Trinuclear CoII and NiII complexes have been assembled using an octadentate Mannich–Schiff‐base proligand H2L2 which is obtained by reacting the Mannich base HL1 with propylenediamine (2:1 molar ratio). HL1 is obtained from 5‐bromo‐salicylaldehyde and N,N,N′‐trimethyl‐ethylenediamine. The reaction of H2L2 with nickel(II) and cobalt(II) as nitrate salts affords the trinuclear complexes [Ni3(L2)(NO3)4]·CH3CN (1) and [Co3(L2)(NO3)4]·CH3CN (2) in which the metal ions are bridged by one phenoxido and a nitrato‐oxygen atoms. Within each complex, two of the four nitrato groups act as chelating ligands against the terminal metal ions. The central metal ions in 1 and 2 are hosted into the salen‐like cavity of the organic ligand. The nitrato bridges can be replaced by end‐on azido or end‐on N‐thiocyanato groups leading to the compounds [Ni3(L2)(N3)2(NO3)2] (3), [Co3(L2)(N3)2(NO3)2] (4), and [Co3(L2)(NCS)2(NO3)2]·2CH3CN (5). The magnetic properties of the five compounds have been investigated, revealing the occurrence on intramolecular antiferro‐ (1 and 2) and ferromagnetic interactions (3, 4 and 5). The nature and size of these interactions are discussed and compared to previously reported results on related systems. [ABSTRACT FROM AUTHOR]