A [Mn18Dy] SMM resulting from the targeted replacement of the central MnII in the S = 83/2 [Mn19]-aggregate with DyIII.

Anisotropy can be introduced into the [Mn(19)]-aggregate, which currently has the highest known spin ground state of S = 83/2, by the targeted replacement of the central Mn(II) cation with Dy(III) leading to a [Mn(18)Dy] complex with the same core topology showing slow relaxation of the magnetisation.