A systematic study of influence of ligand substitutions on the electronic structure and magnetic properties of Mn4 single-molecule magnets

We present a density-functional theory study of the influence of ligand substitutions on the geometric structure, electronic structure, and magnetic properties of Mn4 single-molecule magnets (SMMs), in order to investigate the role of ligands in controlling these features, as well as in developing new SMMs and single-chain magnets (SCMs). Our results show that the peripheral ligands play an important role in controlling the magnetic ground-state of Mn4 SMMs. A new model is proposed to explain the spin state of manganese ions in Mn4 molecules. This model shows that the saving energy from distortion, which can be controlled by peripheral-ligand substitutions, plays a crucial role in determining the spin state of manganese ions in Mn4 molecules. The mechanism of strong exchange couplings between manganese ions in Mn4 SMMs is revealed. The strength of exchange–couplings between manganese ions in Mn4 SMMs as a function of their charge and spin state can be also controlled by substituting peripheral-ligands. The results demonstrate the possibilities of developing new Mn4-based SMMs. In addition, strong spin polarizations on peripheral ligands containing sp2-hybridized carbon sites show that using ligands containing sp2-hybridized carbon sites can enhance exchange couplings between Mn4 building blocks to develop new SMMs and SCMs which operate at high temperatures.