Structures of the spontaneously resolved six-coordinate potassium chloro-(ethylenediaminetriacetato acetic acid) iron(III) monohydrate and the seven-coordinate potassium (ethylenediaminetetracetato) iron(III) sesquihydrate

The molecular structure of K[Fe(Hedta)(Cl)]·H2O (1, edta=ethylenediaminetetraacetate) has been determined: Triclinic, P (No. 1), Z=1, a=6.735(1), b=7.245(1), c=8.815(2) Å, α=72.87(2), β=85.00(2), γ=76.30(2)°, V=399.3(2) Å3, R1=0.0355, wR2=0.0968. Compound 1 is the third spontaneously resolved edta-complex containing an uncoordinated, protonated acetate arm. The Δ λE enantiomorph has been refined during the structure determination. The reasons for this exceptional behavior are discussed in the framework of related transition metal complex structures with monoprotonated edta as a ligand. Important forces behind the formation of optically pure crystals are: the strong FeCl bond and the presence of potassium as a counter ion. Trials to prepare the six-coordinate derivative of 1 by simple deprotonation of the detached acetate arm did not result in the formation of K2[Fe(edta)(Cl)] but the seven-coordinate salt K[Fe(edta)(H2O)]·1.5H2O (2) was obtained with the following crystallographic parameters: Monoclinic P2/c (No. 13), Z=4, a=15.287(4), b=7.697(2), c=14.380(3) Å, β=104.98(2)° V=1634.5(7) Å3, R1=0.0338, wR2=0.0821.