Effect of Protonated Organic Cations and Anion−π Interactions on the Magnetic Behavior of Hexabromorhenate(IV) Salts

Two novel ReIV compounds
of formula (Hbpym)2[ReIVBr6]·4H2O (1) and (H4biim)­[ReIVBr6]·4H2O (2) [Hbpym+ = 2,2′-bipyrimidinium
cation and H4biim2+ = 2,2′-biimidazolium
dication] have been prepared and magnetostructurally characterized. 1 and 2 exhibit distinct crystal packing, and
the presence of weak intermolecular contacts, such as Re–Br···Br–Re
(1 and 2), Re–Br···(H2O)···Br–Re (1 and 2), and Re–Br···π···Br–Re
(2), lead to different magnetic behaviors. While 1 is antiferromagnetic, 2 is a ferromagnetic
compound and indeed the first example of ferromagnetic salt based
on the hexabromorhenate­(IV) anion. These results suggest a straightforward
synthetic route to the preparation of new ferromagnetically coupled
ReIV compounds.