Hexakis(diethylacetamide)iron(II) hexahalorhenate(IV) ionic salts: X-ray structures and magnetic properties

Abstract

a b s t r a c tTwo novel Fe II -Re IV compounds of general formula [Fe II (DEA) 6 ][Re IV X 6 ] where DEA = diethylacetamide and X = Cl (1) and Br (2) have been prepared and magnetostructurally characterised. Complexes 1 and 2 are isomorphic ionic salts that crystallise in the trigonal crystal system with space group R(À3). The rhenium(IV) ion in 1 and 2 is six-coordinate with six chloro (1) or bromo (2) ligands building a regular octahedral chromophore. The Fe II ion is also six-coordinate, and bonded to six oxygen atoms from six DEA molecules. [Fe II (DEA) 6 ] 2+ cations and [Re IV X 6 ] 2À anions alternate in the crystal lattice of 1 and 2 generating supramolecular structures whose magnetic properties are dominated by the high anisotropy of the six-coordinate iron(II) and rhenium(IV) ions. Variable-temperature magnetic susceptibility data of 1 and 2 are well reproduced by a model of isolated S = 2 (Fe II ) and S = 3/2 (Re IV ) centres with high values of the local zero-field splitting. 1 and 2 are the first examples of hexahalorhenate(IV) salts incorporating Fe II complex cations to have been magnetostructurally investigated.

Anion-Assisted Crystallization of a Novel Type of Rhenium(IV)-Based Salt

“…On one hand, a variety of single salts of mononuclear hexahalo anions of Re IV , of general formula [ReX 6 ] 2– (X = F, Cl, Br, I), have been investigated for decades mainly because of their long-range magnetic ordering in the solid state. − Significant intermolecular antiferromagnetic interactions between the paramagnetic and highly anisotropic Re IV metal ions take place in [ReX 6 ] 2– salts of univalent cations. − The magnetic exchange is mainly transmitted through Re–X···X–Re contacts and other weak intermolecular interactions within the crystal lattice. − This magnetic exchange pathway is indeed supported by DFT type calculations, which have shown that the spin density from the metal ion is somewhat delocalized onto the peripheral atoms of its coordinated ligands. , …”

“…Since in these systems the intermolecular halogen···halogen distance depends on the countercation size, bulky organic cations such as tetraphenylarsonium (AsPh 4 + ) and tetra- n -butylammonium (NBu 4 + ) preclude the magnetic exchange between adjacent hexahalorhenate­(IV) anions. − However, paramagnetic cations can also provide new insights into the properties of this family of magnetic materials. Indeed, previous studies on [ReCl 6 ] 2– salts of organometallic ferrocenium, organic radicals, and Ru III cations revealed the occurrence of other magnetic phenomena, such as ferromagnetism and spin canting. ,− More recently, the use of cationic salicylamidoxime-based [Mn III 6 ] 2+ single-molecule magnets (SMMs) as countercations in [ReCl 6 ] 2– salts has also been explored .…”