Two previously synthesized cobalt(II) coordination polymers; {[Co(μ₂-suc)(nia)₂(H₂O)₂]·2H₂O}n (suc = succinate(2−), nia = nicotinamide) and [Co(μ₂-fum)(nia)₂(H₂O)₂]n (fum = fumarate(2−)) were prepared and thoroughly characterized. Both complexes form 1D coordination chains by bonding of Co(nia)₂(H₂O)₂ units through succinate or fumarate ligands while these chains are further linked through hydrogen bonds to 3D supramolecular networks. The intermolecular interactions of both complexes are quantified using Hirshfeld surface analysis and their infrared spectra, electronic spectra and static magnetic properties are confronted with DFT and state-of-the-art ab-initio calculations. Dynamic magnetic measurements show that both complexes exhibit single-ion magnet behaviour induced by a magnetic field. Since they possess very similar chemical structure, differing only in the rigidity of the bridge between the magnetic centres, this chemical feature is put into context with changes in their magnetic relaxation.