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 NA-4[NI-2(2,4-TDTA)(2)]CENTER-DOT-15H(2)O AND NA-4[CU-2(2,4-TDTA)(2)]CENTER-DOT-20H(2)O

Potentiometric investigations in aqueous solution at 25 degrees C and ionic strength 0.1 mol dm(-3) KCl show that 2,4-toluenediamine-N,N,N', N'-tetraacetic acid (2,4-TDTA) forms with Cu(II), Ni(II), Co(II), Zn(I I) 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 concent rated solution with a ligand:metal ratio 1:1 at pH 6 is suitable for t he synthesis of crystalline salts of the dimeric complex species of Cu (II), Ni(II), Co(II), Zn(II) and Mn(II). X-ray diffraction structural analysis of the complexes Na-4[Ni-2(2,4-TDTA)(2)]. 15H(2)O and Na-4[Cu -2(2,4-TDTA)(2)]. 20H(2)O revealed that the dimer complex of Ni(II) is C-1 and the dimer complex of Cu(II) is centrosymmetrical (C-i). In bo th complexes each metal atom is surrounded by four carboxylic oxygens and two amine nitrogens in a distorted octahedron, for the Ni(II) comp lex, and an elongated bipyramid for the Cu(II) complex. X-ray diffract ion analysis in powder was carried out for the complex Na-4[Co-2(2,4-T DTA)(2)]. 12H(2)O. The electronic properties have been characterised b y spectroscopic techniques and variable-temperature magnetic susceptib ility measurements. An orbital interpretation of the pathway of exchan ge interaction in this series of dimeric complexes is presented. The c omplexes were also characterised by mass and IR spectra and thermograv imetric analysis.