Rational Design of a Confacial Pentaoctahedron: Anisotropic Exchange in a Linear Zn II Fe III Fe III Fe III Zn II Complex

The first confacial pentaoctahedron comprised of transition metal ions namely ZnII FeIIIA FeIIIB FeIIIA ZnII has been synthesized by using a dinucleating nonadentate ligand. The face-sharing bridging mode enforces short ZnII ⋅⋅⋅FeIIIA and FeIIIA ⋅⋅⋅FeIIIB distances of 2.83 and 2.72 A, respectively. Ab-initio CASSCF/NEVPT2 calculations provide significant negative zero-field splittings for FeIIIA and FeIIIB with |DA |>|DB | with the main component along the C3 axis. Hence, a spin-Hamiltonian comprised of anisotropic exchange, zero-field, and Zeeman term was employed. This allowed by following the boundary conditions from the theoretical results the simulation in a theory-guided parameter determination with Jxy =+0.37, Jz =-0.32, DA =-1.21, EA =-0.24, DB =-0.35, and EB =-0.01 cm-1 supported by simulations of high-field magnetic Mossbauer spectra recorded at 2 K. The weak but ferromagnetic FeIIIA FeIIIB interaction arises from the small bridging angle of 84.8° being at the switch from anti- to ferromagnetic for the face-sharing bridging mode.