Fusion of ferric citrate and zirconium hexafluoride: Synthesis, structure and magnetic properties of [Fe 6 O 2 Zr 2 F 6 (cit) 4 (H 2 O) 10 ]

Abstract The introduction of hexafluorozirconium(IV), [ZrF 6 ] 2− , to a solution containing Fe(III) and citrate ions produced a rather unexpected condensation product, namely, [Fe 6 O 2 Zr 2 F 6 (cit) 4 (H 2 O) 10 ] ( 1 ). X-ray crystal structure study has revealed that complex 1 is centrosymmetric, consisting of two FeZrO 2 units interconnected to a central planar Fe 4 O 2 core through fluoride and citrate bridges. The Fe⋯Fe separation within the Fe 4 O 2 unit of 2.8952(6) A is similar to that found in other planar or bent Fe 4 O 2 cores found in discrete complexes. Magnetic susceptibility as a function of temperature has revealed that the compound is paramagnetic with a Curie-Weiss behavior over the temperature range 5–150 K. The derived values are C  = 24.7 emu K/mol Oe and a θ value of −6.6(1) K, consistent with six independent HS d 5 centers. Mossbauer spectra of compound 1 ·24H 2 O at 92 and 295 K exhibits one apparent symmetric broad doublet suggesting that there are at least two very similar sites, which cannot otherwise be resolved.