Molecular Engineering of High Energy Barrier in Single-Molecule Magnets Based on [MoIII(CN)7]4− and V(II) Complexes

Molecular engineering of high energy barrier Ueff in single-molecule magnets (SMMs) of general composition MoIIIkVIIm based on orbitally-degenerate pentagonal-bipyramidal [MoIII(CN)7]4− complexes with unquenched orbital momentum and high-spin V(II) complexes is discussed. In these SMMs, the barrier originates exclusively from anisotropic Ising-type exchange interactions −Jxy(SixSjx + SiySjy) − JzSizSjz in the apical cyano-bridged pairs MoIII–CN–VII, which produce a double-well energy profile with a doubly degenerate ground spin state ±MS. It is shown that the spin-reversal barrier Ueff is controlled by anisotropic exchange parameters Jz, Jxy, and the number n of apical MoIII–CN–VII groups in a SMM cluster, Ueff ~ 0.5|Jz − Jxy|n; it can reach a value of many hundreds of wavenumbers (up to 741 cm−1). This finding provides a very efficient straightforward strategy for further scaling Ueff to high values (>1000 cm−1) by means of enhancing exchange parameters Jz, Jxy, and increasing the number of [MoIII(CN)7]4− complexes in a SMM molecule.