A facile synthesis of the [ReF₆]^2- ion and its use as a building block to synthesize magnetic systems are reported. Using dc and ac magnetic susceptibility measurements, INS and EPR spectroscopies, the magnetic properties of the isolated [ReF₆]^2- unit in (PPh4)2[ReF₆]•2H2O (1) have been fully studied including the slow relaxation of the magnetization observed below ca. 4 K. This slow dynamic is preserved for the one-dimensional coordination polymer [Zn(viz)4(ReF ₆)]1 (2, viz=1-vinylimidazole), demonstrating the irrelevance of low symmetry for such magnetization dynamics in systems with easy-plane-type anisotropy. The ability of fluoride to mediate significant exchange interactions is exemplified by the isostructural [Ni(viz)4(ReF₆)]1 (3) analogue in which the ferromagnetic NiII-ReIV interaction (+10.8 cm-1) dwarfs the coupling present in related cyanide-bridged systems. These results reveal [ReF₆]^2- to be an unique new module for the design of molecule-based magnetic materials.