A family of six acyclic bis-bidentate Schiff base ligands, Lx (prepared by condensation of 3,6-diformylpyridazine with a range of anilines: 2,4-dimethylaniline Lo,p-Me; 3,5-dichloroaniline Lm,m-Cl; 3,5-difluoroaniline Lm,m-F; p-toluidine Lp-Me; 4-aminophenol Lp-OH; 2,4,6-trimethylaniline Lo,o,p-Me), was complexed, 1:1, with cobalt(ii) or nickel(ii) perchlorate or tetrafluoroborate in refluxing dry acetonitrile. A family of dinuclear, doubly pyridazine-bridged complexes, M2II(Lx)2(solvent)n(ClO4)4 and [Ni2(Lo,o,p-Me)2(2H2O)4](BF4)4, resulted. An X-ray crystal structure determination on [Co2II(Lo,o,p)2(H2O)2(MeCN)2](ClO4)4·MeCN confirmed that it has the expected side-by-side architecture with axial solvent molecules completing the octahedral coordination sphere of the two cobalt(ii) ions. Magnetic analysis showed that the pyridazine bridges mediate weak-to-medium antiferromagnetic interactions between the metal ions. Specifically, for the cobalt(ii) complexes J was in the range –12 to –6 cm–1, while for the nickel(ii) complexes J was in the range –22 to –17 cm–1. There is no clear cut correlation of J values with electron-donating or -attracting properties of ligand substituent peripheral groups, although it is noted that the smallest J occurs in both the NiNi and CoCo families for the ligand Lo,o,p-Me.