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[CoIII(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 ReIVCoII 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 [ReIVBr4(ox)]2− anions and [CoIII(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 [JReM = +11.0 (1) and +12.2 cm−1 (2), the Hamiltonian being defined as Ĥ = −JReMŜRe·ŜM] 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 (DRe = +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.