The present study reports the isolation and the structural (X-ray), UV-vis-near-IR, and ESR characterization of a series of Fe(III) complexes of formula [(η 2 -dppe)(η 5 -C 5 Me 5 )Fe-(CtCC 6 H 4 X)][PF 6 ] (1a[PF 6 ]-1k[PF 6 ]; with X ) NO 2 , CN, CF 3 , Br, F, H, Me, t Bu, OMe, NH 2 , NMe 2 ). The electronic substituent effect of the remote X group on the electronic structure is experimentally evidenced by means of correlations with electronic substituent parameters (ESPs) and is theoretically investigated. The spectroscopic and ESR data are discussed in connection with the DFT computations. A consistent picture of the electronic structure of these Fe(III) radical cations is obtained. Notably, the near-IR absorption observed for 1a[PF 6 ]-1k[PF 6 ] is assigned to a SOMO-2/SOMO electronic transition. Chart 2Scheme 1

We report the observation of magnetochiral birefringence in a ring laser configuration for two different chiral compounds. Such a setup allows isolation of true magnetochiral variation of the refractive index independent of associated polarization effects. The change in refractive index Dn is measured to be 10 210 in limonene at 488 nm with a magnetic field of 1.3 kG. This value, characterizing the fundamental magnetochiral anisotropy, is in agreement with earlier theoretical predictions.Since the pioneering work of Pasteur [1], numerous studies have been performed in search of a link between the natural optical activity, explored by Biot [2], and the Faraday effect [3], as both effects result in a rotation of the plane of polarization of light. The effect of magnetochiral birefringence constitutes such a link. An implicit prediction of such an effect appeared in 1962 [4], followed by investigations in crystals [5,6]. For molecules, it was first predicted by Baranova, Bogdanov, and Zel'dovich [7]. Independently, its analog in absorption was predicted by Wagnière and Meier [8], followed by the formulation of a molecular theory for the magnetochiral anisotropy, both birefringence and dichroism [9]. Magnetochiral anisotropy appears as a change in the optical index of chiral media subject to a static magnetic field parallel to the direction of propagation of light. It is worth noting that it has opposite sign for the two enantiomers (mirror images) of the chiral medium, and depends on the relative orientation of the light-field wave vector k and the magnetic field B. However, it is independent of the state of polarization of light. The magnetochiral anisotropy is important in the context of fundamental interactions between light and matter because of the governing symmetry principles, and in biochemistry for providing a possible explanation for the homochirality of life [10]. The magnitude of this cross effect is weak. The first observation in the case of dichroism was reported only in 1997 [11]. Concerning the magnetochiral birefringence, the first experiment dedicated to the detection of the change in the refractive index was performed one year later [12]. However, the experimental values reported in Ref.[12] are about 2 orders of magnitude larger than the theoretical predictions of Ref. [13]. In this Letter, we address this problem and try to resolve this discrepancy using a new experimental setup to isolate the change in refractive index selectively.First, let us briefly recall the interpretation of the magnetochiral effect of Ref. [13]. For nonmagnetic materials, the propagation of light is governed by the relative dielectric tensor´. The magnetochiral effect can thus be deduced from an expansion of´to first order in k and B. When considering chiral liquids in magnetic fields parallel to the wave vector of incident light, the relative dielectric constants´2 and´1 for right and left circularly polarized light, respectively, can be written aś 6 ͑v, k, B͒ ´͑v͒ 6 a F ͑v͒B 6 a OA ͑v͒k 1 a MC ͑v͒ ͑B ? k͒ , (1) where v...