Two new cobalt(II) complexes of formula [Co₂(bta)(H₂O)₆]_n·2nH₂O (1) and [Co(phda)(H₂O)]_n·nH₂O (2) [H₄bta = 1,2,4,5-benzenetetracarboxylic acid, H₂phda = 1,4-phenylenediacetic acid] have been characterized by single crystal X-ray diffraction. Compound 1 is a one-dimensional compound where the bta⁴⁻ ligand acts as 2-fold connector between the cobalt(II) ions through two carboxylate groups in para-conformation. Triply bridged dicobalt(II) units occur within each chain, a water molecule, a carboxylate group in the syn-syn conformation, and an oxo-carboxylate with the μ₂O(1);κ²O(1),O(2) coordination mode acting as bridges. Compound 2 is a three-dimensional compound, where the phda²⁻ group acts as a bridge through its two carboxylate groups, one of them adopting the μ-O,O′ coordination mode in the syn-syn conformation and the other exhibiting the single μ₂-O′′ bridging mode. As in 1, chains of cobalt(II) ions occur in 2 with a water molecule, a syn-syn carboxylate group, and an oxo-carboxylate constitute the triply intrachain bridging skeleton. Each chain is linked to other four ones through the phda²⁻ ligand, giving rise to the three-dimensional structure. The values of the intrachain cobalt−cobalt separation are 3.1691(4) (1) and 3.11499(2) Å (2) whereas those across the phenyl ring of the extended bta⁴⁻ (1) and phda²⁻ (2) groups are 10.1120(6) and 11.4805(69 Å, respectively. The magnetic properties of 1 and 2 have been investigated in the temperature range 1.9−300 K, and their analysis has revealed the occurrence of moderate intrachain ferromagnetic couplings [J = +5.4 (1) and +2.16 cm⁻¹ (2), J being the isotropic magnetic coupling parameter], the magnetic coupling through the extended bta⁴⁻ and phda²⁻ with cobalt−cobalt separations larger than 10 Å being negligible. The nature and magnitude of the magnetic interactions between the high-spin cobalt(II) ions in 1 and 2 are compared to those of related systems and discussed as a function of the complementarity-countercomplementarity effects of the triple bridges.