Three novel heterobimetallic Re(IV) compounds of formulae [ReBr₄(μ-ox)M(4,7-Cl₂phen)₂]·CH₃CN·CH₃NO₂ [M = Co(II) (1) and Ni(II) (2)] and [ReBr₄(ox)]₃[Co^III(5,6-dmphen)₃]₂·CH₃CN·2CH₃NO₂·4H₂O (3) [ox = oxalate, 4,7-Cl₂phen = 4,7-dichloro-1,10-phenanthroline and 5,6-dmphen = 5,6-dimethyl-1,10-phenanthroline] have been synthesised and the structures of 1 and 3 determined by single crystal X-ray diffraction. Compound 1 is an oxalato-bridged Re^IVCo^II heterodinuclear complex where the [ReBr₄(ox)]²⁻ unit acts as a bidentate ligand towards the [Co(4,7-Cl₂phen)₂]²⁺ entity, the separation between Re(IV) and Co(II) across the oxalate being 5.482(1) Å. Compound 3 is an ionic salt whose structure is made up of [Re^IVBr₄(ox)]²⁻ anions and [Co^III(5,6-dmphen)₃]³⁺cations plus acetonitrile, nitromethane and water as solvent molecules. The magnetic properties of 1–3 were investigated in the temperature range 1.9–300 K. Relatively large ferromagnetic interactions between Re(IV) and M(II) through the bis(bidentate) oxalato occur in 1 and 2 [J_ReM = +11.0 (1) and +12.2 cm⁻¹ (2), the Hamiltonian being defined as Ĥ = −J_ReMŜ_Re·Ŝ_M] which are explained on the basis of orbital symmetry considerations. A behaviour typical of a magnetically diluted Re(IV) complex with a large and positive value of zero-field splitting for the ground level (D_Re = +43 cm⁻¹) is observed for 3 in the high temperature range, whereas it exhibits spin canting in the low temperature domain as well as magnetic ordering below ca. 4.8 K.