title: Structure of sodium bis(N-methyl-iminodiacetato)iron(III): trans-meridional N-coordination in the solid state and in solution.
abstract: The results of a detailed solid state and solution structural study of the Fe(III) bis-mida complex [Fe(III)(mida)(2)]- (mida = N-methyl-iminodiacetate) are reported. The structure of the sodium salt Na[Fe(mida)2][NaClO4]2.3H2O (1) was determined by single-crystal X-ray analysis. The complex anion in 1 contains a six-coordinate Fe(III) centre bound to two tridentate mida ligands arranged in the meridional configuration, and the mer Fe(III)N2O4 chromophore shows a high degree of distortion from regular octahedral symmetry. Raman- and UV/VIS/NIR spectroscopic measurements showed that no gross changes take place in the Fe(III) coordination sphere upon redissolution in water. Quantum chemical calculations of all three possible configurations of the [Fe(mida)2]- complex ion in the gas phase support the finding that the mer isomer is more stable than the u-fac (cis) and s-fac (trans) isomers. Redox potential measurements of the Fe(III/II)(mida) couple in dependence of pH led to the following values for the equilibrium contants: log beta(III)(101) = 11.98 +/- 0.05, log beta(III)(102) = 20.49 +/- 0.01, pK(III)(a1 OH) = 7.81; log beta(II)(101) = 6.17 +/- 0.01, log beta(II)(102) = 11.39 +/- 0.01.
authors.affiliation: Institut für Anorganische Chemie, Universität Erlangen-Nürnberg, Egerlandstrasse 1, 91058, Erlangen, Germany.
authors.forename: Roland
authors.initials: R
authors.lastname: Meier
authors.forename: Michel
authors.initials: M
authors.lastname: Molinier
authors.forename: Chris
authors.initials: C
authors.lastname: Anson
authors.forename: Anne K
authors.initials: AK
authors.lastname: Powell
authors.forename: Bernd
authors.initials: B
authors.lastname: Kallies
authors.forename: Rudi
authors.initials: R
authors.lastname: van Eldik