Bent and Linear Forms of the (μ‐Oxo)bis[trichloroferrate( III )] Dianion: An Intermolecular Effect − Structural, Electronic and Magnetic Properties

We have analyzed the great diversity of Fe−O−Fe angles, 140−180°, found in the X‐ray structures of the (μ‐oxo)bis[trichloroferrate( III )] dianion [Cl 3 FeOFeCl 3 ] 2− from both experimental and theoretical points of view. Theoretical calculations show that only the linear isomer is found as a minimum on the potential energy surface. Detailed analysis of the crystal packing indicates that the angular form is due to attractive intermolecular interactions. Analysis of a selected reduced set of the 45 crystal structures retrieved from the Cambridge Structural Database allowed us to classify the bending of the [Cl 3 FeOFeCl 3 ] 2− dianion in three categories, depending on the balance and strength of the intermolecular O ··· H−X contacts. A crystal diffraction study on the bis(benzyltrimethylammonium) salt has shown both bent (144.6°) and linear (180°) forms of the (μ‐oxo)bis[trichloroferrate( III )] dianion. The magnetic susceptibility of this compound has been fitted by assuming two equally weighted contributions ( J ang and J lin ) of the two forms, considering J ang − J lin estimated by theoretical calculations. The obtained J ang and J lin of −117 and −133 cm −1 respectively, agree well with B3LYP results. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)