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 Zn(II)Fe(III) (A)Fe(III) (B)Fe(III) (A)Zn(II) has been synthesized by using a dinucleating nonadentate ligand. The face‐sharing bridging mode enforces short Zn(II)⋅⋅⋅Fe(III) (A) and Fe(III) (A)⋅⋅⋅Fe(III) (B) distances of 2.83 and 2.72 Å, respectively. Ab‐initio CASSCF/NEVPT2 calculations provide significant negative zero‐field splittings for Fe(III) (A) and Fe(III) (B) with |D (A)|>|D (B)| with the main component along the C (3) 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 J (xy)=+0.37, J (z)=−0.32, D (A)=−1.21, E (A)=−0.24, D (B)=−0.35, and E (B)=−0.01 cm(−1) supported by simulations of high‐field magnetic Mössbauer spectra recorded at 2 K. The weak but ferromagnetic Fe(III) (A)Fe(III) (B) interaction arises from the small bridging angle of 84.8° being at the switch from anti‐ to ferromagnetic for the face‐sharing bridging mode.