A novel proton transfer compound (HClABT)(+)(HDPC.H2DPC)(-) (1) and its Fe(III), Co(II), Ni(II) and two different Cu(II) complexes (2-6) have been prepared and characterized by spectroscopic techniques. Additionally, single crystal X-ray diffraction techniques were applied to all complexes. All compounds, including acetazolamide (AAZ) as the control compound, were also evaluated for their in vitro inhibition effects on human hCA I and hCA II for their hydratase and esterase activities. Although there is no inhibition for hydratase activities, all compounds have inhibited the esterase activities of hCA I and II. The comparison of the inhibition studies of 1-6 to parent compounds, ClABT and H2DPC, indicates that 1-6 have superior inhibitory effects. The inhibition effects of 2-6 are also compared to the inhibitory properties of the simple metal complexes of ClABT and H2DPC, revealing an improved transfection profile. Data have been analysed by using a one-way analysis of variance for multiple comparisons.