Oxidation‐State and Coordination‐Site Specificity Influencing Dimensional Extension and Properties of Two Iron Complexes with Similar Helical Chains

Two new iron coordination frameworks, {[NH2(CH3)2]2FeII(pydc)2}n (1) and {[NH2(CH3)2]FeIII(pydc)2}n (2) (pydc = 2,5‐pyridinedicarboxylate), have been synthesized through the reaction of FeCl3 with H2pydc in dimethylformamide (DMF). 1 crystallizes in an achiral space group C2/c, while 2 crystallizes in a chiral space group P43212. Both crystal structures consist of 21 helices with similar units: [FeII(pydc)2]2− and [FeIII(pydc)2]−, respectively. The iron oxidation states have been confirmed by means of ESR spectra and bond valence calculations. Quantum chemistry calculations and thermogravimetric analysis have demonstrated their energy and thermal stability. Magnetic studies have revealed that 1 and 2 show weak antiferromagnetic and ferromagnetic interactions between the metal centers, respectively. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)