Magnetic studies on hexahalorhenate(IV) salts of ferrocenium cations [Fe(C5R5)2]2[ReX6] (R = H, CH3; X = Cl, Br, I)

The hexahalorhenate(IV) salts of formula [Fe(C5H5)(2)](2)[ReX6], with X = Cl (1), Br (2), and I (3), and [Fe(C5Me5)(2)](2)-[ReX6], with X = Cl (4), Br (5), and I (6) ([Fe(C5Me5)(2)](+) = decamethylferrocenium cation), have been synthesized and the structures of 1, 2, and 4 determined by single-crystal X-ray diffraction. 1, 2, and 4 crystallize in the orthorhombic system, space groups Pbca (1 and 2) and Ibam (4), with a = 14.099(2) Angstrom, b = 16.125(2) Angstrom, and c = 22.133(15) Angstrom, for 1, a = 14.317(3) Angstrom, b = 16.848(3) Angstrom, and c = 22,099(2) Angstrom for 2, and a = 15.8583(5) Angstrom, b = 15.9368(5) Angstrom, and c = 16.9816(6) Angstrom for 4. The three structures are made up of discrete [ReX6](2-) anions and ferrocenium cations held together by electrostatic forces. There are anion-anion contacts in 1 and 2 but only through one direction. The [ReX6](2-) octahedra are arranged along the y axis forming chains of Re and X atoms, -Re-(XX)-X-...-Re-(XX)-X-...-Re-, where the intermolecular (XX)-X-... distances are shorter than the van der Waals distances. A somewhat greater separation between the anions occurs in 4. The magnetic properties of 1-6 were investigated in the temperature range 2.0-300 K. 1, 2, 4, and 5 exhibit an antiferromagnetic coupling between the anions, whereas a ferromagnetic coupling between anions and cations is the dominant interaction in 3. 6 behaves as a magnetically isolated compound, its susceptibility being the simple addition of the independent contributions of the uncoupled paramagnetic cations and anions.