Binuclear Metal Complexes. XLIII. Magnetic, Spectroscopic, and Electrochemical Studies on Hetero-metal Binuclear Complexes of N,N′-Bis(3-carboxysalicylidene)-1,1-dibenzylethylenediamine

Abstract Copper(II)–M(II) and copper(II)–iron(III) hetero-metal binuclear complexes of N,N′-bis(3-carboxysalicylidene)-1,1-dibenzylethylenediamine (H4fsadb), CuM(fsadb)·nH2O (M=Co, Ni, Cu, Zn, Mg, Ca, Ba) and CuFe(fsadb)Cl·1.5H2O, have been prepared and characterized. Cryomagnetic measurements (78–300 K) revealed that an antiferromagnetic spin-exchange interaction operates between the metal ions in the cases CuM(fsadb)·nH2O (M=Co, Ni, Cu) and CuFe(fsadb)Cl·1.5H2O, exchange integrals being evaluated on the basis of the Heisenberg model. Ligand field bands due to the copper(II) ion bound at the N2O2-site of CuM(fsadb)·nH2O (M=Co, Ni, Cu, Zn, Mg) and CuFe(fsadb)Cl·1.5H2O are in the range 1.9×103–21.4×103 cm−1, while in the cases of CuCa(fsadb)·4H2O and CuBa(fsadb)·3.5H2O the frequencies of the bands are close to that (17.8×103 cm−1) of the mononuclear complex Cu(H2fsadb)·H2O. This spectral feature has been explained in terms of the configuration of the second metal ion adjacent to the copper(II) ion: trans-octahedral in the cases of small metal ions (Fe(III), Co(II), Ni(II), Cu(II), Zn(II), Mg(II)) and presumably cis-octahedral in the cases of large metal ions (Ca(II), Ba(II)). Copper(II/I) redox potentials of the hetero-metal complexes are much low compared with that of Cu(H2fsadb)·H2O. This shift has been discussed in terms of the electronic effect of the carboxylate group and the covalency in the bonding between the bridging phenolic oxygen and the second metal ion.