The heterobimetallic complex [Cu(II)Mn(III)(L) 2 (py) 4 ](ClO 4)·EtOH (1) built using the pro-ligand 2,2'-biphe-nol (LH 2), 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 fre-quency 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). Calcu-lations reveal that the antiferromagnetic interaction essentially stems from the Mn(d x 2 −y 2)–Cu(d x 2 −y 2) interaction. The computed single-ion anisotropy and cluster anisotropy also correlates well with exper-iment. 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.