Non-Heisenberg magnetic behavior of a triangular bridged heterometallic Fe2(III)Co(II) complex: Evidence of strong orbital contributions

We report the synthesis, magnetization and ac susceptibility of the triangular μ3-oxo-bridged heterometallic complex [Fe2CoO(CH3COO)6(3-Cl-Py)3], in powder form. The model Hamiltonian is elaborated involving isotropic exchange interactions Fe(III)-Fe(III) and Co(II)-Fe(III) dealing with the real spins of high-spin Co(II) and Fe(III) ions, and also spin-orbit coupling and low-symmetry crystal field (C2v) acting within the 4T1g ground manifold of Co(II) ion. The outlined general model takes into account strong anisotropic orbital contribution to the magnetic characteristics of the whole system arising from Co(II) ion with unquenched orbital angular momentum. The treatment of the Hamiltonian is performed with the use of the irreducible tensor operator technique. The influence of the exchange and spin-orbital interactions on the magnetic properties of Fe2(III)Co(II) clusters is revealed. The result of calculations in the framework of the isotropic model (neglecting low-symmetry crystal field) are in a good ag...