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The assembly of [Co₂^III(μ-2,5-dpp)(CN)₈]²⁻ anions and [M^II(CH₃OH)₂(DMSO)₂]²⁺ cations resulted into the formation of two heterobimetallic 1D coordination polymers of formula [M^II(CH₃OH)₂(DMSO)₂(μ-NC)₂Co₂^III(μ-2,5-dpp)(CN)₆]<i>_n</i>·4<i>n</i>CH₃OH [M = Co^II (<b>1</b>)/Fe^II (<b>2</b>) and 2,5-dpp = 2,5-bis(2-pyridyl)pyrazine. The [Co₂^III(μ-2,5-dpp)(CN)₈]²⁻ metalloligand coordinates the paramagnetic [M^II(CH₃OH)₂(DMSO)₂]²⁺ complex cations, in a bis-monodentate fashion, to give rise to neutral heterobimetallic chains. Cryomagnetic dc (1.9–300 K) and ac (2.0–13 K) magnetic measurements for <b>1</b> and <b>2</b> show the presence of Co(II)_HS (<b>1</b>) and Fe(II)_HS (<b>2</b>) ions (HS – high-spin), respectively, with <i>D</i> values of +53.7(5) (<b>1</b>) and −5.1(3) cm⁻¹ (<b>2</b>) and slow magnetic relaxation for <b>1</b>, this compound being a new example of SIM with transversal magnetic anisotropy. Low-temperature Q-band EPR study of <b>1</b> confirms that <i>D</i> value is positive, which reveals the occurrence of a strong asymmetry in the <i>g</i>-tensors and allows a rough estimation of the <i>E/D</i> ratio, whereas <b>2</b> is EPR silent. Theoretical calculations by CASSCF/NEVPT2 on <b>1</b> and <b>2</b> support the results from magnetometry and EPR. The analysis of the ac magnetic measurements of <b>1</b> shows that the relaxation of <i>M</i> takes place in the ground state under external magnetic dc fields through dominant Raman and direct spin-phonon processes.