Structure and properties of tetraaquabis(hydrogenmaleato)iron(II)

The title compound tetraaquabis(hydrogemnaleato)iron(II), Fe(C4H3O4)(2)(H2O)(4) (1) forms large orange-coloured crystals that are remarkably stable against air-oxidation and weight loss until similar to 160 C. Crystal structure analysis of compound 1 has been performed by single crystal X-ray diffraction. The basic octahedral complex consisting of two centrosymmetrically related monodentate hydrogenmaleato ligands and four water molecules coordinated to Fe(II) remains firmly hydrogen-bonded through intra- and inter-molecular interactions to form a robust three-dimensional network structure in the solid state. Comparison between the simulated and experimental powder X-ray diffraction patterns confirms bulk purity of the product. The solid-state UV-Vis-NIR spectrum for this yellow-orange compound shows bands at 227, 383 (broad) and 917 (broad) nm among which the last one is assignable to the expected T-5(2g)-->E-5(g) band for octahedral Fe(II) complexes. The variable temperature magnetic susceptibility measured for compound 1 in the 2-300 K range shows Curie-Weiss behaviour with weak antiferromagnetic interactions occurring at low temperatures as observed from the chi(M)T versus T curve and a Weiss constant of -2.4 K found from the 1/chi(M) versus T plot. An aqueous solution prepared by dissolving crystalline samples of 1 is indefinitely stable in air and it is possible to recover 1 from the solution. The yellow-orange solution displays nearly identical redox stability (E-1/2 = 0.15 V vs. Ag/AgCl) with the well-known Fe(CN)(6)(3-)/Fe(CN)(6)(4-) couple. (C) 2002 Published by Elsevier Science Ltd.