title: 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.
authors.affiliation: Dipartimento di Scienze Chimiche e Geologiche, Università degli Studi di Cagliari, S.S. 554 - Bivio per Sestu, I09042 Monserrato (Cagliari), Italy. mercuri@unica.it.
authors.forename: Matteo
authors.initials: M
authors.lastname: Atzori
authors.forename: Flavia
authors.initials: F
authors.lastname: Artizzu
authors.forename: Elisa
authors.initials: E
authors.lastname: Sessini
authors.forename: Luciano
authors.initials: L
authors.lastname: Marchiò
authors.forename: Danilo
authors.initials: D
authors.lastname: Loche
authors.forename: Angela
authors.initials: A
authors.lastname: Serpe
authors.forename: Paola
authors.initials: P
authors.lastname: Deplano
authors.forename: Giorgio
authors.initials: G
authors.lastname: Concas
authors.forename: Flavia
authors.initials: F
authors.lastname: Pop
authors.forename: Narcis
authors.initials: N
authors.lastname: Avarvari
authors.forename: Maria Laura
authors.initials: ML
authors.lastname: Mercuri