Interaction of Fe(III) with herbicide-carboxylato ligands - Di-, tri- and tetra-nuclear compounds: Structure and magnetic behavior

The iron complexes with the phenoxyalkanoic acids 3,4-D, 2,3-D and 2,4,5-T in the presence or not of a nitrogen donor heterocyclic ligand, phen, were prepared and characterized. Interaction of Fe(III) with phenoxyalkanoic acids and phen leads to dinuclear neutral complexes while the absence of phen favours trinuclear cationic or tetranuclear neutral forms. The crystal structure of hexakis(2,3-dichlorophenoxyacetato)tris(methanol)oxotri-iron(III) chloride-methanol(1/3), [Fe3O(2,3-D)(6)(MeOH)(3)]Cl center dot 3MeOH (2), and tetrakis(dimethyl-sulfoxide)octakis(2,4,5-trichlorophenoxyacetato)dioxotetra-iron(III) methano](1/2)-water(1/1)-dimethylsulfoxide(1/0.8),{[Fe4O2(2,4,5-T)(8)(dmso)(4)]center dot 2MeOH center dot H2O center dot 0.8dmso} (3), have been determined and refined by least-squares methods using three-dimensional Mo K alpha data. Magnetic data of the trimer show antiferromagnetic interaction. The ground state of the system is S = 1/2 with a small percentage of S = 5/2 paramagnetic impurity rho = 0.7%. For the tetramer, the magnetic data suggest antiferromagnetically coupled system with S = 0 ground state, while for the dimer, {[Fe2OCl2(3,4-D)(2)(phen)(2)] center dot H2O center dot 3.5MeOH} a very strong antiferromagnetic exchange interaction between the two ions has been observed. The fitting results give an exchange interaction of J = 254.1 cm(-1), with S = 0 ground state with a small amount of paramagnetic S = 5/2 impurity (rho = 0.3%). (c) 2006 Elsevier Ltd. All rights reserved.