Two Cobalt(II) Cubane Compounds: The Key Role of Small Ligand Changes on the Crystal Packing and Magnetic Properties

The synthesis and the structural and magnetic characterization of two new cobalt(II) compounds [Co 4 (TTA) 4 (OMe) 4 (EtOH) 4 ] ( 1 ) and [Co 4 (TTA) 4 (OMe) 4 (MeOH) 4 ] ( 2 ) (TTA = 4,4,4‐trifluoro‐1‐thienoyl‐2,4‐butanedione) are reported. The structures consist of a tetranuclear Co 4 O 4 core in a cubane framework. Both systems were modeled by a spin Hamiltonian with two isotropic exchange interactions and local orthogonal anisotropy axis configuration. The temperature‐dependent susceptibility was successfully simulated yielding many low‐lying mixed eingenstates that cannot be approximated by a giant spin model. A surprising fact is that despite the structural similarities there are striking differences between their magnetic properties. DC magnetic susceptibilities showed only ferromagnetic interactions between cobalt(II) ions for 2 , whereas 1 has ferromagnetic and weaker antiferromagnetic interactions among their ions. In addition, compound 1 presented split zero‐field‐cooled and field‐cooled susceptibility around 6 K and a frequency dependent ac susceptibility typical of slow magnetization not observed in 2 . The temperature dependence of this relaxation is similar to what is observed for cluster‐glass systems and may be related to a complex process involving many low‐level mixed states.