Stellated cuboctahedron of FeIII

Abstract The solvothermal reaction of FeCl 2 ⋅ 4H 2 O and H 4 TBC[4] in a basic dmf/EtOH solution affords an [Fe III 18 ] Keplerate conforming to a stellated cuboctahedron. Magnetic and heat capacity measurements reveal spin frustration effects arising from the high symmetry. A crossover between inverse and direct magnetocaloric effects is observed at ~10 K for applied‐field changes lower than 3 T.