The reaction between pyridine-2-ylmethanol (HL), anhydrous CoCl₂ and NaH afforded polynuclear Co(II) complexes [Co₇(L)₁₂]Cl₂ (1), [Co₆Na(L)₁₂]Cl (2) and [Co₄Cl₂(L)₆] (3), depending on the HL:CoCl₂ ratio set in the reaction. The core structures of the centrosymmetric complexes 1 and 2 are of the M@Co₆ type (M = Co or Na, respectively) with a coplanar arrangement of the metals whereas that of centrosymmetric 3 is of an incomplete dicubane type. The experimental conditions allowing interconversions between these polynuclear complexes have been determined, which provides a more rational control of their synthesis. Thus, 1 transforms to 3 when reacted with CoCl₂ in a 1 : 1 ratio, whereas the same reaction performed with a large excess of CoCl₂ gave the tetranuclear pseudo-cubane complex [Co₄(L)₄Cl₂(MeOH)₄] upon recrystallization. Conversely, 1 was isolated from the reaction of 3 with HL and NaH. The crystal structure of these compounds is reported, along with the magnetic behaviour of 1 and 3. The analysis of the magnetism using the effective spin-1/2 Hamiltonian approach revealed single-molecule metamagnetic behavior in 3.