Theoretical design of a new, high spin, organic molecule

The search for ferromagnetism in compounds only made of light elements succeeds in a very few cases. One fundamental key is to start with high spin molecules as building blocks for the solid. Looking for such entities may be rationalised by theoretical investigations. Quantum chemistry calculations were performed on a “virtual” organic neutral molecule. This molecule is a derivative of TTF, and it is predicted to be planar. The level of theory (semi-empirical vs. ab initio, ab initio vs. DFT), the effect of basis set quality and of electron-electron correlation were analysed. These results show that there is a strong evidence for a triplet ground state. The singlet-triplet splitting ranges between 0.2 and 2 eV depending on the method. Moreover, there is a strong tendency for these molecules to build dimers with a quintet ground state. Consequently, this molecule, if its synthesis should be possible, appears to be quite attractive to build new organic ferromagnets.