TETRAMETHYL CARBOXYLIC-ACIDS DERIVED FROM O-PHENYLENEDIAMINES AS SEQUESTERING AGENTS FOR IRON(III) - THERMODYNAMIC STUDIES - X-RAY CRYSTAL-STRUCTURE OF SODIUM IAMINE-N,N,N',N'-TETRAACETATO)FERRATE(III)-WATER(11.5)/

The coordinating ability of the ligands 3,4-toluenediamine-N,N,N',N'-t etraacetic (3,4-TDTA), ortho-phenylenediamine-N,N,N',N'-tetraacetic (o -PhDTA), and -chloro-1,2-phenylenediamine-N,N,N',N'-tetraacetic (4-Cl- o-PhDTA) acids, H4L, with Cu(II) and Fe(III) is described. The stabili ty constants and the partial molar enthalpies of the complexes formed (25 degrees C, I = 0.5 mol dm(-3) in KNO3) were respectively determine d by means of emf and calorimetry measurements, For the system 3,4-TDT A-Fe(III) (25 degrees C, I = 0.5 mol dm(-3) in NaClO4), the stability constants of the complexes FeL- and [FeL(OH)](2-) were also determined spectrophotometrically, The calorimetric measurements shaw that the c omplex formation is entropy driven, exothermic for Cu(II) and endother mic for Fe(III). The partial molar entropy of complexation (Delta S de grees) is much the same as that of the EDTA complexes, X-ray diffracti on structural analysis of Na[Fe(4-Cl-o-PhDTA)(H2O)]. 1.5H(2)O revealed that, in [FeL(OH2)](-) (monoclinic C2/c, a = 10.693(3) Angstrom, b = 23.931(3) Angstrom, c = 24.686(6) Angstrom, beta = 94.21(2)degrees, V = 3667(2) Angstrom(3), Z = 8), the iron(III) is seven coordinated, wit h one water molecule filling the seventh position, similar to the iron (III) anionic chelates of 3,4-TDTA, o-PhDTA, and EDTA. The presence of the Cl atom in the aromatic ring produces an asymmetry in the Fe-N bo nd distances.