A POTENTIOMETRIC AND SPECTROSCOPIC STUDY OF COPPER(II) DIAMIDODIAMINOCOMPLEXES

Five diamidodiamino compounds, N,N'-bis[2-(dimethylamino)ethyl]propane diamide dihydrochloride L(2) . 2HCl, N,N'-bis[2-(diethylamino)ethyl]pr opanediamide dihydrochloride (L(5)), N,N'-bis[2-(dimethylamino)ethyl]- and N,N'-bis[2-(diethylamino)ethyl]-ethanediamide (L(1) and L(4)) and N,N'-bis[2-(dimethylamino)propyl]-ethanediamide (L(3)), have been syn thesized and characterized. Their acid-base behaviour complexation wit h copper(II) ions in aqueous solution at 25 degrees C and I = 0.15 mol dm(-3) Cl- have been investigated by potentiometric and spectrophotom etric techniques. Relatively small differences observed between the pr otonation constants may be explained in terms of electronic induction effects of the alkyl side chains. The primary and tertiary amine group s show differences in basicity which conform to the general pattern of behaviour found with amines and attributable to changes in solvation of the reacting species in the protonation reactions. Copper(II) ions have been found to form several soluble complexes with L(1)-L(4). On t he other hand, L(5) precipitates in the presence of copper(II) ions. T he stoichiometries of the mononuclear copper(II) complexes are propose d as CuL, CuLH(-1) and CuLH(-2) with L(3) also forming CuLH(-3). Dinuc lear complexes, Cu(2)LH(-2) are proposed for L(1), L(3) and L(4). In a ddition, Cu(2)LH(-3) is proposed for L(1). The co-ordination sites and structures are suggested to be as follows: CuL, two contiguous chelat e rings with the copper(II) co-ordinated to one amine N, one amide N a nd one carboxylate O; CuLH(-1), similar to CuL but with co-ordination to both amide N and one of the amine N; CuLH(-2), three contiguous che late rings with co-ordination to all four N; CuLH(-3), the same as CuL H(-2) but with a proton removed from a water molecule axially co-ordin ated to the copper; Cu(2)LH(-2) (L = L(1) or L(4)) and Cu(2)LH(-3) (L = L(1)), similar to CuL but incorporating two sets of co-ordination si tes, one amine N plus one amide N plus one carboxylate O, per copper, giving four contiguous chelate rings; in Cu(2)LH(-3) a proton is remov ed from a water molecule co-ordinated to one of the coppers; Cu(2)LH(- 2) (L = L(3)), one of the coppers is co-ordinated to all four N and th e other to the two carboxylate O.