Charge-transfer-induced magnetism in mixed-stack complexes

Explanation of the ferromagnetic anomaly in two recently synthesized mixed-stack charge-transfer (CT) complexes (1) (HMTTF)[Ni(mnt)₂] (HMTTF = bis(trimethylene)-tetrathiafulvalene, mnt = maleonitrile dithiolate) and (2) (ChSTF)[Ni(mnt)₂] (ChSTF = 2,3-cyclohexylenedithio-1,4- dithia-5,8-diselenafulvalene) is the cornerstone of this investigation. Because these systems are reported to achieve magnetic properties through charge transfer from the neutral organic donor to the neutral organometallic acceptor stack, their magnetic interaction is assessed through the charge-transfer energy and the spin densities on the concerned sites following one of our recent formalisms. The positive value of J obtained in this way is found to be in good agreement with that evaluated through abinitio and density functional theory (DFT). In DFT framework, broken symmetry (BS) approach is adopted to evaluate J using spin-projection technique. No overlap between singly occupied molecular orbitals (SOMOs) suggests a through-space ferromagnetic interaction between the donor and the acceptor in the ground state of the complexes. Apart from the ground state, the magnetic status of the molecules is studied by varying interlayer distance d, the extent of slippage (slipping distance r, r ^/, and deviation angle α), and rotational angle θ, which play a crucial role in magneto-structural correlation. Furthermore, it is categorically observed that the ferromagnetic interaction reaches its zenith at minimum energy crystallographic stacking mode resulting in maximum value of coupling constant in the ground state.