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Dimer complexes of 2,4-toluenediamine-N,N,N′,N′-tetraacetic acid (2,4-TDTA) with copper(II), nickel(II), cobalt(II), zinc(II) and manganese(II). Studies in aqueous solution and solid state. X-ray crystal structures of Na4[Ni2(2,4-TDTA)2]·15H2O and Na4[Cu2(2,4-TDTA)2]·20H2O

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Abstract Potentiometric investigations in aqueous solution at 25°C and ionic strength 0.1 mol dm−3 KCl show that 2 2,4-toluenediamine-N,N,N′N′-tetraacetic acid (2,4-TDTA) forms with Cu(II), Ni(II), Co(II), Zn(II) and Mn(II) the following complexes (ligand, H4L): monomers [MH2L], [MHL]− and [ML]2−; dimers [M2HL2]3− and [M2L2]4−; with excess of ligand [MH2L2]4−, [MHL2]5− and [ML2]6− (Cu(II), Ni(II) and Zn(II)) and with excess of metal [M2HL]+ (Ni(II), Co(II)and Mn(II) and [M2L] (Cu(II)). The formation constants of the complexes have been determined. The species distribution diagrams indicate that a concentrated solution with a ligand:metal ratio 1:1 at pH 6 is suitable for the synthesis of crystalline salts of the dimetric complex species of Cu(II), Ni(II), Co(II), Zn(II) and Mn(II). X-ray diffraction structural analysis of the complexes Na4[Ni2(2,4-TDTA)2] · 15H2O and Na4[Cu2(2,4-TDTA)2]· 20H2O revealed that the dimer complex of Ni(II) is C1 and the dimer complex of Cu(II) is centrosymmetrical (C1). In both complexes each metal atom is surrounded by four carboxylic oxygens and two amine nitrogens in a distorted octahedron, for the Ni(II) complex, and an elongated bipyramid for the Cu(II) complex. X-ray diffraction analysis in powder was carried out for the complex Na4[Co2(2,4-TDTA)2] · 12H2O. The electronic properties have been characterised by spectroscopic techniques and variable-temperature magnetic susceptibility measurements. An orbital interpretation of the pathway of exchange interaction in this series of dimeric complexes is presented. The complexes were also characterised by mass and IR spectra and thermogravimetric analysis.