A family of six acyclic bis-bidentate Schiff base ligands, L-x (prepared by condensation of 3,6-diformylpyridazine with a range of anilines: 2,4-dimethylaniline L-o,L-p-Me; 3,5-dichloroaniline L-m,L-m-Cl; 3,5-difluoroaniline L-m,L-m-F; p-toluidine Lp-Me; 4-aminophenol Lp-OH; 2,4,6-trimethylaniline L-o,L-o,L-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, M-2(II)(L-x)(2)(solvent)(n)(ClO4)(4) and [Ni-2(L-o,L-o,L-p-Me)(2)(2H(2)O)(4)](BF4)(4), resulted. An X-ray crystal structure determination on [Co-2(II)(L-o,L-o,L-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 L-o,L-o,L-p-Me.