Switching the orientation of Jahn–Teller axes in oxime-based MnIII dimers and its effect upon magnetic exchange: a combined experimental and theoretical study

Abstract

A family of Mn^III dimers of general formula [Mn^III₂(R-sao)₂(dpa)₂](ClO₄)₂ (1–5) has been synthesised using derivatised phenolic oximes (R-saoH₂, where R = H, Me, Et, Ph) in combination with di-(2-picolyl)-amine (dpa). Their structures reveal a double-oxime bridged [Mn^III(NO)]₂ magnetic core in which the Jahn–Teller axes lie perpendicular to the bridging plane, in contrast to two previously reported family members (6, 7). The switch in the orientation of the Jahn–Teller axes is enforced through the use of the chelating ligand which is present in 1–5 and absent in 6–7. Dc magnetic susceptibility measurements reveal that the exchange interactions between the Mn^III metal centres in 1–5 are antiferromagnetic in contrast to that observed for 6 and 7 which are ferromagnetic. DFT calculations performed on complexes 1–6 reproduce both the sign and strength of the J values found experimentally. Molecular orbital analysis unlocks a common mechanism of magnetic coupling based upon the orientation of the Jahn–Teller axis, with the magneto-structural correlation also dependent upon the Mn–N–O–Mn angles – with ferromagnetic interactions at smaller dihedral angles.