Synthetic, structural, spectroscopic and theoretical study of a Mn(iii)–Cu(ii) dimer containing a Jahn–Teller compressed Mn ion

Abstract

The heterobimetallic complex [Cu(II)Mn(III)(L)₂(py)₄](ClO₄)·EtOH (1) built using the pro-ligand 2,2′-biphenol (LH₂), contains a rare example of a Jahn–Teller compressed Mn(III) centre. Dc magnetic susceptibility measurements on 1 reveal a strong antiferromagnetic exchange between the Cu(II) and Mn(III) ions mediated through the phenolate O-atoms (J = −33.4 cm⁻¹), with magnetisation measurements at low temperatures and high fields suggesting significant anisotropy. Simulations of high-field and high frequency powder EPR data suggest a single-ion anisotropy D_Mn(III) = +4.45 cm⁻¹. DFT calculations also yield an antiferromagnetic exchange for 1, though the magnitude is overestimated (J_DFT = −71 cm⁻¹). Calculations reveal that the antiferromagnetic interaction essentially stems from the Mn(d_x²−y²)–Cu(d_x²−y²) interaction. The computed single-ion anisotropy and cluster anisotropy also correlates well with experiment. A larger cluster anisotropy for the S = 3/2 state compared to the single-ion anisotropy of Mn(III) is rationalised on the basis of orbital mixing and various contributions that arise due to the spin–orbit interaction.