumor cell differentiating agent hexamethylene bisacetamide (HMBA) with manganese (II) and cobalt(II) halides which include M-2(HMBA)(3)X-4 (M = Mn and Co; X = Cl cut Br) have been reported. The complexes have been characterized by elemental analysis and their structures have been established on the basis of their electronic spectra, e.s.r. spectra and magnetic susceptibilities. All these complexes have been assigned the mixed octahedral-tetrahedral structures and similar to the corresponding nickel complexes [1], can correctly be formulated as [M(HMBA)(3)][MX4].