A trianionic ligand H3L [2‐hydroxy‐N‐(2‐{[(2‐hydroxyphenyl)methylene]amino}‐2‐methylpropyl)benzamide] with an inner N2O2 coordination site and an oxygen atom coming from an amide function not involved in this site yields a monoanionic LCo‐pipH+ complex, in which the CoII ion is in a square‐planar environment and a low‐spin state S = 1/2. Further reaction with GdCl3·6H2O and tetramethylheptanedione (Hthd) yields a dinuclear Co–Gd complex that self‐assembles into a tetranuclear species, as demonstrated by the structural determination of the [LCoGd(thd)2(MeOH)]2 complex. This genuine entity is the first example in which a CoII ion in a low‐spin state is associated with a gadolinium ion. The magnetic studies confirm that two antiferromagnetic interactions are active through the double phenoxo bridge (J = –1.0 cm–1) and through the single amide bridge (j = –0.1 cm–1). Contrary to the large majority of 3d–Gd complexes that present ferromagnetic interactions, the involvement of a dxy or dyz cobalt orbital is responsible for the presence of an antiferromagnetic interaction.