Antiferromagnetic Co–Gd Interactions in a Tetranuclear [CoGd] 2 Complex with Low‐Spin Square‐Planar Co Ions – Role of the Singly Occupied 3d Co Magnetic Orbital

A trianionic ligand H 3 L [2‐hydroxy‐ N ‐(2‐{[(2‐hydroxyphenyl)methylene]amino}‐2‐methylpropyl)benzamide] with an inner N 2 O 2 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 Co II ion is in a square‐planar environment and a low‐spin state S = 1/2. Further reaction with GdCl 3 · 6H 2 O 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 Co II 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 d xy or d yz cobalt orbital is responsible for the presence of an antiferromagnetic interaction.