Halogen-bonding in a new family of tris(haloanilato)metallate(iii) magnetic molecular building blocks

Abstract

Here we report on new tris(haloanilato)metallate(III) complexes with general formula [A]3[M(X2An)3] (A = (n-Bu)4N(+), (Ph)4P(+); M = Cr(III), Fe(III); X2An = 3,6-dihalo derivatives of 2,5-dihydroxybenzoquinone (H4C6O4), chloranilate (Cl2An(2-)), bromanilate (Br2An(2-)) and iodanilate (I2An(2-))), obtained by a general synthetic strategy, and their full characterization. The crystal structures of these Fe(III) and Cr(III) haloanilate complexes consist of anions formed by homoleptic complexes formulated as [M(X2An)3](3-) and (Et)3NH(+), (n-Bu)4N(+), or (Ph4)P(+) cations. All complexes exhibit octahedral coordination geometry with metal ions surrounded by six oxygen atoms from three chelate ligands. These complexes are chiral according to the metal coordination of three bidentate ligands, and both Λ and Δ enantiomers are present in their crystal lattice. The packing of [(n-Bu)4N]3[Cr(I2An)3] (5a) shows that the complexes form supramolecular dimers that are held together by two symmetry related I···O interactions (3.092(8) Å), considerably shorter than the sum of iodine and oxygen van der Waals radii (3.50 Å). The I···O interaction can be regarded as a halogen bond (XB), where the iodine behaves as the XB donor and the oxygen atom as the XB acceptor. This is in agreement with the properties of the electrostatic potential for [Cr(I2An)3](3-) that predicts a negative charge accumulation on the peripheral oxygen atoms and a positive charge accumulation on the iodine. The magnetic behaviour of all complexes, except 5a, may be explained by considering a set of paramagnetic non-interacting Fe(III) or Cr(III) ions, taking into account the zero-field splitting effect. The presence of strong XB interactions in 5a are able, instead, to promote antiferromagnetic interactions among paramagnetic centers at low temperature, as shown by the fit with the Curie-Weiss law, in agreement with the formation of halogen-bonded supramolecular dimers.

Complete Series of Chiral Paramagnetic Molecular Conductors Based on Tetramethyl-bis(ethylenedithio)-tetrathiafulvalene (TM-BEDT-TTF) and Chloranilate-Bridged Heterobimetallic Honeycomb Layers

“…The iron−oxygen bond distances in compounds 1−3 vary in the 1.987(8)−2.030(5) Å range and are close to those observed for the [PPh 4 ] 3 [Fe(Cl 2 An) 3 ] precursor 21 and for its BEDT-TTF radical cation salts 22 (Table 1). These data are in accordance with a high spin character of the Fe(III) ions (vide inf ra).…”

Recent Advances on Anilato-Based Molecular Materials with Magnetic and/or Conducting Properties

“…The best fit had J/kB of −165 K (115 cm −1 ), g = 2.07, θ = −1 K, and the spin impurity ρ = 0.05. This experimentally determined J value for 3 is in the range observed for other oxo-bridged Fe(III) complexes with TPA as capping ligand, that is, J = −107 ± 10 cm −1 [118].…”

From mononuclear to linear one-dimensional coordination species of copper(ii)–chloranilate: design and characterization

“…2 The magnetic properties can be designed and ne-tuned by choice of the bridging ligand; small ligand strongly affects exchange interaction and spin coupling, whereas some ligands with conjugated p-electron systems are able to mediate exchange interactions at long distances. 11-20 They are prone to form a variety of coordination modes [19][20][21][22][23][24] and to mediate electronic effects between paramagnetic metal ions via their four oxygen donors and p-electron systems, respectively. Generally, the use of nitrogen-and oxygen-donor ligands prevails in the construction of coordination polymers.…”